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ECOLOGY AND MANAGEMENT OF PRATYLENCHUS ZEAE
ASSOCIATED WITH MAIZE PRODUCTION-IN ZIMBABWE
COMMUNAL FARMS

By

Paul Muchena

A DISSERTATION

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Entomology

1988

ECOLOGY 1

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ABSTRACT

ECOLOGY AND MANAGEMENT OF PRATYLENCHUS ZEAE ASSOCIATED WITH
MAIZE PRODUCTION IN ZIMBABWE COMMUNAL FARMS

 

BY

Paul Muchena

Pratylenchus zeae and Pratylenchus brachyurus, the major nematode
pests of maize in Zimbabwe communal farms, had relative population
densities of 50 and 38.5% and absolute frequencies of 52.6 and 21.9% during
a 1985/86 survey, respectively. Maize plants which were infected with
>1,000 Pratylenchus spp. per 10.0 grams of fresh root weight during the
survey had a 48% mean yield reduction. 3. gas were identified to be a major
problem of maize especially in natural regions II to IV with sandy soils and a
soil pH of 4.8-6.8. High population densities of 3. £933 were recovered from
maize roots from farms with rainfall range of 600-1,000 mm per year and
temperature range of 22.6-30.1°C.

Third to fourth stage juveniles and mature females were identified as
the main overwintering stages of 3. 2.632 in a field study and these stages
constituted 51.9 and 46.3% of the total population of vermiform stages,
reSpectively. The population was aggregated at depth 0-20 cm but migrated
to lower depths during hot and dry months. Clean fallow for one year
reduced 519$ in the soil by 87.5%.

Maize roots and E. z_e_a_g were aggregated at depth 020 cm in a study
conducted in pits. g. zea_e in this study had a Pf/Pi ratio of 170. Very few
second stage juveniles were recovered in this study. The optimal time for
sampling maize roots for E. z_e§_e_ was 4 weeks after planting at a soil depth

10-20 cm and radius of 0-10 cm.

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Maize root growth was reduced at 11.7% gravimetric soil moisture in
loamy sand soil and E zflg population density was only slightly reduced at
5.0% gravimetric soil moisture in a greenhouse study. Another greenhouse
study demonstrated the importance of applying adequate soil nutrients in
maize plants infected with E. zeae.

Carbofuran, fenamiphos, isazofos and terbufos reduced 3. fig in
maize roots by 95, 96, 95 and 93% and increased yield by 67, 54, 37 and 66%,
respectively, in a field study. Organic amendments in field and greenhouse
studies reduced 3. z_e_§g and increased maize growth and grain yield.

Research and literature data on E. zgg were summarized in a E. gag
maize simulation model. The model predicted E. zeae in maize roots with
mean error of 7% and below and above ground biomass of maize with mean

errors of 17.7 and 11.1%, respectively.

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ACKNOWLEDGMENTS

I would like to thank my major professor, Dr. George Bird, for his excellent
guidance and support during my graduate studies at Michigan State University
and Plant Protection Research Institute, Zimbabwe; and for his discovery that
when a map of Zimbabwe is turned upside down it looks like a root-knot
nematode mature female. My appreciation is also extended to the members of
my committee, Drs. Stuart Gage, Joe Ritchie, Don Hall, and Frank Fear, for their
time, assistance, and enthusiasm in sharing their knowledge and experiences
with me.

I have enjoyed and benefited from my association with the faculty, staff
and students of the Entomology Department. I also would like to thank Mrs.
Becky Mather for sacrificing her weekends while preparing this dissertation.

All members of the Zimbabwe “Nematology Group“ deserve special thanks
for their friendship and support of my research efforts. I also would like to thank
the MSU 'Nematology Group“ for their friendship and support for all the time
thatl have been at MSU. '

I would like to thank computer programmers Messers Ed Martin and
Rodwell Zvarayi for their assistance with the Fortran coding. Also the
biometricians in the Department of Research and Specialist Services deserve a
sPecial thanks for their help.

Finally, I would like to thank my family, Head of Plant Protection Research
Institute, Assistant Director, Research Services, and Director, Research and

Specialist Services for their support to the fulfillment of my educational goals.

Listofiable
Unofhgun
1. lntrodu
1.1 21!
1.2 Ge
1.3 T1
1.4 Re
2. LIIQIBIL
2.1 fl
2.

2.

2.

2.2

IN

TABLE OF CONTENTS

 

 

List of Tables ...................................................... viii
List of Figures ...................................................... xi
1. Introduction ................................................... I 1
1.1 Zimbabwe natural regions and farming areas ................ 1
1.2 General hematology ....................................... 3
1.3 Thesis goal and objectives .................................. 5
1.4 Rationale and research approach ........................... 6
2. Literature Review ........................................... 13
2.1 Pratylenchus zeae ........................................ 13
2.1.1 Classification ....................................... 13
2.1.2 Description ........................................ 13
2.1.3 Distribution and hosts ............................... 14
2.1.4 Biology and life history ........... , ................... 15
2.1.5 Pathogenicity ...................................... 16
2.1.6 Interactions between Pratylench us zeae and abiotic
factors ........................................... 18
2.1.6.1 Temperature ............................... 18
2.1.6.2 Moisture ................................... 18
2.1.6.3 Soil texture ................................ 20
2.1.6.4 Soil pH .................................... 21
2.1.7 Control ........................................... 22
2.2 _Z_e_a_ _m_ay§ L. ........................................... 29
2.2.1 The origin of maize ................................. 31

iv

2.2.1
2.2..

2.2.

2.2.
2.2.

3- EXperim

3.1

3.2

3.3

Pl;
211

3.
3.

2.2.2 Life history ......................................... 31

2.2.3 Influence of temperature on maize growth and

development ....................................... 31
2.2.4 Influence of moisture on maize growth and

development ....................................... 34
2.2.5 Nutritional requirements of maize ................... 36

2.2.6 Influence of pests on maize growth and development . . 42

2.2.6.1 Weeds ..................................... 42
2.2.6.2 Diseases ............. . ..................... 43
2.2.6.3 Insects ..................................... 46
2.2.6.4 Nematodes ................................ 48
Experimentation ........................................... 55
3.1 Plant-parasitic nematodes associated with maize in
Zimbabwe ........................................... ‘55
3.1.1 Introduction ....................................... 55
3.1.2 Methods and Materials .............................. 55
3.1.3 Results ........................................... 61
3.1.4 Discussion ......................................... 71
3.2 Overwintering and vertical distribution of E. zeae under
clean fallow .......................... . ................. 75
3.2.1 Introduction ....................................... 75
3.2.2 Methods and Materials .............................. 75
3.2.3 Results ........................................... 77
3.2.4 Discussion ......................................... 80

3.3

Spatial and temporal distribution of gravimetric soil moisture,
maize root system and E. zeae: with special reference to E. zeae

sampling schemes ........................................ 84
3.3.1 Introduction ....................................... 84
3.3.2 Methods and Materials .............................. 84

3.3.3 Results ........................................... 88

3.4

3.5

3.6

3.7

3.8

3.3

Inf
syS‘

3.4
3.4
3.1
31

3.4

3.5

3.6

3.7

3.8

3.3.4 Discussion ......................................... 97

Influence of gravimetric soil moisture on E. zeie and maize root
system development ..................................... 103
3.4.1 Introduction ...................................... 103
3.4.2 Methods and Materials ............................. 103
3.4.3 Results ....... I ................................... 106
3.4.4 Discussion ........................................ 107
Evaluation of maize varieties and inbreeds against E. z_eag

infection ............................................... 109
3.5.1 Introduction ...................................... 109
3.5.2 Methods and Materials ............................. 109
3.5.3 Results .......................................... 111
3.5.4 Discussion ........................................ 111
Influence of soil nutrients on 3. fig population density and maize
growth parameters ...................................... 113
3.6.1 Introduction ...................................... 113
3.6.2 Methods and Materials ............................. 113
3.6.3 Results .......................................... 116
3.6.4 Discussion ........................................ 120
Effect of granular nematicides on P. age associated with

maize .................................................. 122
3.7.1 Introduction ...................................... 122
3.7.2 Methods and Materials ............................. 123
3.7.3 Results .......................................... 126
3.7.4 Discussion ........................................ 129
Influence of organic amendments and early plowing on 33.9.19.
pathogenicity on maize .................................. 131
3.8.1 Introduction ...................................... 131
3.8.2 Methods and Materials ............................. 132

vi

H

 

5.
6.

3.8.3 Results .......................................... 134

3.8.4 Discussion ........................................ 137
3.9 Effect of organic amendments and the time of application on 3.
fl pathogenicity on maize ............................. 140
3.9.1 Introduction ...................................... 140
3.9.2 Methods and Materials ............................. 140
3.9.3 Results .......................................... 143
3.9.4 Discussion ........................................ 146
3.10 Simulation model of E. E infecting maize ............... 148
3.10.1 Introduction ..................................... 148
3.10.2 Model development .............................. 149
3.10.3 Model evaluation ................................. 160
Summary and Conclusions ..................................... 174
4.1 Research program overview .............................. 174
4.2 Problem identification ................. ' .................. 174
4.3 Ecology of the pest ...................................... 175
4.3.1 Analysis of survey results ........................... 175
4.3.2 Controlled field and greenhouse studies ............. 177
4.4 Management of the pest ................................. 180
4.5 Simulation model of the pest ............................. 181
Appendix .................................................... 183
Literature Cited .............................................. 225

vii

Table 1.

Table 2
Table 2
Table 2

Tabiez

Table)
TabIeZ
Table;

Tab'ie;
Tab'ie}

Table}

T3019:

T5039:

T5019;

Table 1.4.1
Table 2.1.1

Table 2.1.2

Table 2.1.3

Table 2.2.1

Table 2.2.2

Table 2.2.3

Table 2.2.4

Table 2.2.5
Table 3.1.1

Table 3.1.2

Table 3.1.3

Table 3.1.4

Table 3.2.1

LIST OF TABLES

Research program overview ............................. 9

Influence of temperature on E. zeae penetration,
reproduction and pathogenicity in maize ................ 20

Influence of P. zeae initial population density on percent
invasion into maize roots ............................... 20

Influence of drought on E. brachyurus over a period of
20 weeks ............................................. 21

Identifying characteristics and approximate average
dates and days from emergence for the different
stages of growth of corn ............................... 32

Quantities (kgft) of major nutrients available to crops
in undiluted slurries ................................... 39

Quantities (kg/t) of major nutrients available to crops

in farm yard manure ................................... 39
Commercial herbicide treatments for control of

annual weeds in maize in Zimbabwe .................... 44
Plant-parasitic nematodes associated with maize ......... 50

Plant-parasitic nematodes associated with maize
in Zimbabwe communal farms .......................... 62

Plant-parasitic nematodes found associated with maize
in different natural regions of Zimbabwe ................ 64

Relationships observed between natural farming regions

of Zimbabwe and population densities of Pratylenchus
brachyurus and Pratylenchus zeae recovered from maize

roots ................................................. 66

Relationships observed between manure, ammonium

nitrate and compound D fertilizer application and

Pratylench us zeae population densities and subsequent

maize yield in Mlanicaland Province ...................... 69

 

Influence of the depth of sampling on the population density
of Pratylenchus zeae recovered from 100 cm3 of soil
in Chinamora communal area ........................... 78

viii

Table

Table

Table

Tabie

.abIe

Tabie

Tabie
Table

Tabie

Table 3.3.1

Table 3.3.2

Table 3.3.3

Table 3.3.4

Table 3.3.5

Table 3.3.6

Table 3.3.7

Table 3.3.8
Table 3.3.9

Table 3.4.1

Table 3.5.1

Table 3.6.1

Table 3.6.2

Table 3.7.1

Table 3.7.2

Table 3.8.1

Effect of the time of sampling on the population density of
Pratylench us zeae recovered from 100 cm3 soil
around maize roots ................. _ ................... 89

Influence of the time of sampling on maize root weight
and the population densit of Pratylenchus zeae
recovered in 10.0 grams 0 roots ........................ 90

 

Impact of the depth of sampling in ravimetric soil moisture
and the population density of Praty enchus zeae recovered
from 100 cm3 of soil ................................... 91

Influence of the depth of sampling on maize root wei ht and
the population density of Pratylenchus zeae recovere
in 10.0 grams of roots .................................. 91

 

Effect of the radius of sampling on the po ulation density of
Pratylenchus zeae recovered from 100 cm of soil ......... 92

Influence of the radius of sampling on maize root weight
and the population density of Pratylench us zeae recovered

 

 

in 10.0 grams of roots .................................. 92
Sampling schemes of Pratylench us zeae in soil around

maize roots ........................................... 96
Sampling schemes of Pratylenchus zeae in maize roots . . . . 98

 

Adjusted sampling schemes of Pratylenchus zeae in
maize roots and soil around the roots .................... 99

Influence of gravimetric soil moisture on Pratylench us
zeae and maize root system development ............... 107

Evaluation of maize varieties and inbreeds against
Pratylench us zeae infection ............................ 1 12

Impact of nutrients on Pratylenchus zeae population density
and maize growth parameters 8 weeks after seeding ..... 1 17

Influence of nutrients on Pratylench us zeae population
density and maize growth parameters 16 weeks after
seeding .............................................. 118

Effect of several granular nematicides on Pratylench us .
zeae associated With maize in Zvumba communal area . . . . 128

Comparative economic analysis for using nematicides
in controlling Pratylenchus zeae in maize ............... 128

Impact of several management ractices on Pratylench us
zeae associated with maize in C inamora ............... 135

ix

Table

Table

Table

Table

Table

Table

Table

Tabii

Table 3.9.1 Influence of the time of applyin manure on the population

 

 

 

 

density of Pratylenchus zeae an maize growth ......... 144
Table 3.9.2 Percent reduction of Pratylench us zeae and subsequent

maize growth increase after applying manure ........... 145
Table 3.10.1 Influence of temperature on B. zeae life cycle, fecundity

and mortality factors ................................. 154
Table 3.10.2 Effect of soil water on the number of Pratylenchus l2 that

die per day ........................................... 154
Table 3.10.3 Impact of E. zeae population density in maize roots on

_P. zeae fecundity ..................................... 154
Table 3.10.4 Influence of E. zeae population density on new root

growth of maize ..................................... 154
Table 3.10.5 State variables used in the subroutine NEMPOP .......... 157

Table 3.10.6 Maize growth parameters which were influenced by
E. zeae infection in the simulation model ............... 173

Figur

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Figure 1.1
Figure 1.4.1

Figure 3.1.1

Figure 3.1.2

Figure 3.1.3

Figure 3.2.1

Figure 3.10.1

Figure 3.10.2

Figure 3.10.3

Figure 3.10.4

Figure 3.10.5

Figure 3.10.6

LIST OF FIGURES

Zimbabwe natural regions ............................. 2

Conceptual diagram on how the various research
components are inter—related .......................... 8

Communal farms sampled for plant-parasitic
nematodes in Zimbabwe ............................. 57

Communal farms sampled for plant-parasitic nematodes in
Manicaland province ................................. 58

Relationships which were observed between maize grain
yield and Pratylenchus zeae population densities
In Manicaland province .............................. 70

Influence of the time of sampling on the population
density of Pratylench us zeae recovered from 100 cm3
of soil In Chinamora communal area ................... 81

Simplified flowchart for the Pratylenchus zeae maize
simulation model ................................... 150

 

Flowchart of the subroutine NEMPOP which simulates
the development of Pratylenchus zeae in maize roots . . 151

Simulated and measured population densities of _E. zeae
in 1. 0 gram dry root weigt of man variety R 215
during the 1987 growing season ..................... 161

Simulated influence of the initial population density of

P. _z__eae in the soil on the population dynamics of

P. zeae in 1.0 gram dry root weight of maize variety R 215
aurIng the 19 7 growing season ..................... 163

Measured degree days (base 8°C) accumulated In two-
weeks intervals for Zimbabwe 1986/87 growing
season and for Michigan 1985 growing season ........ 164

Simulated populationd namics of P. z_e__ae in 1.0
gram dry root weight 0 maize variety R 215 using
(Zjimbabwe 1986/87 and Michigan 1985 weather
ata ............................................... 165

xi

Figure

Figure

Figurl

FigUTI

Figure 3.10.7 Simulated and measured number of leaves of
maize variety R 215 during the 1987 growing season . .. 167

Figure 3.10.8 Comparison of simulated and measured maize
dry s oot weight of maize variety R 215 during the
1987 growing season ............................... 169

Figure 3.10.9 Simulated and measured maize dry root weight of
maize variety R 215 during the 1987 growing season . .. 170

Figure 3.10.10 Simulated dry plant biomass of maize variety R 21 5
growing in soil infested with different initial population
densities of E. zeae per 100 cm3 soil during the 1987
growing season .................................... 172

xii

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1. INTRODUCTION

1.1 ZIMBABWE NATURAL REGIONS AND FARMING AREAS

Zimbabwe can be divided into five different natural regions and
farming areas according to annual rainfall (Fig. 1.1). Natural regions I to III
are in general ideal for intensive maize production and natural regions IV to
V receive inadequate rainfall for intensive maize production.

A review of the 1984/85 growing season shows that about 5,485
commercial farmers occupy 9.2 million hectares of land whereas 923,312
communal farmers utilize 2.0 million hectares of agricultural land. The
average size for a commercial farm is 1,669 hectares and the average size of a
communal farm is 2.5 hectares. Almost all commercial agricultural farms are
in natural regions I to III; whereas, only 30% of communal farms are in
natural regions I to lll. Commercial farmers had 194,586 hectares of land
under maize with a mean yield of 3.4 tons/ha; whereas, communal farmers
had 1.3 million hectares under maize with a mean yield of 1.0 ton/ha.

The distribution of commercial and communal farmers in Zimbabwe
before independence in 1980, was a result of the Land Apportionment Act of
1930 and Land Tenure Act of 1969 which discriminated communal farmers
from good agricultural land. Also before independence, communal farmers
received very limited services from the Department of Research and Specialist
Services, in particular, the Nematology Section which had one nematologist
who primarily serviced the commercial farmers. After independence, the

establishment of the Nematology Section expanded to four so that the

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relevant to communal farm socio-economic considerations.

1.2 GENERAL NEMATOLOGY
Root-lesion nematodes (Pratylenchus spp. Filipjev, 1936) have a world-
wide distribution. Corbett (1969) listed the species with the widest

distribution as _E. _tlachyurus, E. coffeae, P. crenatus, E. neglectus, _P.

 

genetrans, E. scribneri, _P_. Magi, and P. z_ea_e. Oteifa (1962) found all of
these except 3. crenatus on crops in the Nile Delta. Egunjobi (1968) found 4
of these in one apple orchard in New Zealand. Gotoh and Ohshima (1963)
observed 6 of Corbett's list in Japan, while Sethi and Swarup (1971) and Van
Den Berg (1971) found all 8 in northern India and South Africa, respectively.
Siddiqi gt g1. (1973) listed the following 12 species from California: 3.

brachyurus, _P. coffeae E. convallariae, _E. crenatus, E. goodeyi, _P_. hexincisus, E.

 

neglectus, E. genetrans, E. scribneri, E. thornei, E. vulnus, and E. zeae.
Thames (1982) listed crops of economic importance that are infected by
Praylench us spp. as follows:

1. alfalfa and pasture legumes - E. coffeae E. neglectus, E. genetrans,

 

and _E. scribneri.

cereal crops - E. crenatus, E. neglectus and E. thornei.

corn - E. brachyurus, _P. hexincisus, E. genetrans, and E. z_e__ae.
cotton - E. brachyurus. I

peanut - fl. brachyurus.

peppermint - _P. penetrans.
potato - P. brachyurus, P. crenatus and E. genetrans.

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rice - E. brachyurus, _E. indicus and P. zeae.

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9. soybean - _P. alleni, _P_. brachyurus, g. coffeae, E. crenatus, P.

hexincisus, l3. penetrans, E. scribneri and E. zeae.

 

10. sugarcane - P. brachyurg E. coffeae E. delattrei, E. scribneri, E.

 

Mel, and E. gage;-
11. tobacco - P. brachyurus, E. hexincisus, E. neglectus, E. penetrans, E.
thornei, P. vulnus, and E. _Z_e_a_;
All the 39 spp. of genus Pratylenchus (Loof, 1978) are phytoparasites and alter
the physiology and ontogeny of host plants. Nematodes in this genus reduce
growth, yield and marketability of host plants at high infestation levels.

Plant stress and resulting crop loss caused by plant-parasitic nematodes
are governed by soil environment (especially physical structure and water
content) and temperature, which in turn strongly dictates the population
dynamics of plant-parasitic nematodes (Endo, 1959; Olowe and Corbett,
1976; Norton, 1979). The abundance of P. z_e_ag also influences the
population dynamics and pathogenicity of many species and other organisms
contributing to plant damage. For example, infection of tobacco by E. fie
decreases the reproduction of Meloidogyne incognita (Johnson and
Nusbaum, 1970). Holtzmann and Santa (1970 and 1971) reported that 3. fl
increased 220-fold at 30 C in 12 weeks when inoculated alone to sugarcane;
when inoculated in combination with Pythium graminicola, the increase was
8-fold. On the contrary, Khan (1959) found populations of E. z_eg; to be
higher in sugarcane roots containing Phytophthora spp. than in those
containing 2. z_e_a_e_ alone.

Population dynamics of E. z_e1e_ are influenced by the initial population
density (P3) of P. ge_a_e at the beginning of the growing period (Olowe and
Corbett, 1976); soil texture (Endo, 1959); soil moisture (T ownshend, 1972);
temperature (Acosta and Malek, 1979; Olowe and Corbett, 1976); complex

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biological associations (Holtzmann and Santo, 1971; Khan, 1963); soil pH
(Willis, 1972); and management practices (Endo, 1967; Johnson gt 1!. 1975).
To adequately assess the population dynamics of P. _z__eie, it is necessaryto
understand the nature of the association among these factors, and the life
history of this plant-parasitic nematode. This information is required for the
development of predictive pest-crop ecosystem simulations and integrated
nematode management programs appropriate to Zimbabwe small-scale

farmers.

1.3 THESIS, GOAL AND OBJECTIVES
Thesis

The standard of living of Zimbabwe communal farmers can be improved
by appropriate management of the maize root-lesion nematode host-
parasite relationship.
Goal

Evaluate the ecology and host-parasite relationships of _P. z_ea_e
associated with maize (_Z_e_a my; L.) in relation to the development of future
integrated nematode management programs which can be incorporated into
the national rural development programs to:

a) improve crop production so that self-sufficiency in food is achieved,

b) raise the living standards of the rural population,

c) improve the local diet,

d) educate the communal farmers about nematode pests of maize.

Objectives
1.3.1. Identify plant-parasitic nematodes of socio-economic significance

associated with maize in Zimbabwe communal farms.

1.3.2.
1.3.3.

1.3.4.
1.3.5.

1.3.6. I

1.4 M‘

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Zimbab
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thlsareé
resenle,
allerage
and 2.0
farms. It
in (mm
pests an
contribu.
plant‘llal
35°11th

1.3.2. Evaluate the overwintering mechanisms of _P. _Zfl under clean fallow.

1.3.3. Assess the temporal and spatial distribution of gravimetric soil
moisture and how this influence 3192.9. population density and maize
root density.

1.3.4. Evaluate the impact of organic and inorganic nutrients on E. zei and
subsequent maize growth.

1.3.5. Evaluate the role of cultural practices as alternative control methods of
E. _Z_e_a_g associated with maize in communal farms.

1.3.6. Develop a predictive 3. gig simulation model that will be interfaced

with an existing CERES-MAIZE simulation model.

1.4 RATIONALE AND RESEARCH APPROACH

Maize was first cultivated in Southern Africa before the arrival of Jan
Van Riebeeck in 1652 (Louw, 1982), and is the most important crop in
Zimbabwe communal areas. During the 1985/86 growing season, 1,314,000
hectares were under maize production and about 76.1, 15.2, 5.6 and 3.1% of
this area under maize was in communal farms, large scale commercial farms,
resettlement farms and small scale commercial farms, respectively. The
average yield of maize in the respective farming systems were 1.2, 5.7, 1.6
and 2.0 tons/ha. It is apparent that except for the large scale commercial
farms, the yield of maize was sub-optimal. The low yield of maize, especially
in communal farms, could have been a result of several factors which include
pests and diseases. In particular, plant-parasitic nematodes appear to
contribute to low yields of maize in communal farms. The magnitude of
plant-parasitic nematode problems in Zimbabwean communal farms, where
about 80% of the population live (Africa South of the Sahara, 1982-83) is not

known. Hence, research associated with improvement of agricultural yields is

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imperative to achieve the national rural development goals. The research
was divided into four components (Fig. 1.4.1), presented in relation to the
objectives (Table 1.4.1).

A survey to identify the extent of plant-parasitic nematode problems
associated with maize production will increase the awareness of communal
farmers to plant-parasitic nematode problems and possible diagnostic
symptoms. Also, this will identify farms with plant-parasitic nematode
populations above the potential pathogenicity thresholds. The survey will
also identify plant-parasitic nematode species which are of economic
importance in maize production in the communal farms. Once the primary
nematode pests of maize have been identified, this information can be used
to help structure future research requirements for the communal farms in
relation to achievement of some of the national rural development goals.

The current survey was conducted so that it would equally cover all soil
textures, rainfall and temperature regimes and different farming systems.
Because of logistical problems, it was not possible to cover the whole country
in great detail, therefore the detailed survey was conducted in Manicaland
province, because this province has examples of all the different farming
regions, soil textures and temperature regimes.

After host and soil texture, soil moisture is the most important
parameter which dictates nematode population densities, directly or
indirectly (Norton, 1979). There are three major methods of measuring soil
moisture; volumetric, gravimetric and soil water potential. In the past, soil
moisture has been measured using all the three methods, but lack of detailed
specifications of soil texture for the first two methods, has led to
contradictory results with regards to critical soil moisture for plant-parasitic

nematodes (T ownshend, 1972; Trivedi gt £11., 1978; Upadhyaygta_l., 1974). It

 

 

“Sure

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PROBLEM IDENTIFICATION ‘
1. Survey of plant-parasitic
nematodes associated with
maize. ‘
ECOLOGY OF PEST
1. Influence of abiotic factors:
, . a Soil moisture
b. Soil temperature
c. Soil texture
d Soil pH
e Soil nutrients
SIMULATION MODEL
1. Summarize existing data
2. Identify research gaps
A
V V
MANAGEMENT OF PEST
1. Influence of:

 

 

a. Granularnematicides
b. Cultural practices

 

 

 

Figure1.4.1. Conceptual diagram of how the various research
components are inter-related.

Table

probli
Identi

Ecolc

 

 

[ft/IT

Table 1.4.1. Research program overview.

 

Problem
Identification

Exp. NO. 3.1

Plant-parasitic nematodes
associated with maize in
Zimbabwe

'. No.

1.3.1

 

Ecology of the Pest

Exp. NO. 3.1

Exp. No. 3.2

Exp. NO. 3.3

Exp No. 3.4

Exp. No. 3.6

Plant-parasitic nematodes
associated with maize in
Zimbabwe

Overwintering and vertical
distribution of 3. fig under
clean fallow

Temporal and spatial
distribution of gravimetric soil
mositure, maize root system and
E- 2.629

Influence of gravimetric soil
moisture on 3. fig and maize
root system development
Influence of soil nutrients on _P.
Lag population density and
maize growth

Obj.

Obj.

Obj.

Obj.

No.

No.

'. No.

NO.

NO.

1.3.1

1.3.2

1.3.3

1.3.3

1.3.4

 

Management of the
Pest

Exp. NO. 3.5

Exp. No. 3.7

Exp. NO. 3.8

Exp. No. 3.9

Evaluation of maize varieties and
inbreeds against E. &
infection

Effect of granular nematicides
on E. gea_e associated with maize
Influence of organic
amendments and early plowing
on 3. 593g pathogenicity on
maize

Effect of organic amendments
and the time of application on E.
;_e_a_e; pathogenicity on maize

Obj.

Obj.

'. NO.

'. No.

No.

No.

1.3.5

1.3.5

1.3.5

1.3.5

 

Simulation Model of
the Pest

 

 

Exp. NO. 3.10

Simulation model of E. zeae
infecting maize

 

'. No.

1.3.6

 

 

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10

is therefore essential to relate all soil moisture measurements to soil water
availability (soil moisture potential) in nematology, which will take into
account different soil textures.

Influence of soil moisture on E. z_e__ae population dynamics is not
documented in the literature. It was imperative, therefore, to evaluate the
spatial distribution of E. _Z_e_ag in relation to soil moisture for an entire year at
one month-intervals. Information on soil moisture is required for the
initialization of computer simulation models of E. z_e__ag. This information can
also be used to show the impact of soil moisture on g. zg_a_e_ mortality and
fecundity. Once the computer initialization has been completed and E. £a_e
has penetrated root tissue of the host, then the crop will dictate the
population dynamics of the nematode. Limits of available water for growth
of plants is between the 'permanent wilting point' and 'field capacity' with
water contents at potentials of -15 bar and -0.33 to 010 bar, respectively
(Ratliffgt a_|., 1983; Ritchie, 1981).

Information on the influence of soil moisture on temporal and spatial
distribution of maize root density and E. zei population densities was
generated in studies conducted in large pits (3.0 m x 1.0 m x 0.75 m). The pits
were ideal for this study because maize root system could grow for at least
sixteen weeks without being pot-bound. Soil and root systems were sampled
at two weeks intervals so that changes in the E. _z_gg population densities and
maize root system densities could be observed in detail. This detailed
information can be used to validate E. z_e_ag - maize computer simulation
model output data. Also this information can be used in the development of
equations for calculating certain parameters in the computer program.

The impact of 3. £93 on maize is documented in the literature (Chevres-

Roman _e_t_ al., 1971; Endo, 1959; Olowe and Corbett, 1976; Martin e_t al.,

11

1975). The cited information, however, does not have detailed studies on the
influence of different initial population densities of 3. L36, soil texture and
different fertilizer levels on maize below ground (root-weight, length and
volume) and above ground (shoot weight, leaf length, number of leaves,
number of degree days to silking and physiological maturity and total grain
yield) biomass.

This infOrmation was generated in a host-parasite relationship study
conducted in large clay pots at the Plant Protection Research Institute. The
study was carried out at this location to enable frequent monitoring of the
experiment. The experiment was conducted in large pots to enable
harvesting of the entire root system on sampling days.

_P_. _z_gag can be controlled with several management strategies.
Selection of a specific tactic is influenced by social constraints, economics,
biotic and abiotic environments, crop, and level of nematode infestation.
When the level of infestation is above a pathogenicity threshold, chemical
control is generally an option because of its immediate reduction of the
nematode population density. Fumigant nematicides can be used to lower
population densities of E. _Z_e_a_; (Johnson and Chalfant, 1973; Martin e_t _I.,
1975). Fumigant nematicides, however, have encountered major concerns
including phytotoxicity and persistence of residues in the environment.
Increasingly, nonfumigant nematicides have been adopted during the last 25
years. They are less phytotoxic, relatively easier to apply, compared to
fumigants; require no special equipment, are effective in controlling
nematodes at much lower dosages, and leave less persistent residues in the
environment (Wright, 1981). The major concerns related to nonfumigant

nematicides include their high toxicity to humans. During the last 10 years,

nematode control strategies have concentrated towards the integrated

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nematode management (INM). With this approach, cultural and biological
control of plant-parasitic nematodes have become increasingly important.
Cultural control of E. _z_e_a_e_ in Zimbabwe is compatible with the socio-
economic structure Of the communal farmers. Research was conducted in a
communal farm to assess the role of several cultural practices as alternative
methods for controlling E. ge_ae associated with maize. This information is
required in the implementation of integrated nematode management
programs favorable to beneficial microorganisms in the soil. Also, this
information can be incorporated into the P. iae-maize simulation model
and used as a decision-support system.

A preliminary E. E predictive simulation model was developed to
structure existing information about 3. gas associated with maize and to
identify knowledge gaps in the literature. The literature review show that
several abiotic factors including temperature and soil texture heavily
influence the population dynamics of P. w associated with maize (Olowe
and Corbett, 1976; Endo, 1959).

The influence of soil moisture on P. _z_ege population dynamics on maize
is not well documented in the literature. Also, it is apparent that P. z_ea_e has
been successfully controlled by several nematicides in maize (Johnson and
Chalfant, 1973; Martin gt _a_l., 1975), but clearly there is lack of information
pertaining to use of cultural and biological control and use of resistant maize
cultivars in controlling P. ;e_a_e_ on maize. Consequently, research was tailored
to address some of the knowledge gaps. The information collected was used
to update the preliminary P. yea—e predictive simulation model which uses
temperature as the main abiotic input.

The updated preliminary P. z_ea_e predictive simulation model was

interfaced with an existing CERES-maize simulation model. The CERES-maize

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simulation model has world-wide applicability as long as all the initial inputs
for a specific locality are fully specified. The _P. z_ea_e-maize simulation model
can be used to predict the population dynamics of E. z_ea_e_ and the impact of
13. Egg on maize growth and development under defined environmental
conditions. The E. Egg-maize simulation model was validated with research

conducted in Chinamora communal area.

2. LITERATURE REVIEW
2.1 Pratylenchus zeae
2.1.1 Classification
Aschelmintha: Nematoda: Secernentea: Tylenchida: Tylenchina:

Tylenchoidea: Pratylenchidae: Pratylenchinae: Pratylenchus Filipjev,

 

1936: type species B. _z_e_ag.

Pratylenchus zeae Graham, 1951 commonly known as the maize root-

lesion nematode was described by Graham in 1951.
2.1.2 Description 1

Female: The female has a slender body which will be almost straight

when relaxed by gentle heating. It has a lateral field with 4 incisures which
extends along the tail beyond the phasmids. The female has a lip region with
3 annules and the stylet is 15-17 pm long with broad anteriorly flattened
basal knobs. The dorsal esophageal gland opening is 3-4 pm behind the stylet
base. The ovary does not extend to the eSOphagus and has oocytes in double
rows. The monodelphic vulva for the mature female is 68-76% of the body
length. The tail shape is generally round or sub-acute with about 20-25

annules (Fortuner, 1976; Nath gt_§_l_., 1976).

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1976;

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2.1.3.

F

14

Male: Males are extremely rare and are not essential for reproduction.
The body is ventrally curved when relaxed and is morphologically similar to
the females. The male has testis which are outstretched and has multiple
rows of spermatocytes. It has well developed spicules which are enveloped by
a bursa which extends beyond the anterior end of the spicules (Fortuner,
1976; Nath e_t §_l., 1976).

Juveniles: The juveniles are similar to adults except in body size and
development of the reproductive parts. The tail tip of second-stage juveniles
is slightly pointed (Nath gt a_l., 1976).

2.1.3. Distribution and Hosts

Fortuner, 1976 reported E. zeae as a pest of the following crops:

Cotton - USA

Maize - Brazil, Egypt, India, Panama, South Africa, USA, and
Zimbabwe.

Rice - Brazil, Cuba, Ivory Coast, Malawi, Senegal, USA, and
Zimbabwe.

Sugarcane - Hawaii, Iraq, Malawi, Nigeria, Trinidad, USA,
Venezuela, and Zimbabwe.

Tobacco - Madagascar and USA.

Other hosts are sorghum, millet, rye, soybeans, tomato, oat, sweet
potato, wheat, peanut, barley, strawberry, blue lupin, cowpea, Amaranthus
gginosus, Ambrosia artemisiifolia, Andropogo_n v_irginicus, Chenopodium
a_lbgm, g. ambrosioides, Crotalaria mucronata, _C_. gpectabilis, Cynodon
dagylon, Dactyloctenium aegygtium, t)_igitaria sanguinalis, Diodia teres.
Echinochloa crusglli, Eremochola gphiuroides, Heterotheca subaxillaris,
Lespedeza sp., Solidago gtgantea, Tribulus terrestris, Xanthium pungens in
the USA (Ayoub, 1961; Graham, 1951), Panicum maximum and E.

purpurascens in Brazil (FOrtuner, 1976), Pennisetum flucum and sorghum x

 

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15

sudangrass hybrids (Johnson and Burton, 1973), ggpsicum annum in Trinidad
(Singh, 1974) andnatural uncultivated grassland in Japan (Gotoh, 1970) and
in South Africa (Van der Vegte and Heyns, 1963).
2.1 .4 Biology and Life History

3. z_ea_g has seven developmental states: egg, four juvenile stages,
mature female and mature male. Relatively few eggs are laid, either singly or
in scattered groups of 3-4 within a single lesion (Fortuner, 1976). The eggs
undergo the process of embryogenesis, and the first-stage juvenile molts to
the second-stage juvenile in the egg. Hatching takes about 10-20 days
depending on temperature (Fortuner, 1976; Olowe and Corbett, 1976).

Second, third and fourth-stage juveniles and adults are all infective (can
penetrate roots). Second stage juveniles are 0.21-0.26 mm in length and have
a stylet of 11-15 pm in length (Nath _t _l_., 1976). Second-stage juveniles molt
and become third-stage juveniles. Third-stage juveniles are 0.38-0.46 mm in
length and have a stylet 15-17 mm long (Nath _e_t gl_., 1976). Third-stage
juveniles molt and become fourth-stage juveniles. Fourth-stage juveniles,
developing females are 0.41-0.56 mm in length and have stylet 11-15 pm long
and a vulva at 66-70% body length (Nath gt glt, 1976). Developing females
molt and become adult females. Females are 0.50-0.60 mm in length and
have a stylet 15-18 pm long and a vulva at 70-80% of the body length (Nath
gt a_l., 1976). Very few developing juveniles molt to become males. Males are
0.40-0.42 mm-in length and have a stylet 15 pm long (Fortuner, 1976; Nath e_t
gl_., 1976).

E. gg_ag penetrates maize roots at the point of emergence of lateral
roots with the main root (Olowe and Corbett, 1976). Penetration occurs at

preferred sites in large numbers rather than singly (Olowe and Corbett,

1976). Krusberg (1960) assayed homogenates and extracts of E. zeae for

various
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16

various enzymes: he found cellulolitic enzyme activity, which probably helps
the nematode to penetrate cell walls.

The optimum temperature for invasion of maize roots by _P_. ggg is 20°C
(Olowe and Corbett, 1976). After invasion, 3. _zgig moves both inter- and
intra-cellular causing mechanical breakage of cells and necrosis resulting in
cavities in the cortex and stele of maize root. 3. fig also cause a deposition
of dense staining substances that occludes phloemtissues and xylem vessels
(Olowe, 1976; Olowe and Corbett, 1976).

Optimum movement of E. z_egg in the soil occurs when pore sizes range
between 180 to 40 pm, when pore size is less than 40 pm, migration of E. _z_g_a_g
is markedly reduced (Olowe and Corbett, 1976; Endo, 1959). The presence of
plant roots is conducive to nematode migration and there is little or no
migration in the absence of root exudates (Endo, 1959).

E. _z_e_a_g survives the dry season mainly in volunteer maize plants and
weed species in harvested maize plots (Egunjobi and Bolaji, 1979; Fortuner,
1976). The main weed species in which E. ga_e survives are Digitaria spp.
(Fortuner, 1976), Axonogus compressus, Amaranthus viridis L. and
Commelina nudiflora L. (Egunjobi and Bolaji, 1979). Nematodes are also able
to survive the dry season in clean fallow soiI(Fortuner, 1976) and eggs as well
as motile stages are capable of surviving the dry season (Egunjobi and Bolaji,
1979).

2.1.5 Pathogenicity

Pathogenicity by nematodes on maize is a concept documented only
relatively recently (Norton, 1984). Papers by Graham (1951) and Christie
(1953) are important because they were some of the early works that

implicated nematodes as pathogens of maize. Endo (1959) showed that

17

maize, crabgrass, millet, rye, soybean, sorghum and sudan grass were good
host plants for 3. gig reproduction. ‘

Gross symptoms of damage caused by Pratylenchus spp. vary with the
degree of nematode infestation and the environmental conditions. Above-
ground symptoms range from severe stunting with no yield to losses
demonstrated only by carefully controlled experiments (Norton, 1984).
Chlorosis or other discoloration often is evident in severe instances, but
frequently is absent in mild infestations.

Reduction of plant height, stalk diameter; and stalk and root weights of
infected plants compared with noninfected ones has been demonstrated
(Norton, 1984). These symptoms are common in the field when large
populations of Pratylenchus spp. occur and agree with the negative
correlations of yield with nematode numbers (Bergeson, 1978; Egunjobi,
1974).

Graham (1951) reported that early water-soaked root lesions containing
3. z_e_ag could be easily overlooked. Later the lesions become distinctly
discolored, and contain up to 80 eggs and 80-100 nematodes in lesions 5 mm
long. Feeding in the fibrous roots can result in the destruction of the cortical
parenchyma, resulting in sloughing off of this tissue. Severe pruning of the
roots can occur. Olowe and Corbett (1976) reported that E. E can damage
maize roots in the absence of other organisms.

Maize yield increases of 13-14% in India (Bergeson, 1978), 31% in
Georgia (Johnson and Chalfant, 1973), 33-52% in Zimbabwe (Martin e_t gt,
1975; Muchena _e_t _a_l., 1987), 10% in Iowa (Norton _e_t _a_l., 1978), 54% in South
Dakota (Smolik, 1978), and 33-100% in South Africa (Walters, 1978) have
been attributed largely to control of root-lesion nematodes over small or

wide areas. Extensive pathogenicity depends on optimum temperature

con
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18

conditions and soil texture for development of the nematode and the disease
(Olowe and Corbett, 1976; Endo, 1959).
2.1 .6 Interaction Between 3. _z_egg and Abiotic Factors

There are many abiotic factors that affect the development of E. zga_e.
The most important are temperature, moisture, soil texture, and soil pH.
2.1.6.1 Temperature

Temperature is one of the most thoroughly studied edaphic factors that
affect Pratylenchus spp. Gradations in temperature may occur laterally in the
field as well as vertically where there is a lag in diurnal fluctuation from the
surface to the deeper layers. The degree of fluctuation and time lag at
different depths are strongly influenced by soil texture and moisture (Norton,
1979).

Temperature affects all life stages of Pratylenchus spp. About 16-32%
of E. gag eggs hatch in 15-20 days at 24-27°C (Norton, 1984). Olowe and
Corbett (1976) reported that penetration, reproduction and pathogenicity of
E. z_e_ag in maize are related to ambient temperature (Table 2.1.1). Olowe and
Corbett (1976) also reported that percent invasion of E. mg into maize roots
is related to the population density of E. gag in the soil (Table 2.1.2).
2.1.6.2 Moisture

Moisture and temperature often interact. Consequently, it is usually
difficult to separate the effect of the two. Overall, however, moisture is an
important abiotic parameter governing nematode populations, directly or
indirectly (Norton, 1979). Constant soil moisture isdifficult to maintain and
thus there are a few direct observations on the effect of soil moisture on
nematode population dynamics.

Optimum plant growth occurs between 75 and 100% of field capacity
(Norton, 1979). It might be expected that when nematodes reach large

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19

population densities, the growth requirements relative to moisture and other
abiotic parameters are those similar to the host. Townshend (1972) reported
that penetration of E. penetrans and _P. Mug peaked at moisture tensions
between 10 and 100 cm H20. Koen (1967) reported that decrease in soil
moisture content significantly lowered the population density of E.
brachyurus in the soil faster compared to the control in which moisture
content was maintained around 12% (Table 2.1.3)

Penetration of roots by Pratylenchus spp. tend to peak at higher
moisture tensions as temperature increases, particularly in loam soil, and thus
nematodes gain access to roots from smaller pores. This increased
penetration as temperature increases may be the result of reduced surface
tension (74.2 dynes/cm at 10°C and 71.2 dynes/cm at 30°C) and viscosity (1.3
centipoises at 10°C and 0.8 centipoises at 30°C) of the soil moisture
(T ownshend, 1972). The quantity of available water is a major difference in
two different soils and in part determines the degree of stress placed on a
crop. Thus a crop on sandy loam with only 5% available water would be
under greater stress than one on'silt loam with 17% though both crops may
be equally infected and damaged (T ownshend, 1972).
2.1.6.3 Soil Texture

Certain nematodes develop more frequently and more abundantly or
cause greater damage in certain soil textures than in others (Norton, 1979).
For example, P. g is most common in sandy soils, but 3. hexincisus is most
common in medium to heavy textured soils (Norton, 1979). Endo (1959)
reported that growth rate (dN/N dt) of E. brachyurus on cotton was 0.6, 27.9,
8.4 and 0.65 on sand, sandy loam, loam, and clay loam soil, respectively. This

implies that nematode reproduction is influenced by soil aeration, pore

Tal

 

l—T‘l lfij

 

20

Table 2.1.1. Influence of temperature on E. zeae penetration, reproduction

and pathogenicity in maize (Olowe and Corbett, 1976).

 

 

 

 

 

 

 

 

 

 

 

Temp. % invasion Days for a Population density % decrease in
(°C) after 60 hrs. life cycle after 90 days root growth
5 15 45 84 1581
20 55 42 2602 14
25 40 28 901 1 21
30 30 21 13358 25
Z35 25 21 758 6

 

1Initial population density (Pi) = 275 t 15.

Table 2.1.2. Influence of E. zeae initial population density on percent

invasion into maize roots (Olowe and Corbett, 1976).

 

Initial population density

Percent invasion

 

 

 

 

 

 

 

 

 

 

 

in 10.0 cm3 of soil after 60 hours

10 20

50 45

80 65

100 75

200 76

400 70

700 60

800 45

1000 15

 

 

 

21

Table 2.1.3. Influence of drought on E. brachyurus over a period of 20
weeks (Koen, 1967).

 

 

 

 

 

 

 

Soil left to dry Control (wet soil)
Weeks 3. brachyu rus % E. brachyurus %
in 250 cm3 soil moisture in 250 cm3 soil moisture
soil soil

0 188.2 12.1 188.5 12.2
4 102.6 4.2 90.0 12.4
12 46.3 2.1 71.2 12.3
20 30.3 2.0 56.1 12.5

 

 

 

 

 

 

space, particle size, and nematode motility. 3. fig motility in soil is heavily
influenced by soil texture, Endo (1959) reported that after four months: 72.3,
24.5 and 3.2% of E. ggg (Pi) will travel one inch in sandy loam, loam and clay
loam soil, respectively.

It is therefore quite apparent that soil texture plays a significant role in
E. zggg growth and development. Soils of good tilth are of low bulk density
(Db 1.5) and thus soil aggregates and pore sizes are most suitable for
penetration of roots by a nematode (T ownshend, 1972). It is now becoming
generally recognized that pore sizes associated with different crumb sizes are
as important or more important than sizes of the individual particles (Norton,
1979).
2.1.6.4 Soil pH

The literature suggests that the pH of the soils may well be a significant
factor in nematode behavior (Norton, 1979). Using initial pH values of 4.0,
6.0 and 8.0, Burns (1971) found that the greatest colonization of soybean
roots by E. gllgn_i was at pH 6.0 (P = 0.01). Morgan and MacLean ( 1968) found
that P. penetrans grew best in vetch roots at pH 5.5-5.8 and declined rapidly

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22

at pH 6.6 and above. In greenhouse studies, 30-week specific growth rates of
E. penetrans in alfalfa were 64.4 and 47.1 at pH 5.2 and 6.4 respectively, but
only 4.1 and 2.9 at pH 4.4 and 7.3, respectively (Willis, 1972). There are no
studies on pH that have been related to _P_. g. It is, however, believed that
the behavior of _E. g in relation to pH should be similar to other
Pratylench us spp. studies cited.
2.1.7 Control

Plant-parasitic nematodes cause economically significant crop losses in
tropical, subtropical, and temperate agricultural production systems (Bird,
1981). Recognizing the significance of plant-parasitic nematodes is an
important part of early modern nematology, 1845-1907 (Bird, 1981). In the
last century, few economically appropriate nematode control tactics were
available for protecting major food and fiber commodities from nematodes
(Bird and Thomason, 1980). In the 1940's, the discovery of the soil fumigants,
suitable for controlling phytopathogenic nematodes, gave added impetus to
the Science of Nematology. Much more recently, the development and
availability of non-fumigant organophosphate and organocarbamate
nematicides, increased the range of agricultural crops where nematode
populations can be managed with chemicals. In the past 10 to 15 years, the
effort to include all plant protection disciplines in a systems approach to
integrated pest management (IPM) greatly enhanced nematological studies
(Bird and Thomason, 1980). Integrated pest management can be defined as:
a systems approach to reduce pests to tolerable levels through a variety of
techniques, including predators and parasites, genetically resistant hosts,
natural environmental modifications, and when necessary and appropriate,

chemical pesticides (Bird, 1981). Management procedures should usually be

an
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23

implementedwhen the marginal revenue derived from the management

input is equal to or exceeds the marginal cost (Ferris, 1978).

MC = 2711
ON
where MC = marginal cost, TC = total cost of production, N = total yield, d

= derivative, and

OTR
MR = —

where MR = marginal revenue, TR = total revenue, N = total yield or output
and d = derivative. The economic threshold (MC = MR) is a dynamic concept.
It depends on the cost of the management input, agricultural production
system economics, nature of the nematode and population density, and
other environmental parameters (Bird, 1981).

There are four primary means of controlling plant-parasitic nematodes:
cultural, chemical, biological, and physical.
a. Cultural means of control

The cultural means of nematode control can involve several different
practices used separately or jointly. These are fallow, crop rotation, organic
amendments, early plowing during the dry season, time of planting, and
resistant varieties.

Fallowing. The land should be kept free of all vegetation, including
weeds, for varying periods of time by frequent soil disking, plowing,
harrowing or application of herbicides to prevent plant growth. The end
result is the reduction of the nematode population through starvation and

desiccation (Lehman, 1978; Norton, 1978; Smolik, 1979). At planting, seeds

ar

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24

are placed in upper layers with low plant-parasitic nematode populations. If,
however, the farmer plows the field just before planting, the soil that was
least exposed to solar radiation and drying will be turned up and the
seedlings will be exposed to much higher plant-parasitic nematode
population densities (Lehman, 1978). Fallow is primarily effective under
conditions of high soil temperatures and no spring rainfall (Ayoub, 1980).

Egunjobi and Bolaji (1979) reported that clean fallow reduced the
population density of Pratylenchus spp. in Western Nigeria during the dry
season. This method may be a viable nematode control option in Zimbabwe
where spring temperatures are generally very high and its dry.

Crop rotation. Crop rotation is the Oldest and still most widely used
field control measure for nematodes (Mai, 1971). An effective crop rotation
involves the introduction of a nematode-resistant plant which can be grown
successfully within the same climatic conditions as the principle crop.
Unfortunately, it is difficult to pick crops which will be compatible because
some plant-parasitic nematodes thrive on a wide range of host plants (Ayoub,
1980); Endo (1959) reported the following crops as non-hosts for P. ggg:
bean (Phaseolus vulgaris L. var. Cotender), clover (Trifolium [gm L. var.
Crimson, Ladino and Red), cotton (Gossypium hirsutum L. var. Coker 100-W)
and water melon (Citrullus vulgaris Schrad. var. Congo). Therefore, where
possible, these non-host plants should be rotated with maize.

Crop rotation has some limitations. Most notably, populations of
nematode species which do not feed on one crop in the rotation may occur
on the alternate crop. There are also some economic problems involved with
this method since the non-host crop grown in the rotation may be of low
monetary value. The most serious limitation of this method in Zimbabwe is

that most communal farmers have land resources of very limited sizes and

meyo
foodc
the rot
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nnxed‘
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leaf hc
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%:
“The be:

other e

25

they can not afford to grow any other crop besides maize which is the staple
food crop. Crop rotation is also disadvantageous because the various crops in
the rotation may require different equipment and expertise (Ayoub 1980)..
Organic amendments. Tarjan (1977) found the application of municipal
solid waste compost to one-year-old Citrus limon seedlings infested with E.
_cgf_fg_a_e at rates of 2, 4, 9, or 18 MT per ha increased weights of all plants
treated over weights of controls. Miller (1978) found that freshly ground
green leaves of some plants, reduced populations of P. penetrans when
mixed with soil in a ratio of 1:25. After 21 days, the number of _P_. genetrans
were reduced to less than 20 percent compared to those in untreated soil by

leaf homogenates of Pachysandra terminalis, dogwood (Cornus florida),

 

tomato (tygpersicon esculentum), white pine (Pinus strobus L.), red oak
(Qgercus borealis), and blue-grass (Poa gratense). Gommers (1981) listed the
toxic effects of asparagusic acid and dihydroasparagusic acid from asparagus
on g. penetrans. Organic amendments appear to be a viable nematode
control option in small scale farming.

Resistant varieties. Veech (1982), in discussing the resistance of plants
to nematodes, stated that there are two general classes of resistance:
preinfection resistance and postinfection resistance. In postinfection
resistance the plant may produce morphological defenses ('walling off') or
biochemicals such as hydrolytic enzymes, protein inhibitors, or phytoalexins
that interfere with development of the invading organism. In his review of
the production of phytoalexins in response to infection by Pratylenchus, the
author included the production of phaseolin by red kidney bean (Phaseolus
vulgaris) inoculated with E. genetrans and the production of coumestants by
lima bean (Phaseolus lunatus) invaded by P. scribneri. While there may be

other examples of resistance to Pratylenchus based on phytoalexins

pnx

phyt

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bree.
bggj
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Pant-
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26

production by the host, these appear to be the only ones in which the
phytoalexin has been isolated and identified.

Graham and Heggestad (1959) found some evidence for a
hypersensitive reaction to P. brachyurus in certain tobacco cultivars and
breeding lines. Tobacco cultivar 'PD 406' was found to be resistant to E.
brachyurus. Resistance of maize plants to _E. g_a_g has also been reported.
Maize varieties Nab Elgamal, Early American and Giza Baladi showed less
damage from E. ggg than Single Cross 14 and Double Cross 67 (Oteifa and
Taha, 1964). Tiflate pearl millet is more resistant than other millets and
sorghums to injury by _E. g_ag (Johnson and Burton, 1973).

b. Biological control

Mankau (1980) reviewed recent developments in biological control of
plant-parasitic nematodes and concluded that research on natural enemies of
nematodes showed promise for the future. Pastueria penetrans was shown
to reduce the numbers of P. scribneri recovered from soil and roots of beans.
Other tests demonstrated that small amounts of soil infested with spores of
Pastueria penetrans could be used to transmit the organism to uninfested
sites. Tests with seven nematicides currently used for control Of nematodes
did not show noticeable effect on the parasite.

c. Chemical control

A 'good" nematicide should have most of the following characteristics:
(1) penetrate barriers such as soil, plant tissue and the nematode cuticle; (2)
control the major groups of plant-parasitic nematodes (sedentary, semi, and
migratory endoparasites and ectoparasites); (3) not phytotoxic to the plants;
(4) not leave harmful residues in soil or plants; (5) degrade within a
reasonable time after application; (6) offer no hazard to man, domestic

animals or wildlife; (7) have a short waiting period or none at all between

treatmi
effectii
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So
1980). '
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27

treatment and planting; (8) be easy and safe to apply; (9) be inexpensive and
effective in small amounts; (10) not permit the nematode to build up
resistance to the toxic effects.

There are two basic types of nematicides: fumigants and non-
fumigants. Soil fumigants are injected into soil, vaporize, and extent their
toxic action as a gas. Non-fumigants do not vaporize and are applied as
granules or liquid.

Soil fumigation is a widespread form of nematode control (Ayoub,
1980). This method Of applying chemicals to soil originated in France in the
early 1860's. The present soil fumigants, however, originated in 1943 with
the discovery of dichloropropene-dichloropropane (D-D). Soil fumigants can
be divided into classes based on the method of application: pre-plant, at
planting and post-plant treatments. All of them are designed to inject the
fumigant into the soil or to mix it with soil. The equipment used in the
fumigation is basically the same. There may be slight modifications in
equipment to accommodate the root structure for existing plants during
post-plant treatments.

Pre-plant treatments. In some cases, a soil fumigant is too phytotoxic to
be applied directly in the presence of a plant. When this is true, the pre-plant
method of application is used. The soil is fumigated before the crop is
planted and significant time is allowed to elapse before planting so that the
chemical vapors dissipate. Although this treatment usually does not
eradicate-the nematode population, a very high percentage of control is
Obtained.

Pre-plant treatments should only be applied after the land is properly
prepared so that the volatile gases of the fumigant will be most effective.

This involves plowing, chiseling, or disking the soil to the proper depth. The

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28

release of volatile gases requires maintenance of an adequate moisture level
in the soil. The temperature of the soil is also important. Depending on the
specific fumigant, the soil temperature at the depth of application should
generally be at least 10°C. For maximum effectiveness, the soil should be
sealed by ringroller or tarpaulin immediately after the fumigant has been
applied so that the nematicidal chemicals can not escape. At-plant
treatments can also be applied like the pre-plant treatments.

In Zimbabwe, I_’_. g has been controlled by the following fumigant
applied two weeks before planting (Martin _e_t g_l., 1975):

EDB 99% 3.5 mI/planting station.

In Georgia, 3. z_eag has been controlled by the following fumigants
(Johnson and Chalfant, 1973):

1.3-D 15.3 liters active ingredient/ha

EDB3.8 liters active ingredient/ha

Non-fumigant nematicides. Non-fumigant nematicides have several
advantages when compared to fumigants which sometimes outweigh their
greater basic cost. They are generally much less phytotoxic, relatively easier
to apply, are effective in controlling at much lower dosage rates, and have
less persistent residues (Wright, 1981). Non-fumigant nematicides can be
grouped into organophosphate and organocarbamate compounds. It is
generally accepted that nematicides belonging to these groups act by
impairing nematode neuromuscular activity, thereby reducing movement,
invasion, feeding, and consequently the rate of development and
reproduction (Starr _e_t _a_l., 1978; Steele, 1977; Wright, 1981). It is also
apparent that low concentrations of these compounds can affect the sensory
behavior of nematodes and this may be an important component in crop

protection (Wright, 1981).

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29

Organophophates and carbamates act principally by inhibition of
acetylcholinesterase (AChE) at cholinergic synapses in the nematode nervous
system (Ware, 1978). AChE is thought to be the most important enzyme
involved in transmitter destruction at cholinergic synapses, although
pseudocholinesterase (acycholine acylhydrolase) may also contribute (Wright,
1981). One of the general features of the action of organophosphate and
carbamate nematicides is that effects on the nematode are reversible on
removal from the pesticide (Steele, 1977; Wright, 1981). Wright (1981)
reported that recovery of nematodes can be more pronounced following
treatment with carbamates than with organophosphates.

In Zimbabwe maize production, 3. zei can be controlled by carbofuran
(Furadan 1OG) applied at a rate of 20 kg/ha at-planting in furrows and
incorporated (Martin _t a_l., 1975). Muchena gt gt. (1987) have also shown
that effective control can be obtained by applying isazofos (Miral 106) and
terbufos (Counter 106) applied at 20 and 10 kg/ha, respectively in furrow and
incorporated.

E. g_ag has been controlled by aldicarb (T emik), carbofuran (Furadan),
phenamiphos (Nemacur), and ethoprop (Mocap) in Georgia applied at a rate

of 6.7 kg a.i.lha (Johnson and Chalfant, 1973).

2.2 Zgg m L.

Maize (Zgg mgyg L.) differs from most other species of the grass family in
being monoecious. The terminal inflorescence (the tassel) produces pollen
only; whereas, the ear shoot, with the grain, develops as a lateral branch
from the lower central portion of the stem. In the inflorescence of maize and
other Gramineae the flowers are borne in 'spikelets'. These occur in pairs and

each spikelet contains two flowers. In the tassel the flowers have three

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30

anthers and each produces about 10,000 pollen grains for every potentially
fertilizable ovule (Bunting, 1978). Only one of the two flowers in the female
inflorescence in each spikelet normally develops. In each female flower the
single ovary terminates in a long style, and together. the styles form the 'silks'.
The fertilized ovary develops into a kernel, the rate of development depends
primarily on temperature. The row number of an ear is genetically controlled
and extends from 4-30, though 8 to 16 is the range most commonly
encountered in most varieties (Bunting, 1978).

The maize kernel is botanically a fruit, a caryopsis, as in all Gramineae.
A thin, normally colorless, pericarp surrounds the endosperm and embryo.
The endosperm comprises about 85% of the seed weight and consists mainly
of starch. In maize, the hot water soluble starch, amylase fraction, usually
comprises about 25% of the total, and the insoluble amylopectin fraction the
other 75% (Bunting, 1978).

Characteristics of the endosperm starch are the basis of commercial
classification of maize into flour, flint, pop, dent, sweet, and waxy corns.
Flour corns have a mealy endosperm. Flints have a central core of softer
starch completely surrounded by hard starch, so that the kernel retains its
round shape as it ripens. Most popcorns have a smaller and more pointed
kernel than the flints, with an even greater percentage of hard starch, which
ruptures (pops) when ripe kernels are heated. The dents have hard starch at
the sides of the grain but the soft starch in the central reaches the crown, and
during the later stages of ripening the soft starch shrinks to produce the
characteristic indentation. In sweet com, a single gene mutation slows down
the conversion of sugar to starch in the ripening kernel and ripe sweet corn

'seed' has a very wrinkled appearance, while in waxy com a different gene

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31

mutation produces starch composed entirely of amylopectin, used
commercially as a substitute for tapioca (Bunting, 1978).
2.2.1 The origin of maize

The closest relative of maize is annual teosinte, which survives in the
wild in Western Mexico, Guatemala and Honduras (Bunting, 1978). Teosinte
has the same number of chromosomes as maize (n = 10), crosses readily with it
and the hybrids backcross to either parent. Maize has been cultivated for
about 10,000 years (Galiant, 1978).
2.2.2 Life history

Growth of maize plants can be divided into 11 different stages (Table
2.2.1) and these stages have definite characteristics which can be observed in
the field (Hanway, 1963).
2.2.3 Influence of temperature on maize growth and development

Temperature has a profound influence on the time taken for crops to
reach maturity and on the final yield of the crop. Seeds of most maize hybrids
germinate very slowly at temperature below 10°C, although cultivars capable
of germinating at 6 to 8°C have been reported. There appears to be no close
correlation between the minimum temperature for germination determined
in the laboratory and seedling growth in the field (Carr and Hough, 1978).
The start of the growing season for maize is therefore normally determined
in temperate areas by the expected date when soil temperatures stabilize at
10°C or above. Provided seeds are planted in contact with moist soil, the time
taken for seedlings to emerge is then a function of soil temperature. Even
after emergence, soil temperature is important, as the growing point remains
below the soil surface for 6 to 8 weeks after sowing (Beauchamp and
Lathwell, 1967; Reinhardt, 1971). The leaves of young seedlings are yellow if

soil temperature remain low or if maximum daytime temperatures do not

 

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33

exceed 15°C because higher temperatures are needed for chlorophyll
formation than for germination (Alberda, 1969).

When the stem starts to extend, air temperatures assume a greater
importance. In southern England, mean monthly maximum and minimum
temperatures reach about 20 to 22°C and 11 to 13°C, respectively in July and
August. In Michigan mean monthly maximum temperature reach about 26 to
28°C in July. In Zimbabwe mean monthly maximum temperature reach about
27 to 29°C and 25 to 27°C for the lowveld and highveld, respectively. Daily
maxima are nearly always below the optimum (30 to 33°C) for photosynthesis
and development in maize (Carr and Hough, 1978). Differences in rates of
development of maize from place—to-place and year-to-year are therefore
influenced by soil and air temperatures.

Accumulated temperatures and maize development. Traditionally,
maize cultivars have been classified according to the average number of days
taken from sowing to maturity at a standard location. This approach leads to
many anomalies, as it fails to take into account the effect of temperature
differences between sites or between years.

Many attempts have been made to define the relationship between
temperature and plant development in simple quantitative terms. Despite
both theoretical and practical limitations, accumulating temperature as 'day
degrees' or so-called 'heat units' has proved to be a useful guide for
classifying maize hybrids according to their earliness and for delineating the
areas most suitable for production. This is a particularly useful approach in
places such as Canada or northern Europe where it is important to define as
closely as possible the areas where maize is likely to be grown successfully

and/or the most suitable cultivars for a given locality (Carr and Hough, 1978).

34

Many different methods of accumulating temperature have been
devised and used for predicting rate of development in maize, and other
crops. Often a base temperature, considered to be the minimum required for
growth and development, is subtracted from the daily mean temperature to
give the effective daily temperature. Positive values of effective
temperatures are then accumulated between prescribed stages of
development. The base temperature for maize is usually taken to be 10°C,
but thresholds between 6 and 8°C have been advocated for northern Europe
conditions. In the USA, limits are often prescribed to the recorded maximum
and minimum temperatures. The method now adopted by the USA National
Weather Service regards all maximum temperatures above 30°C as 30°C and
all minima below 10°C as 10°C. All these methods assume that the rate of

development is a linear function of temperature over the range considered;

2.2.4 Influence of moisture on maize growth and development.

One of the more important factors in maize production is the supply
and use of water (Shaw and Burrows, 1967). When moisture is not available
to the plant, evapotranspiration is reduced, a moisture stress is created. This
results in yield reduction. Limits of available water for growth is between the
'permanent wilting point' and 'field capacity', with water contents at
potentials of -15 bar and -0.10 bar, respectively (Ratliff, e_t a_l., 1983; Ritchie,
1981). Available soil moisture is the result of the amount of moisture in the
soil, and soil texture (moisture in sand tend to be more available than in clay).

Crop establishment. It is important to make sure that seeds are sown in
soil with adequate moisture level to avoid uneven establishment and low
plant populations. Under dry seedbed conditions a sowing depth in excess of

5.0 cm may be beneficial, and a single pass with a ring-roll will usually ensure

goods
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35

good seed-soil contact. Under wet soil conditions, however, compaction of
the soil above the seed can reduce seedling establishment. Once the seeds
have germinated, the roots start to extend into moist soil. Provided there is
no restriction to root growth, or excessive weed competition, maize seedlings
growing at relatively low temperatures (15-20°C) will tolerate periods of dry
weather without any apparent adverse effect.

Vegetative growth. Six to seven weeks after sowing the plant reaches
the 6—leaf stage and rates of stem extension and leaf expansion begin to
increase rapidly. Water stress at this time leads to a reduction in the rate of
cell and leaf expansion. If leaf growth is restricted, less incident radiation is
intercepted and crop growth rates and plant size are reduced. In areas of
Australia where the maize crop is normally irrigated, severe water stress
during male meiosis, two or three weeks before the tassels begin to emerge
from the upper leaf whorl, reduced final yield of dry matter by 29% (Downey,
1971).

Water stress during the period of rapid stem elongation reduces plant
height, although only the two or three internodes in the elongation phase
during the stress period are normally affected (Claasen and Shaw, 1970a;
Duncan, 1975). Stress during the elongation of the tassel and/or upper leaf
internodes also cause a delay in tasseling and silking, leading to a reduction
in grain yields (Claasen and Shaw, 1970b). In extreme cases, silking can be
delayed until nearly all the pollen has been shed.

Flowering. Early work in the USA showed that grain yield was reduced
by as much as 22% following wilting for only one or two days during
pollination, and by 50% if the period of stress was extended to six or eight
days (Reinhardt, 1971). Similar studies with container grown plants have

confirmed that grain yield is very sensitive to water stress during flowering

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36

(Claasen and Shaw, 1970b). Possible reasons for this include resultant
abnormalities in embryo-sac development and delayed silk emergence (Moss
and Downey, 1971) although other factors such as desiccation of the pollen
or of the silks may also prevent fertilization (Boyer and McPherson, 1975).
Recent work in California, however, has indicated that susceptibility of maize
plants to water stress during pollination is reduced if plants are previously
stressed or 'conditioned' during the late vegetative stage (Stewart gt a_l.,
1975). A consequence of severe water stress during pollination is that grain
develops on only part of the cob. Although some yield compensation can
occur by increase in individual grain size and weight, there is evidence that
this will be limited (Begg and Turner, 1976).

Grain development. In contrast to the effect of stress during flowering,
water stress during the period of grain development may be more important
for forage maize production than for grain. Low leaf water potentials and
stomatal closure will restrict photosynthesis, but the translocation of reserves
from the stem to the ear continues (Boyer and McPherson, 1975). Although
this will minimize losses in the yield of grain, the yield of forage will be
reduced. Water stress during ripening causes premature leaf senescence,
beginning with the lower leaves.

2.2.5 Nutritional requirements of maize

An adequate supply of nutrients is essential for normal growth of maize
and the production of high yields of grain. Soils generally contain large
quantities of plant nutrients but they are often in complex compounds that
cannot be absorbed by plants. These reserves are replenished naturally by
rainfall, decomposition of plant and animal remains and by weathering of

parent rock. Soils continually release nutrients in simpler forms that can be

taken up by plants, but rarely at a rate sufficient to match the needs of _an

37

actively growing and high yielding crop. The amount of fertilizer needed to
give maximum yields, or the most profit from an area of land, varies with soil
condition, climate and crop management. An understanding of these
interactions is necessary to implement an effective fertilizer policy.

Supplies of plant nutrients can be provided by rain, soil reserves, plant
residues, chemical fertilizers and manures:

Rain. The amounts (kg/ha) of plant nutrients in the annual rainfall in
eastern England have been estimated to be 16 nitrogen, 0.2 phosphorus, 3
potassium, 13 calcium, 4 magnesium, 18 sulphur, 27 sodium and 50 chlorine
(Bunting, 1978).

Soil. Most of the nitrogen (N) in soils is in the organic form and
constitutes a reserve that continuously releases plant-available N through
mineralization. This can supply 80 to 100 kglha N in fertile soils. When
manure or crop residues are freshly added to the soil, much of the N they
contain is unavailable to plants until the organic matter is decomposed by
microorganisms. Nitrogen is released from organic matter with a CM ratio of
less than 20 at an early stage of decomposition. Well-decomposed manure,
where the CM ratio has been reduced, will rapidly release plant available N
when incorporated into the soil.

A proportion of the phosphorus (P) in soils is also in the organic form
and unavailable to plants until decomposition releases inorganic phosphates.
Phosphates do not move easily in soils and are generally precipitated in forms
with low solubilities which cannot be absorbed by maize.

Potassium (K) is not leached from soils like N, nor is it combined into
insoluble forms to the same extent as P. Although most soils, especially clays,

contain large amounts of K, only a small fraction is soluble in the soil solution

 

and ava
requirer
Ex<
of a nun
(Cooke,
soils cor
needed.
All
tempera
Unlike K
is lost by
soil and
failure. 5
andthUS
SUI;
but in vei
with 10W
Che
of the N,
Nutrients,
Live
their diet
““351ng
additiona
beddinge
pmduced

38

and available to plants. Even in fertile soils, this cannot supply the major
requirement of a crop such as maize, which has a high demand for K.

Exchangeable magnesium (Mg) in soils is derived from the weathering
of a number of minerals. Generally soils provide 5 to 25 kg/ha of Mg per year
(Cooke, 1975). This is often sufficient for crop requirements. Clay and silt
soils contain the largest amounts and additional Mg is most likely to be
needed on acid, sandy soils, in regions of moderate to heavy rainfall.

All calcareous soils contain free calcium carbonate, and most soils in
temperate regions contain large amounts of exchangeable calcium (Ca).
Unlike K, there is no mechanism for conserving surplus Ca in the soil. Most Ca
is lost by leaching. The amounts lost, depend on rainfall, Ca reserves in the
soil and soil texture. Shortages can lead to soil acidity and eventually crop
failure. Some fertilizers, especially ammonium salts, accelerate the loss of Ca
and thus increase acidity.

Sulphur (S) is present in soils in both inorganic and organic compounds
but in very variable amounts. Deficiencies are most likely in well-drained soils
with low organic matter in non-industrialized areas.

Chemical fertilizers. The value of fertilizers is usually measured in forms
of the N, P and K content, although they may also contain other useful
nutrients.

Livestock manures. Most of the N, P and K ingested by farm animals in
their diet is voided in the feces or urine. This can be re-used to grow crops.
Livestock manures may be a mixture of feces plus urine, with or without
additional water. It may be in the form of a semi-liquid slurry, or mixed with
bedding as farmyard manure. The amounts and composition of the manure
produced depend on the type of livestock, housing and diet. Chumbley

(1977) reported median values for the quantities of plant available nutrients

39

in undiluted slurry (Table 2.2.2). Cooke (1975) reported the median values for
the quantities of plant available nutrients in solid farmyard manure (Table
2.2.3).

Crop residues and green manuring. Growing legumes add N to
cropping systems and it has been estimated that symbiotic fixation ranges
from 50 to 150 kg N/ha by arable legume crops to 200 to 400 kg N/ha by
clovers and lucerne (Cooke, 1975). Much N, however, may be lost by leaching
during wet springs as the roots decay. This, however, does not usually

happen in Zimbabwe because the springs are relatively dry.

Table 2.2.2. Quantities (kg/t) of major nutrients available to crops in
undiluted slurries (Chambley, 1979).

 

 

 

 

 

 

 

Type of slurry N P205 K20
Cattle 2.5 1.0 4.5
Pigs (dry meal fed) 4.0 2.0 2.7
Poultry 9.0 5.5 5.5

 

 

 

Table 2.2.3. Quantities (kg/t) of major nutrients available to crops in
farmyard manure (Cooke, 1975).

 

 

 

 

 

 

 

 

 

 

Type of Slurry N P205 K20
Cattle 1.5 ' 2.0 4.0
Pigs 1.5 4.0 2.5
Poultry (deep litter) 10.0 9.0 10.0
Poultry (broiler litter) 14.5 1 1.0 10.5

 

MAJ

wns
mns
NB

(mm
Nilrc
Whe
pole

redu

esser
thOu

matu

“We
direg
Siren
resist,-
apmn
COnCE
9??in
pmpo
SECOI

“elm.

40

MAJOR NUTRIENTS

Nitrogen. Nitrogen is essential for plant growth because it is a
constituent of all protein and is taken up by plants as ammonium or nitrate
ions. When soil conditions are favorable for the growth of maize, ammonium
N is rapidly converted to nitrate by nitrifying bacteria. Cold, wet, acid soil
conditions that inhibit nitrification of ammonium N are unsuitable for maize.
Nitrogen is the most important nutrient in determining the yield of maize.
When N is deficient, the embryonic leaf bud does not develop to its full
potential, cell division in the growing tip is retarded, and the result is a
reduction in leaf area, plant size and productivity.

Phosphorus. Phosphorus is a contituent of the cell nucleus. It is
essential for cell division and for the development of meristematic tissue. It is
thought that P also stimulates r00t formation in the maize plant, aids crop
maturity and affects the development of the grain (Arnon, 1974).

Potassium. Potassium, absorbed through the roots as the K+ ion, is
necessary for the normal progression of many physiological processes and
directly affects the rate of growth and yield of the crop. It contributes to the
strengthening of the schlerenchyma in the fibres and so increases the
resistance to lodging, a matter of special importance when high N has been
applied to maximize yields. Photosynthesis is markedly affected by the
concentration of extractable K in the leaves. Potassium is important for the
efficient use of water by maize and also has a considerable influence on the
proportion of grain in the ear.

SECONDARY NUTRIENTS

Calcium. Calcium is important in the formation of cell walls and in

neutralizing organic acids. It is an essential nutrient but soils usually contain

sufficient for crop requirements.

41

Magnesium. Magnesium forms a central part of the chlorophyll
molecule, and the rate of photosynthesis in maize leaves is closely related to
Mg concentration in the leaf tissue.

Factors affecting the response of maize to fertilizer. The magnitude of

the response of maize to fertilizer is not only dependent on the nutrient,
moisture and. temperature status of the soil, but is also affected by other
cultural practices involved in growing the crop.
Soil nutrient, temperature and moisture. The effect of the soil nutrient status
on the response of maize to fertilizer is dependent on the estimated
availability of N, P and K in the soil (Pain, 1978). The supply of nutrients must
be balanced according to the requirements of the maize crop to obtain
maximum yields. Abiotic factors that adversely affect soil aeration, such as
water-logging or compaction, can reduce nutrient uptake and hence the
response to fertilizers, especially on clay soils. Maize with an adequate water
supply has a deeper and more extensive root system that takes up more
nutrients by exploring a greater volume of soil (Arnon, 1974). Generally,
there is a yield response to larger amounts of N fertilizer in years with ample
rainfall than in dry years (Black, 1966). Increases in soil moisture increase the
amount of P in the soil solution and its availability to plants (Cooke, 1975).

Crop management practices. Fertilizer is only partially effective when
yield is limited by other supporting practices involved in growing the crop
such as poor seed bed preparation, late planting, low plant population, or
heavy weed infestation. The high plant densities necessary for maximum
yields from modern hybrids cause severe competition for plant nutrients.
Plant density and fertilizer rates must be increased simultaneously, assuming
that other factors are not limiting yield. For example, in the USA, the N

fertilizer needed to maximize forage yields of irrigated maize increased from

42

100 to 300 kg N/ha as plant density increased from 37,500 up to 75,000
plants/ha.

Cultivation improves soil aeration and the rate of decomposition of
organic matter, assuming soil moisture is adequate, and increases the amount
of N available to the crop. It has been reported that direct drilling, or zero
tillage, necessitates high rates of fertilizer application (Aldrich et al., 1975).
However, the mulching effect of the herbicide-treated crop residues left on
the surface can help to maintain adequate moisture for root growth in the
upper soil layers and improve the availability of nutrients to the crop.

Response to fertilizer in different maize growing areas. The results of
many field experiments in the USA suggest that 160 kg N/ha is required to
produce maximum yields of forage from modern hybrids. In France, in the
main maize growing areas in the south-west, where summer months are
relatively moist, 120 to 150 kg N/ha is recommended as a split-dressing. In
Germany and Austria, rates in kglha range from 100 to 140 for N, 50 to 60 for
P, and 125 to 175 for K. In Italy, best results are obtained with applications of
160 to 200 kg mm, 45 to 50 kg P/ha and 80 to 100 kg tha. In Zimbabwe, 300
kglha of compound D fertilizer (8% N, 14% P205, 7% K20 and 6.5% S) and
150 kglha of ammonium nitrate fertilizer (34.5% N) are recommended rates
for most maize growing areas.

2.2.6 Influence of pests on maize growth and development.
2.2.6.1 Weeds

Weeds are a major hazard to successful maize production. The risk of
severe weed infestation during the period of crop establishment is
considerable, especially for maize grown in the cool climate.

Couchgrass (Agropyron m). Recommendations for control of

heavy infestations of couch grass involves a two-year program with split

43

applications of atrazine in the first year. A fairly heavy rate of atrazine (2.2
kg a.iJha) is applied to growing couch grass in autumn before sowing,
followed by ploughing a few weeks later and then after cultivations to level
the land, then spraying a similar quantity of atrazine again. The residual
effects from atrazine applied in these amounts means that a second maize
crop must be taken, and a relatively low rate of atrazine (1.0 kg a.i.lha) is
applied a month before this is sown. EPTC is approved for couch control, but
satisfactory results are very dependent on accompanying cultivation
treatments. The herbicide should be applied to actively growing rhizomes
about two weeks before the maize crop is sown.

Perennial broad-leaved weeds. Deep-rooting weeds such as creeping
thistle (M mg), dock (Ru—mg spp.) and bindweed (Convolvulus spp.)
can be controlled by application of 2,4-D amine (1.1 kg a.i.lha) when the crop
is 8—1 5 cm tall with 4-6 leaves.

Late germinating annual weeds. Such weeds as fathen (ChenopodiUm
QM), knotgrass (Polygonum aviculare), redshank (E. persicaria) and
nightshade (Solanum M) may emerge late in the season when atrazine
activity has been largely dissipated or arrested by drought. In such
emergencies, 2,4-D amine is the most useful herbicide. Post-emergence
applications of mecoprop, dicamba + MCPA and other hormone weedkillers

also have possibilities for commercial use. Herbicides used for weed control
in maize in Zimbabwe are listed together with the rates normally applied
(Table 2.2.4).

2.2.6.2 Diseases

Seed-borne fungi. The most common fungi found on seed in the soil

are the Fusarium spp. which are responsible for root, stalk and ear rots in

mature plants. Surveys in 1984-85 showed that Fusarium graminearum,

Table 2.2.4. Commercial herbicide treatments for control of annual weeds

in maize in Zimbabwe.

44

 

 

 

 

 

 

 

 

 

 

Recommended dosage rate/ha
(kg or litres)
Herbicide Trade name .
Herbicide Commercial
kg a ilha product
' litres/ha
Metolachlor Dual 72 EC 094- 1.08 1.3 - 1.5
Metolachlor 4» Dual 72 EC + 0.94 - 1.08 1.3 - 1.5
atrazine Gesaprim 80 WP 1.76 - 2.80 2.2 - 3.4
Atrazine Gesaprim 80 WP 1.76 - 2.80 2.2 - 3.4
Cyanazine Bladex 50 WP 0.75 - 1.75 1.5 - 3.5
EPTC Eptam Super 72 EC 1.51 - 3.02 2.1 - 4.2
Bentazon Basagran 48 SL 1.44 3.0
Terbuthylazine + Gesaprim «- 3.5 - 5.5
metolachlor
Atrazine + EPTC Gesaprim 80WP 1.76- 2.80 2.2 - 3.4
+ Eptam 72 EC 3.2 - 5.3

 

 

 

 

 

 

Fusarium moniliforme and Qiplodia maydis are the major causal agents of
cob rots (Page e_t 21., 1985). Control measures include use of resistant
varieties, early harvest and use of carbofu ran 10G or dimethoate 40 e.c.

Seedling blight. Pfihium spp. are widely distributed in all soils and are
most active in wet conditions. These fungi cause root and hypocotyl rot with
brown, water soaked, lesions and sloughing of the cortex. Soil-borne
Fusarium spp. can also infect and kill seedlings. Because of the risk of soil-
and seed-borne fungi infecting maize, the application of a seed treatment
chemical is essential. The best protection is given by captan or thiram.

Stalk rot. The main causal organism of stalk rot include Diplodia

maydis, Gibberella zeae, Ervvinia carotovora and Fusarium spp. (Page e_t a_l.,

1985). The symptoms of stalk rot are similar regardless of the species of

§u_s_.
ma:

CdU

0.5

and
Hee

max

syst
The
the

infe

IS aj

Obli

M

will

45

Fusarium responsible. Weakened stems collapse at the nodes and lodging
may be severe in wet windy weather. Reductions in grain yield and quality
caused by stalk rot have been reported from many countries and Cook (1978)
estimated that stalk rot can reduce the dry-matter yield of a 12t/ha crop by
0.5 tlha.

Smut diseases. Maize is susceptible to two smut diseases; head smut
and common boil smut. The latter is widespread and occurs in most regions.
Head smut is of minor importance. Common smut is caused by Ustilago
m. This disease causes yield reductions of up to 10%.

The build-up of spores in soil is best prevented by use of cropping
system in which maize is not grown on the same land at frequent intervals.
The removal and destruction of galls from lightly infected crops may reduce
the build-up of inoculum. Seed treatment with benomyl can reduce smut
infection.

Leaf diseases. Southern leaf blight caused by Helminthosmrium maydis
is an important disease of maize. Typical lesions of southern leaf blight are
oblong (6 x 20 mm), have parallelsides and are tan or straw colored.

Northern leaf blight caused by Helminthosporium turcicum reduces
yield in maize. This fungus causes the development of long, elliptical lesions
which are larger than those found in southern leaf blight.

Common maize rust (Puccinia sorghj) occurs sporadically on maize.
Occasionally up to 25% of the leaf area may be affected. Also _P_. polysora has
been reported in Zimbabwe.

Virus diseases. Maize streak virus (MSV), which is transmitted by
_C_Zicadulina mbila (Naude), is the most important virus disease of maize in
Zimbabwe. Control of the vector with carbofuran 1OG applied at 2.0 kg
a.iJha effectively increases maize yield by up to 40% (Mzira, 1984).

46

2.2.6.3 Insects

As the acreage of maize has increased , population densities of insects,
as well as the number of species attacking maize has increased. With each
new development in maize production, whether in plant breeding, fertility,
irrigation, or even insecticides, insects adapt to the new environment.

Insects that attack seed. Seed-maize maggot (Hylemya platura) may
devour the entire seed contents leaving only the seed coat. Attacks by this
insect reduce maize stands.

Seed-maize beetles (Agonoderus lecontei and Mg i_m_pressifrons)
devour the contents of the seed. Any condition which retards germination
results in increased seed bettle damage.

Wireworms (Elateridae spp.) hollow out maize seeds before
germination occurs. After germination the worms feed on the underground
stem or drill holes in the base of the stalk.

Delay in maize planting until soil temperature and moisture are
conducive to rapid germination is a cultural method used to control insects
attacking maize seeds. Summer fallowing, autumn plowing, and control of
weed growth are said to aid in controlling wireworms. Aldrin insecticide is
also used to control these insects.

Insects that parasitize maize roots. White grubs such as (Eulepida
mashona) feed on the roots of the maize plant; this results in severe stunting.
In light infestations, lodging may occur because of the weakened root system
and yields may be reduced. Autumn plowing will reduce the population of
white grubs in the soil. Also aldrin and carbofuran insecticides can be used to
control white grubs. I

Insects that feed on the underground portion of the stalk. The black

cutworm (Agrotis ipsilon) is most damaging to small maize plants. Cutworms

normally re
rotation w
populations
tutworms.
Insect
(m
infestations
controlled b
Grasshi
outer edges
0’ the Stalk a
causing thee
never reach
enemies. cg
c°”"°' grassl
Maize I;
leaves, will c;
alid silks may
alihids.
insects ‘
(W M
borer that "la
in 1% Fitment.
is reCOmmen d
diazino” (an
Maize Si

47

normally remain hidden in the soil during the day and feed at night. Crop
rotation with some other crops other than maize can reduce cutworm
populations. Aldrin, carbofuran and cypermethrin can be used to control
cutworms.

Insects that feed on exposed maize leaves. The true armyworm
(Pseudaletia unipuncta) cause a serration or stripping of the leaves. If
infestations are severe, yield losses may be great. Armyworm can be
controlled by carbaryl.

Grasshoppers (Melanoplus spp.) are chewing insects that feed from the
outer edges of leaves inward. When numerous on maize, they may eat part
of the stalk and ears. They attack fresh silks, reducing pollination and often
causing the ears to be barren. Plowing buries the eggs so that young hoppers
never reach the surface, or it exposes the eggs to weather and natural
enemies. Carbaryl, diazinon, fenitrothion and malathion can be used to
control grasshoppers.

Maize leaf aphid (Rhopalosiphum maidis), when heavily infesting maize
leaves, will cause wilt, curl, and show yellow or even dead patches. Tassels
and silks may be covered with honeydew. Malathion can be used to control
aphids.

Insects that feed in whorls, stalks and ears. European corn borer
(Ostrinia nubilalis) first generation decreases yields by 3 to 4 percent for each
borer that matures per plant. Second generation borer decreases yields by 4-
to 14- percent for each mature borer per plant. Midseason plantings of maize
is recommended for control of the European corn borer. Also carbaryl and

diazinon can be used to control borers.

Maize stalk borer (Busseola fusca) and pink stem borer (Sesamia

M) are the stem borers which are commonly found in Zimbabwe.

48

Larvae of these insects damage leaves (causing windows and short holes),
create tunnels in the maize stems and destroy grain on cobs.

Other insect pests of maize. Termites (Hodotermes and Microtermes
spp.) cause high maize crop losses in Zimbabwe by cutting down plants using
their sharp mandibles prior to damaging cobs on the fallen stalks. Termites
can be controlled by aldrin.

Leaf hopper (Cicadulina mbila) is an important vector of the maize
streak virus. This hopper can be controlled by applying carbofuran or
dimethoate. Culturally, the insect can be controlled by eliminating weeds and
volunteer maize plants, practicing crop rotation and planting early before
high g. M populations. I

Snout beetles, comprising three main species, Systates exaptus,
Mesoleurus dentig and Tanymecus destructor, normally damage maize
seedlings. These beetles can be controlled by applying carbaryl 85 w.p. Good
weed control together with delay by three weeks in planting also provide
effective control. A delay in planting by three weeks permits the grubs to
undergo pupation, the developmental stage which does not damage
seedlings.

Elegant grasshopper (Zonocerus EIElaI’IS) is a polyphagous insect
capable of damaging young maize severely. This insect is a periodic pest of
maize in Zimbabwe communal farms. Carbaryl 85 w.p. and diazinon 30 e.c.
are effective for the control of this pest whenever it occurs in numbers large
enough to warrant chemical application.
2.2.6.4 Nematodes

Maize is an important crop in the world and about 120 million hectares
are under annual production (Norton, 1984). Several plant-parasitic

nematodes are, however, of economic importance in maize production.

he
the
DO
iOC

GXC

W8!
NOI
6,0i

are
botl
DEn.
SUbs
Ziral
heig
i"Oil

"We

49

Plant-parasitic nematodes that have been found associated with maize,
either singly or jointly with other plant-parasitic nematodes are listed in
Table 2.2.5.

Root-lesion nematodes, Pratylenchus spp. Different species of
Pratylenchgs can affect the growth of maize. Bird (1978) and Laughlin (1977)
reported thatfi. penetrans was an important pest of maize in Michigan and in
Texas, _P_. gga_e_ caused considerable damage to maize roots in localized spots
in the field (Harrison, 1952). Endo (1959) showed that maize was an excellent
host of E. brachyurus and E. E. In Zimbabwe, Martin 33 2'; (1975) reported
that E. brachyurus and 3. 593g can cause maize yield loss of up to 30% and
population densities of the nematodes can be as high as 2,100 per 1.0 gramof
root. Koen (1967) found 3. brachyurus and _P. g population densities in
excess of 1,300 per 1.0 gram of maize root in S. Africa with percent incidence
of 29 and 51, respectively. Chevres-Roman gt _a_l. (1971) showed that E. gag
was a serious parasite to both maize and sorghum in greenhouse studies in
North Carolina. The population at which damage occurred appeared to be
6,000 and 8,000 nematodes per 475 cm3 of soil.

Olowe and Corbett (1976) demonstrated that E. brachyurus and E. 29$
are pathogens of maize in Nigeria. They found in monoxenic culture that
both nematodes broke through cells of the endodermis of maize and
penetrated the stele. This feeding led to the deposit of a reddish-brown
substance in phloem and xylem tissues which occluded many of the elements.
Zirakparvar (1980) found that E. hexincisus caused significant reduction in
height and in top and root weights of maize in clay pots 90 days after
inoculation with 20,000 nematodes per pot. Norton and Hinz (1976)

increased maize yields in sandy 'soils in Iowa up to 26 percent by application

50

Table 2.2.5. Plant-parasitic nematodes associated with maize.

 

Nematodes

Distribution

 

Aghelenchoides spp.

Zimbabwe (Martin, 1955; Martin 3i 1969)

 

Aghelenchus spp.

Zimbabwe (Martin e_t§_l., 1969)

 

Belonolaimus spp.

Belonolaimus longicaudutus

Georgia (Johnson and Chalfant, 1973)

 

South Africa (Louw, 1982)

 

Criconemella ornatug

Georgia (Johnson and Chalfant, 1973)

 

Criconemella spp.

Zimbabwe (Martin, 1955)

 

Ditylenchus digsaci

Europe (Kort, 1972), S. Africa (Louw, 1982) and Zimbabwe
(Martin, 1955)

 

H. multicinctus

Helicotylenchus egthri nae

Malawi (Mughogho and Choo, 1969)

 

Malawi (Mughogho and-Choo, 1969)

 

Helicotylenchus spp.

Malawi (Mughogho and Choo, 1969), S. Africa (Louw, 1982)
and Zimbabwe (Martin, 1955)

 

 

Heterodera avenae S. Africa (Louw, 1982; Walters, 1979)
H. zeae India (Kaul and Sethi, 1982a; Kaul and Sethi, 1982b)

 

Hoglolaimus galeatgg

Iowa (Norton and Hinz, 1976)

 

H. indicus

India (Siyanand e_tgt., 1982)

 

Zimbabwe (Page et al., 1985)

 

.F-__—
H. ararobustus
‘ Hoglolaimus spp.

Zimbabwe (Page e_ta_l., 1985)

 

Lon idorus brevinculatus

Michigan (Bird, 1985 pers. comm.)

 

Meloidogyne arenaria

Zimbabwe (Martin e_tgl_., 1969)

 

M. iavanica

Malawi (Mughogho and Choo, 1969) and Zimbabwe
(Martin e_t. 21., 1969)

 

Mm

India (Kaul and Sethi, 1982a; Kaul and Sethi, 1982b),
Tennessee (Southards, 1971) and Zimbabwe (Martin _t _I.,
1969)

 

Meloidggyne spp.

Malawi (Mughogho and Choo, 1969), S. Africa (Louw, 1982;
Walters, 1979) and Zimbabwe (Martin, 1955)

 

Paralongidorus spp.

Zimbabwe (Page gt a_l., 1985)

 

Paratrichodorus spp.

S. Africa (Walters, 1979)

 

Pratylenghgs MM

Nigeria (Egunjobi, 1974; Egunjobi and Bolaji, 1979; Olowe,
1977; Olowe and Corbett, 1976), North Carolina (Endo,
1959), S. AFrica (Louw, 1982; Koen, 1967) and Zimbabwe
(Martin gt. gl_., 1975; Martin gt_gl_., 1969).

 

P. crenatus

Europe (Kort, 1972)

 

 

 

E. hexincisus Iowa (Zirakparvar, 1980; Zirakparvar, 1979; Zirakparvar gt
gt, 1980)
. P. minyus Ontario (Townshend, 1972)
E. neglectu; Europe (Kort, 1972)

 

l3. genetrans

Michigan (Bird, 1978; Caswell, 1982; Laughlin, 1977),
Ontario (Townshend, 1972) and S. Africa (Louw, 1982)

 

 

P. thornei

 

EuroE (KortI 1972) and India (Siyanand et al., 1982)

 

 

L... .mLR.....:::.... m... .mfl..w..w..m..m. Em. E8080:

 

Table

Table 2.2.5. Continued.

51

 

Nematodes

Distribution

 

I‘D
N
0
0
0

Nigeria (Olowe, 1977; Olowe and Corbett, 1976), North
Carolina (Endo, 1959), Panama (Tarte, 1971), S. Africa
(Louw, 1982; Koen, 1967), Tennessee (Chevres-Roman e_t g[.,
1971; Southards, 1971), Texas (Harrison, 1952) and
Zimbabwe (Martin gt gl_., 1975; Martin gt _a_l_., 1969)

 

Ragogholus simili;

S. Africa (Keetch, 1972) and Zimbabwe (Anon, 1973; Martin
gt a_l., 1969)

 

Rotylenchulus rvus

 

flfrica (Furstenberg, 1974) and Zimbabwe (Martin e_t. 91.,
1969; Page _e_t gl_., 1985)

 

3. variabilis

Zimbabwe (Anon, 1973)

 

Rotylenchulus spp.

S. Africa (Louw, 1982) and Zimbabwe (Martin, 1955)

 

F'—_—'_"-.—
Rotylenchus incultus

 

Zimbabwe (Page gt a_l., 1985)

 

Rotylenchus spp.

S. Africa (Louw, 1982)

 

Paratrophurus spp.

Zimbabwe (Page gt a_l., 1985)

 

Scutellonema brgghyurum

Malawi (Mughogho and Choo, 1969) and Zimbabwe (Page
e_t 91., 1985)

 

swam

 

M—alawi (Mughogho and Choo, 1969) and Zimbabwe (Page
gt 91-. 1985)

 

S. unum

 

Zimbabwe (Page _et 91., 1985)

 

—

Telotylenchus obtusus

Zimbabwe (Page’gt an. 1935)

 

Telotylenchus spp.

S. Africa (Louw, 1982)

 

Trichodorus christei

Georgia (Johnson and Chalfant, 1973)

 

Trichodorus spp.

Malawi (Mughogho and Choo, 1969), S. Africa (Louw, 1982)
and Zimbabwe (Anon, 1969; Martin, 1955 and Martin gt a_l.,
1975)

 

Tylenchorhynchus ngdus

Michigan (Bird, 1978)

 

I. vulgaris

India (Kaul and Sethi, 1982a; Kaul and Sethi, 1982b;
Siyanand gt§_l., 1982)

 

Tylenchorhynchus spp.

' S. Africa (Ga-w, 1982) and Zimbabwe (Martin, 1955)

 

Xighinema louisi

Zimbabwe (Page gt a_l., 1985)

 

 

Xighinema cf. variable

 

Zimbabwe (Page e_t a_l., 1985)

 

Xighinema spp.

 

 

S. Africa (Louw, 1982) and Zimbabwe (Page gt a_l., 1985;
Martin 1955)

 

 

52

of nematicides. The difference between treated and untreated plots was
attributed to damage caused by _P. hexincisus and flgplolaimus galeatus.
Bergeson (1978) reported that maize plants that were infected by
Pratylenchus spp. had 14% lower yeield in Indiana.

The penetration of maize roots by E. genetrans and E. m_in_y_i_i§ was
tested by Townshend (1972) in three Ontario soils. Low bulk densities
generally favoured nematode penetration of maize roots in all soils. Kort
(1972) reported that E. crenatus, E. neglectus and E. th_orn_ei caused more
damage in maize in light soils, loamy soils and heavier soil textures,
respectively.

Stubby root nematodes, Trichodorus spp. In Zimbabwe, Martin _t gt.
(1975) found that Trichodorus spp. can cause severe early stunting of maize
plants. Perry (1956) found that Trichodorus spp. caused damage to maize in
the USA. Johnson and Chalfant (1973) also showed that Belonolaimus
lo_n_gicaudatus, Trichodorus christei, Pratylenchus zeae and Criconemella
mtg; reduced maize yield by up to 31 % in Georgia.

Root-knot nematodes, Meloidogyne spp. The root-knot nematode, M.
iavanica, induced pathological symptoms including galling of roots and
depressed growth vigor on maize in Egypt (Ibrahim and Rezk, 1976). In
Zimbabwe, when maize was sown in sandy soils heavily infested with M.
iavanica, 350 root-knot juveniles parasitized the root system of a single plant
within seven days of sowing, and by the 33rd day, egg-producing females
were seen in small galls (Martin gt §_l., 1969). Martin (1955) found swellings
on the roots of maize infested with M. arenaria and moderate infestations of
M. incognita acrita, although there were few females with egg masses. Van
der Linde (1956) tested different maize cultivars for their susceptibility to

Meloidogyne species and found infestation with M. incognitg acrita, M.

num

l969

blacl

53

javanica and M. arenaria th_a_r_ng§_i but not with M. hgglg. Kaul and Sethi
(19823 and 1982b) observed 72% and 61% penetration of Heterodera zeae
and M. incognita in maize roots, respectively when inoculated simultaneously
in the presence of Tylenchorhynchus vulggris. Southards (1971) reported that
fall tillage in Tennessee, significantly reduced the population density of M.
incognita the following growing season.

Other nematodes. Kort (1972) reported that Ditylenchus djgsggi cause
local hypertrophy and hyperplasia in maize. Others symptoms include basal
swellings, dwarfing, twisting of stalks and leaves, and shortened internodes.
Q. M is a problem on sandy loam but is rarely a problem on light sandy
soils. In Zimbabwe, Radopholus similis, root-lesion nematode and root-knot
nematode juveniles were found in dissected lesions (Martin gt §_I., 1969). In
addition to the above mentioned nematodes, Aphelenchus spp.,
Aphelenchoides spp. and Helicotylenchus spp. were observed in small
numbers in the roots. In Zimbabwe, I}, _s_im_ili§_ often parasitize maize (Anon,
1969) and Keetch (1972) found in South Africa that the root damage caused
by R. si_m_ili_s on maize was extensive and consisted of large brown to reddish
black lesions along the roots.

Anon (1973) found that the most numerous plant-parasitic nematodes
in maize included species of Rotylenchulus and Helicotylenchus. The
population density of Rotylenchulus variabilis rose rapidly under maize in
March and April, falling again slightly when the plot was plowed, but
moderately high levels of Helicotylenchus spp. were maintained. Cultivation
of maize on previously undisturbed land in South Africa was followed by a
massive increase in the population density of Rotylenchulus garvus
(Furstenberg, 1974). High population densities of 5. w have also been

recovered in maize roots in Zimbabwe (Page gt a_l., 1985).

54

In Michigan, Longidorus brevinculatus is reported to cause extensive
damage to maize plants grown in sandy soils (Bird, 1985 pers. comm.). This
nematode is a major problem is areas which have been recently put under
maize cultivation with the advent of extensive irrigation facilities/machinery.
In Zimbabwe, Paralonggidorus spp. was associated with extensive damage of
maize plants in one communal area with very sandy soils. The pathogenicity
of this nematode on maize, has not been established. Also Hoplolaimus
girarobustus was found parasitizing maize roots in Zimbabwe but damage
caused by this nematode on maize has not been established (Page gt a_l.,
1985).

Other plant-parasitic nematodes that have been found associated with
maize production include X_ighinema louisi, 5. cf. variableJ Scutellonema
brachyurum, _S. magniphasmum, S. unum, Telotylenchus obtusus,
Paratrophurus spp., and Rotylenchus incultus (Page t a_l., 1985), but their

pathogenicity on maize has not been established.

3. EXPERIMENTATION

3.1 PLANT-PARASITIC NEMATODES ASSOCIATED WITH MAIZE IN ZIMBABWE
3.1.1 Introduction

The extent of damage on maize that plant-parasitic nematodes cause in
communal areas, has not been accurately assessed. Also, the incidence and
population densities of the major nematode pests of maize have not been
related to edaphic factors which are known to influence the population
dynamics and pathogenicity of plant-parasitic nematodes.

The objectives of this study were to: (a) assess the incidence and
population densities of plant-parasitic nematodes associated with maize in
communal farms, (b) evaluate the relationships between the population
densities of Pratylenchus spp. and natural farming regions, (c) evaluate the
relationships between population densities of E. ge_ae_ and environmental
factors such as soil temperature, moisture, texture and pH, and (d) evaluate
the relationships between population densities of E. z_ea_g and maize yields in
Manicaland province.

3.1.2 Materials and Methods

A nematode survey was used to identify plant-parasitic nematodes
associated with maize in Zimbabwe communal farms. Three months before
, the survey was started, data on communal farms was collated from the
Department of Agriculture Technical and Extension Services. The data
collection included grouping all the communal areas into their respective
provinces, then information on the natural farming regions, soil type,

average summer and winter temperatures, number of farming families and

55

area U!
which
maize I
would
for plan
and mi
area W
ratio w
TI
to let
could b
Chlorot
restrim
detailm
Zimbab
of Ag”
Would
admimS
Proving.
designe
9'0Wn;
Used an

56

area under maize for each communal area were tabulated. Communal areas
which were to be sampled for plant-parasitic nematodes associated with
maize were selected so that all the natural farming regions in the province
would be equally covered. About 25% of the communal areas were selected
for plant-parasitic nematode sampling in each province. The number of soil
and root samples which were to be collected from each selected communal
area were a function of the area under maize in the communal area. The
ratio was one soil and root sample per 1,000 hectares under maize.

The survey was conducted in all the provinces from 3rd February, 1986
to 21st March, 1986, when symptoms of plant-parasitic nematode damage
could be easily observed. The symptoms included patchy stunted growth and
chlorotic maize plants. Logistical problems caused the detailed survey to be
restricted to one province, Manicaland. This province was selected for the
detailed survey because it has all of the five farming regions found in
Zimbabwe. Visits to all the communal areas were made with the Department
of Agricultural Technical and Extension Services so that their local staff
would assist us in locating farms to be sampled. A questionnaire was
administered to most of the farms that were visited, especially in Manicaland
province, before any samples had been collected. The questionnaire was
designed so that it evaluated location of the farm, name of the farmer, crops
grown and their estimated yields, crop rotation used, fertilizer and pesticides
used and their estimated expenses, seed grown, size of the farm, size of the
household, and whether the farmer was self-sufficient (Appendix 5.1.2).

Soil and root samples were collected from 49 communal areas (Fig.
3.1.1) and 18 of these communal areas were in Manicaland province. (Fig.
3.1.2) A sample was composed of five sub-samples collected at random from

about one tenth of a hectare where maize plants were stunted and chlorotic.

57

Fig. 3.1.1. Oomunal farms sampled for plant-parasitic nematodes

  
  

in Zimbabwe.
Korlbo
. is... ..
' ndeya ‘
kao
I x Oma x Maramba
nga N ..

m x Nkayzl. m

x Chiwundura
\ 06m
X Ntflbfilifld ' '- ‘ 0
Mo 0 .
\ QBJLAWAYD fl : u x if)

x 011' 1 CNN"?
I! c1 ’
Mpande Mberengwa x '(
x . Godlw v x Nye na Ndowoyo \
‘9
'% Mphoengs x x Mara . . oCh’ndzl .o'
Gwaranyomba
We” I X Hatib

" 80..
I -- 1000mm° \ /
no—

750 - 1000mm. \A~
m’ w-.\/

III - 550-500m . City
at Comunal area

Ill " ‘50- 650 mm.

Y - Below 650 Zambezi \blley.
Below 600 Saw-um \hflq

Fig. .

58

Fig. 3.1.2. Communal farms sampled for plant-parasitic nematodes

in Manicaland province.

     
   
  

he Ho aenby

ta North

u ask South

 

p...

. City
x Communal area

59

Moist soil samples were collected from a depth of about 10-20 cm and put

into a labeled plastic bag and sealed. Root samples were collected by

randomly digging the root system of five plants then soil was shaken off the

root system and part of the root system was cut into labeled plastic bags. The

samples were put into a wooden cooler box (100 x 50 x 50 cm) painted white

and lined with a thin layer of tin inside. The following parameters were

evaluated from the collected samples:

1.

The maize root system was chopped into small pieces about 0.1-0.5
cm long and 10.0 grams were selected at random and processed
using the marceration-centrifugal-flotation technique (Southey,
1985 p. 54) and the recovered nematodes were fixed using the
killing heat technique (Southey, 1985 p.65). The fixed nematodes
were counted under a stereoscopic microscope. After identifying
the nematodes to genera level, the nematodes were prepared for
mounting using the rapid lactophenol method (Southey, 1985 p. 68-
9). Several nematodes of the same genera were mounted on a glass
slide using the mounting microscope slide technique (Southey, 1985
p. 75). The mounted slides were then clearly labeled with the name
of the farmer and communal area, crop in which the nematodes
were recovered, name of the nematode genera on the slide and
date when the sample was collected. After labeling, the slides were
packed into boxes and they were sent to Drs. M.R. Siddiqi and DJ.
Hunt, taxonomists at the Commonwealth Agricultural Bureaux,
International Institute of Parasitology, for species identification.

Soil was thoroughly mixed in a tray and 100 cm3 was processed

using the centrifugal-flotation technique (Jenkins, 1964) then the

60

fixing, counting, mounting and labeling techniques outlined for
roots were followed.

Soil samples from Manicaland province were also submitted to the
Chemistry and Soils Research Institute for texture analysis and pH
measurements (Appendix 5.1.2).

Population densities of E. _z_e_ag spp. which were generated from the
study were related to environmental factors, namely, rainfall and
temperature for 1985/86 growing season. The weather data was
collated from 41 stations and 71 sub—stations under the Zimbabwe
Department of Meteorological Services (Appendices 51.3-51.4).

3. gggg and maize yield data that were estimated during the survey
were transformed (logarithmic transformation) during analysis
because the data exhibited a lognormal distribution. The data were
analyzed using a statistical package GENSTAT. One way analysis of
variance with unequal number of replications between E. z_egg
population densities and different natural regions, rainfall and
temperature regimes was carried out using the national survey
data. Also one way analysis of variance with unequal number of
replications was carried out between E. fig population densities
and soil texture and pH regimes and level of nutrient applications.
After the analysis of variance, parameters which had greater than
two levels, orthogonal comparisons were carried out. To contrast

the totals, the following formula was used for the F-test:

F = K 26:25 )/ M83]

 

61

where: MSE (residual mean square error) is taken from the

ANOVA table.

r; = number of observations (replications) within the
level

c; = orthogonal contrast coefficient for the totals to be
compared

The totals of the variables to be compared were derived by multiplying
the mean in the ANOVA table for each level by the number of
observations within that level.
Q = 2 c; xi the linear function for the contrast
where: x; are the totals to be compared.
An example for 2 totals, x1, x;
O = 1 * x1 + (-1) * x2 linear function for contrasting totals
X1. X2
where: c1 = land C2 = -1 the orthogonal contrast coefficients.
Regression analysis was also carried out between the population
densities of _E. _z_e_ag that were recovered and annual rainfall, February
and March temperatures and maize yield in the respective farms.
3.1:3 Results
Thirteen plant-parasitic nematode genera were found associated with
maize plants from the 114 soil and root samples that were collected (Table
3.1.1). The most prevalent plant-parasitic nematodes were Pratylenchus
zeae, Scutellonema spp., Helicotylenchus spp., Rotylenchulus Spp.,
Pratylenchus spp., Pratylenchus brachyurus, Criconemella spp.,
Rotylenchuslus parvus and Scutellonema unum. Plant-parasitic nematodes
which were occasionally found associated with maize were Meloidogyne

spp., Trichodorus spp., Tylenchorhynchus spp., Paratrichodorus minor,

Tal

—A__ A; A; C; C; H; H.h|rl; 9.; 3,;0 £9; p; 01; finish; 5: S; a}; r}; (.8.

«N!

Ki

62

Table 3.1.1. Plant- arasitic nematodes found associated with maize in
Zimba we communal farms.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Nematode
Plant-parasitic nematodes Abso'Utfii,3$quency p0 3:21:13???
100 cm3 soil
Aphelenchoides sp. 0.9 42.0
Aphelenchus gw 0.9 13,3150
Aghelenchus sp. 0.9 78.0
Criconemella sphaeroceghala 1.8 7.0
Criconemella sp. 16.7 7.0
Helicotylenchgg sp. 32.5 10.0
Hoglolaimus sp. 0.9 1,191.0
Meloidogyne sp. 6.1 35.3
Paratrichodorus Mg; 2.7 319.0
Pratylenchus sp. 21.9 107.0
Pratylenchus brachyurus 21.1 4,415.1
Pratylenchus goodeyi 1.8 836.0
Pratylenchus _z_e_a_ig 52.6 2,284.9
Rotylenchulus sp. 38.9 129.8
Rotylenchulus m 15.8 224.3
Rotylenchtg brevicaudatus 1.8 175.0
Scutellonema sp. 52.6 21.5
Scutellonema brachyurum 2.7 46.8
Scutellonema labiatum 0.9 24.0
Scutellonema magnighasmum 2.7 51.0
Scutellonema gm 13.2 53.0
Trichodorus sp. 4.4 22.4
Tylenchorhynchus sp. 3.5 3.7

 

 

Key
1Absolute frequency (%) = no. of samples contgining a species
no. of samples collected

63

Scutellonema brachyurum, Scutellonema magliphasmum, Pratylenchus
QOOdEJi, Criconemella sphaerocephala, Rotylenchus brevicaudatus,
Aphelenchoides spp., Aphelenchus avenae, Aphelenchus spp., Hoplolaimus
spp., and Scutellonema labiatum.

Only a few species of plant-parasitic nematodes were, however,
recovered in high population densities from all the samples that were
collected. Plant-parasitic nematodes which had high population densities
were 3. brachyurus and E. gggg which constituted 38.5 and 50.0% of the total
population of plant-parasitic nematodes that were recovered from all the

samples, respectively. Rotylenchulus spp., R. parvus and Pratylenchus spp.,

 

had intermediate population densities and they each contributed 1.6, 1.5,
and 1.0% of the total population of plant-parasitic nematodes that were
recovered from all the samples (relative density), respectively. Plant-parasitic

nematodes which had low population densities were Aphelenchoides spp., _A_.

 

avenae, Criconemella spp., g. gphaerocephala, Helicotylenchus spp.,
Hoplolaimus spp., Meloidogyne spp., _P. goodeyi, P. M, R. brevicaudatus,
Scutellonema spp., §. brachyurum, _S_. labiatum, _S. magniphasmum, §. m,
Trichodorus spp., and Tylenchorhynchus spp., which each constituted less
than 0.6% of the total population of plant-parasitic nematodes recovered
from the samples that were collected.

Different natural farming regions affected the diversity and population
densities of plant-parasitic nematodes (Table 3.1.2). The number of plant-
parasitic nematodes species that were recovered from samples were 4, 16, 16,
18, and 7 for natural regions I, II, III, IV, and V, respectively. B. brachyurus
and _P_. Egg were equally prevalent in natural regions II to IV, but in natural
regions I and V, E. gag was more prevalent than B. brachyurus (Table 3.1.3).

Similarly, Scutellonema spp. were equally prevalent in natural regions I to IV

64

Table 3.1.2. Plant-parasitic nematodes found associated with maize in
different natural regions of Zimbabwe.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Nematode

Natural . . Absolute ulati on
region Plant-parasitic nematodes frequency (%)1 denim/210.0 grams
roots + 100 cm3 soil

1 Hglicotylenchus sp. 25.0 (n = 4) 68.0

Pratylenchus brachyurus 25.0 3,676.0

Pratylenchus z_eg 75.0 1,140.7

utellonema sp. 100.0 11.8

ll Criconemella sp. 10.3 (n = 29) 17.0

Criconemella sphaeroceghala 3.4 1 1.0

Helicotylenchgg sp. 34.5 17.4

Meloidogyng sp. 13.8 53.8

Pratylenchus sp. 10.3 22.7

E. brachyurus 34.5 3,800.3

Latvlenmgg qoodeyi 3.4 815.0

E. Legg 51.7 6,343.5

Rotylenchulus sp. 31.0 240.9

Rotylenchulus parvus 10.3 260.7

Rotylenchgs brevicaudatus 3.4 340.0

Sgutellonema sp. 58.6 32.3

gutellonema unum 10.3 148.7

Trichodorus sp. 6.9 46.5

Tylenchorhynchus s1 3.4 3.0

III Aphelenchus gvegg 4.2 (n = 24) 13,3150

Criconemella sp. 12.5 3.3

g. sghaerocephala 4.2 3.0

Helicotylenchus sp. 29.2 14.7

Paratrichodorus minor 12.5 319.3

Pratylenchus sp. 33.3 283.8

E. brachyurus 37.5 5,649.6

E. goodeyi 4.2 846.0

E. 23g 29.2 3,502.6

Rgtylenchus sp. 4.2 23.0

3. garvus 16.7 183.8

_R_. brevicaudatus 4.2 10.0

§_c_utellonema sp. 54.2 24.0

§. brachyurum 4.2 51.0

Trichodorus sp. 4.2 12.0

Tylenchorhynchus sp. 4.2 2.0

IV Aghelenchoides sp. 2.0 (n = 51) 42.0

Aphelenchus sp. 2.0 78.0

Criconemella sp. 23.5 7.3

Helicotylenchgg sp. 31.4 45.5

Hoplolaimus sp. 2.0 1,191.0

Meloidmyne sp. 5.9 20.7

 

 

65

Table 3.1.2. Continued.

 

 

 

 

 

 

 

 

 

 

 

 

 

Nematode

Natural . . Absolute ulation
region Plant-parasitic nematodes frequency (%)1 (19112123100 grams
roots + 100 cm3 soil

Pratylenchgs sp. 17.6 64.7

E. brachyurus 7.8 3,661.7

E. ;e_ag 64.7 2,281.5

Rotylenchulus sp. 35.3 144.0

5. garvus 21.6 217.0

§gutellonema sp. 49.0 1 1.3

§. brachyurum 3.9 45.5

§_. labiatum 2.0 48.0

g. magnighasmum 5.9 59.0

g. unum 21.6 51.7

Trichodorus sp. 3.9 3.5

Tylenchorhynchus sp. 2.0 8.0

V grigonemella sp. 16.7 9.0

Helicotylenggs sp. 50.0 23.3

Pratylenchus sp. 66.7 33.8

E. ge_ag 16.7 340.0

Rotylenchulus sp. 50.0 1 1 1.7

Scutellonema sp. 16.7 14.0

Tylenchorhynchus sp. 16.7 1.0

Key

1Absolute frequency (%) = no. of gmgles containing a sggcies
no. of samples collected

66

Table 3.1.3. Relationships observed between natural farming regions of
Zimbabwe and population densities of Pratylenchus brachyurus
and Pratylenchus zeae recovered from maize roots.

 

Natural farming region 3. brachyurus/10.0 grams roots
I (n = 1) 3,620.0
II (n = 7) 2,527.0
III (n = 9) 6,747.2
IV (n = 7) 6,840.1
Natural farming region 3. zeae/10.0 grams roots
I (n = 3) 1,077.0
II (n = 14) 3,690.4
Ill (n=8) . 3,113.9
IV (n = 34) 2,205.9
V (n = 1) 340.0

 

 

 

but g. magniphasmum and §. M were mainly prevalent in natural region
IV. Helicotylenchus spp. were equally prevalent in all the five natural regions
and Criconemella spp. were more prevalent in natural region IV only.
Rotylenchulus spp. were more prevalent in natural regions IV and V.

The mean population densities of E. _z_e_a_e which were recovered from
maize roots were a function of the total rainfall which had been received in
the farm and rainfall regimes of >1,000, BOO-1,000, 600-799, 400-599 and <
400mm per year, had mean 3. gag population densities of 2,138.5; 4,615.8;
6,767.7; 1,747.0 and 651.3 per 10.0 grams of roots respectively. The
relationship between annual rainfall and Pratylenchus spp. population

densities can be fitted by the quadratic equation:

Log, (3. zeae in 10.0 grams roots) = (2.619 :1: 1.973) + (0.0092 1' 0.0047) (rainfall amount

in mm) - (5.28x 10 '6 i' 2.77x 10-6) (rainfall amount in mm)2

67

There were significant differences (P = 0.01) in the mean population
densities of 3. gas which were recovered in the roots of maize plants
growing in farms with rainfall regimes >1,000 and 800-1,000, 800-1,000 and
400-599, 600-799 and < 400, and 400-599 and < 400mm per annum
(Appendix 5.1.5). There were, however, no significant differences in the
mean population densities of E. z_egg which were recovered in roots of maize
plants growing in farms with rainfall regimes of >1 000 and 600-799 mm per
annum. Low population densities of E. z_e_ag were recovered in roots of maize
plants growing in farms with either very high rainfall or very low rainfall per
annum.

Mean population densities of E. _z_gg which were recovered from maize
roots were also a function of the average temperatures for February and
March and average temperature regimes of 20.0-22.5, 22.6 -25.0, 25.1-27.5,
27.6-30.1, 30.1-32.5 and > 325°C had mean 3. _z_gae population densities of
595.0, 10,3525, 4,871.5, 3,170.6, 705.0 and 0; and 595.0, 8,113.0, 6,786.5,
3,580.5, 363.6, and 0 per 10.0 grams of roots for February and March,
respectively. The relationship between average February and March
temperatures and E. at; population densities can be fitted by quadratic

equations:

8) Log. (_E. zeae in 10.0 grams roots) = (-58.62 :t 27.89) + (4.88 :t 2.04) February
temp. —(0.09:t 0.037) (February temp.)2
b) Log, (_12. zeae on 10.0 grams roots) = (-59.16 i 29.13) + (4.89 :t 2.11) March

temp. -(0.091 :t 0.038) (March temp.)2

The highest population densities of E. zeae were recovered in roots of
maize plants growing in farms with temperature regimes of 225-299°C for

both February and March average temperatures. There were significant

68

differences (P = 0.05) in the mean population densities of E. _z_e_a_e which were
recovered in roots of maize plants growing in farms with February and March
mean temperature regimes of 200-224 and 22.5-24.9, 27.5-29.9 and 30.0-
325, and 30.0-32.5 and > 325°C (Appendices 5.1.6-5.1.7). There were no
significant differences (P = 0.05) in the mean population densities of _E. zeae
which were recovered in roots of maize plants growing in farms with
February and March mean temperature regimes of 22.5-24.9 and 25.0-27.4.
3. z_ea_g was not recovered in roots of maize plants that were sampled from
farms with temperature regimes > 32.5 °C and very low population densities
of _E. _zefi, were recovered from farms with mean February and March
temperature regimes of 20.0-22.4 and 30.1 -325°C.

Soil texture influenced the population densities of E. ze_a£ which were
recovered in roots of maize plants growing in farms with different soil
textures. In Manicaland province, a mean of 1,512.5, 1,587.3, 2,592.0 and
2,664.3 E. zgae per 10.0 grams of roots were recovered in roots of maize
plants growing in sandy clay loam, sandy loam, loamy sand and sand soil,
respectively. There were significant differences (P = 0.01) in the mean
population densities of E. & which were recovered in roots of maize plants
growing in farms with sand and sandy clay loam, sand and loamy sand, loamy
sand and sandy loam, and sandy loam and sandy clay loam soil texture
(Appendix 5.1.8).

The mean population densities of E. z_e_ag which were recovered in roots
of maize plants growing in soil with pH ranges 4.2-4.7, 4.8-5.3, 5.4-5.9 and
6.0-6.8 were 1,080.2, 2,701.5, 2,605.5 and 4,037.6.per 10.0 grams of roots,
respectively. Comparisons of mean population densities of E. z_e_a_e recovered
in roots of maize plants growing in farms with pH ranges of 4.2-4.7 and 4.8-

5.3, and 5.4-5.9 and 6.0-6.8 had significant differences (P = 0.05) but there

69

Table 3.1.4. Relationships observed between manure, ammonium nitrate
and Compound D fertilizer application and Pratylenchus zeae
population densities, and subsequent maize yield in Manicaland

 

 

 

 

 

province.
Nutrients 3' Em” 9'3"“ Maize yield (tons/ha)
roots
+ Manure (n = 10) 630.0 2.86
- Manure (n = 24) 2,631.8 1.81
+ Ammonium nitrate (n = 22) 2,210.1 2.20
- Ammonium nitrate (n = 12) 1,646.8 1.88
+ Compound D (n: 16) 1,1113 2.52
- Compound 0 (n: 18) 2,786.9 1.89

 

 

 

 

 

were no significant differences in the mean population densities of E. _z_ea_e_
which were recovered in roots of maize plants which were growing in farms
with pH ranges 4.2-4.7 and 6.0-6.8, and 4.8-5.3 and 5.4-5.9 (Appendix 5.1.9).

Communal farms in which manure was applied had a significantly lower
(P = 0.01) mean population density of E. zggg in maize roots compared to
farms in which manure had not been applied (Table 3.1.4) and the nematode
control subsequently increased (P = 0.01) the mean maize yield (Appendix
5.1.10). The other nutrients, ammonium nitrate and compound D fertilizers,
did not influence the mean population densities of 3. fl and subsequent
mean maize yields.

Maize plants that were infected with high population densities of E.
gag (>1,000 per 10.0 grams of roots) had a significantly lower (P = 0.01)
grain yield. There was a linear decrease in maize grain yield with increase in
E. ;e_a_g population densities in maize roots (Fig. 3.1.3) and maize plants which
were infected with <1,000 3. L39. per 10.0 grams of roots had a 2-fold

higher mean yield.

70

 

 

 

5 F Y. = 6.61-0.67X
N =19
5 _ D R2 = 0.52
4 l—
MAIZE 3
YIELD F
(tons/ha)
2 _.
1 _
o l
3 4 5 6 7 8 9 10

Loge (g. zeae/10.0 grams roots)

Figure 3.1.3. Relationships which were observed between maize rain yield and
Pratylenchus _zeae population densities in Manicalan province.

3.1.4 Discu

The 5
Zimbabwe
nematode
parasitic ne
of maize ir
I973; Endc

E. 294

‘

Mm
Qfiflhliflg

Zimbabwe
the inciden
adVantage
function of
tolerance i:
(OlowQ anc
ismore iOIe
0cm; in a!
mainly rest]

Thedi
WEre “Ecov

regions. Ne
heaWsoin

region I and

71

3.1.4 Discussion

The survey indicates that the major nematode pests of maize in
Zimbabwe communal areas are E. brachyurus and E. _zga_e and these two
nematode species reduced maize grain yield by up to 48%. These two plant-
parasitic nematode species have also been reported as major nematode pests
of maize in North Carolina, South Africa and Nigeria (Chevres-Roman gt a_l.,
1973; Endo, 1959; Louw, 1982; Olowe and Corbett, 1976).

E. gage, however, occurs more frequently in maize roots than B.
brachyurus. The higher incidence of E. _z_fig in maize roots compared to E.
brachyurus was similar to that reported in Nigeria, South Africa and
Zimbabwe (Olowe and Corbett, 1976; Louw, 1982; Martin g; §_l., 1975) where
the incidences were reported as 51 and 29%, respectively. The competitive
advantage of _E. gggg over 3. brachyurus in maize roots appears to be a
function of shorter life cycle, faster reproductive rate, faster migration and
tolerance to a wider range of temperatures and gravimetric soil moistures
(Olowe and Corbett, 1976; Martin gt _a_l., 1975). Consequently, E. _z_egg which
is more tolerant to a wider range of soil temperatures, textures and moistures

occurs in all the five natural regions of Zimbabwe, whereas 3. brachyurus is

 

mainly restricted to natural regions II to IV.

The diversity and population densities of plant-parasitic nematodes that
were recovered in maize roots during the survey were affected by natural
regions. Natural regions I and V had the least diversity and lowest population
densities of plant-parasitic nematodes and this appears to be a result of
heavy soil texture, high soil moisture and low soil temperature in natural

region I and the converse in natural region V.

72

Low population densities of Pratylenchus spp. which were recovered in
areas with sub-optimal gravimetric soil moisture compared favorably with
reports from Georgia, New York and South Africa (Good and Stansell, 1965;
Kabel and Mai, 1968; Koen, 1967). The low population densities of

Pratylenchus spp. in area with very high gravimetric soil moistures, especially

 

in soils that do not drain well, appear to be a function of expended energy
reserves in movement and maintenance of osmotic balance, toxin production
by anaerobic bacteria and/or limited oxygen supply (Kabel and Mai, 1968)
whereas in soil with very low gravimetric soil moisture, it appears the low
population densities of Pratylenchus spp. are primarily due to desiccation.
However, 3. _zga_e_ which has been reported to survive in air-dried soil (2%
gravimetric soil moisture) for longer than two years (Martin gt gl, 1975) was
also recovered even in areas which receive less than 400mm of rainfall per
year.

Low population densities of Pratylenchus spp. in natural regions V
appear to be a result of very high soil temperatures in these areas. High soil
temperatures 3 35°C inhibits development of Pratylenchus spp. and this has
been reported in California, Japan, New York and Nigeria (Radewald _t __l.,
1971; Mamiya, 1971; Kabel and Mai, 1968; Olowe and Corbett, 1976). These
high temperatures primarily inhibit the hatching of eggs (Mamiya, 1971). On
the other hand, low population densities of Pratylenchus spp. in natural
region I were due to low soil temperatures and cropping patterns in these
areas. Low population densities of Pratylenchus spp. (mainly E. brachyurus
and _E. z_ea_e) in cool environments have also been reported in California,
Nigeria, South Africa and South Carolina (Radewald _e_t gl, 1971; Olowe and

Corbett, 1976; Koen, 1967; Graham, 1951). Low soil temperatures increase

the time that is required to complete a life cycle because development will be

73

slow and if the soil temperature is very low, the life cycle might not be
completed in a season (Olowe and Corbett, 1976; Mamiya, 1971).

Data on population densities of Pratylenchus spp. in natural region I
indicate that heavy soil textures in this region could have contributed to the

low population densities of Pratylenchus spp. Heavy soil textures have also

 

 

been shown to impede rapid buildup of Pratylenchus spp. in Canada, Nigeria,
North Carolina and South Africa (T ownshend, 1972; Olowe and Corbett,
1976; Endo, 1959; Walters, 1979). The reproduction of Pratylenchus spp. is

 

influenced by soil aeration and nematode motility and the optimum soil
texture for P. brachyurus and P. _z_g_a_e_ migration are sandy soils (Fortuner,
1976; Olowe and Corbett, 1976).

The population density of E. gga_e was also affected by soil pH and low
soil pH adversely impacted the population density of E. _z_egg. The adverse
impact of low pH on the population density of E. _z_ggg spp. compares
favorably with reports in Canada and Iowa (Morgan and Maclean, 1968;
Willis, 1972; Burns, 1971) where optimum pH range for 3. fig was reported
as 5.2-6.4. Low pH appears to inhibit the hatching of E. E eggs (Willis,
1972).

The survey results also indicate that fields in which manure was applied
had significantly lower population densities of E. z_ea_e and higher maize
yields. Control of plant-parasitic nematodes (mainly Meloidogyne spp. and
Pratylenchus Spp.) by use of organic amendments has been reported in
Alabama, Connecticut, Egypt, New York and Nigeria (Mian and Rodriquez-
Kabana, 1982 a-c; Miller, 1978; Badra and Mohamed, 1979; Walker, 1969;
Egunjobi and Larinde, 1975). Organic amendments are effective in
controlling plant-parasitic nematodes because they release ammonical

nitrogen during their decomposition in the soil (Egunjobi and Larinde, 1975;

74

Mian and Rodriquez-Kabana, 1982 b; Muller and Gooch, 1982), increase
microfauna inimical to plant-parasitic nematodes (Badra and Mohamed,
1979; Egunjobi and Larinde, 1975; Mankau and Das, 1974), create
unfavorable environmental conditions for the nematode in the soil (Mankau
and Das, 1974) and increase host vigor (Mankau and Das, 1974).

Use of organic amendments can be a viable plant-parasitic nematode
control strategy to most communal farmers who generally keep 4.08 i 0.285
cattle per household (Zimbabwe National Household Survey Capability
Program, 1985/86). The study also indicates that maize yield can be increased
by use of inorganic fertilizers in plants infected with P. _z_e_ag but the inorganic
fertilizer will not adversely impact the population density of the nematodes
at the recommended fertilizer application rates.

The survey results highlight the importance of E. ggag as a major
potential constraint of maize production and this subsequently affects the
living standards of communal farmers. The relationships which were
observed between E. _z_e_a_g population densities and maize yield are
important in the development of regional crop loss assessment programs and
E. _z_g_a_g maize simulation models. The data presented in this study also
demonstrate the importance of soil moisture, temperature and texture on
Pratylenchus spp. reproduction and subsequent pathogenicity on maize
growth. This information is well suited for the development and/or
validation of E. _ze_ag-maize simulation models. Also the abiotic and biotic
relationships which were reported in this study can be utilized for within-year

crop management decisions to optimize maize yields.

75

3.2 OVERWINTERING AND VERTICAL DISTRIBUTION OF

3. _Z_E_A_E UNDER CLEAN FALLOW
3.2.1 Introduction

Information on the overwintering of E. gag is important in the
development and initialization of predictive computer simulation models and
for recommending appropriate _E. _z_e_ag control strategies to farmers. The
objectives of this study were to: (a) assess the reduction of E. _z_e_a_g population
density achieved by leaving a piece of land fallow for one year, (b) evaluate
whether 5. ge_a_e migrates to deeper depths if soil temperature and/or
moisture conditions were sub-optimal in the upper layers and (c) assess life
stages of _P_. z_e_a_g which are prevalent during the overwintering period.
3.2.2 Materials and Methods

The site for this study was in Chinamora communal area (Grid ref. 30 25'
East and 17 30' South). Soil texture on this site wasloamy sand (6% clay, 5%
silt, 25.2% fine sand, 38.4% medium sand and 25.9% coarse sand), sandy
loam (12% clay, 5% silt, 21.2% fine sand, 33.6% medium sand and 28.7%
coarse sand), sandy clay loam (22% clay, 3% silt, 24.5% fine sand, 28.8%
medium sand and 22.2% coarse sand), sandy clay loam (32% clay, 7% silt,
20.3% fine sand, 21.2% medium sand and 19.8% coarse sand) and sandy clay
(36% clay, 6% silt, 19.7% fine sand, 17.1% medium sand and 21.3% coarse
sand) for depths 0-10, 10-20, 20-30, 30-40 and 40-50 cm, respectively. The
respective depths had soil at pH 4.4, 4.3, 4.6, 5.1 and 4.7; bulk density of 1.42,
1.46, 1.53, 1.61 and 1.57 grams/cm3; and volumetric moisture content of 5.3,
8.9, 16.2, 23.2 and 26.2%. The soil was naturally infested with E. ggag and a
plot 10x10m was marked out on 21st July, 1986. The plot was cleared of

weeds using a hoe and randomly sampled 10 times at monthly intervals.

76

Samglianrocedure

On each sampling date, soil was collected at depths of 0-10, 10-20, 20-
30, 30-40 and 40-50 cm. The diameter of the soil core was 20 cm. The soil was
dug using a crow bar and soil from each cylinder was thoroughly mixed in a
plastic bucket, and a sub-sample (g 1,500 cm3) was put in a labeled plastic
bag. The plastic bags were closed to prevent any loss of moisture from the
soil. The samples were put into cooler boxes and taken to the laboratory.
The following parameters were evaluated from the samples:

i) Gravimetric moisture content:

Labeled crucibles (capacity = 10cm3) were put in an oven at 105°C for
about 12 hours and then cooled in a dessicator for 1 hour. When the crucible
had cooled to room temperature, they were put on a balance with an
accuracy of $0.001 grams using tongs to determine the weight of the
crucible. After the second weight had been recorded, the crucibles were put
into the oven at 105°C for about 24 hours. After the 24 hours, the crucibles
were put into a dessicator for about 1 hour. When the contents had cooled
to room temperature, the crucibles were reweighed. This procedure was
repeated whenever soil moisture content was determined. The soil moisture

content was calculated using the following equation:

weight of soil — weight of oven dry soil t 100

 

% soil moisture = ,
weight of oven dry sod
ii) Distribution of E. zeae:
Soil was thoroughly mixed in a tray and 100cm3 of soil was processed

using the centrifugal-flotation technique (Jenkins, 1964) and observed under

astereoscc
juveniles a
iii) 3. z_eg
Imuare ro
distributio
flmeandi
depth of 5.-
filled in tr
19% Stage
the analysi
and coeffic
123 Resul

The p
Veil low a1
There Was,
Stage IUVer
also had a

DGSpite the
there Was <
from th e So

The p1

5°" “1.1mmi

77

a stereoscopic microscope to enumerate _E. E second, third to fourth stage
juveniles and mature females in the soil.
iii) E. _z_ea_e and soil moisture data in this experiment were transformed
(square root transformation) during analysis because it exhibited a Poisson
distribution. Two way analysis of variance between. E. gga_e_ stages in the soil,
time and depth of sampling was carried out. For the different time and
depth of sampling; linear, quadratic and cubic orthogonal polynomials were
fitted in trend analysis. Also regression analysis was carried out between E.
zei stages recovered in the soil and gravimetric soil moisture content. After
the analysis of variance, least significant difference (LSD), standard error (SE)
and coefficient by variation (CV) were calculated.
3.2.3 Results

The population density of E. zgg second stage juveniles in the soil was
very low and it did not change (P = 0.05) throughout the sampling period.
There was, however, a significant linear decrease (P = 0.05) of P. _z_e_a_g second
stage juveniles in the soil with depth (Table 3.2.1). The population density
also had a significant linear decrease (P = 0.05) with increase in gravimetric

soil moisture content, which increased with depth:

flzeae J2 in 100cm3 soil = (0.967 i 0.097)-(0.028 :I: 0.014)’

sq. rt. (‘70 soil moisture)

Despite the low population density of E. flg second stage juveniles in soil,
there was considerable variability (c.v.% = 25.1) in the numbers recovered
from the soil.

The population density of P. _zeig third to fourth stage juveniles in the

soil significantly changed (P = 0.05) with time (Fig. 3.2.1). The population

78

density fluctuated in a linear (P = 0.05) and quadratic (P = 0.01) manner.
The population density of P. gggg third to fourth stage juveniles was initially
high at the beginning of the sampling period (July and August) then it
decreased by 74%, possibly in a quadratic manner in about five months.
From February to June, the population density of E. z_e_ag third to fourth stage
juveniles increased by 41%, possibly in a linear manner. The population
density of E. ggg third to fourth stage juveniles in the soil had a significant
linear decrease (P = 0.01) with depth and the population density at depth 0-
10 cm was 3.4 x greater than the population density at depth 40-50 cm (Table
3.2.1). In July and August, 3. ggag third to fourth stage juveniles were more
abundant at depth 20-40 cm. In November and December, the population
density of 3. fl third to fourth stage juveniles was high at 0-10 cm. From
January to June, the population density of E. gggg third to fourth stage

juveniles was generally very low. The population density of E. zeae third to

Table 3.2.1. Influence of the depth of sampling on the population density of
Pratylenchus zeae recovered from 100 cm3 of soil in Chinamora
communal area.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Parameters g. _z_e_ag stages
Sampling

depth (cm) J 2 J3-J4 Mature females Total
0-10 1.01 7.9 12.2 21.1
10-20 0.2 . 4.2 3.6 8.6
20-30 0.1 4.9 0.9 5.9
30-40 0.0 2.3 1.4 3.7
40-50 0.0 0.2 0.0 0.2

Key

1Mean of 10 different sampling times.
Analysis in Appendix 5.22-5.23.

79

fourth stage juveniles also had a significant linear decrease (P = 0.01) with

increase in gravimetric soil moisture content which increased with depth:

3. zeae J3-J4 in 100 cm3 soil = (3.188 i 0.532)-(0.229 i 0.076)‘

sq. rt. (‘70 soil moisture)

There was, however, considerable variability (C.V.% = 62.5) in the number of
_P. gga_g third to fourth stage juveniles recovered from soil despite the square
root transformation of the raw data to normalize it.

The population density of 3. fl mature females in the soil
significantly fluctuated (P = 0.05) with time (Fig. 3.2.1). The fluctuations in
the population density of P. & mature females with time were linear (P =
0.05). The population density was high in July and August, then it decreased
by 54.3% in three months. In December, the population density increased by
61% then decreased by 66.5% in January and thereafter, the population
density increased by 25.4% in three months. The population density of P.
E, mature females in the soil had a significant linear decrease (P = 0.01)
with depth and the population density at depth 0-10 cm was 4.2 x greater
than the population at depth 40-50 cm (Table 3.2.1). In July and August, 3.
ggg mature females were more prevalent at depth 0-10 cm and from
September to November, the population density was uniform up to a depth
of 0-20 cm. In December, 3. gas mature females were again more abundant
at depth 0-10 cm and thereafter, the population density was very low. The
population density of E. 59$ mature females also had a significant linear
decrease (P = 0.01) with increase in gravimetric soil moisture content, which

increased with depth:

80

fl. ggqg mature females in 100 cm3 soil = (3.348 :1: 0.545)-(0.267 i 0.078) '

sq. rt. (% soil moisture)

There was also considerable variability (C.V.% = 62.2) in the population
density of E. gag mature females recovered from soil despite the
transformation of the raw data.

The total population density of 3. Egg in the soil fluctuated (P = 0.05)
with time (Fig. 3.2.1). The fluctuation of the total population density of 3.
E with time was linear (P = 0.01) and it followed the same trend as E.
z_egg mature females in the soil. Similarly, the total population density of E.

zeae had a significant linear decrease (P 0.01) with depth and the

population density at depth 0-10 cm was 5.1 x greater than the population
density at depth 40-50cm (Table 3.2.1). The population density also
followed a similar trend to that outlined for _P_. gggg third to fourth stage
juveniles and mature females. The total population density of 3. fig in the
soil had a significant linear decrease (P = 0.01) with increase in gravimetric

soil moisture content:

E. 2839 in 100cm3 soil 2 (4.807 i 0.741)-(0.390 :t 0.106)’

sq. rt. (% soil moisture)

3.2.4 Discussion

Data presented in this study show that _E. _z_ggg mainly overwinter as
third to fourth stage juveniles and mature females and these life stages
constitute 51.9 and 46.3% of the total population of vermiform stages,
respectively. Similar results have also been reported from California where 56

and 41% of E. coffeae population density was reported to overwinter as third

81

20 P O 1344
. :1 Mature Females
A Total

15 _—
Eli:
I100
CM3
SOIL 10 ‘

 

 

 

0 40 80 120 160 200 240 280 320

SAMPLING PERIOD (DAYS)

Figure 3.2.1. Influence of the time of sampling on the population density of
Prtatylenchus zeae recovered from 100 cm3 of soil in Chinamora
communal area.

82

to fourth stage juveniles and mature females, respectively. It appears during

development, Pratylenchus spp. spent the least amount of time in the second

 

juvenile stage in the soil and perhaps this is the reason why this
developmental stage has a very low incidence when samples are processed.
The low population densities of 3. fl second stage juveniles in the soil may
be a function of the extraction method which was used. It is possible that a
greater number of g. z_e_a_e_ second stage juveniles passed through the 400-
mesh (30-pm) sieve. Viglierchio & Schmitt (1983) reported a relative
efficiency of 17-29% for extracting Pratylenchus spp. with the centrifugal-
flotation technique. The field which was used for this study was also infested
with other plant-parasitic nematodes, therefore, it was not possible to
differentiate E. E eggs from eggs of other plant-parasitic nematodes. It
was, however, apparent that some 3. _z_gg eggs hatched after the rainfall in
November and the population density of third to fourth stage juveniles and
mature females increased in December. In Nigeria, it has been reported that
rainfall and low temperatures favor the hatch of Pratylenchus spp. eggs
(Egunjobi and Bolaji, 1979).

Data presented in this study also show that the population density of E.
_z_e_a_g in the soil decreased with time when the land was left clean fallow for
about a year. The decrease of E. z_ea_e population density was mainly during
the hot and dry months possibly through desiccation. The decrease of
Pratylenchus spp. to very low population densities was similar to that
reported in Nigeria and South Africa (Egunjobi, 1974; Koen, 1967). In spite of
this decrease in the population density with time, the resistance of E. _z_ga_ag to
adverse conditions, especially desiccation, has been noted as remarkable
(Olowe and Corbett, 1976; Louw, 1982) and E. gag can survive in air dried

soil for longer than two years (Martin e_t a_l., 1975). This investigation,

83

however, demonstrates the importance of removing old maize roots and
weeds as an important condition to any cultural sanitation program for the
maize crop in communal farms. It should, however, be noted that the
population density of 3. £3 builds up very rapidly when a susceptible host

has been planted during the growing season. Rapid build up of Pratylenchus

 

spp. after planting maize has been reported in Nigeria (Egunjobi, 1974;
Egunjobi and Bolaji, 1979; Olowe and Corbett, 1976), North Carolina (Endo,
1959), South Africa (Koen, 1967), Tennessee (Southards, 1971) and Zimbabwe
(Martin gt__a_l., 1975; Muchena gt a_l., 1987).

This research also shows that the highest population density of P. gegg
was mainly confined at a depth of 0-20 cm and the population density of P.
z_ggg at this depth constituted about 78.2% of the total population density of
_13. z_e_gg that was recovered from a depth of 0-50 cm. It appears 3. gm was
mainly confined at a depth of 0-20 cm because the maize crop which was
previously growing on this land had most of its root system restricted to the
same depth. In general, the distribution of the root system of the host crop,
dictates the distribution of the nematode pests. Higher population densities
of Pratylenchus spp. associated with maize, at a depth of 0-20 cm have also
been reported in Nigeria, North Carolina, and South Africa (Egunjobi, 1974;
Barker, 1968; Koen, 1967). The data also show evidence of _E. gag migration
to deeper depths (20-40 cm) especially during the hot and dry months of
September and October. It appears 3. gee—e migrates to deeper depths to
avoid adverse soil temperature and moisture conditions especially at a depth
of 0-10 cm. The vertical migration of Pratylenchus spp. as a means of
avoiding the adverse effects of the dry season was similar to what has been

reported in Nigeria and South Africa (Egunjobi, 1974; Koen, 1967).

IL
|
I
l.
I-
I-L

 

84

The research confirms the hypothesis that the population density of E.
ggg in the soil can be adversely impacted if the land is left clean fallow for
about a year, despite the migration of _E. fig to deeper depths to avoid the
adverse effects of the dry season. The data also illustrate that third to fourth
stage juveniles and mature females are the important stages in the
overwintering of E. 29$- The data from this experiment should be well
suited for initialization of _P. gag computer simulation models and
development of a simulation model that predicts the overwintering of _P.

zeae in the soil without a host crop.

3.3 SPATIAL AND TEMPORAL DISTRIBUTION OF GRAVIMETRIC SOIL
MOISTURE, MAIZE ROOT SYSTEM AND 2. fl WITH SPECIAL
REFERENCE TO _E. _Z_EAE SAMPLING SCHEMES

3.3.1 Introduction

Accurate estimation of Pratylenchus spp. in soil or roots is important in

 

the development of integrated pest management strategies and computer
simulation models. Very few studies, however, have been addressed to
evaluate the accuracy of sampling schemes of Pratylenchus spp. associated
with annual crops. The objectives of this study were to assess the a) temporal
and spatial distribution of maize roots and _P. gag, b) impact of gravimetric
soil moisture on the population density of 3. fig and c) optimal sampling
schemes of E. gag in soil or maize roots.
3.3.2 Materials and Methods

This study was carried out in four pits 3.0 m long, 1.0 m wide and 0.75 m
deep at the Harare Research Center (Grid ref. 30° 25' East and 17° 22'
South). The pits were filled with loamy sand (6% clay, 5% silt, 25.2% fine

sand, 38.4% medium sand and 25.9% coarse sand) naturally infested with

85

30.0 E. ggg per 100 cm3 soil. The soil had a pH of 4.4, bulk density of 1.42
grams/cm3 and volumetric moisture content of 5.3%. Basal fertilizer,
compound D (8% N, 14% P205, 7% K20, 6.5% S) was applied at a rate of
300kg/ha to all the pits on 21st January, 1987. After basal fertilizer
application, maize variety R 215 seeds were planted into the pits on the same
date. The seeds were planted in one row at the center of the pit with an
intra-row spacing of 80 cm. After planting the seeds, all the pits were gently
watered. Emergence of the maize seed occurred 7-10 days after seeding and
the maize plants were sampled biweekly for 20 weeks.
Samglianrocedure
On each sampling date, soil and maize roots were collected from one
plant at depths 0-10, 10-20, 20-30, 30-40 and 40-50 cm and radii of 0-10, 10-
20 and 20-30 cm. The soil was dug using a sharpened trowel which cuts roots
and soil and roots from each cylinder was sieved using a 25 mesh sieve and all
the maize roots which were caught on the sieve were put into a labeled
plastic bag. Also a sub-sample (_cg 1,500 cm3) of the sieved soil was put into a
labeled plastic bag. All the plastic bags were closed to prevent any loss of
moisture from the soil or roots. The samples were put into cooler boxes and
then taken back to the laboratory. The following parameters were evaluated
from the samples:
1) Fresh weights of the root system were obtained by weighing on a
balance with an accuracy of i 0.001 grams.
ii) Gravimetric soil moisture content:
Labeled crucibles (capacity = 10 cm3) were put into an oven at
105°C for about 12 hours and then cooled in a dessicator for one
hour. When the crucibles had cooled to room temperature, they

were put on a balance with an accuracy of $0.001 grams using

iii)

86

tongs to determine the weight of the empty crucible. After the
weight had been recorded, about 5.0 cm3 of soil was put into the
crucible using a spatula and the weight of the crucible with soil was
determined. It was important to note that the tongs were not in
contact with the soil when lifting the crucible. After the second
weight had been recorded, the crucibles were put into the oven at
105°C for about 24 hours. After the 24 hours, the crucibles were
put into a dessicator for about one hour. When the contents had
cooled to room temperature, the crucible were reweighed. This
procedure was repeated whenever soil moisture content was
determined. The soil moisture content was calculated using the

following equation:

% soil moisture ___ Weight of soil — weight of oven dry soil It 1 00
mag ht of oven dry sail

 

Distribution of E. zgag :

a) Soil was thoroughly mixed in a tray and 100cm3 of soil was
processed using the centrifugal-flotation technique (Jenkins,
1964) and observed under a stereoscopic microscope to
enumerate E. E second, third to fourth stage juveniles and
mature females in the soil.

b) The whole root system from each cylinder was chopped into
small pieces about 0.1-0.5 cm long and 10.0 grams were selected
at random if the weight of the root system in a cylinder was
greater than 10.0 grams but if the weight of the root system was

less than 10.0 grams, the whole root system was processed using

87

the maceration-centrifugal-flotation technique (Southey, 1985
p. 54) and observed under a stereoscopic microscope to
enumerate E. gag second, third to fourth stage juveniles and
mature females in the roots using the examination of nematode
suspensions technique (Southey, 1985 p.59-60).
iv) Sampling schemes:
The total number of potential sampling schemes for E. ga_1_e_ in the
soil or roots are: 10 sampling times x S depths x 3 radii = 150
different sampling schemes. After determining the number of E.
ggg in 150 soil samples and 150 root samples, the mean number of
g. ygg either in the soil (X5) or roots (31,) were determined. Then
the number of E. ggg in the soil (X5) or in the roots (Xr) were

su bstracted from the respective means:

a) Percent error forsampling soil = . s

 

b) Percent error for sampling roots = r ,

 

‘100

r

The magnitude of percent errors which were generated from the
above two steps were ranked separately for soil or roots. Rank 1
was assigned to the sampling scheme with the least percent error
and the rank 150 was assigned to the sampling scheme with the
highest percent error. After ranking all the sampling schemes, the
ranks were adjusted to compensate for energy and time expended

when sampling at deeper depths. In the adjusted ranks, 0, 1, 2, 3 or

88

4 was added to the rank if the sampling depth was 0-10, 10-20, 20-
30, 30-40 or 40-50 cm, respectively.
v. Three way analysis of variance between P. gag stages in the soil or
maize roots; time, depth and radius of sampling was carried out.
For the different time, depth and radius of sampling; linear and
quadratic orthogonal polynomials were fitted in trend analysis.
After the analysis of variance, least significant difference (LSD) and
standard error (SE) were calculated.
3.3.3 Results
Weight of maize root system was significantly (P = 0.01) influenced by
the time of sampling (Table 3.3.2) and at the beginning of the growing
season, maize root weight had a significant (P = 0.01) linear increase but at
the end of the season, the weight of the root system fluctuated in a quadratic
manner (P = 0.01). The weight of the root system was also significantly (P =
0.01) different for different depths of sampling and the weight of the root
system had a linear (P = 0.01) decrease with increase in depth (Table 3.3.4).
Between depths of 30-50 cm, the weight of the root system fluctuated in a
quadratic manner (P = 0.05). Weight of maize root system was also
significantly (P = 0.01) different for different radii of sampling and the
weight of the root system had a significant (P = 0.01) linear decrease with
increase in sampling radius (Table 3.3.6).

The population densities of E. gag second stage juveniles (J2) in soil or
Thaize roots significantly (P = 0.01) fluctuated with time (Tables 3.3.1-3.3.2).
The population density of _E. ge_ag J2 in soil had a significant (P = 0.01) linear
increase with time and E. w J2 roots initially had a significant (P = 0.01)
'inear increase but later fluctuated in a quadratic manner (P = 0.01). E. E

J2 in soil and maize roots were also significantly (P = 0.01) affected by the

89

Table 3.3.1. Effect of the time of sampling on the population density of
Pratylenchus zeae recovered from 100 cm3 of soil around maize

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

roots.
Parameters E. zeae stages G ravim etri c
Sampling soil moisture
1:222.) 12 «“2221: (%)

2 0.001 33.6 1.88 35.38 6.876

4 0.00 59.8 5.14 64.94 6.291

6 1.93 45.7 2.51 50.14 5.904

8 10.47 5.5 1.46 17.43 4.602

10 7.07 0.3 5.49 12.86 3.987

12 0.07 6.6 1.24 7.91 4.623

14 0.20 5.3 1.71 7.21 6.312

16 0.00 29.8 2.35 32.15 6.069

18 3.00 22.2 3.93 29.13 5.157

20 10.07 56.2 9.51 75.78 4.470

L.S.D. 0.05 3.54 15.44 2.53 2.56 0.390

SF. 1.808 7.88 1.292 1.307 0.199

 

 

 

 

 

 

 

1Mean of 5 different depths x 3 radii.

 

Table

E... mil g E N N C \ 5?:

Mean

QII

90

Table 3.3.2. Influence of the time of sampling on maize root weight and the
population density of Pratylench us zeae recovered in 10.0 grams

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

of roots.
Parameters E. _z_e_ag stages
........., 11.1.11
time 12 j3 - )4 Mature Total
(weeks) females
2 0.051 0.00 10.0 9.0 19.00
4 0.09 0.00 2.0 11.0 13.00
6 0.04 0.00 334.0 59.0 393.00
8 3.55 2.83 143.0 131.0 276.83
10 5.87 5.10 321.0 547.0 873.10
12 10.19 10.70 415.0 35.0 460.70
14 6.09 10.59 421.0 60.0 491.59
16 10.10 2.94 1558.0 110.0 1670.94
18 5.88 20.09 1370.0 110.0 1500.09
20 4.81 210.61 4346.0 462.0 5018.61
L.S.D. 0.05 5.70 3.26 727.2 223.1 853.8
S.E. 2.909 1.665 371.0 113.8 435.6

 

 

 

 

 

 

 

1Mean of 5 different depths x 3 radii.

 

91

Table 3.3.3. Impact of the depth of sampling on gravimetric soil moisture
and the population density of Pratylenchus zeae recovered from

 

 

 

 

 

 

 

 

 

 

100 cm3 of soil.
Parameter E- _zeae stages Gravimetric
Sampling soil moisture
depth _ Mature
(cm) J; J3 14 females Total (%)
0—10 1.231 12.5 2.52 16.25 5.157
10-20 4.47 35.9 3.14 43.51 5.440
20-30 3.03 21.4 2.56 26.99 5.424
30—40 2.83 30.7 2.26 35.79 5.625
40-50 4.83 31.9 2.06 38.79 5.493
L.S.D. 0.05 2.51 10.92 2.35 2.37 0.28
S.E. 1.28 5.57 1.20 1.21 0.141

 

 

 

 

 

 

 

1Mean of 10 different depths x 3 radii.

Table 3.3.4. Influence of the depth of sampling on maize root weight and

the population density of Pratylenchus zeae recovered in 10.0
grams of roots.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Parameters E- $92 513995
Root weight '
Sampling (grams) Mature

depth (cm) 12 J3 - J4 females Total
0-10 12.701 12.18 1039.0 1420.0 2471.18
10-20 5.64 20.08 1270.0 1605.0 2895.08
20-30 3.03 6.36 788.0 961.0 1755.36
30-40 1.26 1.36 698.0 794.0 1493.36
40-50 0.70 1.76 665.0 761.0 1427.76

L.S.D. 0.05 4.04 2.80 514.1 157.8 603.7

5. E. 2.06 1.43 262.3 80.5 308.0

 

lMean of 10 different depths x 3 radii.

 

 

 

Ta

 

1M

92

Table 3.3.5. Effect of the radius of sampling on the po ulation density of
Pratylenchus zeae recovered from 100 cm of soil.

 

 

 

 

 

 

 

 

 

Parameters E. gag stages
Sampling radius
(cm) . J2 J3-J4 Egg: Total
0-10 2.741 22.9 2.65 28.29
1020 3.40 27.3 2.58 33.38
2030 3.70 29.3 2.26 35.26
L.S.D. 0.05 1.94 8.47 2.25 2.27
S.E. 0.99 4.32 ' 1.15 1.16

 

 

 

 

1Mean of 10 different sampling times x 5 depths.

Table 3.3.6. Influence of the radius of sampling on maize root weight and
the population density of Pratylenchus zeae recovered in 10.0

 

 

 

 

 

 

 

 

 

grams of roots.
Parameters 13. z_e_a_e_ stages
Sampling 11133311:
radius 12 j3 - )4 Mature Total
(cm) females
0-10 7.681 3.90 564.0 84.0 651.9
10—20 3.92 6.00 754.0 145.0 905.0
20-30 2.40 6.69 1358.0 231.0 1595.7
L.S.D. 0.05 3.14 2.59 398.3 122.1 467.7
SE. 1.60 1.32 203.2 62.3 238.6

 

 

 

 

 

 

1Mean of 10 different sampling times x 5 depths.

 

 

dep
011‘

128
Inai

thrc

POD

in sc

93

depth of sampling (Tables 3.3.3-3.3.4). E. gag J2 in roots had a linear (P =
0.01) decrease with increase in depth and _E. _z_e_ag J2 in soil also had a linear (P
= 0.05) decrease with increase in depth. The population densities of E. g
J2 at radii 0-10, 10-20 and 20-30 cm were equal (P = 0.01) for both soil and
maize roots. The population density of E. _z_g_ag J2 was generally very low
throughout the whole growing period and it constituted 2.5% of the total
population of 3. mg that were recovered.

The population densities of 3. fig third to fourth stage juveniles (J3-J4)
in soil and maize roots were significantly (P = 0.01) influenced by the time of
sampling during the growing period (Tables 3.3.1-3.3.2). The population
density of E. zgg J3-J4 in the soil fluctuated in a quadratic manner (P = 0.05).
_E. _z_ggg J3-J4-in the soil started with a high population density which
decreased for 10 weeks then increased from the tenth week until the end of
the growing period. The population density of E. gag J3-J4 in roots had a
much more complex fluctuation with significant (P = 0.01) linear, quadratic
and cubic variations. There were four distinct peaks in the population density
of P. tea—e J3-J4 in roots during the 20 weeks growing period which might
imply four generations were completed during the growing period. The
population densities of E. _z_ea_e J3-J4 in soil or maize roots were also
significantly (P = 0.01) affected by the depth of sampling (Tables 3.3.3-3.3.4).
The population density of E. z_e_ag J3-J4 in soil had a significant (P = 0.01)
linear increase with depth and _E. fig J3-J4 in roots had a significant (P =
0.01) linear decrease with increase in depth. The population density of E.
_ze_agJ3-J4 in the soil was not significantly (P = 0.05) influenced by the radii of
sampling (Table 3.3.5). But the population density of E. z_egg J3-J4 in roots
was significantly (P = 0.01) affected by the radii of sampling (Table 3.3.6).

The population density of E. zeae J3-J4 in roots had a significant (P = 0.01)

hn
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94

linear increase with increase in the radii of sampling. The population density
of E. fig J3-J4 constituted 83.2% of the total population of P. g that were
recovered in the experiment.

The population densities of _P_. _z_g_a_g mature females in soil and maize
roots were significantly (P = 0.01) influenced by the time of sampling (Tables
3.3.1-3.3.2). The population density of E. ggg mature females in the soil had
a significant (P = 0.001) quadratic fluctuation. There were three distinct
peaks in the population density during the growing season. On the other
hand, the population density of P. z_eg mature females in roots had s
significant (P = 0.01) linear increase during the early part of the growing
season, then the population density decreased during midseason and then
the population density increased again at the end of the growing period.
The population density of E. gag mature females in roots was significantly (P
= 0.01) influenced by the sampling depth (Table 3.3.4) but the population
density of E. _z_e_ag mature females in soil was not significantly (P = 0.05)
influenced by the sampling depth (Table 3.3.3). However, there was a
significant (P = 0.05) linear decrease of the population density of _P. g
mature females in soil with increase in sampling depth. There was also a
significant (P = 0.01) linear decrease of the population density of E. gggg
mature females in roots with increase in sampling depth. The population
density of E. z_e_a_e_ mature females in soil was not significantly (P = 0.05)
influenced by the sampling radius and was equal (P = 0.05) for the three
different sampling radii (Table 3.3.5). On the other hand, the population
density of g. gag mature females in roots was significantly (P = 0.05)
influenced by the radius of sampling (Table 3.3.6). The population density of
E. ggg mature females in roots had a significant (P = 0.05) linear increase

with increase in sampling radius.

95

The total population density of _P_. ggg in soil and maize roots was
significantly (P = 0.01) influenced by the time of sampling (Tables 3.3.1-
3.3.2). The population density of E. ggg in the soil-fluctuated in a quadratic
(P = 0.001) manner and it started fairly high and the population decreased
during midseason then it increased at the end of the growing season. The
population density of E. ggg in maize roots had a much more complex
pattern with significant linear (P = 0.001), quadratic (P = 0.01) and cubic (P
= 0.01) variations. The fluctuation in the population density of E. E had
four distinct peaks during the growing season. The total population of _P.
ggg in soil and maize roots was also significantly (P = 0.01) influenced by the
depth of sampling (Tables 3.3.3-3.3.4). The population density of E. ggg in
soil had significant (P = 0.01) linear, quadratic and cubic variations). The
population density was lowest at depth 0-10 cm then it increased at depth 10-
20 cm then decreased at depth 20-30 cm and it increased at depth 30-50 cm.
The population density of 3. E in roots had a significant (P = 0.01) linear
decrease with increase in sampling depth. The population density of 3. E
in soil was not significantly (P = 0.05) influenced by the sampling radius but
the population had a significant (P = 0.01) linear increase with increase in
sampling radius (Table 3.3.5). The population density of _E. gag in maize
roots was significantly (P = 0.01) influenced by the sampling radius and the
population also had a significant (P = 0.01) linear increase with increase in
sampling radius (Table 3.3.6).

The sampling schemes of E. z_ggg in soil around maize plants were
ranked in order of accuracy and the best sampling scheme had an error-of
0.46% and the worst sampling scheme had an error of 300.14% (Table 3.3.7).
The adjusted sampling schemes for energy and time which can be expended

digging samples showed that the most practical and accurate sampling

Table 3.3.7. Sampling schemes of Pratylenchus zeae in soil around maize

96

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

roots.
Sampling schemes
Rank % error1
Time (weeks) Radius (cm) Depth (cm)

12 0-10 30-40 1 0.46
2 10-20 10-20 2 0.98
10 0-10 30-40 3 1.92
16 20-30 0-10 4 1.95
6 0—1 0 40-50 5 2.16
4 10-20 20-30 6 2.26
12 0-10 40-50 7 2.66
8 20-30 20-30 8 2.77
8 20-30 0-10 9 2.87
14 0-10 10-20 10 3.19
20 0-10 40-50 141 127.82
4 0-10 40-50 142 143.88
20 10-20 40-50 143 144.69
20 10-20 10-20 144 149.62
20 10-20 0-10 145 151.22
6 10-20 10-20 146 167.56
6 10-20 30-40 147 191.97
20 20-30 10-20 148 202.45
6 20-30 40-50 149 258.32
18 10-20 10-20 150 300.14

 

 

 

 

 

 

1Percent deviation from a mean of 31.80.

 

sci
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sar
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dig
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3.3,.

97

scheme of E. z_ggg in soil was 2 weeks after planting at radius 10-20 cm from
the maize plant and at depth 10-20 cm (Table 3.3.9). The sampling schemes
of E. gggg in maize roots were also ranked in order of accuracy and the best
sampling scheme had no error from the grand mean and the worst sampling
scheme had an error of 548.01% from the grand mean (Table 3.3.8). The
adjusted sampling schemes for energy and time which can be expended in
digging samples showed that the most practical and accurate sampling
scheme of E. gag in maize roots was 4 weeks after planting at radius 0-10 cm
from the plant and depth 10-20 cm (Table 3.3.9).
3.3.4 Discussion

Data presented in this study show that 80.0% of the maize root system
was confined to a depth of 0-20 cm. Berger (1962) also reported that root
system of maize plants is restricted in the topsoil but under adverse soil
moisture conditions, individual roots can reach a depth of up to 250 cm and
radius 100 cm. In general, however, the growth of maize roots occur almost
equally outwards and downwards and branch out in all directions (Berger,
1962). The rate of maize root growth which was observed in this study was
less than what has been reported in the literature (Berger, 1962). The slow
maize root growth may have been in part a result of inadequate soil nutrients
and moisture and the E. gggg infection. Maize root weights at the end of the
growing season were lower than previously recorded root weights and this
could have been a result of senescence and increased 3. w stress on the
root system as the nematodes continued to reproduce and cause more
damage.

The data presented in this study show that E. gag mainly thrives as
third to fourth stage juveniles and mature females and these life stages

constituted 83.2 and 14.3% of the total population of vermiform stages that

Table 3.3.8. Sampling schemes of Pratylenchus zeae in maize roots.

98

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sampling schemes
Rank % error1
Time (weeks) Radius (cm) Depth (cm)
20-30 40-50 1 0.00
6 10-20 30-40 2 0.51
12 10-20 40-50 3 1.26
4 0-10 10-20 4 1.32
14 10-20 40-50 5 1.41
8 10-20 20-30 6 1.56
12 10-20 10-20 7 1.66 .
12 20-30 20-30 8 1.77
14 20-30 20-30 9 3.34
6 10-20 40-50 10 3.44
20 20-30 10-20 141 197.65
20 10-20 0-10 142 214.71
10 10-20 0-10 143 217.78
16 20-30 10-20 144 228.34
20 20-30 40-50 145 245.01
20 0-10 20-30 146 246.1 1
20 0-10 10-20 147 294.31
20 0-10 0-10 148 409.02
20 20—30 30-40 149 433.94
20 20-30 0-10 1 50 548.01

 

1Percent deviation from a mean of 1,108.00.

 

99

Table 3.3.9. Adjusted1 sampling schemes of Pratylenchus zeae in maize roots
and soil around the roots.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

a) Soil
Sampling schemes
Rank % error2
Time (weeks) Radius (cm) Depth (cm)
2 10-20 10-20 1 0.98
16 20—30 0-10 2 1.95
12 0-10 30-40 3 0.46
10 0-10 30-40 4 1.92
4 10-20 20-30 5 2.26
6 0-10 40-50 6 2.16
8 20-30 0-10 7 2.87
8 20-30 20-30 8 2.77
12 0-10 40-50 9 2.66
14 0-10 10-20 10 3.19
b) Roots
Sampling schemes
Rank % error3
Time (weeks) Radius (cm) Depth (cm)
4 0-10 10-20 1 1.32
6 10-20 30-40 2 0.51
6 20-30 40-50 3 0.00
12 10-20 40-50 4 1.26
8 10-20 20-30 5 1.56
12 10-20 10-20 6 1.66
14 10-20 40-50 7 1.41
12 20—30 20—30 8 1.77
14 20—30 20-30 9 3.34
6 10-20 40-50 10 3.44

 

 

 

 

 

 

 

 

1To compensate for energy used to sample at deeper depths, 0, 1, 2, 3 or 4 is added to the
rank of the sampling scheme (adjusted rank) if the sampling depth is 0-10, 10-20, 20-30, 30-40
or 40-50 cm, respectively.

2Percent deviation from a mean of 31.80.

3Percent deviation from a mean of 1,108.00.

Vigliei
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Darash
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Plant;

T

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Latyg
"390m
this San
5§§§‘h3
treatme
DODUIat

pODUIat

100

were recovered, respectively. Comparable results have also been reported in
California (Radewald gt_a_1., 1971) where 56 and 41% of E. ggfiggg population
density was reported to overwinter as third to fourth stage juveniles and
mature females, respectively. It appears during development in the root
system or soil, Pratylenchus spp. spent a very limited amount of time in the
second stage juvenile and this may in part explain the low incidence of
second stage juveniles in samples. The low population densities of E. _z_ggg
second stage juveniles in the soil or maize roots may be a function of the
extraction method which was used. It is possible that a greater number of E.
gag second stage juveniles passed through the 400-mesh (38-pm) sieve.
Viglierchio and Schmitt (1983) reported a relative efficiency of 17-29% for
extracting Pratylenchus spp. with the centrifugal-flotation technique. The
culture which was used for this study was also infected with other plant-
parasitic nematodes namely Helicotylenchus spp. and Scutellonema spp.,
therefore it was not feasible to differentiate E. ggg eggs from eggs of other
plant-parasitic nematodes.

This research shows that 54.5% of the population density of _E. gag in
maize roots was mainly confined to a depth of 0-20 cm. Aggregation of
Pratylenchus spp. associated with maize at depth 0-20 cm was similar to that
reported in Nigeria, North Carolina and South Africa (Egunjobi and Bolaji,
1979; Barker, 1968; Koen, 1967). The high population density of E. _z_ggg at
this sampling depth was in part a function of the available root tissue for E.
ge_ag to penetrate and develop. This phenomenon is analogous to fields or
treatment with higher maize root weights which end up with higher
population densities of Pratylenchus spp. in the roots. The increase in the

population density of P. zeae which was observed as a result of the higher

La

w;
pc
M
19
an
de
g
ter
hig
anc

Sin:

101

maize root weight was similar to that reported in Nigeria (Egunjobi and
Larinde, 1975).

The data also showed that the population density of E. z_egg in the soil
was highest at depth 10-20 cm and lowest at depth 0-10 cm. The high
population density of 3. gig at depth 10—20 cm was similar to what has been
reported in Nigeria, North Carolina and South Africa (Egunjobi and Bolaji,
1979; Barker, 1968; Koen, 1967). At this depth, soil moisture, temperature
and texture and root system availability for E. ggg penetration and
development were optimal. At shallow depths, population densities of E.
gggg were low as a result of very low soil moisture and very high soil
temperatures. Low population densities of Pratylenchus spp. in soil with very
high temperatures above 34 C have also been reported in California, Japan
and Nigeria (Radewald _g_t g_l., 1971; Mamiya, 1971; Olowe and Corbett, 1976).
Similarly, lowipopulation densities of Pratylenchus spp. in soil with very low
moisture have been reported in Canada, Nigeria, South Africa and Zimbabwe
(Townshend, 1972; Egunjobi and Bolaji, 1979; Koen, 1967; Louw, 1982;
Martin gt _a_l., 1975). At depths greater than 20 cm, population densities of E.
gag were sub-optimal possibly because of heavy soil textures and limited
root system for _E. z_egg penetration and development. Low population
densities of Pratylenchus spp. in heavy textured soils have also been reported
in Canada and North Carolina (T ownshend, 1972; Endo 1959).

Data presented in this study show that the population density of _E. gea_e
in soil and maize roots increased with increase in sampling radius. The data
suggest that in order to collect a representative sample of E. _ggg in roots, the
sample should be collected at a radius of 10-20 cm from the stem. This
sampling radius compares favorably with 5-12 cm. that was recommended for

row crops in the USA (Barker, 1985; Barker, e_t a_l., 1978). The distribution of

ITO
IN

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VVE

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IW
IN

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rate
ancl
vvnl
rate
that
that
forF
215

encc
and

91951
100“
afier
SamF
asses.
The 1

(Bark

102

_P_. _z_fl in maize appeared to be in part a function of the distribution of maize
root system attackable sites and the number of attackable sites per root
weight depend on the age of the root system. Young roots have more
attackable sites per unit weight compared to old roots. The distribution of E.
ggag in roots will in turn influence the distribution of 3. fig in the soil.

The data presented in this research show that the population density'of
E. ggg increased very rapidly during the growing season. The population
had Pf/Pi and Pm/P; ratios of 170.0 and 29.5, respectively. High reproductive
rates of E. gag have also been reported in Nigeria and Zimbabwe (Egunjobi
and Bolaji, 1979; Martin e_t _a_l., 1975) where Pf/ P; ratios of _P_. zggg associated
with maize were recorded as 86.0 and 54.2, respectively. The reproductive
rate of P. _z_gag is influenced by host suitability and several edaphic factors
that include soil moisture, temperature, texture and pH. This study illustrates
that the edaphic factors under which the study was conducted were suitable
for E. g reproduction. Also the research demonstrates that maize variety R
215 is very susceptible to _13. gg infection.

This study shows that very large errors (as high as 548.0%) can be
encountered if 3. mg sampling in maize roots or soil is not properly timed
and carried out at the correct depth and distance from the plant. Data
presented in this research show that the optimal time of sampling maize
roots for _P. ggg population density assessment in loamy sand soil is 4 weeks
after planting at depth 10-20 cm) and radius of 0-10 cm. The optimal time of
sampling soil surrounding maize roots for E. _z_ga_g population density
assessment is 2 weeks after planting at depth 10-20 cm and radius 10-20 cm.
The findings compare favorably with the recommendations in the USA

(Barker, 1985; Barker and Campbell, 1981; Barker gt a_l., 1978) where they

advoi

20cm

14 I

141

C
dheq
(None
TESults
Dopuk
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texture
nematc
denshy
Nmub1
Undem1
XMUfic
Swimo
maiZer
theDGr
112““

103

advocated sampling annual plants for plant-parasitic nematodes at depth 10-

20 cm with cores coming from the root zone 5-12 cm from the stems.

3.4 INFLUENCE OF GRAVIMETRIC SOIL MOISTURE ON PRATYLENCHUS ZEAE
AND MAIZE ROOT SYSTEM DEVELOPMENT

 

3.4.1 Introduction

Constant soil moisture is difficult to maintain and thus there are few
direct observations on the effect of soil moisture on nematode populations
(Norton, 1979). The few studies that have been conducted, inconsistent
results have been reported on the impact of soil moisture on nematode
populations and this is because volumetric and gravimetric soil moisture
contents have been measured without complete specification of the soil
texture which will in turn determine the amount of available moisture to the
nematode. Information on the impact of soil moisture on the population
density of E. g is important in the development of E. E predictive
simulation models, design of _E. gag cultural control strategies and in
understanding the overwintering of E. E during the dry season. The
specific objectives of this study were to evaluate the (a) impact of gravimetric
soil moisture on the population density of _P_. gag both in soil and roots and
maize root system development and (b) gravimetric soil moisture content for
the permanent wilting point of maize (variety R 215).
3.4.2 Materials and Methods

B. gegg was maintained for 8 months on maize plants in sandy loam soil
(17% clay, 5% silt, 17% fine sand, 25% medium sand, 35% coarse sand and
0.9% organic matter), in cement built tubs (1.0 m long, 0.75 m wide and 0.75

m deep) in a greenhouse at the Harare Research Center (Grid ref. 30°25' East

ar
co
fe
po
da

ea<

for

Whi
Wat
lrea
exp,
irea'
Sam;
Plan:

label

blast)

Sa"1m

104

and 17°22' South). The culture contained about 100 E. _zga_e_ per 100 cm3 of
soil when used as inoculum for the research and the soil had a pH of 5.0.

Eighteen clay pots (30cm diameter and 45cm deep) were filled with the
_E. _z_e_ag infested soil on 27th April, 1987. The pots were arranged on a
greenhouse bench in a completely randomized block design of three
treatments and six replications. The greenhouse had maximum day and
minimum night temperatures of 32 and 20°C respectively. Immediately after
arranging the pots, each pot received an application of 150 kglha of
compound D fertilizer (8% N, 14% P205, 7% K20, 6.5% 5). After basal
fertilizer application, two maize seeds (variety R 215) were planted into each
pot. All the pots were gently watered and emergence occurred as early as 5
days after planting and was complete 9 days after planting. Maize plants in
each pot were thinned to one plant per pot 10 days after planting.

All the pots were maintained at the same moisture level (daily watering)
for three weeks. After three weeks, watering was terminated for six pets
which constituted treatment three, the second treatment, the pots were
watered twice a week on Monday and Thursday. The pots which constituted
treatment one were watered daily until the end of the experiment. The
experiment was terminated 8 weeks after planting when maize plants in
treatment three were at the permanent wilting point. The maize plants were
sampled at the end of the experiment and on the sampling date, the whole
plant was removed from the pot and the whole root system was cut into a
labeled plastic bag. Soil from the pot was thoroughly mixed and a sub-
sample (c_a_ 1 500 cm3) of the soil was put into a labeled plastic bag. All the
- plastic bags with samples were closed immediately after putting in the

sample to prevent any loss of moisture from the soil or roots. The samples

105

were put into cooler boxes and then taken back to the laboratory. The

following parameters were evaluated form the samples:

1)

ii)

iii)

Fresh weights of the root system were obtained by weighing on a
balance with an accuracy of :t 0.001 grams.

Gravimetric soil moisture content:

Labeled crucibles (capacity = 10 cm3) were put in an oven at 105 C
for about 12 hours and then cooled in a dessicator for 1 hour.
When the crucibles had cooled to room temperature, they were put
on a balance with an accuracy of i 0.001 grams using tongs to
determine the weight of the empty crucible. After the weight had
been recorded, about 5.0 cm3 of soil was put into the crucible using
a spatula and the weight of the crucible with soil was determined.
It was important to note that the tongs were not in contact with
the soil when lifting the crucible. After the second weight had been
recorded, the crucibles with the soil were put into the oven at 105 C
for about 24 hours. After the 24 hours, the crucibles with the soil
were put into a dessicator for about 1 hour. When the contents had
cooled to room temperature, the crucible with the oven dried soil
were reweighed. This procedure was repeated whenever soil
moisture content was being determined. The soil moisture content

was calculated using the following equation:

' ' hto il- ' hto a nd soil
%soil moisture = wag is? wag f "7 'y * 100
weight of oven dry sail

 

Soil was thoroughly mixed in a tray and 100 cm3 of soil was

processed using the centrifugal-flotation technique (Jenkins, 1964)

3.4.3

was m
Signific
WEre C
(Omen
mai111a
WGre 2.
in Soil 11
3.4.1),
elmaizf

“the Er

106

and observed under a stereoscopic microscope to enumerate E.
zggg in the soil.

iv) The whole root system from each pot was cut into small pieces
about 0.1-0.5 cm long and 10.0 grams were selected at random and
processed using the maceration—centrifugal-flotation technique
(Southey, 1985 p. 54) and observed under a stereoscopic microscope
to enumerate _E. _z_ga_g in the roots using the examination of
nematode suspensions technique (Southey, 1985 p. 59-60).

v) E. gag and maize root weight data presented in this study were
transformed (square root transformation) during analysis because it
exhibited a Poisson distribution. One way analysis of variance
between _P_. z_e_ag in the soil and maize roots and gravimetric soil
moisture content was carried out. After the analysis of variance,
least significant difference (LSD), standard error (SE) and coefficient
of variation (CV) were calculated.

3.4.3 Results

Eight weeks after planting, maize plants that were grown in soil which
was maintained at medium and low gravimetric soil moisture contents had
significantly (P = 0.05) lower root weights compared to maize plants that
were grown in soil which was maintained at high gravimetric moisture
content. The maize root weights of plants that were grown in soil which was
maintained at medium (11.7%) and low (5.0%) gravimetric moisture contents
were 21.1 and 55.9% lower compared to root weight of maize plants grown
in soil which was maintained at 16.5% gravimetric moisture content (Table
3.4.1). Also, there was a significant (P = 0.01) difference in the root weights
of maize plants grown in medium and low gravimetric soil moisture contents,

at the end of the experiment.

107

Table 3.4.1. Influence of gravimetric soil moisture on Prgylenchus zeae and
maize root system development.

 

 

 

 

 

 

. . E. zeae in soil and roots

Parameters Gravumetrlc . 8 weeks after planting

soul Root weight
moisture ( rams)
Treatments (%) g 100 cm3 10.0 grams

soil roots

High moisture 16.51 32.4 15.0 927.5
Medium moisture 11.7 19.8 8.5 916.2
Low moisture 5.0 5.5 15.4 523.8

 

 

 

 

 

 

 

1Mean of 6 replications.
Analysis in appendix 5.4.2.

The population density of _P. gag in soil surrounding maize plants was
equal (P = 0.05) for the three treatments eight weeks after planting maize
(Table 3.4.1). The population density of _P. ggg in the soil was generally very
low and it constituted 1.67% of the total population density of _E. gag
recovered from soil plus roots. However, the population density of E. gag in
roots of maize plants grown in soil maintained at a gravimetric moisture
content of 5.0% was significantly (P = 0.05) lower compared to the
population density of E. z_eag in roots of maize plants grown in soil which was
maintained at a gravimetric moisture content of 16.5%. There were no
significant (P = 0.05) differences in the population densities of E. ggg in
roots of maize plants that were grown in soil which was maintained at 16.5
and 11.7% or 11.7 and 5.0% gravimetric moisture contents.

3.4.4 Discussion

Low gravimetric soil moisture adversely impacted the growth of maize
root system and the population density of E. ge_ag in the roots. The data show
that the maize root system was more sensitive to low gravimetric soil

moisture compared to the population density of _E. zeae in the roots or soil. P.

gag has
Ngeha;
appears
which \
030.3
densiti.
also be
I:
that o
caPaci
Systen
Mgh
Optirr
maize
reach
Stress
3- 2g

rainf

(Ont

“0C6

preSl

a$50.
e

Z
~\§§

108

ge_ag has also been reported to be tolerant to low gravimetric soil moisture in
Nigeria and Zimbabwe (Olowe and Corbett, 1976; Martin _e_t _a_l., 1975). Also it
appears the low population density of _E. fl in the roots of maize plants
which were maintained at low gravimetric soil moisture may have been in
part a function of the low root weight in these plants. Low population
densities of Pratylenchus spp. in maize plants with smaller root weight has
also been reported in Nigeria (Egunjobi and Larinde, 1975).

Data presented in this study confirm the hypothesis by Norton (1979)
that optimum plant growth occurs between 100 and 75% of the field
capacity since at 70% and 30% of the field capacity, growth of maize root
system was adversely affected. This research illustrates that E. gea_e can reach
high population densities under soil moisture conditions which are sub-
optimal for maize growth. Thus 3. gag can be expected to cause higher
maize yield losses during seasons of unfavorable rainfall since 3. _z_e_ag can
reach high population densities on plants which are already under moisture
stress. This research, therefore, demonstrates the importance of controlling
P. gg associated with maize especially during seasons of unfavorable
rainfall.

This research also illustrates that it is extremely difficult to effectively
control B. z_eg by cultural practices which reduce gravimetric soil moisture
since _P_. fig is tolerant to very low gravimetric soil moisture contents. Data
presented in this study is well suited for adjusting the development of E. gag
associated with maize under varying gravimetric soil moisture contents in E.

zeae predictive simulation models.

15

351

prod
dens
sodo
temp
larnn
edap
Strata
that

nema

109

3.5 EVALUATION OF MAIZE VARIETIES AND INBREEDS AGAINST E. M

INFECTION
3.5.1 Introduction

There are several 3. gegg control strategies that can be adopted in maize
production. The specific tactic that is adopted will depend on the population
density of E. z_e_ag in the soil at the beginning of the growing season, the
socio-economic status of the farmer, size of the farm, soil texture, soil
temperature and soil moisture. In Zimbabwe communal farms, where
farmers have land resources of limited sizes, minimal financial resources and
edaphic factors are favorable for _E. gag development, most control
strategies of E. g in maize are not viable. Availability of maize varieties
that are resistant to E. gag infection and pathogenicity would be a viable
nematode control option for most small scale farmers.

Information on the resistance of maize varieties to E. gag infection is
important in the development of appropriate control strategies against _P_.
_z_egg infection, for communal farmers who can not afford to use expensive
and very toxic nematicides and in identifying resistant lines (genes) which can
be incorporated into maize breeding programs. The objective of this study
was to evaluate whether major maize varieties and inbreeds commonly
grown in Zimbabwe are resistant to 3. & infection.

3.5.2 Methods and Materials

3. gag was maintained for 6 months on maize plants in loamy sand soil
(6% clay, 5% silt, 25.2% fine sand, 38.4% medium sand, 25.9% coarse sand
and 0.3% organic matter), in cement built pits (3.0 m long, 1.0 m wide and
0.75 m deep) at the Harare Research Center (Grid ref. 30° 25' East and 17° 22'
South). The culture contained about 30 3. g per 100 cm3 of soil when used

as inoculum for the research.

_zg
at tI
tree
the
ferti
lin1e

vark

rnaiz

as ea

Samp

Darar

110

Fifty clay pots (15 cm in diameter and 18 cm deep) were filled with the _E.
_z_e_ag infested soil on 27th March, 1987. The clay pots were arranged in a field
at the Harare Research Center in a completely randomized block design of 10
treatments and 5 replications per treatment. Immediately after arranging
the pots, each pot received applications of 150 kglha of compound D
fertilizer (8% N, 14% P205, 7% K2 0, 6.5% S) and 100 kglha of agricultural
lime (4.5% Mg). After basal fertilizer application, seeds of seven maize
varieties ( R 201, R 215, SR 52, 25 107, 25 206, and ZS 225) and three inbreeds
(83 3WH 59, 83 3WH 27 and 86 3WH 12) were planted into the pots, two
maize seeds per pot. The pots were gently watered and emergence occurred
as early as 5 days after planting and was complete 9 days after planting.

The maize plants were sampled 8 weeks after planting. On the
sampling date, the whole plant was removed from the pot and the following
parameters were measured:

i) Fresh weights of the root system were determined on a mettler

balance which can meaSure one hundredth of a gram.

ii) The whole root system from each pot was chopped into small pieces
about 0.1-0.5 cm long and 10.0 grams were selected at random and
processed using the maceration-centrifugal-flotation technique
(Southey, 1985 p.54) and observed under a stereoscopic microscope
to enumerate 3. fig in the roots using the examination of
nematode suspensions technique (Southey, 1985 p. 59-60).

iii) Soil was thoroughly mixed in a tray and 100 cm3 of soil was
processed using the centrifugal-flotation technique. (Jenkins, 1964)
and observed under a stereoscopic microscope to enumerate E.

zeae in the soil.

111

iv) 3. fl and maize root weight data presented in this study were
transformed (square root transformation) during analysis because it
exhibited a Poisson distribution. One way analysis of variance
between E. _z_gag in the soil and maize roots and the different maize
varieties and inbreeds was carried out. After the analysis of
variance, least significant differences (LSD), standard error (SE) and
coefficient of variation (CV) were calculated.

3.5.3 Results

Eight weeks after planting, all the maize varieties and inbreeds had an
equal (P = 0.05) root weight (Table 3.5.1). B. _zgg infected the root system of
all the maize varieties and inbreeds that were tested in this experiment.
Varieties R 215, 25 206 and 25 225 had a slightly lower population density of
E. _z_g_ag in the roots compared to varieties R 201 and 25 107 (Table 3.5.1).
Varieties R215, SR 52, ZS 202, 25 206, 25 225 and inbreeds 83 3WH 59, 83 3WH
27 and 86 3WH 12 had an equal (P = 0.05) population density of _E. gea_e in
the roots at the end of the experiment. Similarly, varieties R 201 and 25 107
had an equal (P = 0.05) population density of 13. gag in the roots. The
population density of E. gg in the soil was equal (P = 0.05) for all the
treatments, eight weeks after planting.
3.5.4 Discussion

All the maize varieties and inbreeds were susceptible to E. gggg
infection. Maize varieties ASA 80, ASA 81, SR 52 and R 215 have also been
reported to be very susceptible to E. _z_gg infection and pathogenicity (Martin
6411., 1975; Muchena gt al., 1987). The population density of _P. fig in this
study did not build up rapidly possibly because of sub-optimal temperature

conditions during the growing period. This study illustrates that resistance

112

Table 3.5.1. Evaluation of maize varieties and inbreeds against Pratylenchus
zeae infection.

 

 

 

 

 

 

 

 

 

 

 

 

 

Parameters E. gg in soil and roots
Root weight 8 weeks after planting
(grams)
Varieties 100 cm3 soil 10.0 grams roots

R 201 45.21 12.2 24.0
R215 45.8 11.0 9.2
SR 52 39.6 12.8 18.4
zs 107 ' 53.9 13.4 23.8
25 202 40.3 16.4 14.2
25 206 44.5 15.2 10.4
25 225 37.4 10.6 8.8
83 3WH 59 38.8 7.8 14.4
83 3WH 27 38.5 12.2 15.8
86 3WH 12 39.0 14.0 14.6

 

 

 

 

 

 

1Mean of 5 replications.
Analysis in appendix 5.5.2

tor

inr

3.6

3.6.

anc
1,31
198
(011
big!
910'
dev
bee
gro-

den

113

to major root-lesion nematode parasites of maize has not been incorporated

in maize breeding programs.

3.6 INFLUENCE OF NUTRIENTS ON _P. Z_E_A_§ POPULATION DENSITY AND

MAIZE GROWTH PARAMETERS
3.6.1 Introduction

In the USA, maize yield increased from 780 to 6,000 kg/ha between 1895
and 1962 and in Zimbabwe commercial farms, maize yield increased from
1,320 to 1,970 kg/ha between 1934 and 1960 (Berger, 1962) and during the
1985/86 growing season, maize yield was 5,668 kg/ha in Zimbabwe
commercial farms. Most of the maize yield increase can be attributed to new
high yielding hybrids and varieties. However, the productive and quick-
growing hybrids and varieties require an adequate supply of nutrients for full
development of the inherited productivity (Berger, 1962). The nutrients can
be applied as organic or inorganic fertilizer and apart from stimulating maize
growth, the nutrients can adversely or favorably influence population
densities of plant-parasitic nematodes in the soil.

Information on the influence of nutrients on the population density of
13. _z_gg and maize growth parameters is important in the development of
predictive computer simulation models and cultural control strategies and in
understanding the interactions between nutrients, _E. _z_e_a_g population
densities and maize growth parameters. The specific objective of this study
was to evaluate the impact of organic and inorganic nutrients on the
population density of _E. z_ea_e and maize growth.
3.6.2 Materials and Methods

B. _z_g_a_g was maintained for 6 months on maize plants in loamy sand soil

(6% clay, 5% silt, 25.2% fine sand, 38.4% medium sand, 25.9% coarse sand,

0.31
and
17°

whe

fillet
arral
bloc.
treat

recei

114

0.3% organic matter and pH 4.4) in cement built pits (3.0 m long, 1.0 m wide
and 0.75 m deep) at the Harare Research Center (Grid ref. 30° 25' East and
17° 22’ South). The culture contained about 30 _E. gag per 100 cm3 of soil
when used as inoculum for the research.

Forty eight clay pots (30 cm long, 30 cm wide and 30 cm deep) were
filled with the E. ze_ag infested soil on 26th March, 1987. The clay pots were
arranged in a field at the Harare Research Center in a completely randomized
block design of 8 treatments, 3 replications and 2 sampling times per
treatment. Immediately after arranging the pots, six pots per treatment
receive the following treatments:

1. untreated

2. compound D fertilizer (8% N, 14% P205, 7% K20, 6.5%5) at a rate
of 150 kg/ha on the planting date.

3. ammonium nitrate (34.5% N) at a rate of 150 kglha 8 weeks after
planting.

4. cattle manure at a rate of 12 tons/ha on the planting date.

5. compound D fertilizer at a rate of 150 kglha on the planting date +
ammonium nitrate fertilizer at a rate of 150 kglha 8 weeks after
planting.

6. compound D fertilizer at a rate of 150 kglha + cattle manure at a
rate of 12 tons/ha on the planting date.

7. cattle manure at a rate of 12 tons/ha on the planting date +
ammonium nitrate fertilizer at a rate of 150 kglha 8 weeks after
planting.

8. compound D fertilizer at a rate of 150 kg/ha + cattle manure at a
rate of 12 tons/ha on the planting date + ammonium nitrate at a

rate of 150 kg/ha 8 weeks after planting.

811C

stre

sam

Dare

115

After the treatments, 100 kglha of agricultural lime (4.5% Mg) was

applied to all the pots to increase the soil pH and maize seed (variety R 215)

was planted at the center of the pot, two seeds per pot. The pots were gently

watered and emergence occurred as early as 5 days after planting and was

complete 9 days after planting. The plants were thinned to one plant per pot

two weeks after planting. The maize plants were watered daily for six weeks

and thereafter, the plants were only watered when there were signs of water

stress.

The maize plants were sampled 8 and 16 weeks after planting. On the

sampling date, the whole plant was removed from the pot and the following

parameters were evaluated:

i)

ii)

iii)

iv)

Fresh weights of the root and shoot systems were determined on a
Mettler balance which can measure one-hundredth of a gram.

The root system from the plant was chopped into small pieces about
0.1-0.5 cm long and 10.0 grams were selected at random and
processed using the maceration-centrifugal-flotation technique
(Southey, 1985 p. 54) and observed under a stereoscopic microscope
to enumerate _P. z_e_ag in the roots using the examination of
nematode suspensions technique (Southey, 1985 p. 59-60).

Soil was thoroughly mixed in a tray and 100 cm3 of soil was
processed using the centrifugal-flotation technique (Jenkins, 1964)
and observed under a stereosc0pic microscope to enumerate E.
gea_e in the soil.

One way analysis of variance between E. ggg in the soil and maize
roots and different nUtrient levels was carried out. After the
analysis of variance, least significant difference (LSD), standard

error (SE) and coefficient of variation (CV) were calculated.

Eic
ap

tre

fer
ma
con
119
0.0!
had
tree
equ
(Orr
Tree
35%

trea

reCei
ant)
”lira
)Nfig
Treat
manL

00”

116

3.7.3 Results

Maize root and shoot weights were significantly (P = 0.01) influenced
by application of nutrients 8 and 16 weeks after planting (Tables 3.6.1-3.6.2).
Eight weeks after planting, treatments in which nutrients had not been
applied had the lowest (P = 0.01) shoot weight compared to all the other
treatments. Treatments in which manure had been applied, had significantly
(P = 0.05) lower shoot weight compared to treatments in which compound D
fertilizer had been applied. Treatments in which compound D fertilizer plus
manure had been applied, had significantly (P = 0.01) higher shoot weight
compared to treatments which had only received compound D fertilizer.
Treatments in which nutrients had not been applied had the lowest (P =
0.05) root weight eight weeks after planting. Treatments in which manure
had been applied, one treatment in which compound D fertilizer and one
treatment in which compound D fertilizer plus manure had been applied had
equal root weight and the root weight was significantly (P = 0.05) greater
compared to treatments which had not received any nutrients. one
treatment in which compound D fertilizer plus manure had been applied had
a significantly (P = 0.05) higher root weight compared to all the other
treatments except one treatment where manure had been applied.

Sixteen weeks after planting maize, the treatment which had not
received any nutrients had the lowest (P = 0.01) shoot weight compared to
all the other treatments. Treatments in which manure and ammonium
nitrate fertilizer had been applied, had a significantly (P = 0.05) higher shoot
weight compared to the treatment which had not received any nutrients.
Treatments which had compound D fertilizer, compound D fertilizer plus
manure and ammonium nitrate fertilizer plus manure had significantly (P =

0.01) higher shoot weight compared to treatments which had just received

117

Table 3.6.1. Impact of nutrients on Praglench us zeae population density and
maize growth parameters weeks after seeding.

 

 

 

 

 

 

 

 

 

 

Parameters No. of g. zeae Weight (grams)
Nutrients 100 cm3 soil 10.0 grams Root Shoot

Nontreated 4.31 20.0 31.5 39.5
Compound D 3.0 45.0 74.0 160.7
Ammonium 31.7 32.3 21.7 30.7
Nitrate
Manure 14.3 21.3 61.4 95.5
Compound D + 5.7 18.0 62.6 131.4
Amm. nitrate
Compound D 3.0 11.3 68.6 200.0
+ Manure
Amm. nitrate + 4.3 14.7 96.0 109.3
Manure
Amm. nitrate 4.0 21.0 1 12.9 278.3
+ Manure +
Compound D

 

 

 

 

 

 

 

Key
lMean of 3 replications.
Analysis in Appendix 5.6.3.

118

Table 3.6.2. Influence of nutrients on Pratylenchus zeae population density
and maize growth parameters 16 weeks after seeding.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1Mean of 3 replications.
Analysis in Appendix 5.6.4.

Parameters No. of E. zeae Weight (grams)

Nutrients 100 cm3 soil 10.0 grams Root Shoot
Nontreated 20.01 1 16.7 59.2 102.2
Compound D 18.7 83.3 180.5 450.4
Ammonium 18.3 88.3 60.1 210.0
Nitrate
Manure 30.3 149.3 99.5 162.8
Compound D + 12.0 70.7 214.3 440.7
Amm. nitrate
Compound D 25.0 117.0 163.3 350.3
+ Manure
Amm. nitrate + 9.0 182.7 93.9 295.8
Manure
Amm. nitrate 14.3 78.3 200.5 491.8
+ Manure +
Compound D

Key

 

eitl

0 f1

ann

\Nei

pk“
trea
lovv
Trea
beer
the:
nnra
fertil
Dfer
fertil

r001 l

SIgnil
Week
DOpU
treat,

lee

119

either ammonium nitrate or manure. Treatments which received compound
D fertilizer plus ammonium nitrate fertilizer and compound D fertilizer plus
ammonium nitrate plus manure, had significantly (P = 0.05) higher shoot
weight compared to all the other treatments. Also sixteen weeks after
planting, the treatment which had not received any nutrients and a
treatment in which ammonium nitrate fertilizer had been applied had the
lowest (P = 0.05) root weight compared to all the other treatments.
Treatments where manure and ammonium nitrate fertilizer plus manure had
been applied, had significantly (P = 0.01) higher root weight compared to
the treatments which had not received any nutrients or where ammonium
nitrate fertilizer had been applied. Treatments in which compound D
fertilizer, compound D fertilizer plus ammonium nitrate fertilizer, compound
D fertilizer plus manure and compound D fertilizer plus ammonium nitrate
fertilizer plus manure had been applied, had significantly (P = 0.01) higher
root weight compared to all the other treatments.

The population density of E. ggg in soil and maize roots was
significantly (P = 0.05) influenced by the application of nutrients 8 and 16
weeks after planting (Tables 3.6.1-3.6.2). Eight weeks after planting, the
population density of E. gag in the soil was equal (P = 0.05) except for one
treatment which had not received any nutrients. The population density of _P_.
gag in the roots was also equal (P = 0.05) except for two treatments, one
had received compound D fertilizer and the other had not received any
nutrients.

Sixteen weeks after planting, the population density of P. agag in the
soil from pots which had not received any nutrients was equal (P = 0.05) to
population densities of E. gag in the soil from pots which had received

compound D fertilizer, ammonium nitrate fertilizer, manure plus ammonium

nr
an
rel

ihl

nib
COT‘
anc
whi
had
(00‘
filth
lhar

3111

flgni
ai'tEr
Wee;
app“
Dbnt
wnh,
Badra
”duc
am”1c

120

nitrate fertilizer, compound D fertilizer plus manure, compound D plus
ammonium nitrate and compound D plus manure. The treatments which had
received manure had the highest (P = 0.05) population density of E. gag in
the soil. During the same sampling period, the population density of E. _z_g_ag
in roots of maize plants growing in pots which had not received any nutrients
was equal (P = 0.05) to population densities of _E. gag in roots of maize
plants growing in pots which had received compound D fertilizer, ammonium
nitrate fertilizer, manure,compound D plus ammonium nitrate fertilizer,
compound D fertilizer plus manure, ammonium nitrate fertilizer plus manure
and compound D plus ammonium nitrate fertilizer plus manure. Treatments
which had received manure and ammonium nitrate fertilizer plus manure
had the highest (P = 0.05) population densities of E. z_ea_e in maize roots
compared to treatments which and received compound D plus ammonium
nitrate fertilizer and compound D plus ammonium nitrate fertilizer plus
manure.
3.6.4 Discussion

Data presented in this study show that the application of nutrients
significantly reduced the population density of E. gegg in the soil eight weeks
after planting. However, the population density of E. agg in the soil sixteen
weeks after planting was greater in treatments where manure had been
applied. The reduced population density of E. gag eight weeks after
planting was similar to that reported in Alabama, Egypt, Florida and Nigeria
with other plant-parasitic nematodes (Mian and Rodriguez-Kabana, 1982a-b;
Badra and Mohamed, 1979; Tarjan, 1977; Egunjobi and Larinde, 1975). The
reduction of E. gegg in soil with manure may be a function of released
ammoniacal nitrogen during decomposition of manure, increased

microfauna inimical to E. zeae and unfavorable environmental conditions for

Iror
pop
Dob
the
abili
whe
com
was
gree
lave
app!
The
fem
Dara

I0ng

121

P. zeae created by the application of manure. The high population densities

 

of _P. zeae in the soil sixteen weeks after planting, especially in manured soil,

 

compares favorably with data which was reported for Rotylenchulus
reniformis associated with tomatoes growing in sheep dung manured soil in
Egypt (Badra and Mohamed, 1979). It appears after sixteen weeks, plants
growing in soil with manure had higher root weight which allowed 3. z_e_a_gto
reproduce more rapidly and the E. _ze_ag subsequently ended up in the soil.
The number of P. _z__eg in the soil eight weeks after planting was very low and
the data had high variability, therefore, the validity of these findings may be
of limited scope.

The data show that roots from soil which was not treated and roots
from soil where compound D fertilizer had been applied had higher
population densities of E. z_egg eight weeks after planting. The high
population density of E. gag in roots from soil which was not treated despite
the low root weight indicate that E. ggg in this soil was not impaired in its
ability to penetrate and develop in maize roots relative to other treatments
whereas the high population density of E. z_ea_e in roots from soil where
compound D fertilizer was applied may be in part a function of greater root
weight which enabled the population density to build up more rapidly. The
greater root weight as a result of applying compound D fertilizer compares
favorably with the faster root growth that has been reported after
application of fertilizers with a high content of phosphates (Berger, 1962).
The high population density of _P. gea_e in roots from soil where compound D
fertilizer was applied was analogous to high population densities of plant-
parasitic nematodes that result in plant roots after a nematicide in soil is no

longer effective (Muchena and Bird, 1987).

incre
Incre
com;
Nigel
Moha
Larin.
GSpec

mm
3.7 l
3.11

fieldS

122

This study shows that the population density of E. gegg did not
reproduce rapidly as what has been recorded in previous studies in Zimbabwe
(Martin gt al., 1975; Muchena gt a_l., 1987). The low population density of E.
gg in this study may have been in part a function of low soil temperature
during the growing period. As a result of the low population densities of E.
ze_ag during the growing period, it is possible that trends from some
treatments may have been masked, therefore it is essential for this study to
be repeated to evaluate the consistency of the data.

Data from this study also show that maize root and shoot systems were
increased by the application of organic and inorganic fertilizers into the soil.
Increased plant growth after application of nutrients that was recorded,
compares favorably with that reported in Alabama, Egypt, England, Florida,
Nigeria and Zimbabwe (Mian and Rodriguez-Kabana, 1982a-b; Badra and
Mohamed, 1979; Arnon, 1974; Cooke, 1975; Tarjan, 1977; Egunjobi and
Larinde, 1975; Mugwira, 1984). The nutrients increase plant growth
especially by increasing the availability of essential nutrients (N, P, K) and

secondary nutrients (Ca, Mg, 5, Fe, Zn, Cu, Mn) in the soil (Mugwira, 1984).

3.7 EFFECT OF GRANULAR NEMATICIDES ON 3. Z_E_A_E_ ASSOCIATED

WITH MAIZE
3.7.1 Introduction

In Zimbabwe, the incidence of Pratylenchus spp. was 97% in maize
fields sampled during the national survey of pests and diseases in communal
areas during the 1985/86 growing season. Population densities of
Pratllenchus spp. in 54.5% of the fields that were infested were above the
damage threshold, the damage threshold was estimated to be 1,000

Pratylenchus spp. per 10.0 grams of roots, 8 t 2 weeks after planting.

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123

Pratylenchus spp. were especially a major constraint of maize production in
sandy soils where farmers were not practicing crop rotation because they
have limited land resources. The main Pratylenchus spp. which were found
associated with maize are Pratylenchus brachyurus and E. g and had
absolute frequencies of 21.1 and 52.6%, respectively. There are, however,
several strategies that can be adopted for control of Pratylenchus spp. in
maize and they include organic amendments, early land preparation, crop
rotation, use of resistant maize varieties and application of nematicides.

When population densities of Pratylenchus spp. in the soil are very high, as

 

was detected in some of the communal farms, use of nematicides is perhaps
the most reliable method for a quick and effective control of Pratylenchus
spp. in maize (Egunjobi and Larinde, 1975; Muller and Gooch, 1982). The
objectives of this study were to : (a) evaluate the effects of organophosphate
and organocarbamate nematicides in controlling population densities of E.
_z_egg associated with maize in a communal farm and (b) assess the
subsequent maize yield increase associated with the E. gag control.
3.7.2 Materials and Methods

The site for this study was in Zvimba communal area (Grid ref. 30° 5'
East and 17° 50' South). The soil was sandy loam (12% clay, 5% silt, 21.2%
fine sand, 33.6% medium sand, 28.7% coarse sand and 1.2% organic matter)
with a pH of 5.3 and was naturally infested with E. & . The land was
plowed using an ox drawn plow by the farmer after the first effective rainfall
on 25th November, 1986. The land was leveled using hoes and plots (9 x
2.7m) with guard rows of 1.0 m marked out in a completely randomized block
design with five treatments and four replications on 5th December, 1986.
Basal fertilizer, compound D (8% N, 14% P205, 7% K20, 6.5% S) was applied
at a rate of 300 kglha to all the plots immediately after laying out the trial.

Th1
to l
Aft
furr
are
and
nerr
R 21

intra

(Hid:
the n
15-20
Also 5
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124

Then furrows 5 cm deep, 10 cm wide and 90 cm apart, in which the seed was
to be planted using planting chains, were made to all the plots using hoes.
After making the furrows, nematicides were applied into sixteen plots in
furrow and incorporated with a hoe. The nematicides which were applied
are carbofuran 10G, fenamiphos IOG and isazofos IOG at a rate of 20 kglha
and terbufos 10G at a rate of 10 kglha. Four plots were not treated with the
nematicides. After all the treatments had been applied, maize seed (variety
R 215) was planted on the same date with inter-row spacing of 90 cm and
intra-row spacing of 40 cm.

Soil samples composed of five sub-samples collected at random using a 5
cm diameter auger were collected from each plot on the planting date before
the nematicides had been applied. The soil auger was pushed to a depth of
15-20 cm and then moist soil was put into labeled plastic bags and sealed.
Also soil and root samples composed of five sub-samples collected at random
were collected from each plot four and eight weeks after planting. Root
samples were collected by digging the root system of the plant and then soil
was shaken off the root system and part of the root system was cut into a
labeled plastic bag. The samples were put into cooler boxes and then taken
back to the laboratory. The following parameters were evaluated from the
samples:

1. The root system was chopped into small pieces about 0.1-0.5 cm

long and 10.0 grams were selected at random and processed using
the maceration-centrifugal-flotation technique (Southey, 1985 p.
54) and observed under a stereoscopic microscope to enumerate E.
z_ea_e in the roots using the examination of nematode suspensions

technique (Southey, 1985 p. 59-60).

on 5
(34.5
the c
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\NhHe
hand
Smnp

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125

2. Soil was thoroughly mixed in a tray and 100 cm3 of soil was
processed using the centrifugal-flotation technique (Jenkins,
11964) and observed under a stereoscopic microscope to quantify If,
zgg in the soil using the examination of nematode suspensions
technique (Southey, 1985 p. 59-60).

During the growing season, all the plots were hand weeded using hoes
on 5th January, 1987 and 2nd February, 1987. Ammonium nitrate fertilizer
(34.5% N) was applied on 2nd, February, 1987 at a rate of 150 kglha. After
the crop had reached physiological maturity on 28th April, 1987, maize ears
were removed from the stalks and put into bags. The ears were further dried
while they were in the bags using an electric dryer for 7 days. The maize was
hand shelled and the weight of seed per plot was determined. A small
sample of the dried seed was used to determine the percentage of moisture
in the seed using a moisture meter MM250.

Maize dried to a moisture level of 12.5% can be sold to the Grain
Marketing Board (GMB). The controlled price for selling maize to the GMB
was 25180.00 per ton at the end of 1985/86 growing season. During the same
period, the estimated basic cost, excluding labor, for growing 1.0 ha of maize
was 25303.00. The basiccost for maize production included: seed, fertilizer,
bags for packing the maize and transportation of the maize to the GMB from
the nearest main road. If a nematicide was used in the maize production, the
cost of the nematicide, 25193.40 or 25130.40, was added to the basic cost if
the nematicide was carbofuran or fenamiphos, respectively. To evaluate the
return for the farmer after growing maize, the cost of production should be
subtracted from the gross income:

a) Grossincome/ha = Yield (tons/ha) * 25180.00

b) Cost of production/ha = 25303.00 + cost of nematicide

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126

c) Netincome/ha = Grossincome-Cost of production

_13. z_e_ag data in this experiment were transformed (square root
transformation) because it exhibited a Poisson distribution. One way analysis
of variance between E. gegg in the soil and maize roots and different
nematicide treatments was carried out. After the analysis of variance, least
significant difference (LSD), standard error (SE) and coefficient of variation
(CV) were calculated.

3.7.3 Results

On the planting date, all the plots had an equal (P = 0.05) population
density of E. g in the soil (Table 3.7.1). Four weeks after planting, plots
which were treated with nematicides had a significantly lower (P = 0.05)
population density of E. ggg in roots and soil compared to the nontreated
plots. Plots that were treated with carbofuran, isazofos, terbufos and
fenamiphos had population densities of E. gag which were 68.61, 63.10,
56.90 and 53.37% lower than the population density of _13. E in nontreated
plots, respectively. There were, however, no significant differenced in the
population densities of E. z_e_g in roots and soil from nematicide treated
plots. The population densities of g. gea_e in roots and soil four weeks after
planting (Pm) compared to the initial population density in the soil (Pi) had
ratios of 3.3, 4.6, 5.2, 8.3 and 16.6 for plots that were treated with
carbofuran, fenamiphos, isazofos, terbufos and nontreated plots,
respectively.

Eight weeks after planting, plots which were treated with nematicides
had a significantly lower (P = 0.01) population density of E. E in roots and
soil compared to the nontreated plots. Plots that were treated with
carbofuran, isazofos, terbufos and fenamiphos had population densities of E.

zeae which were 94.81, 95.11, 93.14 and 95.97% lower than the population

den:
no si
root
leg
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for p.
and n
and 1
terbu
variab
maize
p
maize
terbufi
and 35
treated
mahey
lP101
With ISa

p'OtSth.

127

density of _13. gag in the nontreated plots, respectively. There were, however,
no significant differences (P = 0.05) in the population densities of 3. Egg in
roots and soil from nematicide treated plots. The population densities of E.
gag in roots and soil eight weeks after planting (Pf) compared to the initial
population density in the soil (Pi) had ratios of 0.96, 1.27, 1.23, 1.32 and 29.64
for plots that were treated with carbofuran, fenamiphos, isazofos, terbufos
and nontreated plots, respectively. The ratio of Pm/Pf was 0.3, 0.15, 0.24, 0.28
and 1.78 for plots that were treated with carbofuran, fenamiphos, isazofos,
terbufos and nontreated plots, respectively. There was considerable
variability (c.v.% = 46.60) in the number of E. ze_ag that were recovered from
maize roots in some treatments.

All the nematicides that were applied, significantly increased (P = 0.05)
maize yield compared to the nontreated plots (Table 3.7.1). Carbofuran,
terbufos, fenamiphos and isazofos increased maize yield by 67.4, 66.0, 54.7
and 36.7% compared to the nontreated plots, respectively. Plots that were
treated with carbofuran, fenamiphos and terbufos, had an equal (P = 0.05)
maize yield and the yield of maize in fenamiphos treated plots was also equal
(P = 0.05) to the maize yield in isazofos treated plots. Plots that were treated
with isazofos had a significantly lower (P = 0.05) maize yield compared to
plots that were treated with carbofuran or terbufos.

Use of nematicides to control P. gg in maize, resulted in loss of
revenue used to buy inputs despite the maize yield increase (Table 3.7.2). The
cost of isazofos and terbufos is currently not available in the country because
the nematicides are not registered in Zimbabwe but it is quite apparent that
the maize yields that were obtained, will not be able to pay for the inputs.
Also the maize yield that was obtained in the nontreated plots, resulted in

loss of revenue used to buy seed, fertilizer and packing material.

128

Table 3.7.1. Effect of several granular nematicides on Pratylenchus zeae
associated with maize in Zvimba communal areas.

 

 

 

 

 

 

 

 

 

 

 

 

Parameters _P_. zeae in E. zeae in E. zeae in
soil1 on roots and roots and Maize yield
. . 2 . 2
Treatments treating sorl 4weeks J sorl 8wks (tons/ha)
date after after
carbofuran 109 48.33 184.3 50.0 1.94
fenamiphos 109 30.3 283.8 37.8 1.79
isazofos 109 36.0 196.0 53.0 1.58
terbufos 109 45.5 229.3 67.0 1.92
nontreated 33.8 502.3 944.5 1.16
Key
1Soil = 100 cm3.

2Roots and soil = 100 cm3 soil + 10.0 grams roots.
3Mean of 4 replications.
Analysis in appendix 5.7.2

Table 3.7.2. Comparative economic analysis for using nematicides in
controlling Pratylenchus zeae in maize.

 

 

 

 

 

 

 

 

 

 

Parameters Maize yield Total cost of Gross1 Net2 Income

Treatments (kglha) inputs (25) income (25) (25)
carbofuran 10 9 1937.00 496.40 348.66 - 147.74
fenamiphos 10 9 1790.00 433.40 322.20 -1 1 1.20
isazofos 10 9 1582.00 284.76 --
terbufos 10 9 1921.00 345.78 -
nontreated 1 157.00 303.00 208.26 -94.74

 

 

 

*Cost of nematicide currently not available.
1Gross income = tons/ha x 25180.00
2Net income = gross income - total cost of inputs.

 

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129

3.7.4 Discussion

All the nematicides significantly controlled _l3. _z_gg for eight weeks and
subsequently increased maize yield. The nematicides equally controlled E.
gag and the magnitude of control was similar to that reported in Georgia,
Indiana and Zimbabwe (Johnson and Chalfant, 1973, 1973; Bergeson, 1978;
Martin gt al., 1975). The population density of _P. gag in maize roots (E. ae_a_g
in the soil was negligible and it constituted about 0.4% of the total
population recovered from roots and soil) was 3 x lower compared to the
population density of E. gag that was recovered in maize roots during the
1985/86 growing season (Muchena gt a_l., 1987).. The lower population
densities of _P. ga_e_ in maize roots during the 1986/87 growing season appear
to be a result of the relatively low rainfall that was received during the
season. Also because of the drought, the nematicides had a higher reduction
of the population density of 3. fig in roots and soil, 94.8% compared to
79.8% during the 1985/86 season (Muchena gt _a_l., 1987). The growing season
with higher rainfall had lower 3. gg control because the rainfall will flush
out the nematicides, hence reduce the efficacy of the nematicides. Reduced
nematicide efficacy because of high rainfall and/or irrigation has also been
observed in California and Michigan (Hough gta1., 1975; Muchena and Bird,
1987).

Also because of the drought, maize yields in this study, were 3.7 x lower
compared to the maize yields that were obtained during the 1985/86
growing season on the same site (Muchena gt al., 1987). The low maize yields
could not generate enough revenue to pay for the nematicides and other
agricultural inputs that had been purchased. Studies that have been carried
out in Nigeria. have also shown that increases in maize yields obtained by use

of nematicides may not be sufficient to cover costs (Egunjobi and Larinde,

l9]
dif1
pk)
ach
yhfl
inai

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the

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obse
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isazc

29$
SUbst,
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SU lted

130

1975). The drought, however, appears to be responsible for the greater
differences in maize yields between nematicide treated plots and nontreated
plots compared to an average of 48.85% maize yield increase which was
achieved during the 1985/86 growing season (Muchena gt a_l., 1987). Maize
yield data presented in this study suggest that E. gag is more limiting to
maize growth and development when there is a stress of low soil moisture
and/or soil nutrients.

Plots that were treated with isazofos had a lower maize yield compared
to the other nematicide treatments despite comparable E. gag control with
the other nematicide treatments. The low maize yield in isazofos treated
plots appear to be a result of slightly lower maize germination which was
observed in this treatment. It appears isazofos was phytotoxic to some maize
seedlings. It is, therefore, important to ensure thorough incorporation of
isazofos with soil before planting the seed, particularly during seasons with
low rainfall.

Data presented in this study illustrate the importance of controlling E.
gag associated with maize in communal farms infested with E. gag to avoid
substantial maize yield losses. The data also illustrate the importance of
judiciously evaluating growing seasons when nematicides can be used to
control B. z_e_ag in maize with resultant terminal benefits to the farmer.
Comparisons of the data from this experiment and the data from the 1985/86
growing season experiment, demonstrate the impact of rainfall on maize
yields and E. agag population densities. This information should be well

suited for validation of E. zeae computer simulation models.

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131

3.8 INFLUENCE OF ORGANIC AMENDMENTS AND EARLY PLOWING ON _P_.

_Z_Egg PATHOGENICITY ON MAIZE
3.8.1 Introduction

The use of nematicides is perhaps the most reliable method for a quick
and effective control of plant-parasitic nematodes infecting crops (Egunjobi
and Larinde, 1975; Muller and Gooch, 1982). However, in Zimbabwe
communal farms, it is unrealistic to recommend such pesticides to farmers
because most nematicides are extremely toxic to humans and require skilled
labor for a successful application; they are also expensive and the increases in
yields obtained by their use may not be sufficient to cover costs. Other plant-
parasitic nematode control strategies which are compatible with communal
farmers socio-economic considerations must, therefore, be found to ensure
increased maize yields in communal farms which are commonly infested with
high population densities of root-lesion nematodes especially 3. aegg.

Research on organic amendments for control of plant-parasitic
nematodes has, however, concentrated on addition of large quantities of
material in the soil and up to 84 metric tons/ha (Egunjobi and Larinde, 1975;
Mian and Rodriguez-Kabana, 1982; Muller and Gooch, 1982). Addition of
such large quantities of organic material especially for field crops such as
maize is unrealistic for most communal farmers.

Early land preparation prior to the dry season or winter is also known to
reduce the population densities of plant-parasitic nematodes in the soil.
During the dry season, soil and roots in the plowed field will be exposed to
solar radiation and drying such that at planting, seeds are placed in upper
layers with low plant-parasitic nematode populations. This study was,
therefore, set up to evaluate E. gag control and subsequent maize yield

response obtained by three cultural practices commonly used by communal

far

pr;
31!

25'

finl

mht

infe
out

repl
prep
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hoes
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ach
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arate
andi
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aDNh

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Dhnu

132

farmers. It was also of interest to compare the effectiveness of the cultural
practices with a registered nematicide on maize.
3.8.2 Materials and Methods

The site for this study was in Chinamora communal area (Grid ref. 30°
25' East and 17° 30' South). The soil was loamy sand (9% clay, 5% silt, 23.2%
fine sand, 36% medium sand, 27.3% coarse sand and 0.64% organic matter)
with a pH of 4.4 and bulk density of 1.46 grams/cm3 and was naturally
infested with E. gag. Plots 9 x 4.5m with guard rows of 1.8m were marked
out in a completely randomized block design with five treatments and four
replications on 2nd September, 1986. Four plots which required early land
preparation were dug using hoes on the same date. This early land
preparation procedure was repeated to the same plots twice at monthly
intervals. After the first effective rainfall on 25th November, 1986, the rest of
the plots were plowed using an ox-drawn plow. The land was leveled using
hoes and all the remaining treatments including basal fertilizer application
were carried out on 2nd December, 1986. The basal fertilizer, compound D
(8% N, 14% P205, 7% K20, 6.5% S) was broadcasted at a rate of 300kg/ha to
all the plots immediately after leveling. Then eight plots were applied with
manure, four with cattle manure and the other four with compost manure at
a rate of 12 tons/ha. The manure was broadcasted into the respective plots
and incorporatedwith a hoe. After the manure application, furrows 5 cm
deep, 10 cm wide and 0.9 m apart, in which the seed was to be planted using
planting chains, were made to all the plots using hoes. Carbofuran IOG was
applied in furrows at a rate of 20 kglha to four plots and incorporated with a
hoe. The remaining four plots out of the twenty plots were not treated..
After all the treatments had been applied, maize seeds (variety R 215) were

planted with inter-row spacing of 90 cm and intra-row spacing of 40 cm.

133

Soil samples composed of five sub-samples collected at random using a 5
cm diameter auger were collected from each plot on the planting date before
the nematicide and the manure had been applied. The soil auger was pushed
to a depth of 15-20 cm and then the moist soil was put into labeled plastic
bags and sealed. Also soil and root samples composed of five sub-samples
collected at random were collected from each plot 4, 8, 12 and 16 weeks after
planting. Root samples were collected by digging the root system of the
plant then soil was shaken off the root system and part of the root system
was cut into a labeled plastic bag. The following parameters were evaluated
from the samples:

1. The root system was chopped into small pieces about 0.1-0.5 cm

long and 10.0 grams were selected at random and processed using
the maceration-centrifugal-flotation technique (Southey, 1985
p.54) and observed under a stereoscopic microscope to enumerate
_P_. z_e_ag in the roots using the examination of nematode suspensions
technique (Southey, 1985 p. 59-60).

2. Soil was thoroughly mixed in a tray and 100 cm3 of soil was
processed using the centrifugal-flotation technique (Jenkins, 1964)
and observed under a stereoscopic microscope to quantify 3. gig in
the soil using the examination of nematode suspension technique
(Southey, 1985 p. 59-60).

During the growing season, all the plots were hand weeded using hoes
on 2nd January, 1987 and 30th January, 1987. Ammonium nitrate fertilizer
(34.5% N) was also applied twice on 16th January, 1987 and 13th February,
1987 at a rate of 150 kglha. After the crop had reached physiological
maturity on 22nd May, 1987, maize ears were removed from the stalks and

put into bags. The ears were further dried while they were in the bags using

va

of

Pol
We
DO;

trea

000'

134

an electric dryer for 5 days. Then the maize was hand shelled and the weight
of the seed per plot was determined. A small sample of the dried seed was
used to determine the percentage of moisture in the seed using a moisture
meter MM 250.

E. z_eag and maize yield data in this experiment were transformed
(square root transformation) during analysis because it exhibited a Poisson
distribution. One way analysis of variance between E. agag in the soil and
maize roots and different treatments was carried out. After the analysis of
variance, least significant difference (LSD), standard error (SE) and coefficient
of variation were calculated.

3.8.3 Results

On the planting day, all the treatments had an equal (P = 0.05)
population density of E. gag in the soil (Table 3.8.1). Four weeks after
planting, plots which were early plowed had a significantly higher (P = 0.05)
population density of E. gag in soil and roots compared to plots which were
treated with carbofuran. There were, however, no significant differences (P
= 0.05) in the population densities of 3. fig in the soil and roots between
nontreated plots, manured plots and early plowed plots. Also on this
sampling date, only carbofuran treatment had reduced the population
density of E. gag in soil and roots by 39.17% compared to the nontreated
plots but in all the other treatments, the population density of 3. fig in soil
and roots had increased compared to the nontreated plots.

Eight weeks after planting, manured, early plowed and nontreated
plots had an equal (P = 0.05) population density of E. gag in soil and roots
(T able 3.8.1). Plots which were treated with carbofuran had a significantly
lower (P = 0.05) population density of E. _z_e_a_e_ compared to all other

treatments. the population density of _P_. zeae in soil and roots in the

 

 

 

 

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136

carbofuran treated plots was 93.7% lower compared to the nontreated plots.
Plots in which cattle manure had been incorporated, the population density
of E. gag was 4.7% lower than in the nontreated plots; the compost manure
and early plowing treatments, still had a higher population density of E. ga_e_
in soil and roots compared to the nontreated plots.

After an additional four weeks, still carbofuran treatment provided
adequate control of E. _zgg in soil and roots and the population density was
significantly lower (P = 0.05) compared to all the other treatments. All the
other treatments including the control, had an equal (P = 0.05) population
density of 3. g in soil and roots (Table 3.8.1). The population densities of
_P. _zggg in soil and roots of carbofuran treated and compost manured plots
were 85.0 and 29.6% lower than in the nontreated plots. Cattle manured
and early plowed plots had higher population densities of E. z_egg in soil and
roots compared to the nontreated plots. It is also noteworthy that there
were considerable variations in the number of E. _zgg recovered from similar
treatments in different replications as reflected by the high coefficient of
variations (51.8%).

Sixteen weeks after planting, carbofuran treated, early plowed and
compost manured plots had a significantly lower (P = 0.05) population
density of _E. z_e_a_e in soil and roots compared to the nontreated plots. The
population density of E. zeie in soil and roots of the respective treatments
were 96, 70 and 70% lower than that of the nontreated plots. The
population density of E. _ziag in soil and roots in the cattle manured plots was
not significantly different (P = 0.05) from that of the nontreated plots even
though it was 18.5% lower.

Maize yield was evaluated when the maize seed was at 9.0% moisture.

All the treatments significantly increased (P = 0.05) maize yield compared to

137

the control (Table 3.8.1). There were, however, no significant differences (P
= 0.05) in maize yield between all the treated plots. Cattle manure,
carbofuran, compost manure and early plowing increased maize yield by
145.7, 118.8, 113.0 and 82.0%, respectively, compared to the control. There
were, however, considerable variations in the maize yield obtained from
similar treatments in different replications as indicated by the considerably
high coefficient of variation.
3.8.4 Discussion

Carbofuran, a nematicide which was used as a standard in this study,
significantly controlled the population density of E. E for sixteen weeks
and subsequently increased maize yield. The magnitude of _P_. gggg control
which was observed in this study, compares favorably with reports from
Georgia, Indiana and Zimbabwe (Johnson and Chalfant, 1973; Bergeson,
1978; Martin e_t g_l., 1975; Muchena gt _a_l., 1987). The nematicide, however,
protected the maize plants from E. ze_ag infection for a considerably longer
period than three months that has been reported in the literature (Bergeson,
1978; Johnson and Chalfant, 1973). The longer persistence of the nematicide
in the soil appears to be a function of very little rainfall that was received
during the growing season. High rainfall and/or irrigation can flush out
carbofuran, hence efficacy of the nematicide is reduced. Reduced nematicide
efficacy because of high rainfall and/or irrigation has been reported to occur
in California and Michigan (Hough gta_l., 1975; Muchena and Bird, 1987).

Also because of the drought, maize yield was generally very low
compared to 4.5-6.8 tons/ha which were harvested in the 1985/86 season
(Muchena gt _a_l., 1987). The low rainfall, however, appears to have caused a
greater difference in maize yield between carbofuran treated and

nontreated plots (Muchena gt _a_l., 1987). Maize yield data in this study

SU

un

138

suggest that E. Leg is more limiting to maize growth and development
under stress of low soil moisture and/or soil nutrients.

Early land preparation did not reduce the population density of 3. Egg
in the soil at the planting time and this can be attributed to the high
tolerance of E. _z_g_a_g to very low gravimetric soil moisture content of up to less
than 2.0% for two years (Martin e_t a_l., 1975) and wide range of temperature
regimes (Olowe and Corbett, 1976). In Tennessee, early land preparation was
also failed to reduce the population density of P. z_e_a_g in the soil (Southards,
1971). In Nigeria, however, early land preparation has been shown to reduce
the population density of Pratylenchus spp. by 90% (Egunjobi and Bolaji,
1979). It appears, for early land preparation to have a significant impact on
the population density of Pratylenchus spp. in the soil, the population density
of Pratylenchus spp. in the soil must be very high (ca 600/100 cm3 soil) and if
the population density is low (30-50/100 cm3 soil) as was recorded in this
study, early land preparation might not have significant impact on the
population density. It should, however, be noted that the low population
density of _P. gggg that remains in the soil at the end of the dry season quickly
builds up when a susceptible host like maize is planted during the growing
season. The rapid build up of very low populationdensities of Pratylenchus
spp. that remain in the soil after the dry season when a susceptible host has
been introduced during the growing season has also been reported in
Nigeria, South Africa, Tennessee and Zimbabwe (Egunjobi , 1974; Koen,
1967; Southards, 1971; Martin gta_l., 1975; Muchena e_ta_l., 1987). At the end
of the growing period, the population density of E. ga_g in early plowed plots
was adversely impacted by organic debris that was plowed in and and started
decomposing during the rain season and/or some organisms that are inimical

to _P_. zeae. their population density increased as a result of the early plowing.

d.

CC

DO
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No
zga
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malZQ
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139

Early land preparation significantly increased maize yield. Increase of
crop yield in early plowed fields has also been reported in Ontario (Thames,
1982). The higher maize yield in early prepared plots appears to be a
function of improved soil moisture content and soil tilth from plowed in
organic debris rather than B. _z_gg control.

Organic amendments initially increased the population of figgg in
maize roots (E. _z_egg in the soil was negligible and it constituted about 0.54%
of the total population recovered from roots and soil) but at the end of the
growing period, the population density of E. z_e_gg was adversely impacted by
organic amendments especially compost manure. Higher population
densities of Pratylenchus spp. in maize roots growing in manured plots
compared to nontreated plots has also been reported in Egypt and Nigeria
(Badra and Mohamed, 1979; Egunjobi and Larinde, 1975). The higher root
population densities of P. fig in manured plots appear to be a function of
greater available root tissue for E. gggg to penetrate since maize plants in
manured plots will have greater root tissue compared to plants in nontreated
plots which have sub-optimal root growth. The low population density of E.
z_e_ag in roots of maize plants growing in manured plots at the end of the
growing period compared to nontreated plots might be attributed to by-
products of manure decomposition. It is unlikely that the by-products of
manure decomposition killed 3. E but rather impaired the reproduction
capacity of _P. _z_e_gg.

Organic amendments significantly increased maize yield despite the
higher root population densities of _P. gga_e in manured plots. The higher
maize yield in manured plots appear to be a result of altered host physiology
such that the host is more resistant to the nematode infection and/or

improved root growth which enhances better utilization of nutrients thus

n81

Egt

the
adc
am
PM

hov

3.9

140

neutralizing the effect of nematode damage (Badra and Mohamed, 1979;
Egunjobi and Larinde,1975).

Data in this study show that communal farmers with g. gegg problems in
their farms especially in sandy soils can derive maize yield increase by
adopting cultural practices such as early land preparation and organic
amendments. The mechanism of how these cultural practices impact the
population density of 3. fl and subsequently increase maize yield,

however, requires further research.

3.9 EFFECT OF ORGANIC AMENDMENTS AND THE TIME OF APPLICATION

ON 2. ZEAE PATHOGENICITY ON MAIZE
3.9.1 Introduction .

There are very few studies on organic amendments that have been
conducted with field crops (Egunjobi and Larinde, 1975; Muller and Gooch,
1982) and no studies have been conducted to evaluate the optimal time for
application of the organic matter into the soil. This information is important
to broaden the scope of organic amendments in small-scale farming. The
information is also important to improve the effectiveness of organic
amendments and subsequently this will lower the rates of application. The
objectives of this study were to (a) evaluate figgg control and subsequent
maize growth response derived by using organic amendments and (b)
evaluate the optimal time for applying organic amendments in maize
production.

3.9.2 Materials and Methods

B. flgwas maintained for 7 months on maize plants in sandy loam soil

(15% clay, 3% silt, 13% fine sand, 25% medium sand, 44% coarse sand,

0.64% organic matter and pH 5.4), in cement built tubs (1.0 m long, 0.75 m

AHt;
facui
Were
Wate
plant

Were

for (0H

exben

141

wide and 0.75 m deep) in a greenhouse at the Harare Research Center (Grid
ref. 30°25' East and 17°22' South). The culture contained about 100 E. E
per 100 cm3 of soil when used as inoculum for the research.
Twenty clay pots (30 cm diameter and 45 cm deep) were filled with the
E. _z_e_gg infested soil on 2nd April, 1987. The pots were arranged on a
greenhouse bench in a completely randomized block design of five
treatments and four replications. The greenhouse had maximum day and
minimum night temperatures of 32 and 20° C, respectively. After arranging
the pots, four pots per treatment received the following treatments:
1. cattle manure applied 12 weeks before planting at a rate of 12
tons/ha and incorporated into the soil.
2. cattle manure applied 8 weeks before planting at a rate of 12
tons/ha and incorporated into the soil.
3. cattle manure applied 4 weeks before planting at a rate of 12
tons/ha and incorporated into the soil.
4. cattle manure applied on the planting date at a rate of 12 tons/ha
and incorporated into the soil.
5. nontreated
All the pots were watered once a week throughout the preplanting period to
facilitate the decomposition of manure. Two maize seeds (variety R 215)
were planted into each pot on 26th June, 1987. All the pots were gently
watered on the planting date and emergence occurred as early as 5 days after
planting and was complete 9 days after planting. Maize plants in each pot
were thinned to one plant per pot 14 days after planting.
All the pots were maintained at the same moisture level (daily watering)
for four weeks. After four weeks, the plants were watered once a week. The

experiment was terminated after 8 weeks. The plants were sampled at the

enc
rerr
sep.
sub-
the

moi-

the:

142

end of the experiment and on the sampling date, the whole plant was

removed from the pot and the root and shoot systems were cut and put into

separate labeled plastic bags. Soil from the pot was thoroughly mixed and a

sub-sample (ca 1,500 cm3) of the soil was put into a labeled plastic bag. All

the plastic bags with samples were closed immediately to prevent any loss of

moisture from the sample. The following parameters were evaluated from

the samples:

0

ii)

iii)

Fresh weights of the shoot and root systems were obtained by
weighing on a balance with an accuracy of '1: 0.01 grams.

Soil was thoroughly mixed in a tray and 100 cm3 of soil was
processed using the centrifugal-flotation technique (Jenkins, 1964)
and observed under a stereoscopic microscope to enumerate P.
z_egg and other nematodes in the soil.

The'whole root system from each pot was cut into small pieces
about 0.1-0.5 cm long and 10.0 grams were selected at random and
processed using the maceration-centrifugal-flotation technique
(Southey, 1985 p. 54) and observed under a stereoscopic microscope
to enumerate P. ggg in the roots using the examination of
nematode suspensions technique (Southey, 1985 p. 59-60).

The data in this study were transformed (square root
transformation) during analysis because the data exhibited a
Poisson distribution. One way analysis of variance between E. z_gag
in soil and roots and maize growth parameters and different
treatments was carried out. After the analysis of variance, least
significant difference (LSD), standard error (SE) and coefficient of

variation were calculated.

143

3.9.3 Results

Eight weeks after planting, maize plants that were grown in nontreated
soil and soil which was treated with manure at planting had an equal (P =
0.05) root weight (Table 3.9.1). The roots weight was significantly (P = 0.05)
lower compared to root weight in pots which had received manure 4, 8 and
12 weeks before planting. There were, however, no significant (P = 0.05)
differences in the root weights of the latter three treatments. The latter
three treatments increased the root weight of maize by 53.5, 49.7 and 47.8%
compared to the control, respectively. Shoot weight of maize plants in
nontreated soil was significantly (P = 0.05) lower compared to all the other
treatments. (Table 3.9.1). The next lowest shoot weight was derived from
pots which were treated with manure at planting and the shoot weight was
68.7% greater compared to that for the nontreated plots. Shoot weight of
maize plants grown in soil which was treated with manure 8 and 12 weeks
before planting was equal (P = 0.05) and it was significantly (P = 0.05)
greater compared to the treatment which received manure at planting. The
shoot weights in the latter two treatments were 138.0 and 119.6% greater
compared to that for the control. Maize plants from pots which received
manure 4 weeks before planting had the highest (P = 0.05) shoot weight
compared to all the other treatments. The shoot weight was 220.9% greater
compared to that for the control (Table 3.9.2).

Treatments in which manure was applied 8 and 12 weeks before
planting had an equal (P = 0.05) population density of E. _z_eg in the soil
eight weeks after planting. The population density of E. g_ggg in these two
treatments was significantly (P = 0.05) lower compared to that of the control
(Table 3.9.1). These two treatments decreased the. population density of _E.
z_e_a_e_ in the soil by 29.0% compared to that for the control (Table 3.9.2). The

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145

Table 3.9.2. Percent reduction of Pratylenchus zeae and subsequent maize
growth increase after applying manure.

 

 

 

 

 

 

 

 

 

 

 

2Roots = 10.0 grams

3. zeae E. zeae . .
Parameters reduction in reduction in . Root weigh: .ShOOt welgtt
soil1 8 wks after roots2 8 wks Infireasle 8 w 5 Infctreasle 8 w 5'
Treatment planting after planting a er ‘1 antmg a er p antlng
(%) (%) (I6) (%)
Manure
applied 12 wks. 29.03 47.60 47.81 119.55
before
planting
Manure
applied 8 wks 28.99 47.60 49.66 138.03
before
planting
Manure
applied 4 wks 1 1.31 49.81 53.53 220.87
before
planting
Manure
applied on the 18.25 39.1 1 6.22 68.66
planting day
Key
1Soil = 100 cm3

 

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146

population densities of g. zeae in the soil in treatments which received
manure 4 weeks before planting and at planting were equal (P = 0.05) to
that of the control. The population densities of other nematodes (mainly

Dorylaimoid and Scutellonema spp.) that were recovered in the soil were

 

equal (P = 0.05) and the population densities were generally very low. Also
there was considerable variability (C.V% = 31.8) in the population densities
of other nematodes in the soil despite the transformation.

The population densities of E. E in the roots from plants which were
manured at planting and from plants in nontreated soil were equal (P = 0.05)
8 weeks after planting (Table 3.9.1). The population density of _E. _ze_a_e_ in
roots from plants which were manured at planting was also equal (P = 0.05)
to the population densities of E. ga_g in roots from plants which were
growing in soil which was manured 4, 8 and 12 weeks before planting. The
manure treatments reduced the population densities of _E. gag in the roots
by up to 49.8% (Table 3.9.1). There was, however, considerable variability
(C.V.% = 42.1) in the population densities of E. gag in the roots.

3.9.4 Discussion

Data presented in this study show that organic amendments reduced
the population density of g. z_e_ag in the soil. The decrease of the population
density of E. zeae in the amended soil by 29% compares favorably with a
decrease of 30-35% that was reported in Egypt and Nigeria (Badra and
Mohamed, 1979; Egunjobi and Larinde, 1975). The decrease of E. ze_ae_ in
amended soil appeared to be in part a function of increased inimical
organisms in the soil since replications in which high population densities of
Dorylaimoid nematodes were recovered had the lowest population densities

of E. zeae in the roots.

This 51

 

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147

This study also shows that organic amendments in the soil subsequently
lowered the population densities of 3. E in maize roots. The decrease in
the population density of E. _z_e_a_e_ in maize roots when manure was applied at
planting was similar to that reported in Egypt after applying poultry
droppings in soil infested with Rotylenchus reniformis (Badra and Mohamed,
1979). Better control of E. ga_e_ in maize roots was, however, obtained by
applying the manure several weeks before planting. This implies that a
period for the decomposition of the manure in the soil before planting is
essential to attain optimal control of 3. Egg.

The data also illustrate that organic amendments subsequently
increased maize growth as measured by root and shoot weights. The
increased maize growth when manure was applied at planting compares
favorably with that reported in Nigeria (Egunjobi and Larinde, 1975). The
data also show that the optimal time for manure application to obtain high
maize growth in g. ze_ag infested soil was 4 weeks before planting. If the
manure was applied 8-12 weeks before planting, good E. & control was
maintained but sub-optimal maize growth was recorded possibly because
some nutrients had been leached from the manure. On the other hand,
when manure was applied into the soil at planting, poor 3. _z_egg control was
obtained hence the sub-optimal maize growth was in part a function of E.
z_eg infection and possibly 'unavailable nutrients' which require a period of
decomposition before they are released from the manure.

The study demonstrates that proper application of organic amendments
in E. _z_ea_e infested soil may be a viable nematode control option for some
small scale farmers if the population density of g. zeig is below a certain
threshold. The study also demonstrates the importance of applying the

manure at the right time but the timing should, however, be adjusted

den
of 4
decr

is ve
3.10

3.10

(Omt
pm
1977
Unde

1987.

148

depending on the rainfall pattern in the area. The decomposition duration
of 4 weeks should be increased if the area is dry to ensure complete
decomposition of the manure and the duration should be reduced if the area

is very wet and hot to minimize leaching of the nutrients.

3.10 SIMULATION MODEL OF PRATYLENCHUS ZEAE ASSOCIATED WITH

MAIZE
3.10.1 Introduction

Many mathematical models have been developed in recent years to
predict changes in the population densities of pests in agroecosystems,
especially in the field of entomology (McSorley and Ferris, 1979). Such
models can prove invaluable if properly integrated into an on-line pest
management system. Modeling efforts for simulations of nematodes are
few, however. Some important simulation models in nematology include: a
simulation model of Heterodera schachtii Schmidt infecting sugar beets
(Caswell e_t 91., 1986), detailed model for the simulation of the Meloidogyne -
grapevine system based on population dynamics data for Meloidogine
(Ferris, 1976), computer simulation and population dynamics for cyst-
nematodes (Jones 9191., 1978), simulated changes in Globodera rostocheinsis
(Wollenweber) Mulvey and Stone population caused by growth of potato
varieties having various degrees of resistance (Jones e_t _a_l., 1967),
combinations of environmental factors to estimate population levels of
Pratylenchus hexincisus Taylor and Jenkins on maize roots (McSorley gt 91.,
1977). These computer simulation models have helped advance our
understanding of nematode-host plant interactions (Duncan and McSorley,

1987; Ferris, 1978).

149

There are no simulation models that have been developed to
summarize data on E. ga_e_ population dynamics and its pathogenicity on
maize. E. _z_egg is, however, widespread in maize fields in Zimbabwe
communal farms and yield losses caused by E. g_egg on maize are substantial
(Martin _1g_l., 1975; Muchena e_ta_l., 1987). A E. z_eie- maize simulation model
will be useful in: ( 1) predicting the population levels of this nematode species
in maize roots throughout the growing season, (2) assessing the impact of soil
moisture and temperature on the population dynamics of E. gag in different
seasons and fields and (3) predicting the pathogenicity of E. z_eag on maize
root system and subsequent maize yield.

3.10.2 Model development

A model that simulates population dynamics of E. gag was interfaced
with an existing CERES - maize simulation model to establish a E. _z__egg - maize
simulation model. The overall model has six basic components: nematode
model, maize model, soil nematode data, agronomic data, weather data, and
soil water data (Fig. 3.10.1). Dyke e_t a_l. (1986) outlined the details of the
CERES - maize simulation model and how the model runs and these details
will not be outlined in this study. The E. gege simulation model is a subroutine
NEMPOP in the CERES - maize simulation model and the subroutine flow is
depicted in Fig. 3.10.2. NEMPOP subroutine reads weather data CLlMT,
calender information DATEC, soil data SOILI, soil water data WATER, and
agronomic data PARAM from the main program. Data which determine the
length of the life cycle, birth rates, and mortality factors of E. g_egg depending
with the temperature are provided in arrays VALT, VALB and VALD,
respectively (Table 3.10.1). The length of the life cycle is variable because time
spent in a given developmental stage DEL in poikilothermic organisms is

variable and depends on ambient temperature. The population density of E.

 

WEATH E R
DATA

 

150

 

 

 

 

 

 

AG RONOM IC
DATA

 

 

 

 

 

 

SOIL

NEMATODE DATA

 

 

 

 

SOIL WATER
DATA

 

 

 

 

 

 

 

MAIZE
MODEL

 

e

 

Y

 

j

 

 

 

 

 

 

NEMATODE
MODEL

 

 

 

Figure 3.10.1.

Simplified flowchart for the Pratylench us zeae-

maize simulation model.

 

151

 

> CERES MAIN PROGRAM

 

 

 

 

   

 

   

IDATE.GE. ISOW AND
ISTAGE.NE.7

 

  

N0

 

CALL SUBROUTINE NEMPOP:
INITIALIZE g. ZEAE/100 CM3 SOIL

l

PROVIDE RELATIONS BETWEEN
TEMPM: 1) E. ZEAE LIFE CYCLE

2) BIRTH RATES

3) DEATH RATES
ESW: 1) DEATH RATES
NPATHO: I) E. ZEAE POPU LATIONS

l

INITIALIZE DATA FOR ARRAYS
VAL, VALB, VALD, MOIST

l

/ UPDATE TIME DT = 1.0 /

/READ TEMP 81 SOIL MOIST. /

l

CALL FUNCTION TABEXE TO
CALCULATE DEL, VAL, VALB,
VALD, MOIST.

l

CALL suanourmc VDEL TO
srrvru LATE DEVELOPMENT or
g. ZEAE

l

®

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3.10.2. Flowchart of the subroutine NEMPOP which simulates
the development of Pratylenchus zeae in maize roots.

152

®

I

CALL FUNCTION TABEXE TO
CALCULATE NPATHO

l

WRITE NEMPDAT: NEMPT,
NPATHO, NRTFAC

 

 

 

 

 

 

 

 

Yes

 

ISTAGE.EQ.6

NO

 

RETURN

l

 

 

 

 

 

 

END ‘

l

 

 

 

 

MAIN PROGRAM CALCU LATES:
1) GERMINATION JDATE, DD3
2) EMERGENCEJDATE,DDg
3) END JUVENILE STAGE JDATE, 003
4) TASSEL INITIATION JDATE, DDg
5) BEGIN GRAIN FILLJDATE, DDg
6) PHYSIOLOGICAL MATURITY JDATE, DDg

 

 

 

l

 

 

MAIN PROGRAM CALCULATES:
1) SILKING JDATE
2) MATURITY JDATE
3) GRAIN YIELD Kglha
4) KERNEL WEIGHT

 

5) GRAI NS/EAR
6) MAXIMUM LAI
STOP

 

 

 

 

 

153

z_e_ag is also influenced by the soil water content and the data is in MOIST
(Table 3.10.2). Pathogenicity of E. E on maize roots is determined by the
population density Of E. ze_ag in roots and the datais defined in VALL (Table
3.10.4). The number Of E. _z_gg mature females that survive and produce eggs
are influenced by the population density Of E. ge_ag in the roots TLOFF and if
the population density is high, the density dependent mortality is high (Table
3.10.3).

NEMPOP subroutine utilizes a table look up function TABEXE to
calculate daily time delay DEL, birth rate BREGG and density dependent
mortality TLOFF. The same function is also used to calculate death rates
DRATE depending on the average daily temperature TEMPM and DRATEM
depending on available extractable soil water content ESW. The minimum
and maximum temperatures are read in the main program from a weather
input file WETZIM and the mean temperature is calculated in the subroutine
NEMPOP:

TEMPM = (TEMPMN + TEMPMX)/2

DEL = TABEXE(VALT,SMALLP,DIFFP,KP,TEMPM)

BREGG I TABEXE(VALB,SMALLP,DIFFP,KP,TEMPM)

DRATE = TABEXE(VALD,SMALLP,DIFFP,KP,TEMPM)

TLOFF = TABEXE(DDMOT,SMALLPP,DIFFDM,KD,NEMPT)

The extractable soil water content is calculated in the main program
and the values are passed through a COMMON statement to subroutine
NEMPOP:

DRATEM :- TABEXE(MOIST.SMALLM,DIFFM,KM,ESW)

The calculated rates are utilized to estimate the number of E. ga_g eggs
laid daily by mature females R(6), second stage juveniles R(Z) and developing

females that die daily:

154

 

 

 

 

 

 

 

 

 

 

 

Table 3.10.1. Influence Of temperature on P. z___eae life cycle, fecundity and
mortality factors (Mamiya, 1971, Olowe and Corbett, 1976).
Da sfora Iifec cle No. Of No. of J; that die
Temp. (C) y VAL y eggs/female/day per day
VALB VALD
<15 84 0.056 0.035
20 42 1.100 0.102
25 28 6.662 0.645
30 21 9.500 0.905
>35 20 0.614 0.155
Table 3.10.2. Effect Of sOil water on the number Of P. _z__eae J2 that die per

day (Egunjobi and Bolaji, 1979; Koen,1967; Martin g_ta_|.,

 

 

1975; Norton 1979; Townshend, 1972; Trivedi e_t a_l.,1978).
Extractable soil water (cm/cm) .00 .04 .08 .120 .160
No. B. zeae J2 that die/day .55 .50 .10 .059 .104
(MOIST)

 

 

 

 

 

 

 

Table 3.10.3.

z___eae fecundIt (tyMcSorley and Ferris, 1979).

Impact of P. zeae population density In maize roots on P.

 

 

 

 

 

 

 

 

 

 

 

 

 

Population/gram dry root 0 500 1000 1500 2000 2500
weight
Fecundity factor DDMOT 1 0.91 0.85 0.81 0.77 0.73
Table 3.10.4. Influence of P. zeae population density on new root growth
Of maize (MartIn e_t a_l.,1975; Muchena g_t al.,1987;Tarte,
1971).
Population/dry gram root 0 500 1000 1500 2000 2500
Pathogenicity factor VALL 0 .635 .9860 .900 .955 .962
New root factor NRTFAC 1 .365 .140 .100 .045 .038

 

 

 

 

 

 

 

 

 

 

 

 

155

BRFEM a: BREGG * R(G)

DVFEM = DRATE * R(6) * 0.2

DRE12 = DRATE * R(Z) + DRATEM * R(Z)

The number of P. 2% second stage juveniles, developing females and
mature females that die daily are subtracted from the number Of E. ggg in
the respective stages:

R(2) :- R(2) - DREJZ

R(S) a R(S) - DVFEM

R(6) = R(6) * TLOFF
The remaining 3. g_ag will undergo a developmental process. NEMPOP
subroutine utilizes a time - varying distributed delay VDEL (Manetsch, 1976)
to calculate the developmental process Of 13. 2% depending on DEL:

VDEL(BRFEM,VOUT.R.DEL,DELP,DT,K)

The total number Of E. z_egg in 1.0 gram dry root weight is the
summation of second stage juveniles R(Z), third stage juveniles R(3), fourth
stage juveniles R(4), developing females R(S), and mature females R(6):

NEMPT = NEMPT + R(2,6)

The pathogenicity of E. ga_e on the root system NPATHO is calculated using a
table look up function TABEXE:

NPATHO = TABEXE(VALL,SMALLPP,DIFFPP,KPP,NEMPT)

NRTFAC = 1.0 - NPATHO
The value Of NRTFAC is transferred into the main program to influence new
root growth.

The program was written in FORTRAN and it requires the user to
interactively input the initial population densities Of _E. g_ag eggs, second
stage juveniles, third stage juveniles, fourth stage juveniles, developing

female, and mature females in 100 cm3 of soil. The program calculates daily

 

156

values Of all the state variables (Table 3.10.5) from the sowing date Of maize
until the crop reaches physiological maturity:

IF(JDATE .GE. ISOW .AND. ISTAGE. NE. 7) CALL NEMPOP
The program does not calculate the fixed initializing arrays used in the
extrapolation function TABEXE.

TO execute the program, the user will have to enter 'PZCORN1'. The
program will return with a list Of 24 variables about weather, soil type, maize
variety, sowing date etc. and if the user does not want to change any Of the
variables, the user should enter '0'. The program will request for the title Of
the run. After the name Of the run has been entered, the program will ask the
user whether this is a multiple year run. The answer to this question should be
no 'N' because this has not been incorporated in the nematode subroutine
NEMPOP. The subroutine NEMPOP simulates the population dynamics Of E.
gag during the growing season only.

After each run, daily simulated values Of the total P. gg population
densities per 1.0 gram dry root weight NEMPT,nematOde pathogenicity
factor NPATHO, and the new root growth factor NRTFAC are stored in the file
NEMP.DAT. This file can accessed by entering 'type NEMP.DAT', if the data is
to be viewed on the screen or 'print NEMP.DAT' if a print out Of the data is
required.

Parameters which were also required in the initialization of the CERES -
maize program were CGENET, CLIMT, SOIL, and WATER. These parameters
were initialized with specific information for Zimbabwe which was derived
from several field and laboratory experiments. Most Of the field studies were
conducted in Chinamora communal area.

Weather data (daily maximum and minimum air temperatures, rainfall

and solar radiation) for the 1985/85 growing season was recorded at the

1S7

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 3.10.5 State variables used in the subroutine NEMPOP.
Variable Definition Initial value
BRFEM Total no. of eggs laid/day compute
DIFFM Difference between adjacent ESW (cm/cm) in MOIST 0.04
DIFFP Difference between adjacent temp. in VALT, VALD. 5.00
VALD

DIFFPP Difference between adjacent E. gag population $00.0
densities/1.0 dry gram of roots in VALL

DREJz No. of second stage juveniles of g. g_ag that die/day compute

DT Time increments being used in the simulation (days) 1.00

ESW(L) Extractable soil water content for soil layer (L) compute

ISOW Day of year for sowing compute

JDATE Day of the year compute

K No. of stages in g. g_ag life cycle 6

KM The no. of intervals between extractable soil 4
moisture contents MOIST

KP The no. of intervals between tempts. for VALT, VALB 4

KD The no. of intervals for E. gg population densities 4

KPP 31:30“ intervals mmm population for S

NEMPO 13. gg population densities in 100 cc soil by life input
stage

NEMPT Total 3. ggg in 1.0 dry gram of roots excluding eggs 0

NPATHO E. g_ag pathogenicity on maize roots (scale 0-1 .0) 0

NRTFAC E. _z_gg root factor (scale 1.0-0) 1

R(1) Eggs per 100 cc soil input

R(2) Second stage juveniles per 100 cc soil or 1.0 gram dry input
root weight

R(3) Third stage juveniles per 100 cc soil or 1.0 gram dry input
root weight

8(4) Fourth stage juveniles per 100 cc soil or 1.0 gram dry input
root weight

R(S) Developing females per 100 cc soil or 1.0 gram dry input
root weight

R(6) Mature females per 100 cc soil or 1.0 gram dry root input
weight

SMALLM The smallest element of the array MOIST (cm/cm) 0.0

SMALLP The smallest element of the arrays VALT, VALB, 1 5.0
VALD (C)

SMALLPP The smallest element of the array VALL (E. ggglI .0 0.0
gram root weight)

TEMPM Mean air temperature (C) compute

TEMPMN Minimum air temperature (C) compute

TEMPMX Maximum air temperature (C) compute

TLOFF Population densitldependent mortality of); zeae compute

 

 

 

1__—‘-—-¢~._-11

158

Harare research center. Maize growth parameters for variety R 215 (root and
shoot weights, number of leaves, number Of days to 50% tassel and silk
emergence and leaf length and width) were measured in plants which were
grown at Harare research center. Also genetic inputs for maize variety R 215
which were estimated for the simulation model are:

P1 (growing degree days base 8 C (GDDB) from seedling emergence tO

the end Of the juvenile phase). This value was estimated to be similar to

values for the southern USA and tropical regions with a range of 260 to

350. A value Of 311 was used in the simulation.

P2 (photoperiod sensitivity coefficient) which ranges from 0 to 0.8 (Dyke

g_t g1., 1986) was estimated to be similar with that for the southern USA

which is 0.75.

62 (potential kernel number) was reported to vary from about 560 tO

834 kernels per plant (Dyke e_t a_l., 1986). In this study, a mean Of 588

kernels per plant was Obtained.

GS (potential kernel growth rate), Dyke _e_t a_l. (1986) reported this

parameter to vary from approximately 6 to 11 mg/kernel day). This was

estimated to be 7.5 mg/kernel day in this study.

SOil data which was used in the simulation was measured in Chinamora
communal area. The data which was measured include the number Of soil
layers NLAYR to reach bedrock, thickness of each layer DLAYR, bulk density
BD Of each layer, textural analysis Of each layer and amount Of organic matter
in each layer. The following parameters were calculated from the data:

Porosity of each layer P0 was calculated from bulk density BD (Dykegt

_a_l., 1986):

P00) 2 1.0 - BD(I)/2.65

159

where 2.65 was mineral particle density. Next a correction factor XC for the
lower density Of organic matter was calculated:

XC = OC(l) * 0.0172
where OC was the organic carbon concentration (%) of the layer. The
maximum bulk density to which the layer could be compacted BDM was then
calculated:

BDM(I) = (1 .0 - X2) / (1 .0 / BD(I) - XZ / 0.224
where BDM(I) was not allowed to exceed 2.5.

The effects Of soil texture on lower limit Of plant extractable water for
the layer LL(I) and the drained upper limit for the layer DUL(I) were estimated
with the variables W1 and W2 (Dyke _t_ a_l., 1986), respectively. When sand
content SAN(I) was greater than 75% :

W1 a 0.19 ~ 0.0017 * SAN(I).

W2 = 0.429 - 0.00388 * SAN(I).

When silt content SIL(I) was greater than 70% :

W1 = 0.16

W2 = 0.1079 + 0.000504* SIL(I)

LL(I) and DUL(I) were calculated:

LL(I) = W1 *(1 .0-XZ)*(1.0 + BDM(I)-BD(I)) + 0.23*XZ

DUL(I) = LL(I) -I- W2*(1.0-XZ)-(BDM(I))*0.2 + .55*XZ
SAT(l)was then calculated with the following equation:

SAT(I) = K(PO(I) - DUL(I)) -I- DUL(I)
where K = 0.5 for sandy and coarse loamy soils and 0.4 for other soils. The
root distribution factor WR was estimated for any sOil layer by the equation:

WR(I) = exp(-4.0 * Z(I)/ 200.0)
where 2(1) was the depth (cm) to the center of the layer 1. In the top soil layer

WR was set to 1.0.

134'. 9351
l

160

Soil reflectivity or albedo SLAB was estimated from a table of sOil
albedo (Dyke gt gt, 1986). The coefficient for the upper limit of stage 1 soil
evaporation U was estimated as 6 mm because the soil Of the top layer was
sandy. The whole profile drainage rate coefficient SWCON was calculated for
each soil layer L from the porosity P00) and drain upper limit DUL(L) for each
layer:

PO(I) = 1.0-BD(L)/2.65

SWCON(L) = PO(L)- DUL(L)/PO(L)
where BD(L) was the moist bulk density of the layer and 2.65 was the
approximate particle density. The runoff curve number CN2 of 78 was chosen
from a USDA Soil Conservation Service, 1972 table (Dyke e_t a_l., 1986).

3.10.3 Model Evaluation

The output of the E. z_eag - maize simulation model was compared with
data of _P. ggg population dynamics and maize growth parameters which
were measured at the Harare Research Station during the 1986/87 growing
season.

2. ggg Population Dynamics

Accurate simulation Of the fecundity and mortality factors Of E. E as
influenced by temperature, soil moisture, host suitability and the carrying
capacity of the root system are important for accurate simulation of the
population densities Of E. g_ag in the root system. Simulated and measured
population densities Of E. gag (initial population density of E. _z_eg = 30/100
cc soil) were similar during an entire growing period (Fig. 3.10.3). The mean
error Of the simulated values for the nine sampling dates was 7% of the
measured values.

Sensitivity of the simulation model was evaluated by running the model

with different initial population densities of E. zeae in the soil. The output

161

 

 

 

2,000 r
1,500 —
E-ZEAE/
1.0GR
DRY
ROOT 1'000 _
WT
500 E—
El Measured
_Simulated
0 L l I 1 J
0 300 , 600 900 1,200 1,500

DEGREE DAYS

Figure 3.10.3. Simulated and measured population densities of _E. zeae in 1.0
gram dry root weight of maize variety R 215 during the 1987
growing season.

162

from the runs, showed that the model was sensitive to the initial population
density of P. z_e_gg in the soil (Fig. 3.10.4). The magnitidue Of the increase in
the population density was a function of the initial population density. The
increase of E. _z_e_ag population densities in different treatments followed the
same trend with a slow build up of the population density at the beginning
of the season followed by a rapid buildup during the middle of the growing
season and a decline in the population density at the end of the season.
McSorley and Ferris (1979) also reported declining population densities Of
root lesion nematodes infecting maize roots at the end of the growing
period, in Indiana. The decline in the population density Of root-lesion
nematodes at the end Of the growing season was attributed tO senescing and
decaying roots which would harbor lower Pratylenchus populations, as
Pratylenchus migrate back into the soil.

The sensitivity Of the model was also evaluated by running the model
with different temperature regimes. Weather data for Zimbabwe and
Michigan growing seasons were used to run the model (Fig. 3.10.5). At the
beginning of the growing season, when the accumulated degree days for
Zimbabwe and Michigan were about the same, the population densities Of P.
z_e_ag in roots for the two sites were equal (Fig. 3.10.6). During the middle Of
the growing period, the simulated population density of E. ggg in roots was
higher in the run where Michigan weather data had been used because the
average temperatures were higher in Michigan. At the end of the growing
period, the temperature in Michigan decreased faster than the temperature
in Zimbabwe (Fig. 3.10.5). The low temperature which was experienced in
Michigan caused a rapid decrease in the population density of E. gag in roots
at the end of the growing season. These results indicate that the model is

sensitive to very small temperature fluctuations which might be experienced

- m“.“-._Z A
helm——
L

163

2,400 r-
1,800 -

3.2 El
10 . 1,200 _

     

 

 

GR

DRY

ROOT

WEIGHT 600 _ 0 “=6
UPI-20
A P1230
X P|=60

0 _ . 3 " L I 1 I I
0 250 500 750 1,000 1,250 1,500
DEGREE DAYS

Figure 3.10.4. Simulated influence of the initial population density of E. zeae in
the soil on the population dynamics Of g. zeae in 1.0 gram dry
root weight Of maize variety R 215 durIng the 1987 growing
season.

164

250 . [1 Michigan
0 Zimbabwe

200 -

ACCUM.

 

 

 

DEGREE 150 T
DAYSIN
2WEEKS ‘
100 -
50 J I l ' I I
0 30 60 90 120 150

DAYS AFTER PLANTING

Figure 3.10.5. Measured degree days (base 8°C) accumulated in two-week
intervals for Zimbabwe 1986/87 growing season and for Michigan
1985 growing season. ‘

WET?

165

2,250 l' DMichigan
0 Zimbabwe

1,500 —

g. ZEAE IN
1.0 GRAM
DRY ROOT
WEIGHT 750 ..

sl—L_

1—_. ' “““1: _

 

 

 

o I I I I J
0 30 60 90 120 1 50
DAYS AFTER PLANTING

Figure 3.10.6. Simulated population dynamics Of P. zeae in 1.0 gram dry root
weight of maize R 215 using Zimbibwe 1986/87 and Michigan
1985 weather data.

166

at different sites. It is however, important that the simulation model be
validated by a minimum of two data sets from different growing seasons.
Maize Growth Parameters
(a) Silking date

Accurate prediction Of silking date requires accurate weather data and
correct adjustment of the genotype - specific coefficients P1 and P2 (Dyke gt
g[., 1986). The predicted and measured silking dates for maize variety R 215
were equal and 50% of the silking occurred 70 days after sowing. Dyke _t _a_l
(1986) reported a mean error of one tenth Of a day between predicted and
measured silking dates for maize hybrid Pioneer 3780 grown in Pennsylvania,
Nebraska and Texas. The silking date Of the hybrid B73 x MO 17 has been
more extensively tested in four states in the USA and five countries in Europe.
The mean error for the silking date Of this hybrid was reported as -2.3 days
(Dyke e_ta_l., 1986).
(b) Physiological maturity

Accurate prediction of the date for physiological maturity requires
accurate air temperatures and correct adjustment Of the genotype - specific

coefficient P5 (Dyke t l., 1986). The predicted and measured dates for

physiological maturity for maize variety R 215 differed by 4 days. For the
hybrid B73 X M017, Dyke gt a_l. (1986) reported a mean error of 2.5 days for
the difference between silking and physiological maturity dates.
(c) Leaf number

Simulated leaf numbers were higher than Observed leaf numbers
throughout the growing period (Fig. 3.10.7). The difference can be
attributed to the fact that the model was simulating leaf tip emergence;

whereas, the measured data is leaf collar emergence. However, the

simulated plants continued to produce leaves after the plants grown at

H. ’_ 9.
I
'L

 

167

 

 

25 F
20 -
15 —
NO' in?!
or
LEAVES 10 ’— l:
j
5 _ .
0 Cl Measured
_Simulated
o I J L I
0 200 400 600 800
DEGREE DAYS
Figure 3.10.7. Simulated and measured number Of leaves of maize variety R 215

during the 1987 growing season.

168

Harare Research Station plants had stopped producing leaves. These
differences may, in part, account for the difference in the total number Of
leaves between the simulated and counted number of leaves. Dyke _t _t.
(1986) also reported overprediction of leaf area index Of maize hybrid
Pioneer 3780 at silking in Pennsylvania.
(d) Above-ground dry biomass

Accurate above-g round biomass is important for accurate simulation of
the nutrient and carbon cycling (Dyke _t _I., 1986). Simulated and measured
total above—ground biomass development were similar for R 215 grown at
the Harare Research Station. For the first three dates of measurement,
simulated and measured values were equal. The last five measurements, the
difference between simulated and measured above-ground dry biomass
increased with time (Fig. 3.10.8). The mean error Of the simulated values for
the eight measurement dates was 17.7% Of the measured values. The higher
weights in the above-ground dry biomass for the simulated maize plants can,
in part be explained by the higher number of leaves on the simulated plants.
(e) Below-ground dry biomass

Simulated below-ground biomass Of maize variety R 215 had a mean
error of 11.1% from the measured values (Fig. 3.10.9). The measured dry root
system was higher than the simulated dry root system, whereas, the
measured above-ground biomass was smaller than the simulated above-
ground biomass. The differences between the simulated and measured
below and above-ground dry biomass might be a result Of how the
researchers separate above and below biomass.
(f) Grain yield

Grain yield prediction represents the integration Of virtually every

system operative in the model. Field studies which were extensively carried

F"T“"M“"”‘l

169

 

 

 

1 0
5 r
100 -
DRY
SHOOT
WT.
(GR)
50 -
C] Measured
_Simulated
o I I L L J
0 250 500 750 1,000 1,2 50 1,500

DEGREE DAYS

Figure 3.10.8. Simulated and measured maize dry shoot weight of maize
variety R 215 during the 1987 growing season.

 

“UR lJ‘ “i

 

 

170

  
 

 

 

20 r—
O
15 —
DRY
ROOT
WT.
(GR) 10 —
5 r—
[3 Measured
_Simulated
o J I L l I
0 300 600 900 1,200 1,500

DEGREE DAYS

Figure 3.10.9. Simulated and measured dry root weight Of maize variety R 215
during the 1987 growing season.

_‘I

171

out by the Crop Breeding Institute in 31 communal farms in Zimbabwe had a
mean grain yield of 6736 kglha for maize variety R 215. The measured maize
grain yield compares favorably with the simulated maize grain yield Of 6907
kglha. Inaccurate estimates Of initial soil water, plant-extractable soil water,
or soil depth could produce large errors in simulated grain yields (Dyke _t _t.,
1986). In addition, genetic coefficients used in the model are Often
unavailable from independent studies and have to be estimated. It appears
the genetic coefficients which were estimated for maize variety R 215 are
approximately equal to the actual values, however, the validation process
should be repeated with maize growth parameters obtained from a second
growing season.

Pathogenicity of g. g_ag on Maize Plants

3. z_egg has been reported to reduce maize yield by up to 25% (Martin e_t
g_l., 1975) and 50% (Muchena gt _a_l., 1987). The magnitude of maize yield
reduction is dependent on the initial population density Of E. gag in the soil.
Simulated maize yield reductions were 20% and 47.5% with P. ggg initial
population densities of 30 and 60 per 100 cc of soil. The simulated maize
yield reductions compare favorably with the measured maize yield
reductions. Other maize growth parameters which were reduced by E. fig
infection include maximum leaf area index, total dry biomass, and number of
grains per ear (Table 3.10.6).

The simulation showed that at the beginning Of the season, both
infected and non-infected maize plants had equal dry biomass (Fig. 3.10.10).
Differences in the amount Of dry biomass were detected five weeks after
planting between non-infected plants and plant growth which was simulated
in soil infested with the highest population density of E. z_e_gg (Pi = 60). Six

weeks after planting, differences were detected between maize plant

L:.‘T‘T‘ 1““ ‘2!

172

1,600 r

1,200 . ./.

 

 

DRY PLANT 5
BIOMASS 800 T / -
(GISQ. ,
METER) / 0 “=0
400 - news
/ A P1220
X PI = 30
e Pi-60
o ___... L l L I J
0 250 500 750 1,000 1 ,2 50 1,500
DEGREE DAYS

Figure 3.10.10. Simulated dry plant biomass Of maize variety R 215 growing in
soil infested with different initial population densities of E. zeae
per 100 cm3 of soil during the 1987 growing season.

 

173

growth simulated in non-infested soil and soil infested with E. ggg (Pi = 20
or 30). Simulated growth in non-infested soil and soil infested with E. g (Pi
= 6) had detectable differences eight weeks after planting.

Further research is required on how 3. _zegg impacts maize new root
growth. This aspect requires further investigation and validation for at least
two growing seasons. Also further development of the simulation model
could incorporate some of the management strategies outlined in this
dissertation to reduce the population densities Of E. ggag infecting maize

roots and subsequently increase maize yield.

Table 3.10.6. Maize growth parameters which were influenced by E. zeae
infection in the simulation model.

 

 

 

 

 

 

 

Grain yield Maximum Biomass
g. zeae/100 cc Grains/ear (grams/sq
(kg/ha) LAI

meter)

0 6907.0 413 3.69 1544.0

6 6874.0 411 3.60 1494.0

20 6295.0 376 3.09 1278.0

30 5540.0 331 2.74 1114.0

60 3625.0 285 2.35 941.0

 

 

 

 

 

 

1...--. 1L

4. SUMMARY AND CONCLUSIONS

4.1 RESEARCH PROGRAM OVERVIEW

The research that has been addressed in this dissertation on plant-
parasitic nematode problems of maize in Zimbabwe communal farms was
divided into four components: (a) problem identification, (b) ecology of the

pest, (c) management of the pest, and (d) simulation model Of the pest.

4.2 PROBLEM IDENTIFICATION

The national survey Of plant-parasitic nematodes associated with maize
in communal farms which was conducted during the 1985/86 growing season,
found thirteen plant-parasitic nematode genera associated with maize. The
major nematode pests of maize were identified as Pratylenchus zeae and
Pratylenchus brachyurus with relative densities of 50.0 and 38.5% and
absolute frequencies of 52.6 and 21.9%, respectively. Other plant-parasitic
nematodes which were found associated with maize are: Aghelenchoides sp.,
Aphelenchus avenae, Aphelenchus sp., Criconemella gphaerocephala,
Criconemella sp., Helicotylenchus sp., Hoplolaimus sp., Meloidggyne sp.,
Paratrichodorus minor, Pratylenchus sp., Pratylenchus goodeyi, Rotylenchulus
sp., Rotylenchulus grvus, Rotylenchus brevicaudatus, Scutellonema sp.,
Scutellonema brachyurum, Scutellonema labiatum, Scutellonema

magniphasmum, Scutellonema unum, Trichodorus sp., and Tylenchorhynchus

sp.

174

175

In Manicaland province, maize plants which were infected with > 1,000
P. gggg per 10.0 grams of fresh root weight during the survey, were estimated
to have mean maize yield of 1 392 kglha. Maize plants which were infected
with < 1,000 P. gag per 10.0 grams Of fresh root weight were estimated to
have a mean grain yield of 2 659 kglha. The findings in this research clearly
demonstrated that E. ga_e is a major limiting factor in communal area maize
production. On the basis of these results, _P_. gag was selected as the target

pest for further research.

4.3 ECOLOGY OF THE PEST

The ecology of the target pest was approached in two phases: (a) survey
and (b) controlled experiments.
4.3.1 Analysis of Survey Results

Different natural farming regions Of Zimbabwe, influenced the
diversity and population densities Of plant-parasitic nematodes recovered
from maize roots. 3. brachyurus and 3. fig were equally prevalent in natural
regions 11 to IV but in natural regions I and V, P. 2% was more prevalent than
_13. brachyurus. This showed that P. g_ag has a competitive advantage over _13.
brachyurus. The mean population densities of E. gtgg per 10.0 grams Of fresh
root weight + 100 cc of soil were 1, 773, 4, 794, 3, 915, 1, 937 and 150 for
natural regions I, II, III, IV and V, respectively. The results demonstrated that
natural regions II to IV had the ideal conditions for E. g_ag high rate of
reproduction. Some of the edaphic factors that influenced the population
dynamics of 13. g are:
(a) Rainfall

Mean population densities of 2, 138.5, 4, 615.8, 6, 767.7, 1, 747.0 and

651.3 E. zeae per 10.0 grams Of fresh root weight were recovered from maize

176

plants growing in rainfall regimes of > 1, 000, 800-1, 000, 600-799, 400-599
and < 400 mm per year, respectively. The results showed that annual rainfall
Of 600-1, 000 mm is the optimum range for g. ggg high population densities
in maize roots. However, it should be noted that P. g was recovered in
maize roots from farms with very low or high soil moisture. The results
showed that E. ga_e was tolerant to a very wide range of soil moisture
conditions. Since rainfall is probably the most important abiotic parameter in
Zimbabwe communal area maize production, the adverse effects of rainfall
on maize growth in fields that are infested with E. ze_ae_ are compounded
because 3. E has a wider optimum soil moisture tolerance than maize.
(b) Temperature

Mean population densities Of 595.0, 8, 113.0, 6, 786.5, 3, 580.5, 363.6
and 0; and 595.0, 10, 352.5, 4, 871.5, 3, 170.6, 705.0 and 0 E. ggg per 10.0
grams of fresh root weight were recovered from maize plants growing in
fields with March and February air temperature regimes of 20.0-22.5, 22.6-
25.0, 25.1-27.5, 27.6-30.1, 30.1-32.5 and > 32.5 C, respectively. The results
demonstrated that the optimum air temperature for 13. gg multiplication
ranged from 22.6 to 30.1 C. Since the summer temperature conditions in
Zimbabwe communal farms are ideal for E. gag reproduction, it. is
conceivable that E. gag population densities reach very high levels and cause
extensive reduction in maize growth.
(c) Soil texture

Mean population densities of 1, 512.5, 1, 587.3, 2, 592.0 and 2, 664.3 E
_z_egg per 10.0 grams Of fresh root weight were recovered in maize plants
growing in fields with sandy clay loam, sandy loam, loamy sand and sandy soil
textures, respectively. The results showed that the reproduction of E. g_ag

was faster in light textured soils. The research demonstrated that P. zeae is a

“’7 l—T' 7::
V‘

177

major limiting factor in maize production in most communal areas since most
communal farms have sandy soils which are ideal for E. gag reproduction.
(d) Soil pH '

Mean population densities of 1, 080.2, 2, 701.5, 2, 650.5 and 4, 037.6 _E.
g_ag per 10.0 grams of fresh root weight were recovered in maize roots of
plants growing in soil with pH ranges of 4.2-4.7, 4.8-5.3, 5.4-5.9 and 6.0-6.8,
respectively. The study showed that the fecundity of E. z_eg was higher in soil
with high soil pH.
(e) Soil nutrients

Communal farms where nutrients (manure, ammonium nitrate or
compound D fertilizer) had been applied, especially manure, had a lower
population density of P. gag in 10.0 grams of fresh root weight and this
subsequently increased maize yields in the respective fields at the end of the
growing season. The research demonstrated that soil nutrients were a major
limiting factor in communal area maize production especially in sandy soils
infested with high population densities of E. ga_e. Therefore, cropping
systems that can increase the amount of available soil nutrients and at the
same time reduce the population densities Of _P. _z_ggg in the soil may enhance
maize yield optimization in the communal farms. Possible cropping systems
may include crop rotation of maize with bean varieties that are tolerant
and/or resistant to _E. ggg.
4.3.2 Controlled Field and Greenhouse Studies
(a) Overwintering mechanism of g. g_ag

A field Observation experiment showed that E. 5% vermiform stages in
the soil overwintered mainly as third to fourth stage juveniles and mature
females and these stages constituted 51.9 and 46.3% of the total population

of vermiform stages, respectively. An increase in the population densities of

 

 

178

_P. g vermiform stages in December appeared to be a result Of hatching
eggs. 1

The study also showed that the highest population densities Of E. ga_e_
were at depth 0-20 cm but the highest population density was at depth 20-30
cm during the hot and dry months of September and October. The latter
confirms the hypothesis that _P. ggg migrates to deeper layers to escape
adverse soil moisture and temperature conditions in the upper layer during
the hot and dry months Of the year.

The research also showed that clean fallow for one year can reduce the
population density of P. g in the soil by up to 87.5%. The E. z_e_ag control
which was obtained from clean fallow can be incorporated into integrated
pest management with other cultural practices to minimize maize yield
reduction caused by E. _z_ea_e. The major set-back of clean fallow in communal
farms is that most farmers have land resources of limited sizes.

(b) Temporal and spatial distribution of E. ggg and maize roots

The study showed that maize root weight increased with time and
81.0% of the root weight was within a depth of 0-20 cm and 82.8% of the
root weight was within a radius of 0-20 cm. The study showed that maize root
system was aggregated in the top soil.

The population density of _E. _zgag also increased with time and had a
Pf/Pi ratio of 170. This showed that maize variety R 215 was very susceptible
to E. gag infection and that the edaphic factors in this study were suitable
for a rapid multiplication of E. ggg. This study also demonstrated that E. ggg
mainly thrived as third to fourth stage juveniles and mature females and
these life stages constituted 83.2 and 14.3% of the total population of

vermiform stages.

179

The research also showed that 54.5% of the total population of E. g_ag
in the roots was within a depth of 0-20 cm. The high population density Of E.
ze_ae_ within a depth of 0-20 cm appears to be dictated by the amount Of root
tissue within this depth. The population density Of E. gag in the soil was
highest at depth 10-20 cm and lowest at depth 0-10 cm. The high population
density of g. E in the soil at depth 10-20 cm appears to be a function of
optimal soil moisture, temperature and root tissue availability at this depth.
The low population density of E. ga_e in the soil at depth 0-10 cm appears to
be a function Of adverse soil moisture and temperature at this depth. Data
presented in this study also showed that the population density of E. gag in
the soil or roots increased with increasing sampling radius.

The study showed that very large errors (as high as 548.0%) can be
encountered if E. gg sampling in maize roots or soil is not properly timed
and carried out at the right depth and distance from the plant. Data
presented in this study showed that the optimal time Of sampling maize roots
for E. g_ag population density assessment in loamy sand soil was 4 weeks
after planting at depth 10-20 cm and radius of 0-10 cm. The optimal time of
sampling soil surrounding maize roots for 12. gg population density
assessment was 2 weeks after planting at depth 10-20 cm and radius 10-20
cm.

(c) Influence of soil moisture on E. E and maize root system development

A greenhouse study showed that maize root system was adversely
impacted at 11.7% gravimetric soil moisture in loamy sand soil but 3. gag
population density was only slightly adversely impacted at 5.0% gravimetric
soil moisture. The study demonstrated that E. z_gg was more tolerant to low

soil moisture than maize. This phenomenonappears to account for the higher

 

180

pathogenicity Of E. g_ag on maize during growing seasons with inadequate
rainfall.
(d) Influence of soil nutrients on E. ga_e_ and maize growth

This study showed that various combinations of soil nutrients increased
maize growth (above and below biomass). The highest maize growth after
applying nutrients was attained by applying compound D + ammonium
nitrate fertilizer + manure and the lowest maize growth was attained by
applying ammonium nitrate fertilizer. This study underlines the importance
of applying adequate soil nutrients especially in E. w infected maize plants
to compensate for the inadequate nutrient and water uptake by infected
maize roots.

The population densities of E. gag in this study did not increase as
expected possibly because of sub-optimal temperature conditions.
Treatments which included manure application had slightly lower population
densities Of _P. z_ea_e in roots 8 weeks after planting. However, the trend was
not maintained 16 weeks after planting and there were no significant
differences in the population densities of _P. E in roots or soil.

4.4 Management of the Pest

Two strategies were evaluated in the management of E. ga_e associated
with maize production: (a) nematicide control and (b) cultural control.
(a) Nematicide control

Carbofuran, fenamiphos, isazofos and terbufos reduced the population
densities of E. g in maize roots by 94.81, 95.97, 95.11 and 93.14% and
subsequently increased maize yield by 67.41, 54.71, 36.73 and 66.03%,
respectively. The research also showed that under sub-Optimal moisture
conditions, a farmer may not obtain a financial return after applying

nematicides to control B. zeae in maize production. This instability in financial

_AAgAa-u‘.‘ A. q
j y.

181

returns is likely to act as a deterrent in the adoption of nematicides by most
communal farmers. Also communal farmers are unlikely to adopt use of
nematicides in maize production because Of socio-economic reasons.

(b) Cultural control

A study to evaluate whether major maize varieties grown in Zimbabwe
are resistant to E. z_eg infection showed that all the varieties were
susceptible to E. gg infection. It is likely that resistance for E. _ze_ag infection
has not been incorporated in the maize breeding programs. However, there
is need for this work to be incorporated into future maize breeding programs
in order to optimize maize yields in the communal farms.

A greenhouse and a field study on organic amendments in maize
production showed that manure can reduce the population density of _P_. g_ag
in roots and Subsequently increase maize growth and yield. The greenhouse
study also demonstrated the importance of timing the application of the
manure in order to get optimal E. ggg control and subsequent maize
growth. Most communal farmers keep some livestock, therefore, this
technology is likely, in part, to assist communal farmers in reducing
population densities of E. gg in maize fields and subsequently increase

maize yields.

4.5 SIMULATION MODEL OF THE PEST

A E. gag simulation model was developed to summarize data from the
research and literature review. The E. ggg simulation model was
incorporated into an existing CERES-MAIZE simulation model. The E. gtgg -
maize simulation model predicted the population density of E. ga_e_ in maize
roots with a mean error Of 7%. The simulation model was sensitive to

different initial population densities of E. zeae in the soil and weather data.

'.’h.r‘..

flrA-‘. L_

182

The simulation model also predicted the correct silking date Of maize variety
R 215 and above and below-ground dry biomass with mean errors of 17.7 and
11.1%, respectively. Simulated values of E. ga_e_ pathogenicity on maize and
measured values were comparable. This research showed the simulation
model could be incorporated in future predictive E. g maize yield and crop
loss assessments. However, most Of the parameters which were predicted
using the simulation model requires further validation. Also further
development of the simulation model could incorporate management

strategies Of P. zeae associated with maize.

-...1'" F
"l
'-

5. APPENDICES

183

.I-_-_nn Mgr-h H2:

184

Plant-parasitic nematodes found associated with maize
durin the 1986/86 national survey of pests and diseases
in Zim abwe.

Appendix 5.1.1.

a. Manicaland Province

 

 

 

 

 

 

 

 

Natural Communal Farmer's Nematode found N0110.0 ~01
Region Area Name assocrated wIth grams 100 cm3
maize roots soil
I Holdenby Peresa Pratylenchus g 1,566 4
Graham, 1951
Scutellonema sp. (juv) 0 3
Muchena 2. 2% 1,110 184
Scutellonema sp. (juv) 0 19
Mutambara Pratylenchus
brachyurus (Godfrey 3,620 56
1929) Filipjev &
Stekhoven, 1941
Helicotylenchus sp. (juv) 28 40
mm sp. (luv) 0 10
Nyamaropa Mubvuta E. ggg 555 3
mm 5P- (luv) 1 15
II Chiduku Mukamha 3. fig 2,510 0
Rotylenchulus Sp. (juv) 0 100
Helicotylenchttg sp. (juv) 7 15
Scutellonema sp. (juv) 0 13
Makoni E. brachyurus 125 0
Rotylenchulus sp. (juv) 10 1 15
Meloidogyne sp. (juv) 15 15
Samatende E. ze_ae_ 1,250 17
Rotylenchulus sp. (juv) 0 301
Scutellonema unum 0 18
Sher, 1964
Tanhuki E. gag 1,100 134
W SP- (luv) 0 1 1 1
Scutellonema unum 0 18
Zem be Pratylenchus sp. (juv) 5 0
Rotylenchulus sp. (juv) 0 141
Scutellonema sp. (juv) 0 3
Mutasa Chademwiri E. gag 2,286 52
North Helicotylenchgg sp. (juv) 0 1
Scutellonema Sp. (juv) 0 1
Mukwindidza E. ga_e 6,350 0
Scutellonema sp. (juv) 0 18
Nyanga Ndau Pratylenchus sp. (juv) 10 0
HelicotylenQIts sp. (juv) 1 0
Kangoni E. g 595 3
Heliggtvlenchyt sp. (juv) 0 2

 

 

 

 

 

 

 

 

a. Manicaland Province, continued.

185

 

Natural
Region

Communal
Area

Farmer's
Name

Nematode found
associated with
maize

NO./10.0
grams
roots

No./

100 cm3

soil

 

Manyika

Masvikeni

Mutasa

Nyadore

g. zeae

Rotylenchulus garvus
(Williams, 1960) Sher,

1961
9052222335:
sghaerocephala
(Taylor, 1936) Luc &
Raski, 1981
Helicotylenchus Sp. (juv)
Scutellonema sp. (juv)

Prgtylenchus goodgyi
Sher 8: Allen, 1953

griconemella sp. (juv)
Helicotylenchus sp. (juv)
Rotylenchulus sp. (juv)
Scutellonema sp. (juv)
freeze
Helicotylenchgs sp. (juv)

Scutellonema sp. (juv)

1 1,200
400

on
gum

b
‘9

2
100

11

SO
30
1 1

 

 

 

Matizi

Mutasa

St. Swithins

 

Mapara
Muromo-

wenyoka
Haukozi

Pfachi

Makura

Kawundo

Satumba
Tsikayi

 

E- 23.3.9.

Scutellonema sp. (juv)
Pratylenchus sp. (juv)
Scutellonema sp. (juv)
E- $9.

Helicotylenchus sp. (juv)

Scutellonema sp. (juv)

Pratylenchus sp. (juv)
Rotylenchulus sp. (juv)

Scutellonema sp. (juv)

Pratylenchus sp. (juv)
Helicotylenchus sp. (juv)
Ssuyflkaranasp.fiuv)

E. zeae
Scutellonema sp. (juv)

Pratylenchus sp. (juv)
Pratylenchus sp. (juv)

Helicotylenchus Sp. (juv)
Scutellonema sp. (juv)

 

1 .870

N
0010

N
N
‘9
o

W
O
\INOO‘IOOU'IOO

1,00

01
O
_e-bhflp-l

 

N
mmoooonwu

 

 

a. Manicaland Province, continued.

186

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sher, 1964

 

 

Natural Communal Farmer’s Nematode found No./10.0 NOJ
Region Area Name aSSOCIated wrth grams 100 cm3
maize roots soil
III Zimunya Musiyanga 2. fig 1,165 81
Helicotylenchtg sp. (juv) 0 1 1
Scutellonema sp. (juv) 0 4
Muzarwetu E. zegg 1,200 0
Scutellonema 0 51
brachyurum (Steiner,
1938) Andrassy, 1958
Helicotylenchus sp. (juv) 0 7
Criconemella sp. (juv) 0 3
Waziweyi Pratylenchus sp. (juv) 735 8
Helicotylenchus sp. (juv) 0 58
g. sghaeroceghala 0 3
IV Chinyauwhera Hwenzira E. ggg 5,040 0
Helicotylenchus sp. (juv) 0 15
Scutellonema sp. (juv) 0 7
Musabayana E. z_e_a_e . 3,105 108
Criconemella sp. (juv) 0 3
S. brachyurum O 60
Musona E. ggg 338 0
Helicotylenchus sp. (juv) 0 76
S. brachyurum 0 31
Criconemella sp. (juv) 0 3
Musukutwa l_’. ze_ae_ 1,330 21
Helicotylenchus sp. (juv) 5 183
Scutellonema sp. (juv) 0 18
griconemella sp. (juv) 0 9
Marange Chinoera 3. fl 2,560 39
Rotylenchulus sp. (juv) 8 25
gutellonema sp. (juv) 0 6
Jera E. gag 1,009 4
Rotylenchus sp. (juv) 0 71
Scutellonema sp. (juv) 0 12
Criconemella sp. (juv) 0 3
Katsidzira g. _zegg 1,015 11
Rotylenchulus sp. (juv) 0 170
Mm sp. (juv) 0 13
Criconemella sp. (juv) 0 3
Muzii E. gag 201 3
Rotylenchulus sp. (juv) 1 1 50
Scutellonema 4 43
magniphasmum Sher,
1964
Scutellonemg unum 1 29

 

 

?‘gh fit...»_.
A F i

a. Manicaland Province, continued.

187

 

 

 

 

 

 

 

 

 

 

 

 

 

Natural Communal Farmer's Nematode found No./10.0 ~01
Region Area Name assocrated wrth grams 100 cm3
maize roots soil
IV Mutambara Chiremba E. z_e;e_ 246 0
Helicotylenchus sp. (juv) O 18
Mangure E. ze_ag 51 1 0
Helicotylenchu_s sp. (juv) O S
Rotylenchulus sp. (juv) O 15
Muwushu Matsikinyire E. brachyurus 1,31 1 62
S. magnighasmum 10 72
Criconemella sp. (juv) 0 8
Helicotylenchus sp. (juv) 0 56
Muzvuzvu Criconemella sp. (juv) 0 2
m sp. (juv) 2 0
W sp. (iuv) 0 2
Ndowoyo Makumbe Hoglolaimgg sp. 1,1 13 78
S. unum 0 6
Nyanga Mavungire _E. z_ea_g and g. 731 0
North (1) brachyurus
S. unum 0 6
Helicotylenchus sp. (juv) 0 1
Mavungire E. _z_e_a_e_ and E. 465 0
(2) brachyurus
S. unum 0 5
Sabi Kanda Pratylenchus sp. (juv) 40 0
Rotylenchulus sp. (juv) 0 62
S. unum 0 70
Makure 13. fig 15,210 214
Helicotylenchus sp. (juv) O 28
Scutellonema sp. (juv) 5 14
Shonhiwa E. g_egg 150 0
3. arvus 0 205
S. unum 0 52
Tanda Dzikiti g. zeae 1,880 O
Meloidogyne sp (jUV) 55 0
Murienge 3. fl 2,145 0
Helicotylenchus sp. (juv) 0 21
Rotxlenchulus sp. (juv) 0 9
Wm SP- (1W) 0 1 1

 

 

b. Mashonaland East Province

188

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Natural Communal Farmer's Nematode found No./10.0 No./
. associated with grams 100 cm3
Region Area Name . .
maize roots 5011
ll Chinamora Gotora E. gfle 114 0
Helicotylenchus sp. (juv) 0 4
Scutellonema sp. (juv) 0 2
Mazvirongwa Pratylenchus sp. (juv) 47 6
Scutellonema sp. (juv) 0 32
Tylenchoqnchus sp. 0 3
CW)
Shongedza E. gas 502 0
(1) Meloidogyne sp. Guv) 10 0
Scutellonema sp. (juv) O 4
Shongedza E. zeae 561 0
(2) Helicotylenchus sp. (juv) 0 5
Scutellonema sp. (juv) 0 7
Chiota Chakadona E. brachyurus 710 10
fl. garvus 16S 45
Scutellonema sp. (juv) 0 30
Munemo E. brachyurus 5,362 147
3. Qarvus 42 30
Scutellonema sp. 0 21
Trichodorus sp. (juv) 0 49
Kunzwi Mutero E. zeae 14,805 0
Rotylenchulus sp. (juv) 5 140
Muzawazi E. brachyurus 3,647 14
Rotylenchulus sp. (juv) 26 221
Zambezi E. brachyurus and 3. 5,900 0
zeae
Scutellonema sp. (juv) O 21
Mangwende Kamundirira E. brachyurus 380 0
S. unum 0 172
Nhende E. brachyurus 1,570 0
Criconemella sp. (juv) 0 44
S. unum 0 256
Trichodorus sp. (juv) 0 44
IV Chimanda Makasa 3. 393 1,920 55
Helicotylenchus sp. (juv) 0 1 1
Scutellonema sp. (juv) 0 13
Maramba Chibanda E. brachyurus 12,660 30
Criconemella sp. (juv) 0 31
Helicotylenchus sp. (juv) 0 10
3. garvus 20 165
S. unum 0 90
Hukuimwe Pratylenchus sp. (juv) 180 0
Helicotylenchus sp. (juv) 0 3
Scutellonema sp. (juv) 0 9
Muchaparara E. E 1,503 35
Scutellonema labiatum 0 48
Siddiqi, 1972 and S.
magniphJasmum
Trichodorus sp. (juv) 0 3
Mkota Chingaubare E. E 1,045 20
Rotylenchulus sp. (juv) S 5
Scutellonema sp. (juv) 0 25

 

 

c. Mashonaland Central Province

189

 

Natural
Region

Communal
Area

Farmer's
Name

Nematode found
associated with
maize

NoJ10.0
grams
roots

No]
100 cm3
soil

 

Bushu

Chinyangiwe

P. zeae

Helicotylenchus sp. (juv)
Scutellonema sp. (juv)

4,001
0
0

 

 

 

 

Mutiwekuziva

 

Pratylenchus sp. cf
goodevi Sher & Allen,

1953
Criconemella sp. (juv)
Helicotylenchus sp. (juv)
Scutellonema sp. (juv)

 

846

COO

 

13
113

 

d. Mashonaland West Province

 

Natural
Region

Communal
Area

Farmer's
Name

Nematode found
associated with
maize

No.110.0
grams
roots

No./
100 cm3
soil

 

Hurungwe
Zvimba

Masamba
Mereki

Neushe

Sakanda

Scutellonema sp. (juv)
E- z_e_a_e
Rotylenchus cf.
brevicaudatus
Colbran, 1970
Criconemella sp. (juv)
E. g_r_a_c_hxurus
Meloidogyne sp. (juv)
Rotylenchulus sp. (juv)
E. brachyurus

Meloidogyne sp. (juv)
Scutellonema sp. (juv)

 

286
125
340

 

Umfuli

Jenga

Kasenga

Pratylenchus sp. (juv)

Tylenchorhynchus sp.
(juv)

Pratylenchus sp. (juv)

 

 

IV

 

Omay

 

Masham-
bakaru

 

Pratylenchus: sp. (juv)
Helicotylenchu_s sp. (juv)

S. unum

 

 

 

 

 

 

 

e. Masvingo Province

190

 

 

 

 

 

 

 

 

 

 

 

Natural Communal Farmer's 2:321:32??? N92111:)? 1 03:1. 3
Region Area Name maize roots soil
III Serima Bere E. brachvu rus 1 .360 18
. 5. garvus 45 75
Kwashi ra E. brachyurus 1,680 12
5. Qarvus 34 132
Trichodorus sp. (juv) 0 12
Varibo E. brachyurus 2,555 85
5. arvus 55 252
IV Gutu Chinyaure E zeae 13,520 85
B. rvus 15 30
S. unum 0 10
Mangezi E. zeae 1,330 145
3. Qarvus 42 100
Nyamande E. zeae 3,700 10
5. Qarvus 220 250
S. unum 0 1 1
Nyajena Mangwadi E. zeae 2,250 0
3. arvus 16 80
S. unum 0 8
gyconemella sp (luv) 0 12
, T_richodorus sp. (juv) 0 4
Mutsikwa fl. zeae 20 0
3. garvus 27 30
S. unum 0 52
Meloidogyne sp. (juv) 40 0
V Matibi 2 Dzviriri Rotylenchulus sp. (juv) 5 125

 

 

 

 

 

 

 

 

fl-‘Iull-l

f. Midlands Province

191

 

 

 

 

 

 

 

 

 

 

 

Natural Communal Farmer's Nematode found No./10.0 No./ 3
. associated with grams 100 cm
“9'0" Area Name maize roots soil
III Chiwundura Khumalo ' Aghelenchus avenae 13,310 5
Bastian, 1865
Criconemella sp. (juv) 0 3
Scutel lonema sp. (j uv) 0 25
Ngezi Kureva E. brachyurus 5,280 20
P_aratrichodorus minor 0 600
(Colbran, 1956)
Siddiqi, 1974
Mupanda- E. brachyurus 5,320 0
wana E. minor 0 196
3. Qarvus 36 106
Midzi E. brachyurus 14,840 63
E. minor 1 161
Sanyati Dhiwiera E. brachyurus and 3 15,940 220
zeae
Scutellonema sp. (juv) 0 35
Mandaka E. brachyurus 7,100 50
Scutellonema sp. (juv) 0 10
Nhendere E. brachyurus 6,650 38
IV Mberengwa Dube Helicotylenchus sp. (juv) 0 4
Scutellonema sp. (juv) 0 28
Mawela B. Qarvus 20 86
Scutellonema sp. (juv) 0 60
Sama E. zeae 170 0
Rotylenchulus sp. (juv) 30 204
Scutellonema sp. (juv) 0 24
Tshuma E. zeae 260 0
Gokwe Bhora Pratylenchug sp. (juv) 2 0
Rotylenchulg sp. (juv) 0 61
Scutellonema sp. (juv) 0 2
Mhazo Pratylenchus sp. (juv) 9 0
V Mazvihwa Tshuma g. z_e_ag 340 0
Rotylenchulus sp. (juv) 16 125

 

 

 

 

 

 

 

g. Matebeleland North Province

192

 

 

 

 

 

 

 

 

 

 

 

Natural Communal Farmer's Nematodezfourgd No./10.0 No./ 3
. associat wit grams 100cm
Region Area Name maize roots soil
III Mzola Ncube E. zeae 720 20
3. brevica tus 0 10
Scu tellonema sp. (juv) 0 35
IV Lupane Silandu E. zeae 1,940 130
3. Qarvus 45 110
Scutellongmgsp. (juv) 0 15
Nkai Sipepa Rotxlenchglus s.sp (juv) 20 270
M'nongo _P. yie 1,226 0
3. garvus 42 130
Scutellonema sp. (juv) 0 24
Moyo E. g_ag 250 0
Nkomo Pratylenchus sp. (juv) 18 8
Ntabazin- Scutellonema sp. (juv) 0 18
duna Majelimana P. z_e__ae 1,300 1
Helicotylenchussp. (juv) 10 20
Rotylenchulus s.sp (juv) 0 24
_S_c____utellonema sp. (juv) 4 10
Ncube Aphelenchus s.sp (juv) 78 0
C_r____iconemella sp (juv) 0 9
Rot—T—lenchulus ss.p (juv) 0 83
Ndhlovu P. ze_a_e 200 0
RotTIenchulus sp. (juv) 10 712
Sithubeni Pratylenchus sp. (juv) 158 0
. Helicotylenchus sp. (juv) 0 8
Rotylenchulus sp. (juv) 9 200
Scutellonema sp. (juv) 0 3

 

 

 

h. Matebeleland South Province

193

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Natural Communal Farmer's 2:522:31 23:? ”91:23? 1 03:;3
Region Area Name maize roots soil
IV Godlwayo Manasa Psraylenchu s.sp (juv) 41 0
C_r____iconemella sp. (juv) 0 2
Rotylenchulus ssp. (juv) 0 29
Scutellonema sp. (juv) 0 12
Ncube Pratylenchus s.sp (juv) 1 14 10
C_r____iconemella sp. (juv) 0 3
Rotylenchulus s.sp (juv) 4 15
Scutellonema sp. (juv) 0 8
Ivlenchorhynchus sp. 0 8
Sibanda E. zeae 2,1 15 14
HelicotylencmLs sp. (juv) 0 4
Meloidogyne sp. (juv) 20 0
Scutellonema sp. (juv) 0 9
Mpande Magama _P. zeae 3,806 263
Helicotylencmlg sp. (juv) 0 254
Rotylenchulus sp. (juv) 16 250
mtellonema sp. (juv) 0 16
Mpofu Aghelenchoides sp. 0 42
(juv)
Pratylenchus sp. (iuv) 2 0
Nswazi Madhuma Rotylenchulus sp. (juv) 0 276
S. unum 0 20
Tshuma E. 19$ 200 0
fl. parvus 10 764
Scutellonema sp. (juv) 0 2
V Gwaran— Chithe Pratylenchus sp. (juv) 16 0
yemba Helicotylenchus sp. (juv) 0 39
Dzingai Criconemeljg sp. (juv) 0 9
Helicotylenchus sp. (juv) 1 4
Pratylenchus ssp. (juv) 14 0
S______cutellonema sp. (juv) 0 14
Tylenchorh—fi-nchus s.sp 0 1
CW)
Mphoenghs Moyo Pratylenchus sp. (juv) 198 0
Roglenchul us sp. (juv) 0 64

 

 

 

194

HIPPIIIVIWW

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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.356... 323222 c. 2.2:... 3.2.. 333. 9:56 3083.8 8.8.... 52..» 88882.3 3. 338: .~. ..m 59.3.?

 

195

Appendix 5.1.3. Monthly rainfall during the 1985/86 national survey of pests
and diseases in Zimbabwe.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Monthly rainfall (mm) season 1985/86
Communal Area Sites
Sep Oct Nov Dec Jan Feb Mar Apr Year
Nyanga North Mavhunglre 0 4.1 142.9 215.3 280.3 140.5 67.8 15.0 865.9
Nyanga Kangom 2.5 75.4 135.4 289.3 491.8 250.9 118.5 42.7 1416.5
Nyamaropa Mubvuta 0 36.9 153.4 364.5 455.1 100.3 52.3 57.8 1220.3
Matizi Marapa 0 4.5 78.0 354.7 133.8 130.0 41.5 0 742.5
Tanda Dziklti 0 9.0 63.0 252.5 314.0 50.0 43.5 49.0 781.0
Mutasa North Mukwindlza 1.5 32.5 110.0 171.0 481.8 161.0 107.0 104.5 1197.8
Holdenby Mutambara 42.2 70.4 198.7 464.2 1024.0 326.8 163.0 240.3 2597.7
Mutasa South Pfachi 2.5 33.0 44.5 211.3 241.5 50.7 35.0 33.0 652.6
Mutasa South Haukozi 0 0 176.0 116.0 246.3 134.3 184.0 109.0 976.6
Manyika Maswkeni 14.4 58.1 62.4 197.3 307.2 121.1 93.5 62.6 936.6
Chinyauwhera Hwenzira ' 6.5 53.2 171.3 76.0 309.5 162.0 98.12 56.5 968.2
Zimunya Muzaruwetu 34.0 86.3 122.7 114.5 260.5 28.2 186.1 68.8 900.9
Marange South Chimoera 3.0 39.4 85.5 156.0 125.0 68.8 60.2 77.9 615.8
Marange North Katsidzira O 22.5 72.0 82.6 245.1 95.0 51.0 49.0 629.1
Mutambara Mangure 4.0 28.0 80.5 143.0 241.5 77.9 49.0 135.7 676.2
Mutema Mtlsi 34.0 57.2 49.0 109.6 134.3 60.9 85.8 156.8 687.6
Sabi North Makure 10.0 37.3 22.0 204.5 231.8 157.0 96.0 140.5 911.1
Chiduku Tanhuki 13.0 30.4 68.7 182.3 160.5 97.0 79.3 5.5 636.7
Chiduku Makoni 15.1 39.4 546.7 240.7 209.8 189.6 148.8 93.8 993.9
Zvimba Mereki 0 23.0 9.0 143.9 214.0 171.2 54.5 98.5 714.1
Umfuli Jenga 0 0 74.5 303.5 209.4 272.5 143.0 108.5 1111.4
Hurungwe North Masamba 0 25.0 56.4 195.4 117.4 157.2 92.1 167.8 811.2
Kandeya Mutiwekuziva O 2.3 27.3 268.6 266.5 171.8 19.4 88.9 844.8
Bushu Chinyangwe 0 5.0 76.5 349.5 234.5 119.0 62.5 103.4 950.4
Chinamora Gotora 0 22.3 58.1 327.8 556.6 284.9 77.2 151.2 1496.8
Chinamora Shongedza 1.5 19.0 34.4 233.5 396.0 184.1 73.0 98.5 1047.6
Chlota Munemo 1.8 30.4 79.9 232.4 382.3 191.9 97.6 106.2 1122.5
Kunzwi Mutero 0 22.5 40.5 383.0 284.3 145.5 74.0 86.5 950.4
Mangwende Kumundirira 0 13.1 41.4 262.8 262.2 174.2 88.5 118.5 960.7
Chimanda Makasa '0 0 37.3 282.3 241.5 171.0 24.5 89.8 846.4
Gutu Chinyaure 18.0 19.1 27.5 141.5 116.5 124.5 72.5 78.0 600.6
Nyajena Mangwadi 22.5 59.8 30.3 121.5 90.7 96.5 80.4 76.4 578.1
Matibi 2 Dzviriri 36.1 1.7 52.5 1.5 45.0 23.0 28.6 55.5 316.3
Chiwundura Khumalo 2.5 6.5 26.4 309.2 120.8 32.6 35.0 94.2 627.3
Ngezi Mupandawana 9.0 9.4 7.0 234.5 31.5 30.0 73.5 118.0 520.1
Sanyati Dhlwlera 0 0 23.0 241.0 206.0 179.0 96.0 167.0 912.0
Belingwe Sama 117.0 22.0 1.0 89.0 352.0 112.0 128.5 222.5 1098.5
Gokwe Bhora 0 0.5 2.5 161.0 206.5 172.0 108.5 222.0 878.0
Mazvihwa Tshuma 4.3 13.0 48.0 139.9 1 12.4 41.7 45.8 131.6 543.8
Mzola Ncube 9.4 7.0 234.5 31.5 30.0 73.5 118.0 7.0 520.1
Lupane Silandu 0 0 47.0 157.0 96.0 10.9 26.0 13.2 350.1
Nkayi M'nongo 0 24.0 0 177.9 60.2 52.7 93.5 106.5 514.8
Ntabazinduna Majelimana 0.6 8.7 22.2 139.9 52.7 36.4 35.5 180.6 496.2
Godlwayo Sibanda 7.0 22.0 41.0 89.0 69.0 42.0 158.5 122.8 561.3
Mpande Magama 0.1 27.0 4.5 136.8 46.4 68.8 60.0 151.3 520.9
Nswazi Tshuma 6.1 46.7 50.1 118.2 57.0 31.8 41.1 153.6 523.3
Gwaranyemba Dzingai 10.1 25.4 9.9 83.4 52.2 13.6 67.9 94.4 369.9
. MBhoenghs Moyo 92.9 58.6 23.3 26.7 37.4 34.9 14.3 119.3 430.8

 

 

I" 3T-

. 8...

PA

196

Appendix 5.1.4.Average monthly maximum and‘minimum temperature
during the 1985/86 national survey of pests and diseases in

 

 

 

 

 

 

 

 

 

 

 

 

Zimbabwe.
Maximum and Minimum Temperatures (0C)
Communal Area November December January February March April
1985 1985 1986 1986 1986 1986

Max Min Max Min Max Min Max Min Max Min Max Min
Mtetengwe 32.5 19.1 33.7 17.5 33.7 21.9 34.4 21.5 34.8 20.9 30.3 18.5
Matibi No. 2 32.5 19.1 33.7 17.5 33.7 21.9 34.4 21.5 34.8 20.9 30.3 18.5 r}
Maranda 32.5 19.1 33.7 17.5 33.7 21.9 34.4 21.5 34.8 20.9 30.3 18.5 L
Ndowoyo 32.2 18.8 32.4 20.3 30,7 20.5 32.5 20.5 33.1 18.9 29.5 17.7 i‘
Sabi 28.3 14.5 27.3 15.3 25.8 15.4 27.5 15.2 27.1 14.0 25.1 13.7 1-.
Ntabazinduna 29.9 15.5 27.8 17.2 27.8 17.1 28.7 15.5 29.0 15.2 25.2 14.5 L
Zvimba 29.0 14.8 25.7 17.0 25.3 15.0 27.2 14.7 27.3 13.5 25.7 13.2
Mutema 32.3 18.5 31.8 19.9 30.3 19.5 31.3 19.2 31.8 17.5 29.0 17.2
Muwushu 32.3 18.5 31.8 19.9 30.3 19.5 31.3 19.2 31.8 17.5 29.0 17.2
Ngezi 28.1 13.8 25.9 15.8 25.2 15.5 25.9 14.5 25.8 13.7 24.5 13.5
Gokwe 30.0 17.0 26.8 17.0 25.1 17.1 25.3 15.5 25.7 15.1 24.5 14.8
Guruve 28.8 17.0 25.1 17.9 25.8 17.4 25.1 17.1 25.7 15.4 25.5 15.0
Chiwundura 28.4 13.1 25.1 15.5 25.4 15.1 25.3 14.3 25.4 13.2 23.8 12.8
Hwange 32.8 18.0 29.8 18.8 28.9 18.2 28.9 17.3 28.9 15.7 27.0 14.0
Sanyati 30.9 15.9 28.0 18.0 27.3 17.5 28.2 15.7 28.5 15.8 25.5 15.1
Omay 33.9 23.0 31.1 22.5 30.5 21.5 30.5 21.3 31.3 20.8 29.2 19.1
Hurungwe 25.9 15.9 24.9 17.1 24.9 15.7 25.2 15.7 25.9 15.8 23.9 14.4
Gutu 28.2 14.7 27.4 15.8 25.7 15.5 27.7 15.9 27.8 15.0 25.0 14.1
Kunzwi 24.7 12.8 23.7 15.0 23.1 14.5 24.2 14.1 24.1 13.0 22.2 12.8
Nswazi . 29.2 14.5 27.9 15.3 27.5 15.9 28.4 15.0 28.9 14.2 24.5 13.0
Kandeya 30.9 17.9 27.4 18.8 27.0 18.7 27.8 18.3 28.2 17.1 27.0 15.8
Mtoko 27.2 15.3 25.5 17.3 25.7 17.1 25.2 17.0 25.7 15.1 25.7 15.1
Chiweshe 25.9 14.2 23.9 15.7 24.3 15.5 24.5 15.4 25.2 14.9 23.4 13.5
Nyanga 21.2 11.5 20.7 12.7 20.9 13.2 20.8 12.7 21.2 11.9 20.2 11.1
Mpande 29.9 15.2 28.0 17.1 28.2 15.8 25.5 15.5 29.1 15.1 24.5 14.2
Chiduku 25.5 13.3 24.9 15.7 24.2 15.0 25.0 14.2 24.7 13.3 23.5 13.0
Chiota 25.5 14.4 25.7 15.2 24.9 15.0 25.0 15.2 25.7 14.4 24.3 14.0
Gwaranyemba 32.1 15.9 31.2 18.9 30.2 18.5 32.5 18.7 32.4 17.4 27.3 15.5
Nyajena 29.7 17.2 29.4 18.9 27.8 19.0 29.2 18.5 29.9 17.4 27.3 15.1
Mberengwa 30.7 17.2 29.7 18.7 28.2 18.4 29.5 18.1 30.5 15.8 25.1 15.5
Zimunya 25.4 15.7 25.0 17.0 25.7 17.3 27.4 17.0 25.4 15.4 25.0 15.5
Chinyauhwera 25.4 15.7 25.0 17.0 25.7 17.3 27.4 17.0 25.4 15.4 25.0 15.5
Chinamora 28.5 13.4 25.8 15.5 25.0 15.0 25.5 15.3 27.1 13.5 25.2 12.5
Bushu 31.1 17.3 27.7 18.9 28.0 18.5 28.5 18.4 28.8 17.1 27.5 15.1
Mzola 33.0 17.4 29.8 17.0 28.2 15.5 28.5 15.0 29.0 15.4 27.2 14.1
Goldwayo 30.5 14.2_ 28.9 17.5 _2_8£ 15.9 30.1 15.5 30.0 15.2 25.5 14.4

 

 

 

 

 

 

 

 

197

Appendix 5.1.5.1nfluence of rainfall on the population density of _E. zeae
recovered from maize roots during the national survey of
pests and diseases.

 

Annual rainfall (mm)

3. zeae/ 10.0 grams roots

 

 

 

 

 

 

 

Transformed‘ Detransformed
> 1000 (n = 15) 6.10 445.85
800-1000 (n = 21) 6.82 915.99
600-799 (n = 10) 6.58 720.53
400-599 (n = 8) 6.87 962.95
< 400 (n = 3) 3.40 30.06
SE 2.759
CV % 46.50
F ratio 1.228 ns
Contrasts F ratio
> 1000vs800- 1000mm 9.76 **
> 1000 vs 600 - 799 mm 3.47 ns
800 - 1000 vs 400—599 mm 35.29 ns
600-799 vs < 400 mm 128.66 ‘*
400~599 vs < 400 mm 143.00 **
Key

1Logarithmic transformation (y = loge x)

* = significance level (P = 0.05)

** = significance level (P = 0.01)

ns = not significant (P > 0.05)

 

 

198

Appendix 5.1..6 Influence of February temperature on the population density
of P. zeae recovered from maize roots during the national
survey of pests and diseases.

 

E. zeae “0.0 grams roots
Average temperature (°C)

in February, 1986

 

 

 

 

 

 

 

 

 

Transformed Detransformed
> 32.5 (n = 1) 0.00 0.00
30.0-32.5 (n = 3) 3.44 31.19
27.5-29.9 (n = 17) 5.76 317.34
25.0-27.4 (11 = 14) 6.21 497.70
22.5-24.9 (n = 2) 8.83 6,836.28
20.0-22.4 (n = 1) 4.39 80.64
SE 3.002
CV % 53.00
F ratio 2.648 ns
Contrasts of Feb. temperature groupings F ratio
20.0-22.4 vs 22.5-249°C 6.960 "
25.0-27.4 vs 27.5-299°C 9.063 **
27.5-29.9 vs 30.0—325°C 33.185 **
30.0—32.5 vs >32.5°C 10.283 **
20.0-22.4 vs >32.5°C 2.850 ns
Key
1Logarithmic transformation (y = loge x)
= significance level (P: 0. 05)
** = significance level (P: 0. 01)
ns = not significant (P > 0.05)

199

Appendix 5.1.7.1nfluence of March temperature on the population density of
E. zeae recovered from maize roots during the national
survey of pests and diseases.

 

E. zeae/ 10.0 grams roots
Average temperature (°C)

 

 

 

 

 

 

 

 

 

Transformed1 Detransformed
> 32.5 (n = 1) 0.00 0.00
30.0-32.5 (n = 7) 3.44 31.19
27.5-29.9 (11 = 12) 5.76 317.34
25.0—27.4 (11 = 1 1) 6.30 544.57
22524.9 (n = 5) 6.88 972.62
20.0-22.4 (n = 1) 4.39 80.64
SE 3.046
CV 96 53.70
F ratio 2.211 ns
Contrasts of March temperature groupings F ratio
20.0—22.4 vs 22.5-249°C 23.05 **
25.0-27.4 vs 27.5-299°C 3.09 ns
27.5-29.9 vs 30.0-325°C 32.22 **
30.0-32.5 vs > 325°C 9.89 **
20.0-22.4 vs > 325°C 2.77 ns
Key

1Logarithmic transformation (y = log, x)

* = significance level (P = 0.05)

** = significance level (P = 0.01)

ns = not significant (P > 0.05)

200

Appendix 5.1.8. Influence of soil texture on the population density of E. zeae
associated with maize in Manicaland province.

 

 

 

 

 

 

 

 

 

 

E. zeael 10.0 grams roots
Soil Texture
Transformed‘ Detransformed
Sandy clay loam (n = 2) 7.17 1299.84
Sandy loam (n = 7) 6.43 620.17
Loamy sand (n = 5) 5.26 192.48
Sand (n = 30) 6.55 699.24
SE 1.995
CV % 31.11
F ratio 0.698 ns
Contrasts F ratio
Sand vs sandy clay loam 25.958 **
Sand vs loamy sand 7.329 **
Loamy sand vs sandy loam 707.814 **
Sandy loam vs sandy clay loam 260.440 **
Key

1Logarithmic transformation (y = loge x)

* = significance level (P = 0.05)

** = significance level (P = 0.01)

ns = not significant (P > 0.05)

Appendix 5.1.9. Influence of soil pH on the population density of _P. z_e__ae

201

associated with maize in Manicaland province.

 

 

 

 

 

 

g.__e/10.0 grams roots
Soil pH
Transformed‘ Detransformed
4.2-4.7 (n : 11) 6.12 454.86
4.8-5.3 (11 : 6) 7.32 1,510.20
5.4-5.9 (11 : 7) 5.74 311.74
6.0-6.8 .(n : 10) 6.52 678.58
SE 2.177
CV % 34.20
F ratio 0.642 ns
Contrasts of soil pH groupings F ratio
4.2-4.7 vs 4.8-5.3 6.798 *
4.2-4.7 vs 6.0-6.8 0.033 ns
4.8-S.3 vs 5.4-S.9 0.227 ns
S.4-S.9 vs 6.0-6.8 7.972 **

 

 

 

Key

‘Logarithmic transformation (y : loge x)

significance level
** significance level
ns not significant

(P = 0. 05)
(P: O. 01)
(P > 0.05)

1'3
l

Appendix 5.1.10.

Influence of manure, ammonium nitrate and compound D

fertilizer on the population density of E. zeae associated

with maize on Manicaland province.

 

E. zeael 10.0 grams roots

 

 

 

 

 

Nutrient
Transformed‘ Detransformed

+ Manure (n : 10) 5.38 217.02
- Manure (n : 24) 6.78 880.06
SE 2.07
CV 96 32.50
F ratio 324*
+ Ammonium nitrate (n : 22) 6.01 407.48
- Ammonium nitrate (n : 12) 7.03 1,130.03
SE 2.12
CV 96 33.20 .
F ratio 1.77ns
+ Compound D (n : 16) 5.91 368.71
- Compound D (n : 18) 6.68 880.06
SE 2.13
CV 96 33.40
F ratio 1.44ns

 

 

 

Key

 

 

‘Logarithmic transformation (y : loge x)
ns : not significant (P > 0.1)
* = significance level (P : 0.1)

203

Appendix 5.1.11. Relationships observed between manure, ammonium
nitrate and compound D fertilizer and maize yield in

Manicaland province.

 

 

 

 

 

 

 

 

 

 

E. zeael 10.0 grams roots
Nutrients
Transformed‘ Detransformed

+ Manure (n : 10) 1.375 2.955
- Manure (n : 24) 0.946 1.575
SE 0.400

CV % 37.300

Fratio 8.118"

+ Ammonium nitrate (n : 22) 1.164 2.203
- Ammonium nitrate (n : 12) 0.094 1.450
SE 0.429

CV % 40.000

F ratio 2.868 ns

1» Compound D (n : 16) 1.180 2.254
— Compound D (n : 18) 0.977 1.656
SE 0.436

CV % 40.600

F ratio 1.846 ns

Key
‘Logarithmic transformation (y : loge x + 1)
** : significance level (P >0.05)

ns : not significant (P = 0.01)

‘ ‘Mi

Appendix 5.1.12.

204

E. zeae and maize yield

Relationships observed between population densities of

in Manicaland province.

 

Maize yield (tons/ha)

 

 

 

 

E._z_eie_ / 10.0 grams roots
Transformed‘ Detransformed

<1000 (n = 16) 1.297 2.659
>1000 (n = 18) 0.872 1.392
SE 0.391
CV 96 36.5000
LSD 0.05 0.274
LSD 0.01 0.406
F ratio 9.978"

 

 

 

Key

‘Logarithmic transformation (y = loge x+ 1)
** : significancelevel (P = 0.01)

...,“l

_ El“.

205

Appendix 5.2.1.Temporal and spatial distributionof P. zeae under clean
fallow in Chinamora communal area.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sampling E- _zeae stages . . .
Sampl1ng date depth Gramgifttu'rceso”

(cm) 12 13-14 Adult

10-20 0 19 10 272

20-30 ' 1 3 2 5.23

30-40 0 2 1 539

8114/86 0—10 1 22 44 2.10

10-20 1 12 7 3_5o

20-30 1 3 4 3.70

30-40 0 O 1 7.50

4 40-50 0 0 0 9.30

10-20 0 4 2 3.21

20-30 0 20 1 4_ 32

30—40 0 13 S 5.34

40-50 0 0 0 7.8(4

10.20 0 4 o 2.94

20-30 0 20 1 4,61

30-40 0 0 0 5.81

1 1/6/86 0-10 0 10 2 1,10

“”0 0 0 2 2.45

20-30 0 0 O 3.85

40-50 0 0 O 7.1 1

12/30/86 0-10 3 6 41 1 , so

10-20 0 0 4 452

20-30 0 O 2 4.30

2128/87 010 0 o 1 3.00

10-20 0 0 1 2,84

20-30 0 O 0 335

- “'50 0 0 0 12.45

3/27/87 0-10 0 2 0 8.28

2930 0 1 0 10.50

3040 0 O 0 8.31

_ 40-50 0 o 0 12.50

10-20 0 1 3 1.16

20-30 0 1 2 1.87

.. 4°50 0 1 0 3.94

5’1/87 0.1 O 0 4 2 2.62

‘0‘20 0 1 1 3.00

20-30 0 1 0 2.24

30.40 0 0 0 5.92

40-50 0 O 0 553

 

 

 

 

 

 

Appendix 5.2.2. Influence of the time of sampling on the population density
of Pratylengh us zeae recovere

206

Chinamora Communal area.

from 100 cm3 of soil in

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

E. geLe stages
Parameters
Sampling J 2 13-14 Mature Total
date
Trans‘ Detrans Trans‘ Detrans Trans‘ Detrans Trans‘ Detrans
7121/86 0.9142 0.335 2.70 6.79 2.32 4.88 3.50 11.75
8114186 1.018 0.536 2.31 4.84 2.69 ' 6.74 3.52 11.89
9111186 0.707 0.000 2.72 6.90 1.49 1.72 3.02 8.62
10130186 0.707 0.000 1.93 3.22 1.18 0.89 2.22 4.43
1116186 0.707 0.000 1.21 0.96 1.06 0.62 1.45 1.60
12130186 0.940 0.383 1.62 2.12 2.72 6.90 3.19 9.68
2128187 0.707 0.000 0.71 0.00 0.91 0.33 0.91 0.33
3127187 0.707 0.000 1.09 0.69 1.08 0.67 1.29 1 . 16
4124187 0.707 0.000 1.15 0.82 1.04 0.58 1.38 1.40
611187 0.707 0.000 1.20 0.94 1.22 0.99 1.35 1.32
L.S.D. 0.05 0.251 1.328 1.247 1.729
L.S.D. 0.01 0.335 1.776 1.667 2.310
S.E. 0.124 0.658 0.617 0.856
C.V.% 25.12 62.50 62.17 62.00

 

1. Square root transformation [y : sq. rt.( x + 0.05)].

2. Mean of 5 different sampling depths.

 

 

“"73

207

Appendix 5.2.3. Influence of the depth of sampling on the population
density of Pratylenchus zeae recovered from 100 cm3 of

soil in Chinamora communal area.

 

 

 

 

 

 

 

 

 

 

 

 

P. zeae stages
Parameters
Sampling J 2 13-14 Mature females Total
depth (cm)
Trans‘ Detrans Trans‘ Detrans Trans‘ Detrans Trans‘ Detrans
0-10 0.9272 0.359 2.59 6.21 2.96 8.26 3.91 14.79
'3'“
10-20 0.759 0.076 1.80 2.74 1.88 3.03 2.60 6.26 (,1.
2030 0.811 0.157 1.86 2.95 1.13 0.78 2.09 3.87 I
3040 0.707 0.000 1.31 1.22 1 . 18 0.89 1.55 1.93
40-50 0.707 0.000 0.76 0.08 0.71 0.00 0.76 0.08
L.S.D. 0.05 0.178 0.939 0.883 1.222
L.S.D. 0.01 0.238 1.256 1.180 1.634
S.E. 0.088 0.465 0.437 0.605
C.V.% 25.12 62.50 62.17 62.00

 

 

 

 

 

 

 

 

 

 

1.
2. Mean of 10 different sampling times.

Square root transformation [y : sq. rt. (x + 0.5)].

208

Appendix 5.3.1.Tempora| and spatial distribution of soil moisture and maize

roots grown in pits filled with sandy soil.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Maize root weight (grams)
. Sampling depth % Soil Rad1us (cm)
Sampl1ng date (cm) Moisture

0-10 10-20 20—30

1128/86 010 9.25 0.70 0.00 0.00
10-20 9.00 0.00 0.00 0.00

20-30 10.16 0.00 0.00 0.00

30-40 8.80 0.00 0.00 0.00

40-50 7.60 0.00 0.00 0.00

2110187 0-10 6.40 0.50 0.00 0.00
10-20 7.46 0.80 0.00 0.00

20-30 6.75 0.00 0.00 0.00

30-40 7.41 0.00 0.00 0.00

40-50 7.77 0.00 0.92 0.00

2/24/86 0-10 4.92 1.60 1.90 1.00
10-20 5.48 0.10 0.30 1.11

20-30 5.90 0.00 0.10 0.70

30-40 8.14 0.00 0.00 0.00

40-50 6.75 0.00 0.00 0.00

3110/87 0-10 3.73 9.00 6.70 3.60
10-20 4.68 2.30 8.10 6.80

20-30 3.03 3.00 3.50 4.50

30-40 3.25 1.90 1.80 2.10

40-50 3.66 0.00 0.00 0.00

3124187 0-10 2.64 27.00 11.50 7.00
10-20 2.22 10.50 10.46 5.30

20-30 3.25 5.00 9.90 0.50

30-40 3.63 0.00 0.50 0.40

40-50 2.33 0.00 0.00 0.00

4/7/87 0-10 2.88 33.40 17.80 8.60
10-20 3.77 16.30 15.30 14.90

20-30 4.01 7.50 13.70 11.10

30-40 4.06 1.50 6.40 2.80

40-50 3.72 0.40 0.50 2.60

4123187 0—1 0 6.27 49.90 6.70 3.40
10-20 5.64 8.60 11.40 3.20

20—30 7.64 1.50 0.50 0.90

30-40 8.78 1.40 1.00 0.30

40-50 8.09 1.00 0.9_(_) 0.60

516187 0-10 4.90 70.40 5.80 3.50
10-20 7.37 14.80 11.50 4.10

20-30 8.33 4.00 8.70 3.00

30-40 5.91 1.60 5.00 3.80

40-50 6.77 2&9 4.80 8.50

5/19187 0-10 6.81 54.90 7.10 10.10
10-20 6.16 3.10 5.00 3.30

20-30 4.40 0.80 1.60 1.00

30-40 2.94 0.10 0.30 0.20

40-50 3.46 0.10 0.30 0.30

6110187 0-10 1.90 35.10 2.50 1.10
10—20 2.98 7.10 4.10 1.13

20—30 2.24 3.20 4.50 2.30

30-40 5.92 1.50 3.10 2.20

40-50 5.63 1.45) 1.5_() 1.40

 

 

 

 

 

209

Appendix 5.3.2.Temporal and spatial distribution of E. zeae in 100 cm3 of soil
surrounding maize roots grown in pits.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Radius (cm)
. Sampling .
Sampl1ng % 5011
date depth Moisture 0 10 10 20 20 30
(cm)
12 J3-Ja adult .12 13-14 adult J2 J3-J4 adult
11 81 0-10 725 0 17 0 0 23 2 0 15 0
10-20 9.00 0 52 2 0 46 0 0 28 4
20-30 10.16 0 27 2 0 34 3 0 46 1
30-40 8.80 0 69 O 0 51 0 0 33 0
40-50 7.60 0 21 0 0 26 2 0 1i 3
211 0187 0-10 6.40 0 18 6 0 24 5 0 28 3
10-20 7.46 0 89 12 0 74 6 0 106 3
20-30 6.75 0 30 2 0 58 1 0 41 7
30-40 7.41 0 43 3 0 69 10 0 83 4
40-50 7.77 0 110 2 0 37 11 O 87 1
2124186 0-10 4.92 0 13 6 0 6 3 0 24 2
10-20 5.48 0 34 13 13 80 4 0 5 1
20-30 5.90 0 14 7 0 43 2 0 66 1
30-40 8.14 2 32 1 6 103 2 0 71 0
40—50 6.75 0 48 0 8 9 1 0 137 0
3110187 0-10 3.73 2 0 0 4 0 0 2 0 1
10—20 4.68 0 0 1 19 2 0 16 3 0
2030 3.03 0 13 0 7 7 2 12 0 2
30-40 3.25 19 10 0 4 7 7 15 6 0
40—50 3.66 14 40 0 8 0 0 3S 0 0
3124/87 040 2.64 0 0 0 I 0 2 7 0 3
10-20 2.22 2 0 1 1 0 0 11 0 1
20-30 3.25 22 0 0 15 0 0 2 0 1
30-40 3.63 0 5 3 1 0 0 19 0 0
40-50 2.33 2 0 0 9 0 0 14 0 2
417187 0-10 2.88 O 3 0 0 7 1 0 3 0
10-20 3.77 0 6 0 0 3 0 0 17 1
20-30 4.01 0 3 0 0 0 0 0 11 0
30-40 4.06 0 7 0 0 0 0 0 10 0
40-50 3.72 0 8 O 1 14 0 0 7 0
4123/87 0-10 6.27 0 3 0 0 0 0 0 7 0
10-20 5.64 3 7 2 0 11 3 0 15 3
20-30 7.64 0 4 1 0 8 3 0 5 0
30-40 8.78 O 3 1 0 4 1 0 4 0
40-50 8.09 0 0 0 0 2 0 0 7 1
516187 0-10 4.90 0 40 9 0 1 1 0 0 17 0
10-20 7.37 0 12 1 0 21 0 0 18 0
20-30 8.33 0 41 5 0 49 7 0 21 0
30-40 5.91 0 45 5 0 18 0 0 22 3
40—50 6.77 0 45 0 0 67 10 0 20 7
5119/87 0—10 6.81 6 19 26 9 18 8 0 40 10
10-20 6.16 0 9 3 20 107 10 0 30 7
20-30 4.40 2 8 5 0 3 0 0 9 0
30-40 2.94 0 4 0 3 17 7 0 15 0
40-50 3.46 5 16 5 0 3 2 0 3S 0
6110/87 0-10 1.90 0 19 10 4 4 5 2 17 3
10-20 2.98 21 68 34 8 115 12 20 119 16
20-30 2.24 20 27 10 4 30 2 7 44 5
30-40 5.92 6 43 12 2 56 9 8 98 9
40-50 5% 11 29 7 23 192 6 15 L3. 15

 

 

 

 

 

210

Appendix 5.3.3.Tempora| and spatial distribution of E. zeae 10.0 grams of
maize roots grown in pits filled with sandy sod.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Radius(cm)
Sampling depth % Soil
date (cm) Moisture 0 10 10 20 20 30 '
J; Jr]. Adult 12 13-14 Adult .12 If]. Adult
—'1/28/85 o-10 9.25 o 157 12'81 o o o o o 61
10—20 900 0 0 0 0 0 0 0 0 0
20-30 10 16 0 0 O 0 0 0 0 0 0
30-40 880 0 0 0 0 0 0 0 0 0
40-50 760 0 0 0 0 0 0 0 O 0
2/10/"87 010 5.40 o o 100 o o o o o 61
10-20 746 0 25 62 0 0 0 0 0 0
20—30 675 0 O 0 0 O 0 0 0 0
30-40 741 0 0 0 0 0 0 0 0 0
40—50 7.77 0 0 0 0 0 0 0 __0 0
2124/86 0-10 4.92 O 1550 19 0 0 1046 0 1050 100'
10-20 5.48 O 600 400 0 0 0 0 145 18
20-30 5.90 0 0 0 0 0 200 0 414 114
30-40 8.14 O 0 0 0 0 0 0
40-50 5.75 o o _o o o o g 0
3110187 010 3.73 17 422 267 20 20 858 14 240 389'
10-20 4.68 21 318 217 8 8 120 4 144 225
20-30 3.03 0 10 0 0 17 0
30-40 3.25 0 0 0 0 0 0 0 0 0
40-50 3.66 _0‘ 0 0 0 0 0 0 0 0
3124/87 0-10 2.64 33 204 65 132 132 1012 94 644 198—2‘
10-20 2.22 22 343 369 99 99 594 43 1331 1746
20-30 3.25 0 172 365 0 0 26 0 482 173
30—40 3.63 0 0 0 0 O 0 0 0 0
40-50 2.33 0 0 0 0 0 0 0 0 0
417187 0-10 2.88 1 1 102 33 98 98' 775 63 685 63'
10-20 3.77 93 122 47 101 101 730 103 1890 9048
20—30 4.01 27 146 19 21 21 437 58 36
30-40 4.06 0 7 0 0 0 1 19 0 225
40-50 3.72 0 175 0 _Q 0 0 jg 31
4123/87 0-10 6.27 18 37 10 35 745 27 426 697 124
10-20 5.64 65 308 54 91 635 50 181 1825 265
20-30 7.64 40 573 94 0 470 30 180 570 180
30—40 8.78 0 47 13 0 50 0 0 267 33
40—50 8.09 0 0 0 0 40 20 O 5_0 0
516187 0-10 4.90 0 750 40 O 40 0 1250 25
10—20 7.37 0 300 25 25 3075 250 225 5050 400
20—30 8.33 30 822 77 55 1428 47 0 4107 214
30-40 5.91 0 1312 181 0 1026 128 0 1749 89
40-50 6.77 0 714 0 240 20 0 70_0 24
5119187 0-10 6.81 20 630 68 336 1046 240 447 2390 332
10-20 6.16 312 2761 403 999 2266 230 331 2831 223
20-30 4.40 0 1767 68 550 1050 50 200 1342 29
30-40 2.94 0 1200 400 0 200 0
40-50 3.46 1 1600 0 0 800 0 O 267 _0_
6110/87 0-10 1.90 25 401 36 133 2416 341 600 11200 267
10-20 2.98 92 1750 75 492 '4237 240 357 6714 1299
20-30 2.24 80 1752 172 455 3150 200 667 3906 1711
30-40 5.92 100 2500 300 240 3480 320 111 8355 416
40-50 5.63 167 4633 288 182 4364 191 §_6;1_ 6333

 

 

Appendix 5.4.1. Influence of gravimetric soil moisture on Pratylenchus zeae

211

and maize root system development.

 

E. zeae in soil and roots

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Root weight 8 weeks after '
. . plant1ng
Parameters GravsugiIletrIc (grams)
Treatments moisture 100 cm3 5011 10.0 grams roots
(%)
Trans' Detrans
Trans‘ Detrans Trans‘ Detrans

High moisture 16.52 5.74 32.95 3.90 15.21 30.2 912.04
Medium moisture 11.7 4.53 20.52 3.06 9.36 29.5 870.25
Low moisture 5.0 2.53 6.40 3.91 15.29 22.6 510.76
L.S.D. 0.05 0.673 1.025 7.456
S.E. 0.523 0.797 5.34
C.V. % 12.3 22.0 23.1

 

 

 

‘Square root transformation [y : sq. rt. ( x)].

2Mean of 6 replications.

2‘1““; .
u A

.__. A" ‘
11!

I
.

212

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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213

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Appendix 5.5.2.Evaluation of maize varieties and inbreeds against

214

Pratylenchus zeae infection.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

E. ze_ae_ in soil and roots 8 weeks after Root Weight
Parameters plant1ng (grams)
100 cm3 soil 10.0 grams roots
Varieties
Trans‘ Detrans Trans‘ Detrans Trans‘ Detrans

R 201 3.532 12.46 4.97 24.70 6.81 46.38
R 215 3.26 10.63 3.01 9.06 6.77 45.83
SR 52 3.56 12.67 4.43 19.62 6.34 40.20
25 107 3.64 13.25 4.60 21.16 7.25 52.56
ZS 202 4.09 16.73 3.63 13.18 6.36 40.45
ZS 206 3.94 15.52 3.12 9.73 6.66 44.36
25 225 3.25 10.56 3.03 9.18 6.18 38.19
83 3WH 59 2.92 8.63 3.58 12.82 6.29 39.56
83 3WH 27 3.57 12.75 3.98 15.84 6.23 38.81
86 3WH 12 3.67 13.47 3.66 13.40 6.28 39.44
S.E. 1.048 1.209 0.799

C.V.% 29.6 31.8 12.3

 

 

‘Square roottransformation [y : sq. rt. (x)].

2Mean of S replications.

6.1...
O

215

Appendix 5.6.1.1nfluence of nutrients in Pratylenchus zeae population
density and maize growth parameters 8 weeks after

 

 

 

 

 

 

 

 

 

 

 

 

planting.
No. of E. zeae in 100 cm3 ‘ Weight
Parameters
100 cm3 soil 10.0 grams Roots Shoot
Nutrients
RI RII RIII R1 R11 RIII RI RII RIII R1 R11 RIII
Untreated 1 1o 2 17 15 27 34.5 15.9 78.9 27.5 13.0 44.0
CompoundD 4 4 1, 55 28 42 70.3 70.3 81.4 115.0 187.0 180.0
Ammonium nitrate 15 34 45 50 14 23 27.4 20.3 17.3 11.5 21.5 57.5
Manure 1 5 37 21 13 30 50.5 95.4 34.2 53.5 85.5 147.5
CompoundD+Amm. 1 5 10 12 10 32 53.5 41.7 31.1 115015401253
nitrate
CompoundD+ 2 3 4 4 5 24 81.2 49.7 52.2 94.0 215.0 291.0
Manure
Amm.nitrate+ 1 5 5 17 22 5 49.9 97.5 140.5 105.0 71.0 152.0
Manure
Amm.nitrate+ 11 1 3 31 19 13 114.5 103.4 120.7 190.0 337.0 308.0
Compound D+
Manuare

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

216

Appendix 5.6.2.Influence of nutrients on Pratylenchus zeae population
density and maize growth parameters 16 weeks after

 

 

 

 

 

 

 

 

 

 

 

planting.
No. of E. zeae in 100 cm3 Weight
Parameters
100cm3soil 10.0grams Roots Shoot
Nutrients
RI RII Rlll RI RII RIII RI Rll Rlll RI RII RIII
Untreated 45 8 7 155 80 115 50.4 75.9 50.4 53.5 115.5 127.5
CompoundD 211 15 24 92 51 107 175.7 158.3 205.5 202.0 308.0 390.8
Ammonium nitrate 23 3 49 50 88 117 54.1 99.5 25.7 350.0 227.3 52.7
Manure 311 28 25 108 92 253 124.4 75.1 98.1 153.5 152.0 172.8
CompoundD+Amm. 11 12 13 33 148 31 158.7 233.5 250.5 410.0 445.0 455.2
nitrate
CompoundD+ 34 29 12 115 100 135 117.5 209.9 152.4 325.0 400.5 325.5
Manure
Amm.nitrate+ 11 7 5 192 255 91 57.9 73.3 150.5 195.5 300.2 390.5
Manure
Amm. nitrate + 211 5 17 125 48 51 187.3 225.4 187.7 529.2 502.0 444.2
Compound 01-
Manuare

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

217

Appendix 5.6.3.|nfluence of nutrients on Pratylenchus zeae population
density and maize growth parameters 8 weeks after

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

planting.
No. of g. zeae in Weight (grams)
Parameters
100 cm3 soil 10.0 grams Root Shoot
Nutrients ‘
Trans‘ Detrans Trans‘ Detrans Trans‘ Detrans Trans‘ Detrans
Untreated 1.862 3.46 4.44 19.71 6.25 39.07 5.16 26.60
Compound D 1.33 1.78 6.61 43.71 8.56 73.40 12.61 158.89
Ammonium 5.51 30.39 6.06 36.78 4.63 21.46 5.20 27.07
Nitrate
Manure 2.77 7.69 4.55 20.75 7.78 60.50 9.57 91.56
Compound D 2.20 4.86 4.09 16.76 6.42 41.20 11.45 131.60
+ Amm.
nitrate
Compound D 1.72 2.96 3.12 9.73 7.98 63.68 16.29 265.36
+ Manure
Amm. nitrate 1.63 2.66 3.68 13.54 9.60 86.40 10.33 106.71
+ Manure
Amm. nitrate 1.85 3.42 4.51 20.34 10.62 112.78 16.56 274.23
1» Compound
D + Manure
L.S.D. 0.05 ' 1.299 1.515 1.815 2.081
L.S.D. 0.01 1.804 2.242 2.518 2.888
S.E. 0.743 0.922 1.036 1.188
C.V.% 74.10 39.50 21.30 16.70
Key

‘Square root transformation [y = sq. rt. (x)] .
2Mean of 3 replications.

 

 

Appendix 5.6.4.lnfluence of nutrients on Pratylenchus zeae population
density and maize growth parameters 16 weeks after

218

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

planting.
P. zeae in Weight (grams)
Parameters
100 cm3 soil 10.0 grams Root Shoot
Nutrients
Trans‘ Detrans Trans‘ Detrans Trans‘ Detrans Trans‘ Detrans
Untreated 4.06 16.49 10.70 1 14.61 7.66 58.61 10.00 100.00
Compound D 4.66 21.77 9.03 81.46 13.35 178.35 17.18 195.05
Ammonium 4.51 20.33 9.31 86.75 7.50 56.23 13.68 187.18
Nitrate .
Manure 5.49 30.08 11.96 143.12 9.93 98.51 12.75 162.66
Compound D 3.46 11.99 7.83 61.24 14.56 212.27 20.99 440.42
+ Amm.
nitrate
Compound D 4.89 23.31 10.80 116.64 12.69 161.04 18.69 349.32
+ Manure
Amm. nitrate 3.68 13.54 8.65 74.82 14.14 199.94 22.16 491.07
+ Compound
D + Manure
L.S.D. 0.05 1.276 2.966 2.003 2.495
L.S.D. 0.01 1.771 4.117 2.781 3.462
S.E. 0.728 1.694 1.143 1.424
C.V.% 34.0 28.4 17.2 14.0
Key

‘Square root transformation [y : sq. rt. (x)].
2Mean of 3 replications.

219

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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220

Appendix 5.7.2. Influence of several granular nematicides on Pratylench us
zeae assocuated wnth maize an Zvnmba communal area.

 

 

 

 

 

 

 

 

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6. LITERATURE CITED

Acosta, N. and RB. Malek. 1979. Influence of temperature on population
development of eight species of Pratylenchus on soybean. J. Nematol.
11:229-232.

Africa South of the Sahara, 1982-83. Zimbabwe. pp 1211-1242. Europa
Publications Limited. Twelfth Edition.

Alam, M.M., M. Ahmad and AM. Khan. 1980. Effect of organic amendments
on the growth and chemical composition of tomato, eggplant and chilli
and their susceptibility to attack by Meloidogyne incognita.

Alberda, T. 1969. The effect of low temperature on dry matter production,
chlorophyll concentration and photosynthesis of maize plants of
different ages. Acta Botanica Neerlandica. 18:39-49.

Aldrich, S.R., Scott, W.D. and Lang, ER. 1975. Modern Corn Production.
Second Edition. Illinois, U.S.A. A. and L. Publications.

Anon, 1969. Report of the Secretary for Agriculture, Rhodesia, for the period
1st Oct. 1968 to the 30th Sept. 1969, p. 30.

Anon, 1973. Tobacco Research Board of Rhodesia. Abridged Annual Report
1973,p.15.

Arnon, I. 1974. Mineral Nutrition of Maize. Bern-Worblaufen, Switzerland:
International Potash Institute.

Ayoub, SM. 1980. Plant Nematology. An agricultural training aid. Nema.
Aid Publication.

Ayoub, SM. 1961. Pratylepchus zeae found on corn, milo and three
suspected new hosts in California. Plant Dis. Rep. 45:940.

Badra, T. and MI. Mohamed. 1979. Influence of combinations of organic
amendments and nematicides on tomato infected with Rotylenchus
reniformis and associated populations of predaceous saprophytTc
arthropods and microphagus nematodes. Indian J. Nematol. 9: 101-1 11.

 

Barker, KR 1985. Sampling nematode communities. (In) An Advanced
Treatise on Meloi o ne. Volume II Methodology. Chap. 1. K.R. Barker,
C.C. Carter, and J.N. Sasser (eds). A Cooperative Publication of the
Department of Plant Pathology and the United States Agency for
International Development. North Carolina State Univ. Graphics.

225

226

Barker, K.R., G.W. Bird, R.A. Champman, D.W. Dickerson, R.A. Dunn, W.F.
Mai, M. Oostenbrink, and LI. Thomason. 1978. Determining nematode
population responses to control agents. (In) Methods for Evaluation of
Fungicide, Nematicides and Bactericides. R.E. Baldwin, I.F. Brown, R.C.
Cetas, and O.L. Coyier (eds). The American Phytopathological Society.
pp. 114-125.

Barker, K.R. and CL. Campbell. 1981. Sampling nematode populations. pp.
451-473. (In) Plant-parasitic nematodes. Volume III. B.M. Zuckerman and
RA. Rohde. Academic Press, New York.

Beauchamp, E.G. and DJ. Lathwell. 1967. Root zone temperature effects on
the early development of maize. Plant and Soil 26:224-234.

Begg, .I.E. and NC. Turner. 1976. Crop water deficits. Advances in Agronomy
28:161-217.

Berger, J. 1962. Maize production and the manuring of maize. Centre
Detude d_e Lagote 5 Geneva.

Bergeson, GB. 1978. Control of lesion nematode (Pratylenchus spp.) in corn
with carbofuran. Plant Dis. Rep. 62:295-297.

Bernard, EC. and CW. Laughlin. 1976. Relative susceptibility to selected
cultivars of potato to Pratylenchus penetrans. J. Nematol. 8: 239-242.

Bird, G.W. 1981. Integrated nematode management for plant protection.
(In) Plant Parasitic Nematodes. Volumelll. pp. 355-375. B.E. Zuckerman
and RA. Rhode (eds.). Academic Press.

Bird, G.W. 1978. The nematodes that attack corn and how they do their
damage. pp. 13-25. (In) Midwest Corn Nematode Conference
Proceedings. Springfield, Illinois.

Bird, G.W. and A.P. Elliot. 1980. Nematode Detection. Michigan State
University Cooperative Extension Bulletin E-BOO. East Lansing,
Michigan.

Bird, G.W. and LI. Thomason. 1980. Integrated pest management: The role
of nematology. BioScience. 30:670-674.

Boyd, F.T. and D.W. Dickson. 1971. Plant-parasitic nematodes: occurrence in
Florida, sensitivity to temperatures, and effect on tropical forage yields.
Soil Crop Sci. Soc. Fla. Proc. 31 :267-268.

Boyer, 1.5. and H.G. McPherson. 1975. Physiology of water deficits in cereal
crops. Advances in Agronomy 27:1-23.

Bunting, as. 1978. Maize in Europe. Chap. 1. (In) Forage Maize: Production
and Utilization. E.S. Buntin , B.F. Pain, R.H. Phipps, J.M. Wilkson, and
R.E.Gunn (eds.).Agricultura Research Council,London.

Burns, NC 1971. Soil pH effects on nematode populations associated with
soybeans. J. Nematol. 3:238-245.

L: 2‘.‘l_h"\ ..‘d .
.Iu I

227

Carr, M.K.V. and MN. Hough. 1978. The influence of climate on maize
production in North-Western Europe. Chap. 2. (In) Forage Maize:
Production and Utilization. E.S. Bunting, B.F. Pain, R.H. Phipps, J.M.
Wilkson, and R.E. Gunn (eds.). Agricultural Research Council, London.

Caswell, E.P., A.E. MacGuidwin, K. Milne, C.E. Nelson, IJ. Thomason and G.W.
Bird 1986. A simulation model of Heterodera schachtii infecting Beta
vulgaris. J. Nematol. 18: 512-519.

Chevres-Roman, R., H.D. Gross and J.N. Sasser. 1971. The influence of selected
nematode species and number of consecutive plantin s of corn and
sor hum on fora e production, chemical composition 0 plant and soil,
an water usee iciency. Nematropica1:40-41(Abstr).

Claasen, MM. and RH Shaw. 1970a. Water deficit effects on com. I.
Vegetative components. Agronomy Journal 62:649-652.

Claasen, MM. and RH. Shaw. 1970b. Water deficit effects on corn. ll. Grain
components. AgronomyJournal 62:652-655.

Cooke, G.W. 1975. Fertilizing for maximum yields. London, UK: Crosby
Lockwood Staples. .

Corbett, D.C.M. 1969. Pratylenchus in uicaudatus n. sp. (Pratylenchinae:
Nematoda) with a key to the genus Pratylenchus. Nematologica 15:550-
556.

Downey, LA. 1971. Effect of gypsum and drought stress on maize (Zea mays
L.). Growth, light absorption and yield. Agronomy Journal 63:569-572.

Duncan, L.W. and R. McSorley. 1987. Modeling nematode populations. pp.
377-390. (In) Vistas on Nematolo y: A Commemoration of the Twenty-
fifth Anniversary of the Society 0 Nematologists. J.A. Veech and SD.W.
Dickerson (eds.). Society of Nematologists, lns., DeLeon Springs, Florida.

Duncan, W.G. 1975. Maize. (In) Crop Physiolo y pp. 23-49. Some Case
Histories. L.T. Evans (ed.). London: Cambri ge University Press.

Duncan, W.G. and AL. Hatfield. 1964. A method for measuring the daily
growth of corn kernels. Crop Sci. 4:550-551.

Dyke, P.T., D.B. Farmer, D.C. Godwin, S.H. Parker, J.T. Ritchie, and DA. Spanel.
CERES-MAIZE: A simulation model of maize growth and development.
C.A. Jones and J .R. Kiniry (eds.) Texas A&M University Press.

Egunjobi, O.A.1974. Nematodes and maize growth in Nigeria. I. Population
dynamics of Pratylenchus brachyurus in and about the roots of maize
ang its effects on maize production at lbadan. Nematologica 20:181-
18 .

Egunjobi, DA 1968. An ecological study of some soil nematodes associated
with apple trees in a New Zealand grassed orchard. New Zealand J.
Agric. Res. 11:386-406.

228

Egunjobi, DA. and El. Bolaji. 1979. Dry season survival of Pratylenchus spp.
in maize fields in western Nigeria. Nematol. Medtt. 72129-135.

 

Egunjobi, 0A. and M.A. Larinde. 1975. Nematode and maize growth in
Nigeria. Il. Effects of some amendments in populations of Pratylenchus
brachyurus and the growth and production of maize (Zea mays)?
Nigeria. Nematologica Mediterranea 3: 65-73.

Endo, B.Y. 1967. Comparative population increase of Pratylenchus
brachyurus and E. zeae in corn and soybean varieties Lee and Peking.
Phytopatho.57:118-120.

 

Endo, B.Y. 1959. Responses of the root-lesion nematodes, Pratylenchus
brachmrus and E. zeae, to various plants and soil types. PhtyopathoT.
49:417-421.

 

Ferris, H. 1981. Mathematical approaches to the assessment of crop damage.
(In) Plant Parasitic Nematodes. Volume III. pp. 405-420. B.E. Zuckerman
and RA. Rhode (eds.). Academic Press.

Ferris, H. 1978. Nematode economic thresholds: derivation, requirements
and theoretical considerations. J. Nematol. 10:341-349.

Ferris, H. 1976. Development of a computer-simulation model for plant-
nematode system. J. Nematol. 8: 255-263.

Fortuner, R. 1976. C.I.H. Descriptions of Plant-Parasitic Nematodes.
Pratylenchus zeae. Set 6, No. 77. Commonwealth Agricultural Bureaux.

Furstenberg, J.P. 1974. The effect of cultivation on soil nematodes especially
Rotylenchglus garvus. Simposio Internacional (XII) de Nematologi'cal
Sciendad Europea de Nematologos, 1-7 Sept. Granada, Spain.

Galiant, WC 1978. The origin of corn. Chap. 1. (In) Corn and Corn
Improvements. G.F. Sprague (ed.). Second Edition.

Gommers, F.J. 1981. Biochemical interactions between nematodes and plants
and their relevance to control. Helminthol. Abstr. 850:24.

Good, J.M. and LR. Stansell. 1965. Effect of irri ation, soil fumigation and
date of harvest on Pratylenchus brachyurus Godfrey) infection of pegs,
peg rot and yield of peanuts. Nematologica 11: 38-39 (abstr.).

Gotch, A. and Y. Ohshima. 1963. Pratylenchus spp. and their geographical
distribution in Japan. Helminthol. Abstr. 36:241.

Graham, T.W. 1965. Tobacco varieties used to show differential response to
roo lesion and root knot nematodes. Plant Dis. Reptr. 49: 822-826.

Graham, T.W. 1951. Nematode root rot of tobacco and other plants. Bull.
South Carol. Agric. Exp. Stn. No. 390.

229

Graham, T.W. and HE. Heggestad. 1959. Growth response and root decay
development in certain tobacco varieties and breeding lines infected
with root-lesion nematodes. Tobacco 149:21-28.

Grandison, G.S. 1973. Soil moisture and nematode parasitism of plants. New
Zealand Department of Scientific and Industrial Research. Information
Services 96:115-1 19. .

Guinez, SA. 1980. Comparative efficacy of organic amendments and 4
nematicides for the control of nematodes on tomato. Agriculture
Tecnia. 40:143-146.

Haider, M.G., R.P. Nath and SS. Prasad. 1978. Studies on the lance nematode
Ho lolaimus indicus. I. Pathogenicity and Histopathogenesis on maize.
In ian J. Nematol. 8:9-12.

Hanw4asy, J..I9. 1963. Growth Stages of Com (Lea mays L.). Agronomy Journal:
7-4 2.

Harrison, AL. 1952. Plant disease notes from Texas. Plant Dis. Rep. 36:491.

Holtzmann, CV and 6.5. Santo. 1971. Effect of temperature on the inter-
relationship of Pratylenchus zeae and Pythium graminicola on
sugarcane. Phytopathol. 61 :1321 (Abstr.).

Hough, A., L]. Thomason and W.F. Farmer. 1975. Behavior of aldicarb in soil
relative to control of Heterodera schachtii. J. Nematol. 7: 215-221.

Jenkins, W.R. 1964. A rapid centrifuge-flotation technique for separating
nematodes from soil. Plant Dis. Reptr. 48:692.

Johnson, A.W. and G.W. Burton. 1973. Comparison of millet and sor hum-
sudangrass hybrids grown in untreated soil and soil treated wit two
nematicides. J. Nematol. 5:54-59.

Johnson, A.W. and RB. Chalfant. 1973. Influence of or anic pesticides on
nematode and corn eanivorm damage and on yiel of sweet corn. J.
Nematol. 7: 158-168.

Johnson, A.W. and C.J. Nusbaum. 1970. Interactions between Meloidogyne

inco nita, M. hapla and Pratylenchus brachyurus in tobacco. J.
Nematol. 2:334-340.

Jones, F.G.W., R.A. Kemptom and J.N. Perry. 1978. Computer simulation and
population models for cyst-nematodes (Heteroderidae: Nematoda).
Nematropica 8:36-56.

Jones, F.G.W., D.M. Parrott and J.G.S. Ross. 1967. The population genetics of
the potato cyst-nematode, Heterodera rostochiensis: Mathematical
models to simulate the effects or growing eelworm-resistant potatoes
b;ed from Solanum tuberosum spp. andigena. Ann. Appl. Biol. 60: 151-
1 1.

_A
A

-‘-“‘l

230

Kabel, P.F. and W.F. Mai. 1968. Influence of soil moisture on Pratylenchus
penetrans. Nematologica 14:101-122.

Kaul, R.K. and CL. Sethi. 1982a. Interaction am‘ongst Heterodera zeae,
Meloido ne inco nita and Menchorhynchus Vlilal’ls on Z_ea mays.
In an J. Nemato . 12: 1-98.

Kaul, R.K. and CL. Sethi. 1982b. Effect of simultaneous inoculations and prior
establishments of Heterodera zeae, Meloidogyne incognita and
Tylenchorhynchus vquaris on penetration oTcyst and root-knot
nematodes into maize roots. Indian J. Nematol. 12:79-85.

Keetch, DP. 1972. Some host plants of the burrowing eelworm, Radopholus
similis (Cobb) in Natal. Phytophylactica 4:51-58.

Khan, S.A. 1963. Occurrence and pathogenicity of Pratylenchus zeae on
sugarcanein Louisiana. Proc. Int. Soc. Sugarcane Technol. 11:711-717.

 

Khan, S.A. 1959. Pathogenic effects of Pratylenchus zeae on sugarcane.
Phytopathol. 49:543 (Abstr.).

Kimpinski, J. H.R. Wallace and RB. Cunningham. 1976. Influence of some
environmental factors on populations of Pratylenchus minyus on wheat.
J. Nematol. 8: 310-313.

Kiniry, J.R., J.T. Ritchie, R.L. Musser, E.P. Flint, and W.C. Iwig. 1983a. The
photoperiod sensitive interval in maize. Agronomy Journal 75:687-690.

Kiniry, J.R., J.T. Ritchie, R.L. Musser, E.P. Flint, and W.C. Iwig. 1983b. Dynamic
nature of the photoperiod response in maize. Agronomy Journal
75:700-703.

Koen, H. 1967. Notes on the host range, ecology and population dynamics of
Pratylenchus brachyurus. Nematologica 13:1 18-124.

Kort, J. 1972. Nematode diseases of cereals of temperate climates. (In)
Economic Nematology, pp. 97-143. J.M.Webster(ed.). Academic Press,
New York and London.

Krusberg, LR. 1960. Hydrolytic and respiratory enzymes of species of
Ditylenchus and Pratylenchus. Phytopathol. 50:9-21.

Lal, A., B.S. Yadav and RP. Nandwana. 1977. Effect of chopped leaves of
various plants and sewage on the plant growth and reniform
nematode, Rotylenchulus reniformis. Indian J. Mycology and Plant
Pathol. 7:68-69.

Lehman, P.S. 1978. The influence of low moisture on plant-parasitic
nematodes. Nematology Circular, Division of Plant Industry, Florida
Department of Agriculture and Consumer Services. No. 46:2.

Lidsey, D.W. 1969. Suitability of soybean host for the root lesion nematode
Pratylenchus brachyurus. J. Ala. Acad. Sci. 40: 139 (Abstr.).

is: ....- -.e_...'..:.i.'-t:-L.n o - . s
. 44 ' I .

231

Loof, P.A.A. 1978. The Genus Pratylenchus Filipjev 1936 (Nematoda:
Pratylenchidae): A Review of its anatomy, morphology, distribution,
systematics and identification. Vaxtskyddsrapporter. Jordbruk 5.
Land bouwhogeschool, Wageningen, The Netherlands.

 

 

Louw, I.W. 1982. Nematode pests of maize. (In) Nematology in Southern
Africa. pp. 69-72. D.P. Keetch and J. Heyns(eds.). Science Bull. No. 400.
Department of Agriculture and Fisheries. Republic of S. Africa.

Mai, W.F. 1971. Controlling nematodes. (In) Plant-Parasitic Nematodes.
Volume I pp.4-6. B.M. Zuckerman, W.F. Mai and RA. Rhode (eds.).
Academic Press.

Mamiya, Y. 1971. Effect of temperature on the life cycle of Pratylenchus
penetrans on Cryptomeria seedlings and observations on its
reproduction. Nematologica, 17: 82-92.

 

Manetsch, T.J. 1976. Time-varying distributed delays and their use in
aggregate models of large systems. IEEE Trans. on systems, man, and
cybernetics, Vol. SMC-6, No. 8.

Mankau, R. 1980. Biolo ical control of nematode pests by natural enemies.
Ann. Rev. Phytopat ol. 18:415-440.

Mankau, R. and S. Das. 1974. Effect of organic material on nematode biomass
in citrus and root-knot nematode infested soil. Indian J. Nematol.
4:138-151.

Martin, G.C. 1955. Plant and soil nematodes of the Federation of Rhodesia
and Ny‘asaland: Preliminary investigations. Nematodes catalogued
under osts or associated plants. Rhod.Agric.Journal 52:346-361.

Martin, G.C., J.l. Way and AM. Armstrong. 1975. Soil fumigation and the
control of Pratylenchus spp. and other plant-parasitic nematodes
affecting maize production in Rhodesia. Presented at the Second
Symposium of the Nematological Society of Southern Africa,
Stellenbosch.

Martin, G.C., G.L. James, J.L. Bisset, and H. Way. 1969. Trials with field crops
and Radopholus similis with observations on Pratylenchus spp.,
Meloidogyne spp. and other plant-parasitic nematodes. Rhod. J. Agric.
Res. 7: 149-157.

 

Masuda, Y. 1976. The effects of nematodes on the physiology of vegetable
crops. V. Influence of farm yard manure application on root-knot
nematode injury in some vegetable crops. Journal of the Japanese
Society for Horticultural Science 45:24-32.

McSorley, R. 1978. Components for a management program for nematodes
on corn. Dissertation Abstracts International 39822121-2124.

232

McSorley, R. and J.M. Ferris. 1979. PHEX: a simulator of lesion nematodes in
corn roots. Research Bull. 959. Purdue University Agricultural
Experiment Station, West Lafayette, Indiana 47907.

Mian, I.H. and R. Rodriguez-Kabana. 19823. Survey of the nematicidal
properties of some organic materials available in Alabama as
amendments to soil for control of MeloidogLne arenaria. Nematropica
12:235-246.

Mian, I.H. and R. Rodriguez-Kabana. 1982b. Organic amendments with high
tannin and phenolic contents for control of Meloidogyne arenaria in
infested soil. Nematropica 12:221-234.

 

Mian, I.H. and R. Rodriguez-Kabana, 1982c. Soil amendments with oil cakes
and chicken litter for control of Meloidgqyne arenaria. Nematropica
12:205-220.

Miller, PM. 1978. Toxicity of homogenized leaves of woody and herbaceous
plants to root-lesion nematodes in water and in soil. J. Am. Soc. Hortic.
Sci. 103:78-81.

Miller, PM. 1977. Organic additives, mulches and nematicides increase crop
yields and decrease populations of Tylenchorhynchus dubis. Division
Meetings, 1977. Abstract No. NE-62. Proceedings oFthe American
Phytopathol. 4: 194.

Miton, N.A., R.D. Hammons and S.A. Parhan. 1970. Infection of shell and pe
gasues of six peanut cultivars by Pratylenchus brachyurus. Phtyopahto .
: 472-474.

Morgan, GT. and AA. MacLean. 1968. Influence of soil pH on an introduced
population of Pratylenchus penetrans. Nematologica 14:311-312.

Morgan, K.T. and AC Tarjan. 1980. Management of sting nematode on
centripedegrass with kelp extracts. Proceedings of the Florida State
Horticultural Society. 93:97-99. Florida Univ. IFAS, Gainsville, Florida
32611.

Moss, GI. and Downey, LA. 1971. Influence of drought stress on female
gametophyte development in corn (_Z_ea mays L.) and subsequent grain
yield. Crop Science 11:368-372.

Moussa, F.F., H.A. Osman and ME. Billiah. 1977. Control of Meloido ne
incognita on tomatoes with marigold and asparagus plants. Bulletin,
Nationa Research Center, Cairo, Egypt 2:359-364.

Muchena, PK and G.W. Bird. 1987. Role of fenamiphos as a nemastat for
control of Heterodera schachtii in cabbage production. Pl. Dis. 71: 552-
554.

Muchena, P.K., B. Dube and O. Machiridza. 1987. Pratylenchus zeae: .A
limitin factor in communal area maize produciton. Zimbabwe Agric.
Journa (In press).

.2 f
“i-

 

 

 

4......i IF

233

Mughogho, L.K. and Choo, EB. 1969. List of plant parasitic nematodes in
' Malawi. Minist. Agric. Tech. Bull. No. 1. Zomba, Malawi. 15 pp.

Mugwira, L.M. 1984. Relative effectiveness of fertilizer and communal area
manures as plant nutrient sources. Zimbabwe Agric. J. 81: 85-90.

Muller, R. and PS. Hooch. 1982. Organic amendments in nematode control.
An examination of the literature. Nematropica 12:319-326.

Mzira, C.N. 1984. Assessment of effects of maize streak virus on yield of
maize. Zimbabwe J. Agric. Res. 22:141-149.

Nath, R.P., G. Swarup and AB. Prasad. 1976. Studies on the morphology and
cytology of Pratylenchus zeae with a report on the occurrence of its
male. Indian J. Nematol. 6:123-125.

Norton, DC. 1984. Nematode Parasites of Com. (In) Plant and Insect
Nematodes. pp. 61-94. W.R. Nickle (ed.). Dekkerlnc. New York.

Norton, DC 1979. Relationships of the physical and chemical factors to
populations of plant-parasitic nematodes. Ann. Rev. Phytopathol.
17:279-299.

Norton, DC. 1978. Corn nematodes populations and biogeography. (In)
Midwest Corn Nematode Conference Proceedings. pp. 27-28.
Springfield, Illinois.

Norton, D.C., J. Tollefson, P. Hinz, and SH. Thomas. 1978. Corn yield increase
relative to nonfumigant chemical control of nematodes. J. Nematol.
10:160-166.

Norton, DC and P. Hinz. 1976. Relationship of Ho lolaimus galeatus and
Pratylenchus hexincisus in reduction of corn yielfisfii sandy soils in Iowa.
Plant Dis. Rep. 60:197-200.

O'Bannon, J.H., J.D. Radewald and A.T. Tomerlin. 1972. Population
fluctuation of three plant-parasitic nematodes in Florida citrus. J.
Nematol. 4: 194-199.

Olowe, T. 1977. Histological changes in maize root induced by Pratylenchus
brachyurus and E. zeae in the absence of other microorganisms.
Nigerian J. Plant Protection 3:41-51.

Olowe, T. and D.C.M. Corbett. 1976. Aspects of the biology of Pratylenchus
brachyurus and E. zeae. Nematologica 22:202-211.

Oteifa, BA. 1962. Species of root-lesion nematodes commonly associated
with economic crops in the. Delta of the UAR. Plant Dis. Rep. 46:572-
575.

Oteifa, BA. and A. Taha. 1964. Screening of maize varieties to root-lesion
infection. Tech. Bull. Bahtim. Exp. Stn, Egypt. Agric. Organ. No. 74, 26

PP-

. AIM—lb". ~
. ' "

Iii-

234

Page, S.L.J., C.M. Mguni and 5.2. Sithole. 1985. Pests and diseases of crops in
communal areas of Zimbabwe. Overseas Development Administration
Technical Report. p.203.

Petty. H.B. and J.W. Apple. 1967. Insects. Chap. 14. (In) Advances in Corn
Production: Principles and Practices. WJ. Pierre, S.R. Aldrich and WP.
Martin (eds.). Iowa State Univ. Press, Ames, Iowa.

Pinochet, J. and PR. Rowe. 1978. Reaction of two banana cultivars to three
different nematodes. Plant Dis. Reptr. 62: 727-729.

Radewald, J.D., J.H. O’Bannon and A.T. Tomerlin. 1971. Temperature effects
on reproduction and pathogenicity of Pratylenchus coffeae and E.
brachyurus and survival of E. coffeae in roots of Citrus jambhiri. J.
Nematol. 3: 390-394. .

Ratliff, L.F., J.T. Ritchie and D.K. Cassel. 1983. Field measured limits of soil
water availability as related to laboratory-measured properties. Soil
Science Society of America Journal 47:770-775.

Reinhardt, H. 1971. Influence of soil and climate on yield reliability and yield
level in maize. Bayerishches Landwirtschaftliches Jahrbuch 48:306-327.

Resck. D.V.S., R.D. Sharma and J. Pereira. 1982. Effects of fifteen species of
green manure on water-holding capacity and nematode control in a
dark-red Iatsol under "cerrado vegetation. Pesguia Agropecuaria
Brasileria 17:459-467.

Ritchie,J.T.1981. Soilwa'ter availability. Plant and Soil 58:327-338.

Ruelo, J.S. 1983. Integrated control of Meloidggyne inco nita on tomato
using orgaenic amendments, marigolds and a nematici e. Plant Disease
67:671-67 .

Santo, 6.5. and O.V. Holtzmann. 1970. Inter-relationships of Pratylenchus
zeae and Pythium graminicola on sugarcane. Phytopatho . 60:1537
(Abstr.).

 

 

Seinhorst, I.W. 1981. Methods for generating different pest/yield
relationships (Nematodes). (In) Crop Loss Assessment Methods-
Supplement 3. pp. 85-89. L. Chiarappa (ed.). Commonwealth
agricultural Bureaux. Food and Agriculture Organization of the United

ations.

Seinhorst, I.W. 1967. The relationships between population increase and
population density in plant-parasitic nematodes. Ill. Definition of the
terms host status and resistance. IV. The influence of external
conditgionszon the regulation of population density. Nematologica
13:42 -44 .

Sethi, RH. and G. Swarup. 1971. Plant-parasitic nematodes of Northwest
India. III. The genus Pratylenchus. Indian Phytopathol. 24:10-12.

235

Shaw, RH. and W.C. Burrows. 1967. Water supply, water use and water
requirements. Chap. 5. (In) Advances in Corn Production: Principles and
Practices. W.H. Pierre, S.R. Aldrich and WP. Martin (eds.). Iowa State
Univ. Press, Ames, Iowa.

Schmitt, D.P. 1976. Relative suitability of soybean cultivars to Pratylenchus
brachyurus. J. Nematol. 8: 302 (Abstr.)

 

Shumba, EM. 1984. A new look at small cereals as persistent droughts hit the
communal sector. Agronomy Institute, Department of Research and
Specialist Services, Causeway, Zimbabwe.

Siddiqi, I.A., S.A Sher and AM. French. 1973. Distribution of plant-parasitic
nematodes in California. Calif. Div. Plant Ind., Dep. Food Agric.,
Sacramento.

Singh, ND. 1974. Nematode pests of sugarcane new to Trinidad. Plant Dis.
Rep. 58:122.

Sitaramaih, K. 1978. Control of root-knot nematodes with organic soil
amendments. Indian Farmers Digest 11:19-22.

Siyanand, A., R. Sehadri and D.P. Dasgupta. 1982. Investi ations on the life
cycles of Tylenchorhynchus vul aris, Pratylenc us thornei and
Ho lolaimus indicus individually an in combined infestations in maize.
In ian J. Nematol. 12:272-276.

 

Smith, O.D., T.E. Boswell and W.H. Thames. 1978. Lesion nematode
resistance. Crop Sci. 18: 1008-1011.

Smolik, JD. 1982. Effect of soil moisture or soil temperature on reproduction
of indigenous nematode populations in a mixed prairie. Prairie
Naturalist 14:61-67.

Smolik, JD. 1979. Effects of tillage practices on nematode po ulations
associated with corn and spring wheat. Proceedings of t e North
Dakota Academy of Science. pp.33.

Smolik, JD. 1978. Influence of previous insecticidal use on the ability to
control nematode populations in corn and the effect on corn yields.
Plant Dis. Rep. 62:95-99.

Southards, CL. 1971. Effect of fall tillage and selected hosts on the
population density of Meloidogyne incognita and Pratylenchus zeae.
Plant Dis. Rep. 55:41-44.

Southards, CL. and C.J. Nusbaum. 1967. Genetic variability of tobacco
response to Pratylenchus brachyurus. Phytopathol. 57: 18-21.

Southey, LP. 1985. Laboratory methods for working with plant and soil
nematodes. Tech. Bull. 2. Ministry of Agriculture, Fisheries and Food.
Her Majesty's Stationery Office, London.

...l

l .1-. ”A-
J - O A .
4 4 "" " —.- _

236

Starr, J.W., W.F. Mai and 6.5. Abawi. 1978. Effects of oxamyl on the
reproduction of Meloidgflne hapla and Heterodera schachtii. J.
Nematol. 10:378-379.

 

Steele, A.E. 1977. Effects of selected carbamate and organophosphate
nematicides on hatching and emergence of Heterodera schachtii on
sugar beet. J. Nematol. 9: 149-154. -

Stewart, J.L., R.D. Misra, W.O. Pruitt, and RM. Hagan. 1975. Irrigation corn
and grain sorghum with a deficient water supply. Transactions of the
American Society of Agricultural Engineers 18:270-280.

Tarjan, AC 1977. Conservation of municipal solid wastes to agricultural
compost beneficial for nematode infected plants. Nematropica 7:8-9.

Tarte, R. 1971. Evaluation of the damage caused by Pratylenchus zeae in corn
under greenhouse conditions. Nematropica 1:16.

Thames, W.H. 1982. The genus Pratylenchus. (In) Nematology in the
Southern Region of the United States. pp. 108-126. R.D. Riggs (ed.).
Southern Cooperative Series Bulletin 276.

Townshend, J. 1972. Influence of edaphic factors on penetration of corn
roots by Pratylenchus penetrans and E. minyus in three Ontario soils.
Nematologica 18:201-212.

Trivedi, PC, A. Bhatnagar and B. Tiagi. 1978. Effect of soil moisture and soil
types on the development of Meloidogyne .incogflita root galls on
C_apsioum annum L. Journal of Indian Botanical Society 57:16.

Ulistrup, A.J. 1967. Diseases of corn and their control. Chap. 15. (In) Advances
in Corn Production: Principles and practices. W.H. Pierre, S.R. Aldrich
and WP Martin (eds.). Iowa State Univ. Press, Ames, Iowa.

Upadhyay, R.S., A.M. Khan and SK. Saxena. 1974. Influence of soil moisture
on nematode population in the presence and absence of host plant. In
Proceedings of the 61st Indian Science Congress. Nagpur, India.

Van Bavel, C.H.M., G.B. Stirk and K.L. Brust. 1968a. Hydraulic properties of a
clay loam soil and the field measurement of water uptake by roots. I.
Interpretation of water content and pressure profiles. Soil Sci. Soc. Am.
Proc. 32:310-317.

Van Bavel, C.H.M., G.B. Stirk and K.L. Brust. 1968b. Hydraulic properties of a
clay loam soil and the measurement of water uptake by roots. II. The
water balance of the root zone. Soil Sci. Soc. Am. Proc. 32:317-321.

Van Den Berg, E. 1971. The root-lesion nematodes of South Africa (genus
Eratylencghus, family Hoplolaimidae). S. Afr. Dep. Agric. Tech. Serv.
Comm.9 .

Van der Linde, I.W. 1956. The Meloidogyne problem in South Africa.
Nematologica, 1:77-83.

 

237

Veech, J.A. 1982. Phytoalexins and their role in the resistance of plants to
nematodes. J. Nematol. 1422-19.

Viglierchio, DR. and RV Schmitt. 1983. On the methodolog of nematode
extraction from field samples: comparison of met ods for soil
extraction. J. Nematol. 15: 45-454.

Vik, F. and M. Holubcona. 1982. Influence of leaf litter earth upon nematode
population in compost with residues of onion contaminated with
Ditylenchus di saci Kuhn. Sbornik Vysoke Skoly Zemedelske Praha,
Fakulta Agronomic a Rada A 37: 171-176.

 

 

Walker, J.T. 1969. Pratylenchus penetrans (Cobb) populations as influenced
by microorganisms and soil amendments. J. Nematol. 1: 260-264.

Walters, MC. 1979. The possible status of parasitic nematodes as limiting
factors in maize production in South Africa. (In) Proceedings of the 2nd
South African maize breeding symposium 1976. Tech. Commun. Dep.
Agric. Tech. Serv. Repub. S. Afr. No. 142,112-118.

Walters, MC. 1976. Present status of knowledge of nematode damage and
control in South Africa. Proceedings of the 3rd South African maize
breeding symposium. Tech. Commun. Dep. Agric. Tech. Serv. Repub. S.
Afr. No. 152,62-66.

Ware, G.W. 1978. The Pesticide Book. pp. 35-40. Freeman and Co., San
Francisco.

Watts, W.R. 1974. Leaf extension in Zea mays. III. Field measurements of leaf
extension in relation to temperature and leaf water potential. Journal
of Experimental Botany 25: 1085-1096.

Willis, CB. 1972. Effects of soil pH on reproduction Pratylenchus penetrans
and forage yield of alfalfa. J. Nematol. 4:291-295.

 

Wright, 5.]. 1.981. Nematicides: Mode of action and new approaches to
chemical control. (In) Plant-Parasitic Nematodes Vol. III. pp. 426-433.
B.M. Zuckerman and RA. Rhode (eds.). Academic Press.

Zimbabwe National Household Survey Capability Pro ramme. 1985/86.
Agriculture and livestock survey in communal Ian 5. Report Number
AL3. Central Statistics Office, Box 8063, Causeway, Harare.

Zimbabwe National Household Survey Capability Programme. 1983/84.
Report on demographic soico-economic survey. Communal lands (of
Manicaland Province. Report Number 2. Central Statistics Office, Box
8063, Causeway, Harare.

Zirakparvar, ME. 1982. Susceptibility of soybean cultivars and lines to
Pratylenchus hexincisus. J. Nematol. 14: 217-220.

Zirakparvar, ME 1980. Host range of Pratylenchus hexincisus and its
pathogenicity on corn, soybean and tomato. Phytopathol. 70:749-753.

 

238

Zirakparvar, M.E., D.C. Norton and GP. Cox. 1980. Population increase of
Pratylenchus hexincisus on corn as related to soil temperature and type.
J. Nematol. 12:313-318.

Zirakparvar, ME. 1979. Population changes of Pratylenchus hexincisus as
influenced by chemicals in fibrous and coarse roots of corn. Plant Dis.
Rep. 63:55-58.