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This is to certify that the
thesis entitled

Genetic System for Reaction in Field Beans
(Phaseolus vulgaris L.) to Three Races of
Colletotrichum lindemuthianum (Sacc. and

Magn. ) Brio, et Cav.
presented by

Catherine S. Muhalet

has been accepted towards fulfillment
of the requirements for

M.S. Crop Science

degree in

%%//%M.

Major professor

mwamc

OVERDUE FINES:
25¢ per day per item
RETURNING LIBRARY MATERIALS:

Place in book return to remove
charge from circulation records

 

 

 

 

 

 

 

© 1980

CATHERINE SYLVESTER MUHALET

ALL RIGHTS RESERVED

 

GENETIC SYSTEM FOR REACTION IN FIELD BEANS

(PHASEOLUS VULGARIS L.) TO THREE RACES

 

OF COLLETOTRICHUM LINDEMUTHIANUM

 

(SACC. AND MAGN.) BRIO. g3 CAV.

BY

Catherine S. Muhalet

A THESIS

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

MASTER OF SCIENCE
Department of Crop and Soil Sciences

1979

ABSTRACT

GENETIC SYSTEM FOR REACTION IN FIELD BEANS
(PHASEOLUS VULGARIS L.) TO THREE RACES
OF COLLETOTRICHUM LINDEMUTHIANUM
(SACC. AND MAGN.) BRIO. El CAv.

 

 

BY

Catherine S. Muhalet

Genetics of resistance for reaction of beans to the

beta, gamma and delta races of Colletotrichum lindemuthianum

 

was studied in ten crosses involving six cultivars. Reac-
tions of individual plants to each race were studied in the
parental, F1 and F2 generations.

Genetic resistance to race beta is explained by
dominant alleles, except in crosses involving Tuscola with
Montcalm and Swedish Brown where susceptibility was domi-
nant. Tuscola transmits dominant genes for resistance to
beta in other genetic backgrounds. A system of multiple
alleles was proposed as governing reaction to race beta
except for the "Are" gene. The genetic pattern of segrega-
tion revealed a distinct system of single dominant genes,
duplicate and complementary factor loci conferring reaction
to race beta.

A system of single dominant genes, duplicate and

complementary factors also governs reaction to races gamma

Catherine S. Muhalet

and delta, but unlike the beta race, there was no evidence
for multiple allelism.

There was a close association in reaction to races
beta, gamma and delta in crosses involving C49242 as a common
parent. It was, therefore, assumed that the association was
between the factors conferring resistance in C49242 to each
of the three races. Hence, the "Are" gene from C49242 was

postulated to be a complex locus.

To my parents . . . .

ii

ACKNOWLEDGMENTS

I wish to express my sincere gratitude to Dr. M. W.
Adams, my major professor, for his kindness, support, gui-
dance and suggestions throughout the course of this work
and during the preparation of this manuscript.

My special thanks are expressed to Dr. A. W.
Saettler for his kindness, moral support, unlimited help in
the greenhouse, for letting me use his laboratory facilities
and for editing this manuscript.

I am also very grateful to Drs. E. Everson and
L. O. Copeland, members of my committee, for their patience,
kindness and valuable suggestions.

My special thanks are also extended to Dr. A. Ghaderi
for his moral support and for reviewing this manuscript, to
J. L. Taylor for his various assistance in the greenhouse
and to Dr. J. E. Kaufmann for taking slide pictures.

I am grateful to my brothers and sisters, my friend
A. Pringle and my other friends for their continuous
encouragement during my study.

Finally, I greatly appreciate the financial support
from the Government of the United Republic of Tanzania and

The International Institute of Tropical Agriculture.

iii

LIST

LIST

I.

II.

III.

IV.

V.

VI.

TABLE OF CONTENTS

OF TABLES . . . . . . .

OF FIGURES . . . . . .

INTRODUCTION . . . . .

LITERATURE REVIEW . .

MATERIALS AND METHODS

RESULTS . . . . . . .

DISCUSSION . . . . . .

SUMMARY AND CONCLUSION

APPENDIX . . . . . . . . . .

LITERATURE CITED . . . . .

Page

0 O O O O O O O O O O O 0 viii

. . . . . . . . . . . . . l
. . . . . . . . . . . . . 3
. . . . . . . . . . . . 16
. . . . . . . . . . 27
. . . . . . . . . . . . . 64
. . . . . . . . . . . . . 81
. . . . . . . . . . . . 86

. . . . . . 96

iv

Table

1.

LIST OF TABLES

Physiological races of Colletotrichum
lindemuthianum to date, year reported
and reactions of bean cultivars
Kaboon and C49242 . . . . . . . . . .

 

 

Bean varieties used, their seed types
and reactions to races beta, gamma
and delta of g. lindemuthianum . . . .

 

Crosses in which F populations were
tested, the race; used and method
of inoculation . . . . . . . . . . . .

Effect of spore concentration on disease
reaction of six bean cultivars to the
beta race using a symptom rating scale
of 1-5 (resistant-susceptible) . . . .

Mean reaction of six bean cultivars to
spore concentration using a 1-5
(resistant-susceptible) scale for
the beta race . . . . . . . . . . . .

Effect of spore concentration on disease
reaction of six bean cultivars to the
gamma race using a symptom rating
scale of 1-5 (resistant-susceptible)

Mean reaction of six bean cultivars to
spore concentration using a l-S
(resistant-susceptible) scale for
the gamma race . . . . . . . . . . . .

Effect of spore concentration on disease
reaction of six bean cultivars to the
delta race, using a symptom rating
scale of 1-5 (resistant-susceptible) .

Mean reaction of six bean cultivars to
spore concentration using a 1-5
(resistant-susceptible) scale for
the delta race . . . . . . . . . . . .

V

Page

10

19

21

28

29

30

31

32

33

Table

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

Page

Reaction of F1 plants to races beta,
gamma and delta . . . . . . . . . . . . . . . 41

Observed number and expected ratios of
resistant and susceptible plants to
beta race in nine F2 pOpulations . . . . . . . 44

Observed number and expected ratios of
resistant and susceptible plants to
gamma race in eight F2 pOpulations . . . . . . 46

Observed number and theoretical ratios
of F2 pOpulations segregating for
resistance and susceptibility to
the delta race . . . . . . . . . . . . . . . . 49

Observed and expected frequencies in
reaction of F2 populations of five
crosses segregating simultaneously
for reaction to the beta and gamma
races . . . . . . . . . . . . . . . . . . . . 52

Observed and expected frequencies in
reaction of F2 populations of six
crosses segregating simultaneously
for reaction to the beta and delta
races . . . . . . . . . . . . . . . . . . . . 56

Observed and expected frequencies in
reaction of F2 populations of four
crosses segregating simultaneously
for reaction to the gamma and delta
races . . . . . . . . . . . . . . . . . . . . 60

Observed number and expected ratio of
normal and lethal plants in six F2
pOpulations . . . . . . . . . . . . . . . . . 67

Proposed genotypes of six parental
bean cultivars with respect to
their reaction to the beta race
of Q. lindemuthianum . . . . . . . . . . . . . 7O

 

Proposed genotypes of six parental
bean cultivars with respect to
their reaction to the gamma race
of g. lindemuthianum . . . . . . . . . . . . . 73

 

vi

Table Page

20. Proposed genotypes of six parental
bean cultivars with respect to
their reaction to the delta race
of g. lindemuthianum . . . . . . . . . . . . . 75

A. Summary of results of inoculating
ten F2 pOpulations, their F and
parents with beta, gamma an delta
races of Colletotrichum lindemuthianum
using a 1-5 (resistant-susceptible)
scale . . . . . . . . . . . . . . . . . . . . 86

vii

LIST OF FIGURES
Figure Page

1. Trifoliolate leaf of C49242 showing
resistant reaction to the beta,
gamma and delta races of g.
lindemuthianum . . . . . . . . . . . . . . . . 36

 

2. Trifoliolate leaf of Kaboon showing
resistant reaction to the beta and
delta and susceptible reaction to
gamma races of Q. lindemuthianum . . . . . . . 36

 

3. Trifoliolate leaf of Montcalm showing
susceptible reaction to the beta and
delta and moderately susceptible
reaction to gamma races of g.
lindemuthianum . . . . . . . . . . . . . . . . 38

 

4. Trifoliolate leaf of Swedish Brown
showing susceptible reaction to
the beta, gamma and delta races of
C. lindemuthianum . . . . . . . . . . . . . . 38

 

5. Trifoliolate leaf of Tuscola showing
resistant reaction to the beta and
gamma and susceptible reaction to
delta races of Q. lindemuthianum . . . . . . . 40

 

6. Trifoliolate of 61294 showing moderately
resistant reaction to the beta, gamma
and delta races of g. lindemuthianum . . . . . 4O

 

7. Semi-lethal Fl plants from the Kaboon X
61294 cross (three weeks old) . . . . . . . . 64

8. Semi-lethal F plants from the Montcalm
X 61294 cross (three weeks old) . . . . . . . 64

9. Kaboon X C49242 F plants segregating
for normal (bacE line) and semi-
1ethals (front line) in two weeks
old pOpulation . . . . . . . . . . . . . . . . 66

viii

I . INTRODUCTION

Anthracnose of common beans (Phaseolus vulgaris L.)

 

caused by Colletotrichum lindemuthianum (Sacc. and Magn.)

 

Brio. gt Cav. is a major disease in many dry edible bean
growing areas of the world. The bean anthracnose fungus is
seed borne and economical losses caused by the disease can
be very high when badly contaminated seeds are planted under
conditions favorable for disease development. Losses are
due to poor germination of infected seeds, destruction of
seedlings and low yield of infected plants. Spotted pods
are unsaleable for table use or canning and seed value is
lowered when the fungus penetrates into the seed. Breeding
for disease resistance is believed to be one of the most
apprOpriate measures of controlling this disease. 9.

lindemuthianum exists as many different physiological races.

 

Various sources of resistance to different races are known
and several of the sources have been utilized in breeding
programs.

A race of the bean anthracnose fungus, identified
as delta, was detected in Ontario, Canada in the growing
season of 1976. This race could easily be introduced into

Michigan through importation of infected seeds. Delta

race attacks cultivars with resistance to races alpha, beta
and gamma. Bean lines, Cornell 49242 and Kaboon, are
resistant to this race. The resistance in C49242 is con—
trolled by a single dominant gene, "Are," which also con-

fers resistance to other races of Q. lindemuthianum except

 

races kappa and iota. Anthracnose resistance in most
EurOpean beans is controlled by the "Are" gene. Inheritance
of resistance due to "Are" gene has not been studied in
other genetic backgrounds. The black seeded nature of
C49242 could be undesirable in some breeding programs.

A second source of resistance to delta race, Kaboon,
was included in this study. This cultivar is a large white
seeded bean which is resistant to most other races except
gamma and iota. Kaboon has been extensively used as a dif—
ferential variety in EurOpe but little is known of the

inheritance of its resistance to races of g. lindemuthianum.

 

The objectives of this study were to investigate:
l. The inheritance of resistance to the delta race in
crosses involving C49242 and Kaboon with other
cultivars.
2. The pattern of inheritance to races beta and gamma

of Q. lindemuthianum and their linkage relation-

 

ships to that of delta race.

In the course of this study some lethals and semi—
lethals resulting from different crosses were observed.
Notes were taken on the pattern of the segregation ratios

of normal to semi-lethal plants.

II . LITERATURE REVIEW

1.0 Causal Organism, Disease Symptoms
and Host Plants

 

 

Anthracnose of common beans (Phaseolus vulgaris L.)

 

is a disease caused by the fungus Colletotrichum linde-

 

muthianum (Sacc. and Magn.) Brio. gt Cav. This disease is

 

known wherever common beans are grown (Butler and Jones,
1949). It was first discovered in Germany in 1875 and
appeared in England five years later.

The causal organism is a member of the Fungi
Imperfecti. The perfect stage of the fungus exists, but
rarely, and was originally termed Glomerella lindemuthianum
(Shear and Wood, 1913). It has recently been renamed g.

cingullata (Kimati and Gali, 1970).

 

The disease affects all plant parts above the soil
level. Characteristic symptoms consist of dark brown to
black rather sunken lesions surrounded by reddish or yellow
and slightly raised margins. The lesions become darker in
color as they enlarge. As the infected tissue becomes dry
and collapses a depression develops at the center which,
under moist condition, becomes pink and oily in appearance
due to liberation of great quantities of spores. Lesions
are very conspicuous on the pods and when pods are Opened

3

the lesions on them are often found to have penetrated
through the seed coat. On the foliage, the lesions are
mostly on the veins and midrib on the underside of the
leaves. Sometimes, a petiole is so badly affected that it
fails to support the leaf.

This disease occurs mostly in common beans but has
also been reported on other hosts, including small lima

beans (Phaseolus lunatus L.), large lima beans (P. limensis

 

Macf.), scarlet runner beans (P. coccineus Willd.), tepary

 

bean (P. acutifolius Gray var. latifolius Freeman), mung

 

 

bean (P. aureus Roxb.), cowpea (Vigna unguiculata Walp.),

 

kudzu bean (Dolichos biflorus L.) and broad bean (Vicia faba

 

 

L.) (8, 33, 43 and 45).

2.0 Environmental Conditions for Disease
Development and Fungal Growth

 

 

Moderately cool, humid or rainy weather during the
early part of growing season is essential for develOpment of
anthracnose in serious levels (Butler and Jones, 1949;
Ransey and Wiant, 1941; Rao 33 31., 1976). Infection does
not occur in the field during hot weather and the highest
temperature during which undiminished infection occurred
on etiolated seedlings was 27°C (Babe and Kuc, 1970). The
authors also found that lesions decreased in size with
increasing temperature of incubation between 28-32°C.

Lauritzen (1919) determined that a temperature of
14°C was the lowest limit for the infection to occur during

a 24 hour period of incubation. The highest temperature

was found to be 32°C at R. H. of 95% and above. Andrus and
Wade (1942) pointed out that initial excess moisture and
falling temperature were important for disease development
in the mist chamber. Burkholder (1923) noticed that very
little infection occurred at a temperature of 27°C and
excellent infection occurred at 17°C. Kruger and Hoffman
(1978) pointed out that at temperatures exceeding 21°C

and at 15°C the intensity of infection decreased using 16
hours of light but at 12 hours of light and 15°C there was
more infection than at higher temperatures.

9. lindemuthianum does not develop at temperatures

 

above 31-32°C in culture and growth of the fungus on bean
pod agar was near maximal at 18-26°C (Rahe and Kuc, 1970).
According to Leakey and Simbwa-Bunnya (1972) the Optimum
growth of the fungus in culture is at 22-25°C.

3.0 Physiological Races of Colletotrichum
lindemuthianum

 

 

Isolates of pathogens of the same species with
similar or identical morphology but differing in patho-
genicity on different varieties of the same host species

are termed physiological races. Colletotrichum lindemuthianum

 

is known to occur in numerous different physiological races.
Barrus (1911) was the first to report that different cul-
tures of the anthracnose-causing organism has different
pathogenicity on different bean cultivars. He also observed
that the races were regional in distribution. In 1918,

Barrus reported results of inoculating a large collection of

dry and snap beans with ten different cultures of g.

lindemuthianum. There appeared to be at least two distinct

 

races of the organism differing in the ability to cause the
disease which he designated as alpha and beta races.

Burkholder (1923) isolated a third race from the
Imperial white bean variety which was distinct from the
alpha and beta races. This race, which Burkholder thought
had arisen from beta by mutation, was named gamma. By
inoculating fourteen different varieties with various iso-
lates from different sources, Leach (1923) found eight
distinct races which were different from the three pre-
viously described races.

Schreiber (1932) characterized thirty-four different
anthracnose races from inoculations of fifty-seven different
bean varieties. Schreiber categorized the races into A, B
and C which_roughly correspond to the alpha, beta and gamma
races of the American system.

Muller (1926) isolated five different physiological
races distinct from alpha, beta and gamma in Holland.
Andrus and Wade (1942) reported the occurrence of race
delta in North Carolina. Waterhouse (1955) and Yerkes and
Ortiz (1956) independently described many new races which
essentially could be classed into four (alpha, beta, gamma
and delta) already existing groups at that time (Hubbeling,
1961). Blondet (1962) described a new race, epsilon, in

France. OliarigE_al. (1973) identified seven physiological

 

races of Q. lindemuthianum in Minas Gerais state in Brazil

which, except for alpha, were different from the American
races.

In the U.S.A. the differential varieties, Michelite,
Dark Red Kidney, Perry Marrow, and Emerson 847 or Emerson
51-2 were used in identifying races alpha, beta, gamma and
delta (Oliari g; 31., 1973). After the discovery of race
epsilon, a new set of differential varieties (Widusa, Dark
Red Kidney, Kaboon and Aiguilles Vert) was established in
which fifteen physiological races belonging to races alpha,
beta, gamma, delta and epsilon could be differentiated (29).

Hubbeling (1961, 1974) isolated a deviant mutant
alpha which broke the resistance to alpha, beta, gamma,
delta and epsilon; the new race was named lambda. Resis-
tance to lambda also controls resistance to races mentioned
so far. This source of resistance was found in the black
seeded bean line Cornell 49242, which Hubbeling (1957)

referred to as Phaseolus vulgaris nanus viridis, originating

 

from Venezuela. The resistance in C49242 is conditioned by
a single dominant gene, "Are" (Mastenbroek, 1960). The
"Are" gene had a good run until 1972 at which time Leakey
(1979) and Leakey and Simbwa—Bunnya (1972) reported that it
failed to confer resistance against Ugandan isolates.
According to Goth and Zaumeyer (1965) and Zaumeyer and
Meiners (1975), bean line C49242 has undesirable genetic
linkages. Fouilloux (1976) and Fouilloux and Bannerot

(1977) developed four pairs of isogenic lines, which were

identical except for "Are" gene, with no apparent unfavor—
able pleiotropic effects.

A new race was detected at Ebnet in Germany in 1973
which broke the resistance of the "Are" gene derived from
C49242. The new race was described by Hoffman 23 31. (1974,
1975) and Schnock (1975) and was named kappa because it was
a killer of previously resistant beans. Hubbeling (1976)
and Kruger g; 31. (1977) identified sources of resistance to
race kappa which included the European bean cultivars,
Kaboon, Coco a la creme, Coco rose selections, Evolutie and
B022, and Asiatic cultivars such as Benishibori and Kiuzwa.
All of these cultivars carry genes for resistance to alpha,
delta and kappa but they are susceptible to lambda.

Hubbeling (1977) reported that in an experiment with
the kappa race, several kappa resistant cultivars became
infected. Anthracnose isolates from kappa-infected seed-
lings broke down the resistance of Kaboon, coco a la creme,
coco rose, B022 and Evolutie as well as the resistance of
"Are" gene to delta. This new race was named iota. The
race does not occur under natural conditions (Hubbeling,
1977). Resistance to the iota race was found in the black,
small seeded Mexican bean PI 165 422 and small light tan
Colombian bean PI 207 262, both of which exhibit a high
degree of resistance to races iota and kappa. Fouilloux
(1976) described a new race, alpha Brazil, which broke down
the resistance from "Are" gene. Fouilloux also in 1978

described another race which was isolated by Hubbeling and

was designated lambda mutant. Table 1 gives a summary of

physiological races of g. lindemuthianum to date.

 

4.0 Genetic Basis for Resistance to Races
of Colletotrichum lindemuthianum

 

 

Burkholder (1918) first provided evidence of the
genetics of resistance of a host to a strain of pathogen.
From a cross between bean varieties, Wells' Red Kidney
(resistant to alpha and beta races) and White Marrow (sus-
ceptible to beta), Burkholder (1918) obtained a 3R:lS
ratio in F2 with race beta. McRostie (1918, 1921) obtained
similar results. In a cross between Wells' Red Kidney and
Michigan Robust (susceptible to alpha) he obtained a 3R:lS
ratio in F2 with resistance being dominant. McRostie (1921)
made crosses between Selection B, a variety resistant to
both alpha and beta races and a variety, German Wax, sus—
ceptible to both alpha and beta races respectively. He

obtained a segregation ratio of 9R:7S in the F pOpulation

2
when beans were inoculated with a mixture of spores from

the two races. In both races the resistance was governed

by a single dominant gene in each case.

Mixed inoculations, as far as genetic studies with
more than one race are concerned, can give information about
resistance to an individual race. However, mixed inocula-
tions cannot provide information about linkage relationship
between the genes conferring resistance to races being

studied. Cardenas (1960) provided a technique of inoculating

each individual leaflet with one race.

10

Table l.--Physiological races of Colletotrichum lindemuth—
ianum to date, year reported and reactions of
bean cultivars Kaboon and C49242.

 

 

 

Varieties and their Reaction

 

 

Races Year Reported
Kaboon C49242
Alpha 1918 R R
Beta 1918 R R
Gamma 1923 S R
Delta 1942 R R
Epsilon 1962 R R
Lambda 1961 & 1974 S R
Kappa 1973 & 1975 R S
Alpha Brazil 1976 ? S
Iota 1977 S S
Lambda mutant 1978 ? ?

 

'0

R = Resistant; S = Susceptible; = No information

available.

ll

Schreiber (1932) studied genetics of resistance to
races alpha, beta and gamma separately in crosses between
Anthracnose Resistant 22 (resistant to all three races) and
Conserva (susceptible). Segregation ratios obtained in F2
were 3R:lS with a single race; 9R:7S with a mixture of two
races and 27R:37S with a mixture of three races. He con-
cluded each of the three factors conferring resistance was
on separate chromosomes.

York (1950) studied inheritance to the alpha, beta

and gamma races of Q. lindemuthianum in crosses involving

 

three bean varieties. Variety Tendergreen was susceptible
to all three races, Emerson 51 was resistant to all three
races and Red Mexican was susceptible to alpha but resistant
to beta and gamma. The F2 populations in each of the
crosses was divided into three parts in order to test for
each of the races separately. In the Tendergreen X Red
Mexican cross all F2 plants were susceptible to race alpha.
Ratios of 3R:lS for race beta and 9R:7S for race gamma were
observed. F2 pOpulation from Tendergreen X Emerson 51
segregated into 3R:lS for alpha, 15:1 for beta and 63:1 for
race gamma.

Rudorf (1958) reported on resistance to alpha,

beta, gamma and delta races in Phaseolus aborigineus, a

 

presumed ancestral bean type. He hybridized P. aborigineus

 

with a fully susceptible bean variety and tested F2 against

all the races. From P. aborigineus, a single dominant gene

 

conferred resistance to race beta, and two complementary

12

dominant genes were required for resistance to alpha, gamma
and delta.

Data from investigations by Andrus and Wade (1942),
Cardenas (1960) and Cardenas 33 31. (1964), suggest that
both simple and complex genetic backgrounds condition reac-
tions to races alpha, beta and gamma. The genetic systems
include both duplicate and complementary genes (2, 9 and 10),
with some linkage between duplicate genes which condition
reaction to races beta and gamma (9 and 10).

Andrus and Wade (1942) studied inheritance of resis-
tance to races beta, gamma and delta separately in thirty
intervarietal crosses. In crosses between resistant X
resistant (R X R), all F1 and F2 progenies were resistant
except in one case where a segregation ratio of 15R:lS was
obtained in F2 against the beta race. For the same race
beta, in crosses of resistant X susceptible (R X S) and
tolerance X susceptible (T X S) resistance was dominant
except in one case where susceptibility was dominant.
Segregation ratios of 3:1, 1:3, 15:1, 13:3 and 63:1 were
obtained. Unusual segregation ratios like 11:5, 14:2 and
62:2 were also observed. These ratios were explained by
the possibility of partial dominance, gene interaction with
the environment, and contribution from lethal factors.

For races beta and gamma, Andrus and Wade (1942)

postulated that there are three series of multiple alleles

with ten alleles such that some alleles in each series

13

conferred resistance or susceptibility depending on the
genes present in the other series.

In the case of delta race, crosses of R X 8 resulted
in segregation ratio of 3:1 and 9:7 in F2 with resistance
being dominant. F1 and F2 progenies of S X S parents were
found to be susceptible.

For the overall genetic interpretation of reaction
to races beta, gamma and delta, Andrus and Wade (1942) made
a complex hypothesis. They postulated that a system of ten
genes in three allelomorphic series involving both duplicate
and complementary gene interaction at three points as a
simple Mendelian hypothesis that could explain data for
races beta and gamma. A system of three independent pairs
of genes was assumed to explain data for delta race. Also,
there was no strong indication of linkage in their results.

Cardenas (1960), Cardenas 33 31. (1964) extensively
studied genetics of reaction to races alpha, beta and gamma
races in nine bean cultivars. They observed simple segre-
gation ratios of 3:1 and 15:1 for reaction to race alpha,
which was explained on the assumption that there are two
loci, the dominant alleles of which are individually capable
of conferring resistance. They encountered much more com-
plex genetic systems conferring resistance to races beta
and gamma. For beta race, Fl progenies in three of the
R X S crosses were susceptible, where segregation ratios in
F were 1:3 for one of the crosses and 7:9 for the second

2
cross and 13:3 for the third. These results were explained

14

by assuming that two loci were involved where one locus
segregated into 3:1 and the other into 1:3 ratios. For
beta race, there were crosses in which both sets of comple—
mentary and duplicate genes were segregating simultaneously
giving ratios of R:S on complete independence in transmission
of loci involved. Bean variety Michigan Dark Red Kidney
transmits dominant genes for susceptibility only when
crossed with Michelite and Brazilian Dark Red varieties
which otherwise express dominant genes for resistance.

Cardenas (1960) and Cardenas 33 31. (1964) also
obtained similar genetic patterns for races gamma and beta.
In the case of race gamma, crosses of Algarrobo and Emerson
847 with Perry Marrow suggested the presence of a third
gene complementary to the two other genes conferring resis-
tance to gamma.

The authors offered proposed genotypes of the nine
bean varieties used in their study relative to their reac-

tions to races alpha, beta and gamma of g. lindemuthianum.

 

In addition, three different linkages were detected in
crosses which involved genes conditioning reaction to races
beta and gamma.

Cardenas (1960) and Cardenas 33 31. (1964) con-
cluded that there are five main genetic aparati in g.
vulgaris conditioning reaction to alpha, beta and gamma as
follows:

1. A duplicate-factor set of loci, with resistance
usually but not always dominant.

15

2. A complementary factor set of loci.

3. The genes belonging to the set(s) pertaining to any
one race are not linked to each other.

4. There exist strong linkages between genes of the
duplicate factor set conditioning reaction to gamma
and genes of the duplicate-factor set and comple-
mentary factor sets conditioning reactions to beta.

5. Multiple allelism at the duplicate— and complementary—
factor loci conditioning reaction to beta.

Hubbeling and Dijke (1979) reported on the genetics
of resistance to races iota, kappa and lambda. In their
study, the only source of resistance to lambda race was
"Are" gene from C49242. The sources of resistance to iota
were a single dominant gene from PI 150414 and a second
dominant gene from PI 165435. A set of single dominant
genes common to both Uberabinha and PI 165422 condition
resistance to race iota. Three duplicate pairs of genes in
cross of Uberabinha and PI 165422 controlled resistance to
race kappa. PI 150414 had two dominant complementary genes
and Kaboon had a single dominant gene conferring resistance
to race kappa.

All the studies so far have dealt with vertical
resistance. I have not encountered any report suggesting

the presence of horizontal resistance to bean anthracnose.

III. MATERIALS AND METHODS

1.0 Cultures of the Pathogen

 

Cultures of the races beta, gamma and delta of Q.

lindemuthianum were obtained from the American Type Culture

 

Collection as numbers 16989 (beta), 16990 (gamma) and 18989
(delta). Cultures were maintained on commercial bean pod
agar (BPA).

Bean pod agar plates were prepared by dissolving
22.5 gm of commercial BPA (Difco) in 1 litre of distilled
water. The suspension was steamed for about 20 minutes
until dissolved, transferred in 250 m1 lots to prescription
bottles, and autoclaved for 20 minutes at 250°F and 15 psi.
Plates containing about 25 m1 of BPA were prepared and
allowed to stand for two days after which any contaminated
plates were discarded. Occasionally, to promote sporulation
a 10 gm of navy bean seeds were steamed in 200 ml of dis-
tilled water for 30 minutes, ground in a mortar and paste,
and added to BPA.

Cultures were transferred at 7-10 day intervals to
maintain sporulation. Small discs of BPA from a culture
plate were transferred to 1.5 m1 of sterile distilled water

in small test tubes. The test tubes were vigorously shaken

16

17

to dislodge spores and the spore suspensions were uniformly
spread onto BPA plates. Plates were incubated in a dark

drawer, and cultures were ready about one week later.

2.0 Pr3paration of Inoculum

 

Plants were inoculated by either a brushing or
Spraying method; there was only a slight difference in the
method of preparing spore suspensions. Phosphate buffer,
0.01M, pH 7.2, was used for preparing Spore suspensions.
Tween 80 (Polyoxythelene Sorbitan Monooleate), a wetting
agent, was added to the buffer at 0.1% v/v. For the brush-
ing method of inoculation, about 25 m1 of buffered, sterile,
distilled water containing Tween 80 was added into a plate
culture and the spores dislodged by scraping with a sterile
microscope slide. Spore suspensions were then delivered to
the underside of the leaflets by using a No. 4 camel's hair
brush.

For the spraying method of inoculation, 25 ml of
sterile distilled water containing 0.1% v/v Tween 80 was
added to the plate culture and the spores were dislodged
with a microsc0pe slide as above. Spore suspensions were
filtered through a double layer of cheese cloth. Spore
concentrations were determined with a haemocytometer and
diluted to contain about 106 spores/m1. Spore suspensions
were atomized in such a way as to deposit a uniform and
fine pattern on the underside of the leaves with just enough

pressure not to damage the leaf tissue.

18

3.0 Standardization of §pore Concentration

 

A preliminary study was performed to determine the
optimum spore concentration necessary to yield consistent
disease readings in a split plot design with three replica-
tions in a randomized complete block. Three different
spore concentrations were used as whole units and six bean
varieties, used as parent plants, as subunits. Each race
was run in a separate experiment. The three different spore
concentrations used were high (106 spores/ml), medium (105
spores/ml) and low (104 spores/m1).

Young fully expanded trifoliates were excised from
plants, transferred into labelled test tubes and sprayed
with spore suspensions. Test tubes were filled with dilute
solution of a complete plant nutrient. Inoculated leaves
were quickly transferred to a mist chamber maintained near
100% R.H. at ambient greenhouse temperature. After 8-10

days in a chamber, leaves were assessed for disease devel-

opment.

4.0 Bean Cultivars and Crosses

 

Six bean varieties all belonging to the Phaseolus

 

vulgaris L. specie were used in this study. Seed type and
reaction of the varieties to each of the three pathogen
races are given in Table 2.

The following crosses were made in the greenhouse

in Spring and Summer of 1978:

19

Table 2.--Bean varieties used, their seed types and reac-
tions to races beta, gamma and delta of g.

 

 

 

 

lindemuthianum.
Reaction to Races
Varieties Seed Types
Beta Gamma Delta
C49242 Small black R R R
Kaboon Large white R S R
Montcalm Kidney S MS 8
Swedish Brown Medium brown S S S
Tuscola Navy R R S
61294 Navy MR MR MR

 

R = Resistant; S = Susceptible; MR = Moderately
resistant, very small lesions on the midrib, petioles and
stems; MS = Moderately susceptible, small lesions on the
midrib, veins and few large lesions on petioles and stems.

 

 

Female/Male Female/Male
Kaboon X C49242 C49242 X Kaboon
C49242 X Montcalm Montcalm X Kaboon
C49242 X Swedish Brown Swedish Brown X Kaboon
C49242 X Tuscola Tuscola X Kaboon
61294 X C49242 61294 X Kaboon

Swedish Brown X Tuscola

Montcalm X Tuscola

The six parents and F1 plants from the above crosses

were tested against each of the physiological races, beta,

20

gamma and delta. The F2 populations tested are given in

Table 3.

5.0 Inoculation of Plants

 

Parental plants were tested by using three methods:

1. Young, newly opened trifoliolates were excised and
transferred into labeled test tubes filled with
dilute solution of complete plant nutrient. The
leaves were then sprayed with spore suspensions.
Separate leaves for each variety were used for each
race. Spore concentrations of about 106 spores/ml
were used.

2. Entire plants possessing fully expanded first tri-
foliolate leaves (14-18 days after planting) were
thoroughly sprayed with spore suspension separately
for each race.

3. One individual leaflet of a newly opened tri-
foliolate each per variety was brushed with spore
suspension of a single race. Plants were inoculated
14-18 days after planting.

Four plants for each variety were used with all
three methods. Immediately after inoculation plants or
excised leaves were transferred into a mist chamber main-
tained at near 100% R.H. at ambient greenhouse temperature.
Inoculations were performed on cloudy days and early in the
morning when temperatures were low. Plants were kept in

the mist chamber for 8-10 days.

Table 3.—-Crosses in which F
races used and metfio

21

pOpulations were tested, the
d of inoculation.

 

 

Crosses Method of Races Used
Female/Male Inoculation
Kaboon X C49242 SP, BR Beta Gamma Delta
C49242 X Montcalm SP, BR Beta Gamma Delta
C49242 X Swedish Brown SP Beta Gamma Delta
Tuscola X C49242 SP, BR Beta Gamma Delta
61294 X C49242 BR Beta Gamma Delta
C49242 X Kaboon SP, BR Beta Gamma Delta
Montcalm X Kaboon BR Beta — Delta
Swedish Brown X Kaboon BR Beta - Delta
Tuscola X Kaboon SP, BR Beta - Delta
Swedish Brown X Tuscola BR Beta Gamma -
Montcalm X Tuscola BR Beta Gamma -

 

SP = Excised leaves were sprayed with spore sus—
pension from individual race.

BR = Each leaflet was brushed with spore suspension

from individual race.

- = Not tested.

22

All Fl progenies were tested together with their
parents and corresponding F2 populations. All genotypes
were tested separately by brushing individual leaflets with
spores of a single race. Inoculated plants were transferred
into mist chamber as described previously.

Each individual plant in each F2 population was
tested against each of the three races. This was accom-
plished by inoculating excised or intact leaves with a
spore suspension from a single race, by either brushing or
Spraying as previously explained. Testing each individual
plant in F2 pOpulations with each of the races facilitated
a test for linkage relationships between host genes con-
trolling the reaction to the races of the pathogen.

Leaves were usually assessed for disease develOpment
8-10 days after inoculation. Occasionally, plants were
left on greenhouse benches for one week, after they had
been removed from the mist chamber, before assessing the
symptoms.

Plants were assessed according to the infection rate
of the disease in a 1-5 scale as follows:

1. 'Clean, no disease symptoms.
2. A few scattered, small lesions on the midrib and
occasionally on main veins. Lesions were corky

in appearance.

3. Many small lesions scattered on the midrib and veins
with collapse of the tissue.

4. Few large lesions scattered over the leaf blade or
many large lesions over the leaf blade.

23

5. Many large coalesced lesions accompanied by tissue
breakdown and sometimes leaves became chlorotic and
abscised.

If one assumes that each of the above categories or
classes represents a different genetic grouping, it would
be necessary to attempt to fit the observed data to genetic
models apprOpriate to five genotypic classes.

An obvious model for five genotypic classes is one
involving two loci, where the following states would exist
in an F2:

4 "+" alleles, respectively AABB

3 "+" alleles, respectively AABb, AaBB

2 "+" alleles, respectively AAbb, aaBB, AaBb

l "+" alleles, respectively Aabb aaBb

0 "+" alleles, respectively aabb

These classes would occur, in the F in proportions

2!
of 1/16, 4/16, 6/16, 4/16 and 1/16 for classes of 4, 3, 2,
l and 0 "+" alleles, respectively. If this kind of model
were actually to prevail in regulating reaction to anthrac-

nose, the distribution of phenotypes in F generations

2
should be symmetrical about the intermediate reaction class;
parental reaction classes should be recovered in only

minimal frequencies, depending on number of genes involved.

Preliminary examination of F data indicates clearly

2
that this was never the case in any cross.
Modifications of the "polygenic" model could include

mixed gene effects, that is some genes showing dominance,

and some showing additivity; some with greater effects and

24

some with lesser effects and so forth. These models, for
testing purposes and fitting of observational data can
become quite arbitrary and in present circumstances cannot
be justified. I have chosen, instead, to fit a series of
possible classical Mendelian gene-number, gene-action models
to the observational data, realizing that ultimately it
would be necessary to conduct F3 progeny tests of F2 plants
classed as l, 2, 3, 4 and 5.

Therefore, classes 1 and 2 were considered as
resistant reactions, while 3, 4 and 5 were considered as

susceptible reactions.

6.0 Analysis of Data

 

The observed numbers of resistant and susceptible
plants in F2 pOpulations were tested against the theoretical
ratios of resistant to susceptible plants by using a X
(chi-square) test.

Data from F2 populations was also analyzed for
joint segregation to simultaneous reaction to two races of
the pathogen. The theoretical joint segregation ratios for
two races are obtained by multiplying together the segre—
gation ratios to each of the races. Plants are classified
as resistant to both races, resistant to the first race but
susceptible to the second race, susceptible to the first
race but resistant to the second race and susceptible to
both races. The observed and expected numbers of plants

in their respective categories compared by using a X2 test.

25

Some seedlings from F2 populations were observed to

be segregating for semilethal at about two seeks after emer-

gence.

The observed and expected number of normal and semi-
2

lethal plants was also tested by using a X test.

ability

1.

7.0 Data Reliability

 

The following points were considered for the reli-
of results:

In every generation that was tested, parents that
were considered as susceptible checks were included;
that is, Montcalm was included when plants were
being tested against beta race, Montcalm or Tuscola
for delta race and Kaboon for gamma race.

Montcalm is very susceptible to beta race, Montcalm
and Tuscola are very susceptible to delta and Kaboon
is very susceptible to gamma race.

For every F2 pOpulation tested, its F (four plants)

1
and parents (four plants for each parent) together
with Montcalm, Tuscola and Kaboon were tested also.
In experiments where the susceptible checks and
parents did not show clear results the eXperiment
was discarded and the test was repeated with a new
set of plants.

Inoculations were done on cloudy days and in the
morning when the temperatures were low. The mist

chamber was covered with newspapers on the outside

to cut off direct sunlight which may otherwise

26

create a local temperature rise inside the
chamber.

Since spores were deposited on individual leaflets
or on whole plants the chances for "misses" would
be very minimal.

Plants were inoculated when the trifoliolates were
just fully opened. Leaves that are too young or
too old do not show proper disease symptoms.
Sometimes when no clear symptoms are observed 8—10
days after inoculation, plants are left on the
greenhouse benches and assessed again for disease

symptoms a week later.

IV. RESULTS

1.0 Standardization of Spore Concentration

 

1.1 Beta Race

 

The analysis of variance (Table 4) for disease
reaction indicates that there was no significant difference
between spore concentrations but there was a significant
difference between cultivars. Consequently, there was no
significant interaction between the spore concentration and
the cultivars.

The results for the treatment means in terms of dis-
ease reaction for six cultivars are given in Table 5.
Montcalm showed a significantly higher degree of suscep-
tibility to beta race. Swedish Brown was moderately sus—
ceptible while 61294, Tuscola, C49242 and Kaboon had similar
reactions and were resistant. There was no significant
difference between the spore concentration although as the
spore concentration was decreased there was a decrease in

infection of the cultivars.

1.2 Gamma Race

 

Results indicate that different spore concentrations

had a significant effect on disease reactions of the bean

27

28

Table 4.—-Effect of spore concentration on disease reaction
of six bean cultivars to the beta race using a
symptom rating scale of 1-5 (resistant-
susceptible).

 

Degrees of Mean

 

 

Source of Variation Freedom Squares F
Blocks 2 0.13
Spore concentration 2 0.91 1.85 NS
Error (a) 4 0.49
Cultivars 5 8.64 34.56**
Spore concentration X

cultivars 10 0.42 1.68 NS
Error (b) 30 0.25

**p i 0.01. NS = None Significant.

cultivars (Table 6). There was a significant difference in

response of bean cultivars to spore concentrations. Inter-
action between spore concentrations and cultivars was also
significant.

The means of the cultivars in terms of disease
reaction showed a significant differential effect of dif-
ferent spore concentrations (Table 7). The concentration
of 1.6 x 106 spores/ml showed the highest significant
effect, according to Tukey's LSD .05. Concentrations of
1.6 x 105 and 1.6 x 104 spores/ml intermediate and low

effects.

29

 

 

 

.ma.o n Imam>fiuanov mo. own
G.H H.H o.H a.H m.m o.H o.H memo:
m.H o.H o.H m.H s.m o.H o.H mos x s.m
G.H o.H o.H R.H o.a o.H o.H aoa x a.m
m.H m.a o.H n.m n.m o.H o.H mod x h.m
memo: vamaw «Homage .um.3m samouaos :oonmm mamaao Aas\mmuoamc
mcofiumuucmocou

um>flpaao

 

.womu moon mcu Row maoom Amanflumoomsmnpcmumflmmuv mud
n mafia: coflumuucmocoo whomm on mum>fluaso coon xwm mo cofluommu comz:|.m manna

30

Table 6.--Effect of spore concentration on disease reaction
of six bean cultivars to the gamma race using a
symptom rating scale of 1-5 (resistant-
susceptible).

 

 

 

Source of Variation Degrees Of Mean F
Freedom Squares

Blocks 2 0.575
Spore concentration 2 6.240 83.20**
Error (a) 4 0.075
Cultivars 5 10.686 82.84**
Spore concentration X **

Cultivar 10 1.752 13.58
Error (b) 30 0.129

**p i .01.

Kaboon had a significantly higher rate of infection
and Montcalm and Swedish Brown had intermediate infection
rate (Table 7). C49242, Tuscola and 61294 were all resis-

tant.

1.3 Delta Race

 

The analysis of variance indicates that there was
a significant difference between spore concentrations and
the difference between the cultivars was also highly sig—
nificant (Table 8). There was also a high interaction
between spore concentration and cultivars.

The mean reaction of bean cultivars to spore con—
centrations is summarized in Table 9. The spore concentra—

tion of 2.33 x 106 spores/ml had a significantly higher

31

.mm. H Amum>fluasov mo. omq

 

 

 

.Hm.o u Acoflumuucmocoo muommv mo. 0mg
~.m m.H m.H m.~ m.m m.m o.H memo:
m.H h.a o.H h.H n.a o.m o.H voa x m.a
H.~ o.H m.H o.m h.m h.m o.H moa x w.a
m.~ m.H >.H o.q o.v o.m o.H moa x m.a
memo vamaw mHoomsB .Hm.3m Eamoocoz coonmx mommvu AHE\mmuommv
z meowumuucmocoo

ua>auaso

1' .111

.momu mEEmm on» How mamom Amanwumwomsmlucmumflmmuv mIH
6 mean: coaumuucmocoo wuomm 0p mum>wuaso coon xflm mo :ofluommu cmm211.n manna

32

Table 8.-—Effect of spore concentration on disease reaction
of six bean cultivars to the delta race, using a
symptom rating scale of 1-5 (resistant-
susceptible).

 

Degrees of Mean

 

 

Source of Variation Freedom Squares F
Blocks 2 0.019
Spore concentration 2 3.574 11.87*
Error (a) 4 0.301
Cultivars 5 14.196 69.59**
Spore concentrations X **

Cultivars 10 1.241 6.24
Error (b) 30 0.204

*p i .05. **p i .01.

effect than the concentration of 2.33 X 104 spores/m1.

5 spores/ml had an inter-

The spore concentration of 2.33 X 10
mediate effect and was significantly different from the
highest and lowest concentrations.

There was no significant difference between C49242,
Kaboon and 61294 although 61294 showed a mild infection
(Table 9). Tuscola and Montcalm had significantly higher
infection rates. Swedish Brown had a significantly lower

infection rate than Tuscola but was not significantly

different from Montcalm.

33

 

 

 

.om.o u Amum>wuasov mo. omq

.Hv.o u Amc0wumnucmocoo muommv mo. emu
m.m m.H n.m H.m m.m o.H o.H memo:
>.H m.H m.~ o.m o.~ o.H o.H «OH x mm.m
m.~ o.H >.m o.m o.v o.H o.H moa x mm.m
>.N >.H o.m m.m o.v o.a o.H Goa x mm.m

m oumn .H .3 E mo :0 :00 m
undo: vmmao a a m m H u z n M mvmmvo AHE\meommv
mcoflumuucmocoo

um>fluaso

 

.oomu muamo map How mamom Amanflummomsmlucmumflmouv mud
8 means coaumuucmocoo muomm ou mum>fluaso coon xwm mo cofluommu cmozun.m manna

34

2.0 Reaction of Parent Bean Cultivars to
Each of the Three Races

 

 

From the results of inoculation with races beta,
gamma and delta, the six bean cultivars showed differential
reactions to the three races of the pathogen. The results
are summarized in Table 2.

Bean cultivar Cornell 49242 is resistant to the
races beta, gamma and delta, and it is completely free of
symptoms (Figure l). Kaboon is resistant to races beta and
delta but very susceptible to race gamma (Figure 2). Under
extremely good conditions for disease development Kaboon
has often been given a score of 2 in the rating scale for
race delta. Montcalm is very susceptible to races beta and
delta but only moderately susceptible to race gamma (Figure
3) which often posed difficulties in classifying plants in
the F2 population. Variety Swedish Brown is susceptible to
races beta, gamma and delta (Figure 4). Tuscola is resis-
tant to race beta and gamma but very susceptible to the
delta race (Figure 5) and breeding line #61294 is moderately
resistant to races beta, gamma and delta (Figure 6).

‘The F plants in all the twelve crosses made were

1
tested against each of the three races beta, gamma and

delta, and the results are given in Table 10. Twelve Fl
plants (four for each race) for each cross were sprayed

with spore suspension and twelve F1 plants for each cross

were used for brushing method.

35

Fig. 1.--Trifoliolate leaf of C49242 showing resistant
reaction to the beta, gamma and delta races of
g. lindemuthianum.

 

Fig. 2.--Trifoliolate leaf of Kaboon showing resistant
reaction to the beta and delta and susceptible
reaction to gamma races of g. lindemuthianum.

 

36

\‘

\\> i
. \ \\ 3 \‘I
~. ‘ .\
3 , "_ I ‘j,

KABOoN

 

37

Fig. 3.--Trifoliolate leaf of Montcalm showing susceptible
reaction to the beta and delta and moderately sus-
ceptible reaction to gamma races of C.
lindemuthianum. —

 

Fig. 4.--Trifoliolate leaf of Swedish Brown showing sus-
ceptible reaction to the beta, gamma and delta
races of g. lindemuthianum.

 

38

 

39

Fig. 5.—-Trifoliolate leaf of Tuscola showing resistant
reaction to the beta and gamma and susceptible
reaction to delta races of Q. lindemuthianum.

 

Fig. 6.--Trifoliolate of 61294 showing moderately resistant
reaction to the beta, gamma and delta races of
g. lindemuthianum.

 

40

J
{k
c
L

..
T.

 

41

Table 10.--Reaction of F1 plants to races beta, gamma and

 

 

 

delta.
Cross Race
Female/Male Beta Gamma Delta
C49242 X Montcalm R* R R
Swedish Brown X C49242 R R R
C49242 X Tuscola R R R
61294 X C49242 R R R
C49242 X Kaboon R R R
Montcalm X Kaboon R S R
Swedish Brown X Kaboon R S R
Tuscola X Kaboon R R R
61294 X Kaboon R R R
Swedish Brown X Tuscola S R S
Tuscola X Montcalm S R S
61294 X Montcalm R R R

 

*R = Resistant; S = Susceptible.

42

All the F1 plants in crosses between C49242 and the
rest of the five bean cultivars used in this study were
resistant to races beta, gamma and delta. Fl plants from
Montcalm X Kaboon and Swedish Brown X Kaboon crosses were
resistant to races beta and delta but susceptible to race
gamma. The F1 plants from 61294 X Kaboon cross were resis-
tant to races beta, gamma and delta, which showed that the
gene(s) conferring moderate resistance in the breeding line
61294 were dominant over the genes conferring susceptibility
to race gamma in Kaboon.

The F1 plants in the crosses between Swedish Brown
X Tuscola and Tuscola X Montcalm were susceptible to races
beta and delta but they were resistant to race gamma. In
this case, the gene(s) for susceptibility to race beta in
varieties Swedish Brown and Montcalm were expressed as
dominant over the gene(s) conferring resistance in Tuscola
to beta. However, Tuscola had dominant gene(s) for resis-
tance to gamma race in these crosses.

Fl plants of 61294 X Montcalm were resistant to
races beta, gamma and delta. Gene(s) for moderate resis-
tance seemed to be dominant over the genes for suscep-
tibility. However, it was not possible to distinguish
whether Fl plants from the crosses of 61294 X Montcalm and
61294 X Kaboon were resistant or just moderately resistant.

These F1 plants were lethal, leaves turned yellow and

abscised before disease symptoms are fully developed.

43

3.0 Segr3gations in F Populations to
Individual aces

 

 

3.1 Race Beta

 

Nine F2 pOpulations were observed for segretation of
resistant and susceptible plants to race beta (Table 11).
All the crosses between resistant X resistant and resistant
X susceptible parents were resistant in F1 except Swedish
Brown X Tuscola and Tuscola X Montcalm whose Fl plants were
susceptible to race beta.

In crosses between C49242 X Montcalm and Swedish
Brown X C49242 the ratio of resistant to susceptible plants
clearly fitted 3:1. This means that a single dominant
gene, possibly "Are" gene from C49242 conferred resistance
to race beta in these two crosses. The "Are" gene was
first reported by Mastenbroek in 1960 (28).

F2 plants from C49242 X Tuscola cross segregated
clearly in a 15R:lS. In this case, there seemed to be two
duplicate genes conferring resistance to race beta. One
could be the "Are" gene from C49242 and the other must have
been from Tuscola since Tuscola is resistant to beta.

Both genes are dominant in this cross.

The observed number of resistant and susceptible
F2 plants in the cross between 61294 X C49242 had a close
fit to a theoretical ratio of 57:7. This ratio can possibly
be explained by three pairs of dominant genes conditioning

resistance in 61294 X C49242. One gene pair, presumably

"Are" from C49242, had a segregation ratio of 3:1 and two

44

.manwumwomsm

m “ucmumflmmm u m«

 

 

 

com. I 0mm. mud mad om mm EHMODCOZ x mHOOmSB
omN. I 00H. muH mNH mm ow mHOOmDB x C3OHm £ma©w3m
00H. I omo. hum boa oh MNH COOQMM x CBOHm nmfl©m3m
own. I com. hum VHH no no :OOQMK x EHMOHCOZ
0mm. I 00H. huhm HmH MH mod coonmx x Nvmmvu
own. I com. huhm ham NN mma Nvmmvo x vamaw
own. I com. HumH «Hm ma mma mHOUmDB x NvavU
0mm. I OOH. Hum 55H vm MNH Nvmmvo x C30Hm nmflUOBm
0mm. I OOH. Hum mmH mm NNH EHMOHCOS x NvavU
cwmzumm oflumm Hmuoa m «m mamz\mHmEmm
muflaflnmnoum cmuommxm mmouo

mucmam mo Hmnasz

.mcoHumazmom N

,l 1||ll1||l11I 'll’!.|’1 I'll"

m we“: CH moon mama ou mucmHm

wanfiumoomSm cam ucmumfimmu mo mowumu couomaxm can nomad: ow>ummn0II.HH manna

45

complementary pairs of genes segregating in a 9:7 ratio.
The two complementary pairs of genes can both be from 61294
or one pair from C49242 and the other pair from 61294.

The F2 plants from the C49242 X Kaboon cross segre-
gated in a 57:7 ratio of resistant to susceptible plants.
This case, as above, revealed that there are three pairs of
genes involved, one a single dominant pair of genes segre-
gating in a 3:1 ratio and the other two being complementary
genes segregating in a 9:7 ratio.

The observed resistant and susceptible plants in

the F crosses between both Montcalm X Kaboon and Swedish

2
Brown X Kaboon segregated in a 9:7. The segregation pattern
in these two pOpulations seem to suggest that there were
two dominant pairs of complementary genes conferring resis-
tance to race beta.

In crosses between Swedish Brown X Tuscola and
Tuscola X Montcalm the F2 plants segregated in a 1:3 ratio
of resistant to susceptible plants. The segregation ratio
obtained indicate a possibility that a single dominant gene

pair conferring susceptibility was expressed over the genes

conferring resistance in Tuscola.

3.2 Gamma Race

 

Segregation patterns of the eight F2 pOpulations
tested against gamma race are given in Table 12. One F2
pOpulation, C49242 X Tuscola, was of a combination of

resistant X resistant and 61294 X C49242 was between

46

.ucmumammm HH<

H mm “manflumoomsm

m uucmpmfiwwm " NHk.

 

 

 

com. I own. Hum mHH mm mm mHOOmDB x Eamoucoz
com. I own. huhm mNH ma MHH CBOHm SmHUOBm x MHOOmSB
com. I 0mm. buhm bmH vm moH coonmx x MHOOmSB
0mm. I 00H. huhm HmH ma mmH coonmx x qumvo
omm. I OOH. Huma mam ma mmH NvavU x vmmao
I I m< «AN 0 vHN maoomsa x Nvmmeu
0mm. I com. Hum mbH vv HMH Nvmmvv x C30Hm £mH©w3m
0mm. I OOH. Hum mma mm NNH Eamoucoz x Nvmmvu
:mm3umm oflumm ANDOB m am mamz\mamfimm
muflawnmnonm pmuommxm mmouo

mucmHm mo HmnEsz

.mcofiumasmom mm unmflm CH moon mEEmm o» mundam
manflumoUNSm can ucmumflmmu mo mofluon owuoomxw pom Hogans pm>ummnoII.mH manna

47

moderately resistant X resistant. Six of the F2 pOpulations
were between resistant and susceptible parents.

The observed ratio of F2 plants in the C49242 X
Montcalm and Swedish Brown X C49242 crosses, closely segre-
gated into a 3:1 theoretical ratio. The segregation ratios
observed in these two pOpulations seem to suggest that
there is a single dominant gene, possibly the "Are" gene
from C49242 conditioning resistance to the gamma race.

In the cross between C49242 X Tuscola, where both

parents were resistant to race gamma, all 214 F plants

2
were resistant. This can be accounted for by assuming that
the genes conferring resistance to gamma race in the two
parents were very closely linked.

The F2 plants in a cross between C49242 X Kaboon
and its reciprocal, Kaboon X C49242 segregated in a 57:7
ratio of resistant to susceptible plants to race gamma. A
single dominant gene, possibly the "Are" gene contributed
by C49242, confers resistance to race gamma. Also, two
additional dominant pairs of complementary genes condition
resistance to the race gamma.

In the crosses Tuscola X Kaboon and Tuscola X
Swedish Brown, there is a clear fit of 57:7 segregation

ratio for resistant to susceptible plants in F This

2.
showed that there could be three gene pairs conditioning
resistance, one pair being a single dominant gene segre-

gating in a 3:1 ratio and the other two being complementary

genes segregating in a 9:7 ratio.

48

In the cross between 61294 X C49242, 216 F2 plants
inoculated with gamma race segregared in a 15:1 ratio of
resistant to susceptible plants. Possibly two duplicate
gene pairs conferred resistance, one pair presumably being
"Are" gene from C49242 and the other one from 61294.

The observed number of resistant and susceptible
plants in 115 plants in Montcalm X Tuscola cross clearly

fitted a segregating ratio of 3:1. In this case, Tuscola

seemed to have a single dominant gene conferring resistance.

3.3 Delta Race

 

In the F2 pOpulations studied for segregation for
reaction to race delta, one cross (C49242 X Kaboon) and its
reciprocal was between resistant X resistant parents and
61294 X C49242 was between resistant and moderately resis-
tant parents. The rest of the F2 populations were derived
from resistant and susceptible parents. The eight pOpula-
tions segregating for reaction to race delta are presented
in Table 13.

The F2 plants from crosses between Swedish Brown X
C49242, C49242 X Montcalm and C49242 X Tuscola segregated
in a 3:1 ratio for resistant and susceptible reactions. A
single dominant gene, probably the "Are" seems to confer
resistance to delta race in these two crosses.

The observed number of resistant and susceptible

plants in a total of 217 F plants from 61294 X C49242

2
clearly fitted the expected segregation ratio of 15:1. It

49

.oanflummomsm n m uucmumfimom u m«

 

 

 

ooa. I omo. harm HmH NH mmH coonwx x mommvo
mmo. I oao. hum nma mm HNH coonmm x NHOUNSB
omm. I ooa. hum baa up ONH coonmx x czoum nmflcmzm
omm. I com. hum mHH me am coonmm x Eamoucoz
com. I omm. Huma ham ma mma Nvmmvu x vmmam
9mm. I ooa. Hum eam mv Nha mHoomsB x Nemmvo
com. I omm. Hum mma mm NNH Eamoucoz x Nvmmvu
com. I own. Hum oma ow vma Nvmmvo x CBOHm nmwcmzm
cwmzumm mum Hmuoe m «m mamz\mamemm
suaafinmnoum oflomm mmouo

muasmmm om>ummno

.momu mummo on» on muflaflnflummomsm can mocmumfimmu new
mcwummmummm mcoflumasmom m mo moflumu HMOfiuoHomnu paw Hogan: ©m>uwmn0II.mH magma

50

appears that there is a possibility of a system of two
dominant pairs of duplicate genes conferring resistance.
One of the pairs could be the "Are" gene from C49242 and
the other pair from 61294.

In a cross between C49242 X Kaboon, the observed
proportion of resistant and susceptible plants in F2 fitted
the theoretical ratio of 57:7. Possibly there were three
gene pairs conferring resistance to delta race, that is a
single dominant gene pair segregating into a 3:1 ratio and
the two dominant complementary gene pairs segregating into
a 9:7 ratio.

The observed proportion of resistant and susceptible
F2 plants from each of the Montcalm X Kaboon, Tuscola X
Kaboon and Swedish Brown X Kaboon pOpulations could be
explained by a theoretical ratio of 9:7. In these two
pOpulations there seem to be two complementary pairs of
genes conferring resistance to race delta.

Some of the F2 populations studied for the reaction
to races beta, gamma and delta were segregating for lethal
plants. As a result, in most cases the number of F2 plants
inoculated per population may not have been large enough.

The lethal plants were not included in the study for segre-

gation for disease reaction.

51

4.0 Joint Segregation in F Populations

2

 

4.1 Beta and Gamma Races

 

Five F2 populations were studied for joint segre-
gation for reaction to races beta and gamma. From the
analysis of X2, three pOpulations showed a degree of associ-
ation in factors conditioning reaction to races beta and
gamma, and two populations showed independent association.
The data for joint segregation for reaction to these two
races is summarized in Table 14.

In the cross 61294 X C49242 the segregation ratio

of resistant and susceptible F plants for race beta was

2
57:7 and 15:1 for race gamma. The theoretical joint segre-
gation which is the product of the two ratios, was 855:57:

105:7. The observed number of plants classified in reaction

classes did not fit the theoretical ratio. The observed

2

X Montcalm population significantly deviated from the

number of F plants segregating for joint reaction in C49242

theoretical ratio of 9:3:3:1.

In the cross C49242 X Kaboon, the observed number
of F2 plants for joint segregation for reaction to races
beta and gamma, significantly deviated from theoretical

ratio of 3249:399:399:49. The observed number of F plants

2
in Tuscola X Swedish Brown population segregating for reac—
tion to races beta and gamma fitted the theoretical segre-

gation ratio of 57:7:171:21 at a probability of .005-.010.

The prOportions of plants observed in the F2 pOpulation of

52

 

 

 

Hoo om.mm oo.mma mmH ma
ma.Hm mm.m vm H m m Aaumvaaumv
hm.o mo.mm mm m m m Eamoucoz
mm.ma mo.mm m m m m x
vm.a ma.hm mm m m m mvmmvu
Hoo mm.¢v mo.hom mom wwo.a
m¢.ov Nv.a m n m m AHHmHVAhuhmV
ma.m m~.Hm ma moa m m qumvo
mm.o mm.HH m mm m m x
wo.o vm.m>a mud mmm m «m vamam
m Nx pouommxm pm>ummno Hmowmwwmwna MEEmo comm MWMMMWOMW

mHCMHm MO ngz

mmmao cofiuommm

 

can muon on» o» c
we mcofiumHzmom

.mmoou mEEmm
wauommn MOM mamsomcmuanaww mcflummmummm mommonu m>Hm
m mo cofiuomou ca mmflocmsomnm omuommxo ocm pm>ummn0II.aH manme

53

 

 

 

Ho.Imoo. om.HH oo.mma mma mmm
mm.H om.oa ma Hm m m AbuanAmuav
mm.H om.mm ma HRH m m czonm amaomsm
om.m om.m o w m m x
vo.¢ om.m~ ow mm m m waoomse
Hoo.v mo.ma oo.HmH Hma mmo.e
aw.m na.m m mv m m AnnemVAhuhmv
mm.m mm.ha m mam m m coonmx
om.m mm.wH m mam m m x
mm.a nm.mva ova mv~.m m m memmvo
m x wouommxm pm>ummno moflumm NEEmo mumm moflpmm mm
N Havaumuoose pew mmouo

mundam mo Hwnasz

mwMHU COHfiUmwm

 

.emscfluaouuu.aa magma

54

 

 

 

 

.manflumoomnm n m uucmumflmom n m«
Ho.Imo. mm.h oo.mHH mHH
nm.a om.HN mm m m w Aanmvxmnav
HH.o mm.vm mm m m m maoomse
mm.m mH.h H H m m x
mm.o mm.am mm m m m Eamoucoz
omuommxm pm>ummno mowumm MEEmo mumm moflumm mm
m Nx HMOfluwnoonB paw mmouo

mucmam mo HmQEsz

mmmHU cofluommm

 

.BmscflucooII.aH magma

55

Montcalm X Tuscola segregating for reaction to races beta
and gamma fitted the theoretical ratio of 3:1:9:3 at a

probability of 0.05-0.10.

4.2 Beta and Delta Races

 

Joint segregation to races beta and delta was
studied in six F2 populations. From the X2 analysis, four
populations showed a degree of association in reaction to
races beta and delta and two populations showed independent
segregation. The data for the joint segregation for reac-
tion to races beta and gamma is summarized in Table 15.

The observed F2 plants in C49242 X Tuscola pOpula-
tion segregating for joint reaction to races beta and delta
significantly deviated from theoretical ratio of 45:15:3:1.
The F2 plants from 61294 X C49242 observed for the joint
segregation for reaction to races beta and delta deviated
significantly from the theoretical ratio of 855:57:105:7.

The observed F2 plants segregating for joint reac-
tion to races beta and delta in C49242 X Montcalm signifi-
cantly deviated from the theoretical ratio of 9:3:3:1.

The observed F2 plants segregating for joint reac-
tion to races beta and delta in C49242 X Kaboon deviated
significantly from the theoretical ratio of 3249:399:399:49.
The observed number of plants segregating for joint reaction
to races beta and delta in Montcalm X Kaboon fitted the
theoretical ratio of 81:63:63:49 at a probability of 0.05-

0.10. Finally, the observed number of F2 plants segregating

56

 

 

 

Hoo.v ON.Nv oo.>HN nHN «No.H
HN.mm mv.H m w m m AHumHVAhnhmv
mm.m mN.NN MH mOH m m Nwmmvo
OH.o mo.NH HH mm m m x
vo.o mH.HmH va mmm m m vaHm
Hoo.v mv.mm oo.vHN vHN we
mv.NN vm.m NH H m m AHAMVAHumHV
m¢.o mo.0H N m m m NHoomse
Nm.h mH.om Hm mH m m x
mN.N mv.omH mmH mg m Rm NvavU
m x pmuommxm om>ummno moHumm muHoo mumm moHumm Nm
N mHGMHm mo quEdz HMOHumuomne mNMHU coHuomom ocm mmouo

 

.mmomu muHmU

can muwn ecu Op coHuommH Mom mHmsomcmuHssHm maHummmnmom mommouo me

mo mcoHumHsmom N

m mo coHuommH :H meocmovmnm pmuommxm pom Uo>umeOII.mH mHnt

57

 

 

 

Hoo om.bH oo.HmH HmH mmo.v
em.H nH.N 0 av m m HenanAbuhmv
NN.v mw.bH m mam m m coonmx
mN.m mm.hH m mam m m x
mm.H nm.mVH mmH mvN.m m m NVvaU
Hoo ww.¢0H oo.mmH mmH oH
HH.wm mo.m mm H m m AHumVHHumV
ow.h mo.mN «H m m m EHmoucoz
mo.hN wo.mN H m m m x
vo.m mH.hm mOH m m m NVwao
m x owHONme pm>uwmno moHpmm muHmQ mumm moHumm Nm
N HmoHuouomca pom mmouo

mucmHm mo monesz

mmmHU :oHuommm

 

.poscHuGOOII.mH mHan

58

 

 

 

 

.mHQHummomsm u m uucmumHmmm n ms
omo.ImNo. om.m oo.>mH hmH mmN
mH.o on.hm mm av m m AnanAnumv
mm.H mv.m¢ mm mm m m coonmx
nm.o m¢.mv Ne mo m m x
mm.m mm.Nm Hm Hm m m c3oum anpw3m
H. mo. Nh.m oo.mHH MHH mmN
vm.H Nm.HN hm me m m AnanHhumv
mn.N Hm.>N mH mm m m coonmx
HN.H Hm.hN NN mm m m x
mm.N m>.mm ma Hm m m EHmoucoz
x pmuommxm po>uomno moHuom muHoo muwm moHumm Nm
N HmoHumuooce new mmouo

mucmHm mo umnfisz

mmmHo coHuomom

.wwscflucoonu.mH mHnme

59

for joint reaction to races beta and delta in Swedish Brown
X Kaboon significantly fitted the theoretical ratio of

81:63:63:49 at a probability of .025-.050.

4.3 Gamma and Delta Races

 

F2 populations from four crosses were studied for
joint segregation for reaction to races gamma and delta.
The X2 test for independent segregation showed association
in three populations and independent segregation in one
population (Table 16).

The observed number of F2 plants from 61294 X
C49242 population for joint reaction to races gamma and
delta significantly deviated from the theoretical ratio of
225:15:15:1.

The observed segregation ratio in F2 plants of
C49242 X Montcalm for joint segregation significantly
deviated from the theoretical ratio of 9:3:3:1. The
observed prOportions of F2 plants from C49242 X Kaboon
segregating for reaction to races gamma and delta signifi-
cantly deviated from the ratio of 3249:399:399:49. The
observed proportion of F2 plants from Tuscola X Kaboon
segregating for reaction to races gamma and delta fitted
the segregation ratio of 513:399:63:49 at a probability of

0.025-0.050.

6O

 

 

 

Hoo.v mw.mN oo.mmH mmH wH
vm.m mw.m mH H m m HHumVHHumv
mm.m mo.mN mH m m m EHmoucoz
oo.m wo.mN SH m m m x
mo.¢ mH.hm moH m m m Nvavo
Hoo. mm.¢w oo.hoN hON mmN
Nm.mm Hm.o m H m m HHumHVAHumHV
hm.o MH.NH 0H mH m m NvavU
HH.o MH.NH HH mH m m x
mo.o mm.HmH th mNN m «m meHm
cmuommxm om>uomno moaumm muHmQ mEEmo modumm N."H
m Nx HNUHuouooce pom mmouo

mucmHm mo Hmnadz

mmMHU coHuommm

 

mEEmm may on God

.MOOMH MUHQU UCM

uommn How hHmsoocmuHsEHm mCHummmummm mommouo HDOM

mo mcoHuoHsmom Nm mo :oHuommu cH mmHocmsvoum pmuommxo cam pm>uomnoII.wH mHnme

61

.mHnHummomsm

m “ucmumHmmm

Hm¥

 

 

 

 

mo.ImNo. mm.m am.mmH hmH vNo.H
mv.o mm.m 5 av m m AnanAhuhmv
om.N om.HH pH mm m m coonmx
vw.N mm.Nn mm mam m m x
vH.H mm.mm «OH MHm m m oHoomsB
Hoo.v HN.mN oo.HmH HmH wmo.v
mh.o hH.N o mg m m HHuhmVHhuhmv
H¢.m mm.hH n mam m m coonmx
hm.h mw.hH m mmm m m x
hm.N hm.mvH NmH mvN.m m m NvavU
pmuommxm Uo>uwmno moHumm muHoo mEEoo modumm N."H
m Nx HmoHudHomce pad mmouo

mucmHm m0 an552

 

mmMHU :oHuomwm

:11' III I.

.6maaflucoouu.mH mHnma

62

5.0 Lethal Plants in F and F Populations

1 2

Lethal plants were observed in F1 of Kaboon X

 

61294 and Montcalm X 61294 and six F populations were

2
observed segregating for lethal plants. Symptoms for the
lethal plants were characterized by chlorosis of primary
leaves and general stunting of the plants was observed two
weeks after germination. Severe yellowing occurred, leaves
dropped and plants died (Figures 7, 8 and 9).

Six F2 populations from ten pOpulations studied
were observed segregating for lethal plants and are pre-
sented in Table 17. The parents and their F1 plants were
normal but F2 plants segregated into normal and lethals
two weeks after germination. The observed number of normal

plants and lethals was compared with the expected ratios

by using X2 test and the results are given in Table 17.

63

Fig. 7.--Semi-letha1 F plants from the Kaboon X 61294
cross (three Reeks old).

Fig. 8.--Semi-lethal F plants from the Montcalm X 61294
cross (three weeks old).

64

 

65

Fig. 9.-—Kaboon X C49242 F plants segregating for normal
(back line) and semi-lethals (front line) in two
weeks old population.

66

 

67

Table l7.--Observed number and expected ratio of normal
and lethal plants in six F2 pOpulations.

 

 

 

FemgIZjMale N* n Total R3310 Pr323511ity
C49242 X Kaboon 181 61 242 3:1 .90 - .95
Tuscola X Swedish Brown 133 2 135 63:1 .90 - .95
Swedish Brown X C49242 180 40 220 13:3 .90 - .95
C49242 X Montcalm 169 39 208 13:3 1.00
Tuscola X Montcalm 128 22 150 13:3 .25 — .50
Tuscola X Kaboon 187 23 210 57:7 1.00

 

*N = Normal; n = Lethal.

 

V. DISCUSSION

1.0 Spore Concentration and Bean
Cultivar Reactions

 

 

Before screening F2 plants it seemed desirable to
determine spore concentration that would give a roughly
clear classification of plants into resistant and suscep-
tible in situations where spraying method was used. A
spore concentration of 106 spores/ml was found to be about
satisfactory for all three races. Reaction of each bean
cultivar, except C49242, was different for different spore
concentrations for each race. Concentration of 104 spores/
ml appeared to be too low for inciting disease reaction
while concentration of 105 spores/ml gave an intermediate

reaction.

2.0 Reaction to Race Beta

 

Data obtained in this study regarding the reaction
of six bean cultivars to race beta revealed that genes
conferring resistance were generally dominant. However,
resistance was recessive in crosses involving Tuscola with
Swedish Brown and Montcalm. In other crosses, Tuscola

transmits dominant genes for resistance to beta race.

68

69

The ratio of 3:1 of resistant to susceptible F2
plants in crosses involving C49242 with Montcalm and Swedish
Brown can best be explained by the presence of a single
dominant gene conferring resistance to race beta. The
segregation ratio of 15:1 in crosses of C49242 X Tuscola
can best be explained on the assumption of two dominant
independent, duplicate loci either of which alleles are
capable of conferring full resistance to race beta. Since
C49242 and Tuscola are both resistant parents, each of them
is likely to be contributing one dominant gene pair.

In the crosses involving Kaboon with Montcalm and
Swedish Brown, a segregation ratio of 9:7 was observed.
These results can be explained by the action of two domi-
nant gene pairs at two separate loci which are interde-
pendent in a complementary way in function.

The segregation ratio of 57:7 observed in crosses
involving C49242 with Kaboon and 61294 is assumed to be
explained by the action of both complementary gene pairs
and a single dominant gene pair segregating simultaneously.
These genes are completely independent of each other in
conferring resistance.

Finally, the crosses involving Tuscola with Swedish
Brown and Montcalm had a segregation ratio of 1:3 and all
Fl plants were susceptible. Tuscola transmits dominant
genes for resistance to race beta in other crosses; its
dominance for susceptibility is specific to Montcalm and

Swedish Brown genetic backgrounds. The dominant genes

70

transmitted by Montcalm and Swedish Brown could be an allele
at d-locus when the genes for resistance in Tuscola to race
beta are assigned at d-locus (see Table 18). The results
obtained for race beta are similar to those of Cardenas
(1960) and Cardenas 33 31. (1964).

Table 18.--Proposed genotypes of six parental bean cultivars

with respect to their reaction to the beta race
of Q. lindemuthianum.

 

 

 

Cultivar Duplicate Complementary

or Line Genes Genes
C49242 AreB AreB clcldld1 elelflf1
Kaboon are are8 clcldldl e2e2f2f2
Tuscola are8 are8 clcldzd2 elelflfl
61294 are8 are8 clcldldl e4e4f4f4
Montcalm are8 are8 c3c3d3d3 elelflfl
Swedish Brown are8 are8 clcld3d3 elelflfl

 

Generally the system of genes for reaction to race
beta appeared to be difficult to explain, but a system of
multiple alleles was assumed to be a suitable one for
explaining this genetic pattern. This system was adopted
from Cardenas (1960) and Cardenas 33 31. (1964). In this
system it is assumed that there are duplicate factors c and
d and complementary factors e and f. According to this

system, alleles c1 d1 e1 f1 and c3 d3 e3 f3 confer suscep-

tibility; alleles c2 d2 e2 f2 and c4 d4 e4 f4 confer resis-

tance. The higher numbered alleles are dominant over the

71

lower numbered alleles. The genetic pattern proposed for
the six parental cultivars in respect to their reaction to
race beta is presented in Table 18. No evidence of multiple
alleles was observed in complementary factors but it was
decided to be appropriate to maintain the system postulated
by Cardenas 33 31. (1960).

The reaction pattern and order of dominance is as

follows:

4 4 4 4 3
c

c d e f > 3e3 3 c2

f > 282 2 l 1 1 l

d f > c d e f

d
Resistant Susceptible Resistant Susceptible

Where > indicates "dominant over."

3.0 Reaction to Race Gamma

The data explaining reaction to race gamma looks
more simple than for race beta. The concept of multiple
allelism is not needed in this case. These results are
also similar to those of Cardenas (1960) and Cardenas 33 31.
(1964).

The segregation ratio of 3:1 in crosses involving
C49242 with Montcalm and Swedish Brown is assumed to be
accounted for by "Are" gene from C49242 conferring resis-
tance to gamma race. A single dominant gene, presumably
from Tuscola, can account for the segregation ratio of 3:1
in Montcalm X Tuscola. The segregation ratio of 15:1 in
61294 X C49242 cross can be explained by the action of

independent dominant pairs of duplicate genes. One of the

72

gene pairs being the "Are" from C49242 and the other pair
being from 61294.

The segregation ratio of 57:7 in C49242 X Kaboon
is assumed to be accounted for by a system of three domi—
nant gene pairs each of which are segregating independently.
Under this assumption one gene pair segregating at 3:1
ratio is the "Are" contributed by C49242, and two dominant
pairs of complementary genes are segregating in a 9:7 ratio.
One pair of complementary genes had to come from C49242 and
the other from Kaboon.

A system of three pairs of dominant genes is assumed
to be operating in cross of Tuscola X Swedish Brown, giving
a segregation ratio of 57:7. This is a similar case as
that of C49242 X Kaboon but different gene pairs, I and J
confer resistance.

All the F plants from C49242 X Tuscola were resis-

2

tant to gamma race. It is proposed that the genes conferring
resistance to gamma in C49242 and Tuscola are tightly
linked and that the 214 F2 plants was too small a number to

reveal any recombinants. See the following sketch:

C49242 (R) Tuscola (R)
AreY g areY G
X -—————— Parents

Are 9 areY G

73

AreY g
‘_“—— Fl All resistant
areY G

AreY g areY G

______ + .______

AreY g areY G P All resistant,

no recombinants
observed

The prOposed genetic pattern of six parental bean

cultivars for reaction to the gamma race of g. lindemuthianum

 

is presented in Table 19.

Table 19.--Proposed genotypes of six parental bean cultivars
with respect to their reaction to the gamma race
of Q. lindemuthianum.

 

 

 

Cultivar Duplicate Complementary

or Line Genes Genes
C49242 AreY AreY gg hh 11 jj kk 11
Kaboon areY areY gg hh ii JJ kk 11
Tuscola areY areY GG hh II jj kk LL
Montcalm areY areY gg hh ii jj kk 11
Swedish Brown areY areY gg hh ii jj KK 11
61294 areY areY 99 HH ii jj kk 11

 

I is complementary

to J, K is complementary to L.

74

4.0 Reaction to Race Delta

 

The reasonable interpretation for the data of reac-
tion to delta race, as in the case Of beta and gamma races,
is that systems Of both duplicate and complementary genes
were Operating. Dominant genes were found to be conferring
resistance to race delta in all populations tested. The
data for the genetic segregation to race delta in crosses
involving C49242 with Swedish Brown, Montcalm, Tuscola and
61294 is assumed to be due to the action Of two dominant
independent loci. Each Of the alleles is assumed capable
Of conditioning full dominance.

In crosses involving Kaboon with Montcalm, Swedish
Brown and Tuscola, the segregation pattern of 9:7 Obtained
was assumed to be due to the action Of dominant complementary
genes. Finally, the segregation pattern of 57:7 is explained
by the system Of two dominant complementary genes and one
single dominant gene acting simultaneously but independently.

The prOposed genotypes of the six bean cultivars
studied for the reaction to race delta are given in Table 20.

In the material studied in this work, genes con-
trolling resistance to beta, gamma and delta in C49242
segregated in a 3:1 ratio. This is the single dominant
"Are" gene reported by Mastenbroek in 1960. However, from
the linkage data to be discussed later, the "Are" gene does
not look to be a single dominant gene.

It has been Observed in this material that Kaboon

has two sets of complementary dominant gene pairs, one

75

Table 20.--Proposed genotypes of six parental bean cultivars
with respect to their reaction to the delta race
Of Q. lindemuthianum.

 

 

 

Cultivar Duplicate Complementary

or Line Genes Genes
C49242 Are‘S Are‘S mm nn pp
Kaboon are‘S area mm NN PP
Tuscola are‘5 are‘5 mm nn pp
Montcalm are6 are(8 mm nn pp
Swedish Brown are5 are mm nn pp
61294 are(8 are(8 MM nn pp

 

which confers resistance to beta and the other confers
resistance to delta. It has also one dominant pair of

genes which complements with another pair of genes in C49242
and Tuscola (see Tables 18, 19 and 20). From this study
also, the breeding line 61294 seems to possess horizontal

resistance.

5.0 Linkage Study

 

When the data from F populations was analyzed for

2
joint segregation to race beta, gamma and delta, it was

found that some populations segregated independently and
others had associated segregations. Parental phenotypes
in populations with associated segregations were Observed
in greater frequency than expected. Recombination values

were calculated according to the method derived by Fisher

and others (Strickberger, 1976).

76

The data from five F2 populations was analyzed for
joint segregations to races beta and gamma whereby three
pOpulations had associated joint segregation and the other
two had random segregations. The three F2 pOpulations that
had associated simultaneous segregations to races beta and
gamma were 61294 X C49242, C49242 X Montcalm and C49242 X
Kaboon, and their recombination fractions were 19.2%, 20.9%
and 20.3%. These pOpulations involved C49242 as their
common parent which contributed the "Are" gene conferring
resistance to races beta and gamma. In the cross between
61294 X C49242 there is a possibility that linkage could
be between the complementary genes conditioning resistance
to beta and the duplicate genes conditioning resistance to
gamma in 61294. This possibility can be checked in cross

Of 61294 X Montcalm but the F progenies Of this cross were

1
lethals.

There is also a possibility that one Of the comple-
mentary genes, the J-locus, conditioning reaction to gamma
race in Kaboon is linked to one Of the complementary genes
conditioning reaction to beta race. It is reasonable to
propose that the genes that show linkage behavior are in
C49242 because Of the behavior Of crosses where C49242 was
a common parent, including a cross of C49242 X Montcalm.
Montcalm has no genes conferring resistance to either of
the races.

A significant association was Obtained in four out

Of six pOpulations analyzed for joint segregation to races

77

beta and delta. The four populations that had associated
joint segregations were C49242 X Tuscola, 61294 X C49242,
C49242 X Montcalm and C49242 X Kaboon and their recombina-
tion fractions were 11.1%, 21.4%, 5.2% and 19.8% respec-
tively. As in the case of beta and gamma, C49242 was
involved as a common parent. In this situation again, it
seems that the genes conditioning reaction in C49242 to
races beta and delta are linked. The recombination fraction
is lower in crosses involving C49242 X Tuscola and C49242 x
Montcalm than in the crosses of 61294 and C49242 X Kaboon.
In the latter crosses there are other dominant genes con-
ditioning resistance tO races beta and delta. The segre—
gation ratios contributed by these genes could influence
the recombination fraction in the linkage system. There
is nO evidence Of linkage between the genes conditioning
resistance to beta and the genes conditioning resistance to
delta race in the cross involving Swedish Brown X Kaboon.
Three F2 populations tested for joint segregation
to races gamma and delta had associated segregation and One
pOpulation had an independent segregation. The crosses
that had associated joint segregation tO races gamma and
delta are C49242 X 61294, C49242 X Montcalm and C49242 X
Kaboon, and their recombination fractions are 20.3%, 24.0%
and 15.1%. In this case, like in the other two previous
cases, C49242 was also involved as a common parent. It
is again prOposed that the genes conferring resistance in

C49242 to races gamma and delta are linked.

78

The recombination fractions in the linkage data
seem inconsistent. Several factors are prOposed to be con-
tributing to the inconsistency Of recombination fraction:

In some Of the crosses, except C49242 X Tuscola and C49242 X
Montcalm, there are also other genes conferring resistance
that are segregating simultaneously; in some crosses the
number Of F2 plants is tOO small; some of the F2 pOpulations
were also segregating for lethal plants. If the factors

for formation of lethal plants are associated with the

genes conferring resistance to these races, the segregation
rations could have been altered.

From the linkage data it seems likely that the
factors linked are in C49242. From the previous study
(Mastenbroek, 1960), C49242 has a single dominant gene "Are"
which confers resistance to these races. From this study
it is unlikely that the "Are" is just one gene controlling
reaction to these races but a system of genes, that are
linked, each Of which act as a single dominant gene.

The "Are" gene is therefore postulated to be a

Y Are6 and a

complex "tri-part" locus as follows: AreB Are
single cross-over produces an array of gametes such that
both R-S and S-R combinations for joint segregation occur

(see sketch below using case of the C49242 X Montcalm

cross).

79

 

 

 

 

 

 

C49242 Montcalm
AreY AreB Are‘S areY are8 are‘5
X (Parents)
AreY AreB Area areY are8 are6
AreY AreB Are‘S
(F1)
areY are8 are(5

Gametes in joint combinations will be as follows:

Beta-Gamma: AreY AreB, areY ares, AreY are8 and areY AreB
Beta-Delta: AreB Areé, areB area, AreB are6 and are8 Are‘S
Gamma-Delta: AreY Area, areY area, AreY are(3 and areY ArecS

It is suggested that, for linkage study in crosses
involving C49242, the other parents be bean cultivars that
are fully susceptible to races beta, gamma and delta. F2
pOpulations from such crosses should not be segregating
for lethal plants, as well as the higher numbers Of F2
plants than those used in this study be used.

6.0 Occurrances Of Semi—Lethals in
El and F2 Plants

 

 

Fl plants from 61294 X Kaboon and 61294 X Montcalm
were lethals. This suggests that there might be a recessive
factor acting in a complementary way, where one factor in
one parent complements a second factor in the second parent.

Van Rheenen (1979) also Observed similar results.

80

Six out of ten F2 pOpulations from normal parents
and normal F1 plants, in this study, segregated for semi-
lethal plants. The genetic pattern for segregation is sum-
marized in Table 18. The segregation ratio Of normal to
semi-lethal plants Of 3:1, 63:1, 13:3 and 57:7, indicate
that factors controlling the formation of semi-lethal plants
are recessive. There is also a tendency that these factors
act in a duplicate and complementary way. Innes (1979)
also has Observed cases of seedling deaths in segregating
populations Of crosses between Michigan-bred navy beans

and cold tolerant colored beans.

VI. SUMMARY AND CONCLUSION

In this work, the inheritance Of reaction to races

beta, gamma and delta Of g. lindemuthianum was studied in

 

six bean cultivars using ten crosses.

Spore concentrations used in the case Of spraying
method Of inoculation were determined to be between 105-106
spores/ml, with the latter concentration allowing better
assessment of disease symptoms.

Parent plants and their Fl progeny were inoculated
by both spraying and brushing methods. All F2 pOpulations
were inoculated by brushing each individual leaflet Of the
first young trifoliolate with spore suspension Of one race.
Individual leaves Of some Of the F2 population were excised,
transferred into labelled test tube containing nutrient
solution, and sprayed with spore suspension of one race.
Inoculated plants or excised leaves were transferred into a
mist chamber kept at near 100% R.H. and ambient greenhouse
temperature.

Inheritance Of reaction to beta race was studied
in nine crosses. Data Obtained from these crosses revealed

that genes conferring resistance were generally dominant

but resistance was Observed to be recessive in crosses

81

82

involving Tuscola with Montcalm and Swedish Brown. Fl
plants in these crosses were susceptible. Tuscola transmits
dominant genes for resistance in other genetic backgrounds
Of this material. The segregation ratios Obtained for
resistance to susceptible F2 plants were 3:1, 15:1, 9:7,
57:7 and 3:1. The segregation ratio Of 3:1 is due to

action of a single dominant gene conferring resistance,
while the segregation ratio of 15:1 is due to the duplicate
pairs Of genes each of which is capable of conferring
resistance. The segregation ratio of 9:7 is explained by
the action Of two pairs of complementary genes, and the
segregation ratio Of 57:7 is explained by the action of

both duplicate and complementary genes segregating simul-
taneously but independently. In the crosses where suscep-
tibility was conditioned by a single dominant gene the
segregation Of 1:3 was Observed.

It became necessary to assume that a system of
multiple alleles was Operating in the inheritance of reac—
tion to race beta because Of dominance of alleles conferring
susceptibility in crosses involving Tuscola with Montcalm
and Swedish Brown. A system Of four alleles was assigned
to each Of the four genes prOposed except the "Are" gene.
Two of the four genes assigned are duplicate factors and the
other two are complementary factors. Two of the four alleles
confer resistance and the other two confer susceptibility.
The high numbered alleles were assigned to be dominant over

the low numbered alleles.

83

Eight crosses were studied for the inheritance of
reaction to race gamma in six bean cultivars. Genes con-
ferring resistance to race gamma were dominant in this
study. The segregation ratios of 3:1, 15:1 and 57:7, which
were similar to those for beta race were Observed. In this
case also a system of duplicate and complementary factor
sets are Operating. The segregation pattern for reaction
tO gamma does not call for a multiple allelic system.

In the cross between C49242 X Tuscola all 214 F2
plants were resistant to gamma. It seems likely that the
genes conferring resistance to race gamma in Tuscola are
closely linked to the "Are" gene from C49242; also that 214
F2 plants is tOO small a number to reveal possible recom-
bination.

The inheritance of reaction to race delta was
studied in eight crosses and segregation ratios Of 3:1,
15:1, 9:7 and 57:7 were Observed. The pattern Of genetic
segregation is similar to that for beta and gamma, in that
there are duplicate factor sets Of loci and complementary
factor sets Of loci. There is, however, no evidence for
the multiple allelic system from the segregation pattern
of reaction tO delta race.

In the F2 population tested for joint segregation
to beta and gamma, beta and delta and gamma and delta a
close association Of reaction was Observed in crosses where
C49242 was a common parent. A recombination fraction Of

about 20% in 61294 X C49242, C49242 X Montcalm and C49242 X

84

Kaboon was Obtained for joint segregation to the beta and
gamma races.

Four F2 pOpulations segregating simultaneously to
beta and delta had recombination fractions Of 11.1% (C49242
X Tuscola), 21.4% (61294 X C49242), 5.2% (C49242 X Montcalm)
and 19.8% (C49242 X Kaboon). The recombination fractions
for populations segregating simultaneously to gamma and
delta were 20.3% (C49242 X 61294), 24.0% (C49242 X Montcalm)
and 15.1% (C49242 X Kaboon).

The recombination fractions observed in these
crosses seem inconsistent and it becomes difficult to deter-
mine map distance for the factors that are linked. Several
factors that might contribute to the inconsistent recombi-
nation fraction are: in these crosses, except C49242 X
Tuscola and C49242 X Montcalm, there are also other genes
conferring resistance that are also segregating, a factor
that may interfere with the calculated recombination frac-
tion; the number Of F2 plants is tOO small in some crosses;
and there were also lethal plants segregating in some of
these populations. If the factors controlling the formation
Of lethal plants are associated with the genes conferring
:esistance to beta, gamma or delta, segregation ratios could
be distorted as well as the information about the linkages
studied.

From the F2 populations observed to have associated

simultaneous segregation to beta, gamma and delta where

C49242 is a common parent, it seems that the factors that

85

are linked are in fact in C49242. C49242 being the donor
of "Are" gene which confers resistance to beta, gamma and
delta, it is likely that the "Are" gene is not one gene
controlling reaction to these races but a system Of genes
that are linked, each Of which act as a single dominant
gene.

Six out Of ten F populations (from normal parents

2
and F1 progeny) studied segregated for lethal plants and

the segregation ratio Of normal to lethal plants Of 3:1,
63:1, 13:3 and 57:7 were Observed. The F1 plants from 61294
X Kaboon and 61294 X Montcalm were lethals. From the
segregation pattern and the lethal Fl plants observed it is
likely that the factors controlling the formation Of lethal

plants are recessive.

APPENDIX

 

 

 

 

 

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90

 

 

 

 

 

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LITERATURE CI TED

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