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THE RELATION OF SOIL
TEMPERATURE AND SOIL MOISTURE
TO THE INFECTION OF ONIONS BY

PHOMA TERRESTRIS HANSEN

Thesis for the Degree of M. S.
MICHIGAN STATE COLLEGE

Axel L. Andersen
194I

... duff

‘

 

fivlflhwh I” . .

1.:

 

 

The Rim” mom 0F SOIL ‘I‘Eizj'blm'l‘UM‘ my SOIL Mona-oh}; To

Th5 INEL‘TIOQ OE ORIONb dY BHORA TLLRESTRIS hfinohfi

 

,x

by _-.’;
.~ Ir '

. 6F” g

Axel L. finaersen

A Thesis
Submitted to tne Graduate School of Michi:an
State College of Arricwlture and Aoplied
Science in partial fulfilment of the
requirements for the denree of
onTfiR OF SCIENCE

Department of Botany

1941

A 0.5.140 I' {L :I‘JDCm. Jill:

The writer is grateful to Dr. Ray Nelson for advice and
assistance in conductive this study, to Dr. W. D. Baten for aid in the
statistical analysis of data, and to Drs. Ray Nelson and E. A. Bessey

for criticism and correction of the manuscriut.

p.
Q:
$4:
I‘D
Q3

W

{DABLFTCfli COREYQTTS

Introduction
Economic inbortance of onion

Relation of disease to production

The disease
History
Importance and distribution
SymptomatOIOgy
Present investigations
Object of study
Materials and methods
Environmental relations
Influence of hydrOgen-ion concentration and temperature

on the growth of Phoma terrestris

 

The relation of soil temperature and soil moisture to the
growth of onion
The relation of soil temperature and soil moisture to the
disease
Infection of onion transolants in naturally infested
soil.
Infection of onions seeded in naturally infested
soil.
Infection of onion seeded in artificially infested

soil.

 

TJLL OE C’CJI'PI‘EL-ES

(continued)

Discussion
Summary
Literature cited

Exolanation of plates

TABLE OF BLuTZS
“*—

h..—

BLATE I. The relation of temperature to the growth of P. terrestris.

 

PLATE II. The relation of soil temperature and soil moisture to the
infection of onion roots by P. terrestris.
PLaTE III. The relation of soil tauperature and soil moisture to
the growth and develoyment of the onion.
LAT; IV. The relstion of soil tempera ure and soil moisture to the
deveIOpment of pink root in onions grown in artifically 1n-

fested soil.

- l -

THE IELATION OF SDIL %“V"“ TL’HI AIL SQIL EOISTULJ TO

TE; IlfilfiTION OF ONI N5 EY FED}; TIFFFBTRIS RANSEK

 

v Trf \-
I} E‘AEC ‘TVi—f (III-{(31 '..

 

c.

The onion is one of the lecoinp truck crops grown on muck
soils in Michigan. That it ranks highly as a cash crOp is shown by
comparing it with a few of the other widely ;rown truck crops of
st te. Iurin; the ye .rs 193. and 1940 its farm value was exceeded only
by str.wberries and celery, and its value was nearly double that of cab-
begs. During the prst OGCuQe plantings in this state have increased from
a;proxim tely 6,900 acres in 1951 to 10,800 acres in 1940. The s ate has
edvz. nced fro"1f:)u:th to third position.emon; the states in total acreage
and production, being surpassed only by Texas and " Yo rk. 'The total
production for l?40, based on statistics ob eined from the U.S.D.A. Crop
harketinn Board (1?), was approximctely ,836,000 hundred pound sacks
valued at 32,20 3,000. 00.

In Kichiéan onion growing ’s practically restricted to muck
soils. This Ina: led to the concentration of the major onion gro1zing

sections in southnestcrn end southcentrol prrts cf the sttte where there

- '2 .- r‘ \‘x . -- r-wv: “"1 ‘- ‘\ w -— - '- 1‘, ‘~ ‘ . -
ere entensive ru L-luncs and where the 1: sets are near at hand. The in

‘;

,...
.

dustry is concentr ted mostly in Alleg n, Newaygo, Calhoun, Ionic, In|§ :
and Jackson counti s, with smaller acre gee in Ottawa, Kent, Berry, Eaton,
Van Buren, Ta.:htcnaw, and Lapeer counties. In Allegan, Berry, 3nd Eaton
counties, especially, and to a less extent in some of the other counties,
the land has been used continuously for onion production many years.

This continuousu :1 of Ir -nd for ;ro1in; one croo yesr after year is es-
pecially conducive to the deveIOpuent of disease. Reports from Allegan,

Barry, and Eaton counties indicate that the total acreage for the coun-

ties has not chan;ed much during the last few years, but on the other

hand, the total yield has been steadily decreasing. In Newaygo and
Calhoun counties the onoosite condition is true. Onion yroduction is
fairly new in those two counties so that yields per acre are consider-
ably higher there than in Allegan county. Continuous crOpping of the
soil, year after year, has stimulated the propagation of soil organisms
parasitic on the roots of onions. Conseouently nink root of onion,
which is strictly a root disease, has become a serious menace to the
onion croo of Hichipen. Because of the great importance of the onion
industry in this state and the potential destructiveness of this disease
to the onion crop, a long range program of control has been started and

the work reported herein is a part.

TLI LI¢%£2§
The early history of onion pink root is somewhat complicated
because several distinct organisms have been suspected as causal agents.
The disease was first mentioned in 1917 by Taubenhaus and Johnson (9),
who resorted it in Texas. In lQPI'Taubenhaus and Melly (10) published
an extensive paper on its etiolOgy and control. They believed the causal

agent was a Fusarium which they named Fussrium malli Taub. Later bideris

 

(7,8) reforted several species of Fusarium which he considered capable
of causing the disease. In 1936 hansen (5), by immersing firm onion

roots showins early pink root syiptoms in 1-500 mercuric chloride for
three minutes, obtained subsecuently on isolation a Phone only. Fan

8 en

(4,5) was unable to reproduce the diseas with cultures of Fusarium nalhi,

 

Fuearium croryoptheron Sideris, and other fusarial species. 0n the other
hand, he readily nroduced the disease with the suecies of Phoma he had

isolated and which he named ghgga terrestris.

 

Insertence end gfietribution

 

Pink rnot of onion has becomecfi'rajor innortsnce in neerly
all of the onion rrowinv sections in the United States. Definite dste
ere not sveileble for the onion erowinr districts of Michieen, but it
can be stated that the effects of tTe disease are reflected in a progres-
sive decrease in yields for many years.

Durins the harvesting season of 1940 every commerciel onion
field in Eaton County res visited to determine the extent of rink root
dieeese in that county end to correlate this information with exnerimentel
results obtained in the ereenhonse. The normal annual yield for onions
in Michigan on noninfested fields which heve been nroyerlv fertilized is

soprorifstelv EGO-1,000 cistes per ecre. The estim ted everaee yield

H.

or Feton C unty in 1940 was 165 crates per acre mith variations from b0-
VOO crates per acre. Freept for one or two fields demaeed by a hail stornn
the reduction in yield was nearly all due to pink root, running as hiph
as 90 per cent in some instences. The disease is even more prevalent and
destructive in the Gun_Marsh area of Alleesn County, one of the oldest
and lereest onion rrovint sections in the stete.

Tanberhens end Jelly (10), as early as 19:1, estintted losses
in Te.ss fields from 35 per cent to an occasional comhlete crew failure
in badly diseased fields. hensen (4) oted in California that where

. the cron fre-

[J

onions are grown in the seme field for two or three season

r

uently is so dininished that no ettemnt is made to hervest it.

The disease is very wide spread. It has been reported in
nearly all of the large commercial onion growing sections in the United
States. In addition it has been resorted from Bermuoa (4), Canada (6),

end South Lfrics (2). hensen (4) isolated P. terrestris from cowpees,

-4-

Lima beans, and potatoes. Thornberry and.Anderson (ll) reported in-

fection of the small lateral roots of tomato with P. terrestris which re-

 

sulted in a stunted condition of the plants. In addition they cited some
unpublished information supplied to them by Dr. E. I. Melhus on the host
range of the fungus. According to this report the following plants are
susceptible: barley, cane, cantaloupe, carrot, cauliflower, corn, cucumber,
millet, muskmelon, oats, pea, pepper, soybean, Spinach, squash, tomato, and
wheat. This indicates that the fungus is not confined to members of the
genus Allium and that care should be taken in the selection of plants to be

used in crop rotations on lands used for onion production.

_§ymptomat010gy

The first evidence of pink root infection in an onion plant is a
gradual loss of turgidity in the older leaves. These leaves soon become soft
and flaccid, droop, and finally die back from the tips. Plants in the later
stages of development are so weakened by the disease that they bend over
at the neck and appear to have reached maturity. If the infection is severe
death may result to the whole plant. These symptoms are similar to those
which result from drought and other unfavorable conditions. An examina-
tion of the roots of infected plants reveals the presence of a pinkish dis-
coloration. In severe infections all, or nearly all, of the roots rot off
or become so disintegrated that they wither and turn a deep red to purple
color. New roots are produced to replace the dead ones. Roots recently
infected are turgid but usually have a yellow or yellowsbrown or even a
slight pink color. The top symptoms are due to disintegration of infected
roots and the consequent impossibility of the few remaining roots to sup-

ply the growing plant with enough salts and water to maintain normal

processes of development. The final result is that the available food
is exhausted in the production of new roots and bulbs of marketable

size are not produced.

PthnhT INVEETIdnTIOhS

 

In testing commercial onion strains and hybrids for relative
resistance to disease it is exceedingly important to know the Optimum
conditions for the growth and development of both the host and the patho~
gen. There are certain limits within which most organisms are capable
of initiating and producing disease. These limits are determined by the
ability of the organism to tolerate various environmental factors among
which temperature, moisture, and pH are very important. Phoma tagggstris
is strictly a soil inhabiting organism :nd the environmental factors of
the greatest importance to it are those of the soil. Previous reports
(4, 10) have indicated that pink root is associated with high soil temr
peretures. There are no data available to indicate the relation of soil
moisture to the infection of onion roots. Hansen (4) planted onion bulbs
in inoculated soil and grew them in constant temperature chambers with
no illumination. He reported the greatest amount of infection at 25° C.
Field observations reveal that the disease does its greatest damage at
the time of rapid bulbing in August. In.Michigan the latter part of July
and the first two or three weeks in August are generally hot and dry.

It is then the fungus does the greatest amount of damage.

In the present investigations the environmental factors influen-
cing the mycelial development of‘gp terrestris have been studied. Cone
comitantly, the soil factors which influence the growth and develOpment

of the onion werestudied under controlled conditions in the greenhouse,

- 5 -

as were those which influence the develOpment of the disease. The ob-
ject was to determine the relationship of soil temperature and soil

moisture to infection of onions by the pink root fungus.

Materials and Eethods
Soil Temperature and Soil Moisture Studies

The soil temperature and soil moisture studies were made through
the use of soil tanks. The tanks consisted of several individual water
baths each with a separate, thermostatically controlled heating unit.
Fluctuations in temperature did not exceed 1 0.2500.

The effects of widely fluctuating air temperatures were elimin-
ated by carrying on the experiments during the fall, winter, and early
spring. Artificial light was provided during the short days to lengthen
the day and so simulate the light conditions of the natural growing sea-
son.

Downing's Yellow Globe onion was used in all the experiments.
The onions were either grown in sterilized sand and transplanted to the
soil cans made especially for the soil tanks, or the seed was sown in
the cans and the seedlings thinned to the required number.

The moisture content of the soil was maintained at a uniform
level throughout each experiment. This was done first by determining
the water-holding capacity of the soil (the amount of water the soil will
retain in opposition to gravity when free drainage is provided). The
soil was then divided into several portions, depending upon the number
of saturation gradients to be used in the experiment, and each portion
was adjusted to the desired moisture content by either adding more water
or by air-drying. After the soil moisture was adjusted a weighed quanr

tity of soil was placed in each can. Onion transplants were then set in

the cans and the soil covered with one inch of ground cork to prevent
undue surface evaporation. At regular intervals each can was restored

to its original weight by the addition of distilled water.

Environmenta;_Relations
Influence of Hydrogen-ion Concentration and.Temperature on The
Growth of Phoma Terrestris
hydrogen-ion Studies

Several synthetic agar media were tried out to determine the
one best suited for growth studies in this eXperiment. 0f the five syn-
thetic media selected for trials, Elliot's agar proved superior.

The fungus was grown at various temperatures in incubators
where the temperature fluctuations did not exceed t 0.250 C. The temp-
eratures ranged from 10° to 34° C. By the use of the colorimetric meth-
od, the agar was adjusted to a pH of 4, 5, 6, 7, and 8 respectively.
There were four replicates for each pH and at each temperature. Records
were taken on the diameter growth of the mycelia after the plates had
been incubated 18 days.

.32222 terrestris grew well over a wide range of hydrOgenrion
concentrations. The Optimum concentration for growth was between an 5
and pH 6. The growth at pH 4 and pH 8 was slightly less than the optimum
at all temperatures. Similar results were obtained by Davis and Henderson
(1), who found the optimum.hydr0gen-ion concentration for the growth of
P. terresgris to be from pH 5.4 to pH 5.8 with a growth range from pH 5.8
to pH 7.6. This is well within the pH range of soil used for onion cul-

ture.

Temperature Studies

The influence of differential temperatures upon the growth of
gérterggstgig'was determined in experiments prior to those on the rela-
tion of soil temperature to the infection of onion roots. The informa-
tion obtained from such studies does not indicate the actual soil temp-
eratures at which the onion plant is susceptible, but it does indicate
those which may be significant.

Three kinds of media were used in this eXperiment. They in-
cluded cornmeal agar, potato-dextrose agar, and Elliot's agar. The
agar was adjusted to pH 5.8 and exactly 30 cc. poured into each plate.
The plates were inoculated by the agar plug method with an isolate of
P. terrestris that had proved highly pathogenic in previous pathOgenicity
tests.

After remaining at room temperature for 24 hours the inoculated
plates were placed in the incubators at 10°, 14°, 18°, 20°, 24°, 26°,
28°, 5 °, and 52° C. Twelve plates, four for each medium, were placed
in each incubator. At the end of 10 days the plates were removed and
the average radical growth for each medium determined for each tempera-
ture. Table 1 gives the average radial growth of the mycelia of P. ter-

restris on artificial media.

TABLE 1. Growth of Phoma terrestris at Various temperatures.
Incubation period 11 days.

 

 

Average radial growth in mms. of 4-mycelia on:

 

 

Temp. 0 C. Elliot's aga Cornmeal agar Potato-dextrose

agar
10 2.5 2.5 2.0
14 8.0 9.0 9.0
18 16.0 15.0 15.0
20 20.0 21.0 22.0
22 22.5 25.0 4b.0
24 27. 50.0 28.5
26 52.0 55.0 51.5
28 55.0 55.0 55.0
50. 52.0 51.0 51.5
52 20.5 14.5 15.0

;A-‘- L‘ ‘~ AMA-‘L_-

The maximum radial enlargement of mycelia occurred at 28° C.
on all media. It will be noted that there was a sharp decrease in growth
at 52° C. and that the growth was as good or even better at 180 C. than
at 52° C. The growth of‘g, terrestris on cornmeal agar is illustrated
in.Plate I. In a previous eXperiment on growth and pH.where the range
extended to 54° C. there was no growth at 54° C. This extablishes the
maximum temperature for this fungus betieen 52° and 54° C. The minimum
temperature for growth was not determined, but at 10° C. mycelial devel-

opment was practically stopped. The minimum temperature can then placed

slightly below 10° C. Hansen (4) found that 26° C. was the optimum

-10...

temperature for the growth of the fungus, while Davis and Henderson

(1) obtained the best growth at 2:0 c.

The Rel tion of Soil Temperature and Soil Eoisturc to the Growth
Of Onion

Onions make the most regid growth and best develOpment during
cool and moist seasons. Pink root does not become epgzrent until the
ol:;nts hazve been e110 53d to the li;h temgeretures 01‘ id- summer. To
aid in erslyzing the drte on the relation of soil temperature and soil
moisture to the disease, some knowledge of the effects of these factors
upon the develop:aent of t). e host is desirable. This iILformotion was ob-
tained by grO'tin the _ol.:nts under controlled conrlitions in noninfested
soil.

In & prel mi_ner ry exp rim(:nt it as fOUIld tJ+t 50 per cent sot-
uration was too dry 1nd thm;85 per cent ssture tion of the soil use too
wet for good onion growth. Many of the plants at 32° C. were killed be-
cause of the high soil temperature. The best root develogment took glace
in soil held at 18° C., but the plants did not bulb very well at this
temperature. In subsequent exocriments these lower end higher soil tem-
peretures and soil moistures were eliminated. In te d the plants were
grown in soil held at 20°, 22°, 24° ,250, 28°, amp 30°C 0., Hith moisture
contents of 60, 70, end 80 yer cent of its water-holding capacity.

The much used in this exfieriment was obtained from an onion
field near Kc—lennzoo, Michi gen. Its texture was imbroved by adding one
p2 rt of em. d to three n) rts of much. All the s;)il wc-s thoroughly steamed

P tored in a covered metal drum for a month before it yes used. Be-

p!
:1
1..
m

fore the onions were needed a 3-12-12 fez rtilizor (600 lbs. per acre) and
m'n.rnese SUlfllh' :te- (200 lbs per acre) wer: thorou hly nixed with the soil.

The results of this experi inent are given in Table 2.

- ll -

TABLE 2. The relation of soil temoereture and soil moisture to the
develoyment of onion. Seed sown directly in cans, and Blunts

‘

grown for 68 days.

 

Per cent Temp. 8011 No. of plants Dry weight of tops - ans.
ssturetion 00.
of soil

 

Totel Average per
plant

 

6O 20

N
(J1

1.730 .069

Ca 26 1.449 .05:
2 2 1.155 .055

D
O
11

1.075 .043

..
r
l

C

{‘3 i, ._
0')
3‘0

.6 .675 .026
50 22 .402 .018

70 20

N

{‘3 ”3 PO (‘0 PO
CROUU'IOWU"

2.066 .023
2.12 .005
1.52 _ .061

.222 .051
1.208 .048
0.692 .050

. To

0') I")
O CO on 0P (‘3)

C)? (\7)

80 20 44 2.880 .120
28 '5 2. 88 .088
24 25 2.244 .090
26 2 1.478 .059
28 25 1.433 .057
30 8 .850 .037

 

The results of his experiment clearly show that soil tempera-
ture and soil moisture exert considerable influence on the top develop-
ment of onions. This is especially noticeable when a comgurison is made
of the average dry weights of the tops per Plant as given in‘Teble 2.
The indications are that the lower soil moistures have 2 tendency to

limit the soil temoernture r nge in which good onion growth takes place.

In the 60 'er cent saturated soil wood growth took olsce onl at 20° C.
b u L

1

Above this temperature ilent L

f.-

eveloynent res retarded consideribly and
became progressively poorer es the soil temperatures increased. In the

70 per cent saturated soil grouth was good at 20° end 220 0., end not

.. .. :5. 1?!!!— I'ltll‘. 1.1%.. mg.t,.4.fl...
, v. .- . .6
..
.

-12—

until the soil temper: ture es res cled 340 C. were there eny indicrtions of
growth retvrdetion. The best top develOpment took place in the 80 per
cent saturated soil. At this moisture level the plants made excellent
top grOLth at soil temperatures of 90°, 220, and 340 C.; but at 26° C.
there was a definite decrease. The effects of these soil temper tures
and soil moistures on the top develOpment of onions are illustrated in
Plate III.

Root deveIOpment was better in the lower than in the hiéher
soil moistures. There use 3 progressive decrease in the extensivenees
of the root system from the 60 to the 80 ;3er cent saturated soil. In
the 60 snl 70 per cent saturated soil the roots were well developed,
showed much secondary breiching, and had penetrated throughout the soil.
In the 80 per cent saturated soil, on th e other hand, root develOpment
was inhibited. Free eater res present in l rge enough quantities to
prevent soil aeration. Because of his the roots were not nearly so
well develOQed, showed very little secondery branching, and did not
penetrate very deeply into the soil. This, however, did not retard the
deVelo ment of tie pl nt It was in the 80 per cent saturated soil th';1t
the best top growth took place.

From 18-24'3 0., incl.1si ve, soil moisture apparently has more
influence on root deveIOpmrnt th:n soil temperature. At these soil tem-
peratures there was very little difference in the root system of plants
growing at a constant soil moisture level. Above 24° 0., however, soil
tem yer ture appeared to heve as much effect upon root develognent as soil
moisture. The root systems became pregressiVely poorer es the soil temr

wei tuies increased from 24° throu;h 30° C.

The plants initiated bulb develogment at all soil temperatures
and all soil moistures, the poorest bulbing taking place in the 60 per
cent and the best in the 80 per cent saturated soil. The difference be-
tween the various Soil moistures, hovev r, was vtry s i;ht for any soil
tempereture. At soil tewperetures of 18° and 30° C., bulbin; was very
poor as conporcd to that at other temper tures. At 18° C. the growth
went into the development of roots instead of bulbs. At 30° C. the
high soil temperature alone probably inhibited bulbing. Optihum bulbing

took place at 20°, 22°, and 24° C. in the 80 per cent saturated soil.

The Relation of Soil Temperature end 8011 Moisture to the Disease

The effects of soil temper:tures and soil noistures were stud-
ied in conjunction in all experiments. This appeared justifiable since
these environmental factors are probably the most important as far as the
infection of susceptible onion roots are concerned. It nes possible by
the use of soil tenks to obtain information on the degree of interaction
between these environmentul factors, in addition to studying the effects
of each one separately. This interaction between tno closely associated
environmental factors is likely to set up e set of conditions which may
be of considerable importance in governing the degree of infection and
the rate at which the fungus will destroy the tissues after infection has
taken place.

In all of the tests the everoge dry weight per plent was used
as a basis for determining the amount of pink root infection. In pre-
liminery tests it was observed that the amount of top development was
closely correlated with the degree of pink root infection. The greetest
:nrount of pink root infection was accompanied by the greetest amount of

stunting, consideration being taken, of course, of the effect of these

same environmental factors upon the deVeloyment of the host. In addi-
tion to the dry weight of the pleats, date were obtained on t11e extent
of infection, the number of giants killed, the relative number of dis-
eased and healthy roots, and other data which seemed pertinent at the
time for drawing specific conclusions in the final analysis.

Previous tests indicated that 26° C. was the Optimum soil temp-

crnture f0: the develoPment of pin}: root in naturally infested soil. In
those tests there were no visible signs of infection at 18° C. and very
few at 20° and 22° 0. Most of the plants at 52° 0. died from the effects
of soil temperatures alone. The giants growing in the 50 and 60 per cent
saturated soils showed tr e lea st pink root infection, while those in the
70 and 85 per cent saturated soils showed the greatest pink root infection.
The 50 per cent saturated soil, however, was too dry for the grovth of
onions and the 85 per cent too let fox the develoument of a healthy root
system. Conse,ucntly, in the experiments to be described these extremes

of soil temperature and soil moi ture Iere eliminated.

Infection of Onion Trensplnnts in Naturally Infested Soil

The muck used in t5 is experiment was obtained from an onion
field ne :r Or213eville, Michigan, in which pink root was very destructive
in 1939. Its texture was improved by adding one gart of son d to three
parts of infested soil. This soil was divided into three lots, each of
which was adjusted to 60, 70, and 80 per cent of its water-holding capac-
ity respec tively. lie 3011 temyermtur3° 2ere m"*t"1n,d at ?00, LLO, 24°,
26° 28° and 20° 0. ht the ti_3 e of planting a 0-9—18 fertilizer (1000
lbs. per acre) and manganese sulohete (220 lbs. per were were edded to

the soil. The plants were h_rv mted 47 61ys after planting. Table 3

shots the effect of soil temperature. and soil moi:ture noon the devolop-

ment of gihk root in these tr1LSyantS 3ro2in5 in naturally infested 5011.

TABLE 3. The relation of soil temperature and soil moisture to the de-
velopment of pink root in onion trtnsplants grown 47 days in net-

urelly infested soil.

 

% Soil Lo. Green wt. Dry Lt. Ave. dry wt. _

SC . Temp. 0 0. Plants of togs & of tops & of toys & bulbs
of bulbs - gms. bulbs - ems. per plant - Ems.
Soil

 

60 20 16

P: 6
24 16
SE 16

9 16

0 16
70 16
16
16
16
16
16

C(OC‘IfiI‘OO

80 20 16
F2 16
2 l 6
56 16
28 16
30 16

58.70
68.97
91.90

r- cm
/ 0 slid

75.20
79.42

91.08
82.77
98.49
68.10
80.81
74.72

76.9L

105.?0
110.70

75.01

100.55

99.04

4.16
4.80
6.15
5.15
5.39

5.63

.0
C3115
(.5303

o
0.5 '

0111119030101
0
01:13.45
HOP-LNG“

4.97
6.74
6.97
4.73
6.59
6.57

0.26
0.30
0.38

r‘()

0.0“
0.3
0.3

0.34
0.35
0.40

.28
0.55
0.33

0.5

0.42
0.44
0.30
0.41
0.41

 

All the plants in the 60 per cent saturated series showed
very uniform growth at all temperatures. At 200 C. there was slight
infection and at all the other temperatures the roots were moderetely
infected. The tops shoved die—beck symftoms at all temper tures. In
all probabilitj this was due to the dry soil Lgd not directly due to
pink root. There was slightly more infection at 260 C. than at any other

tezgercture.

- 15 -

In the 70 per cent sctur ted series the severity of infection

r I“

increesed considerably over the FO per cent series. here ras no visible
evidence of infection in the raots et 200 C., only rodervte infection rt
£00, 240, end 300 C., but severe infection :t P60 and 280 C.

The plents in the $0 per cent setur'trd soils were not es sev-
erely damaged et the lorer temgerrtures as were th3:e in tne other two
series. At 200 end 220 C. there were no visible signs of infection in
the root system. At 240, 290, end 300 C. only sli;ht infection wee not-
iceeble, but st 260 C. the infection wrs severe. fill the glants above 240
C. ShO‘.‘.‘€'d ty‘irzztl die-beck; C-ty'mp‘bOIr‘Ls.

At all soil noi'tures pink root develoyed more rs.idlj end his
more severe at 260 C. than at any other sail temgersture. ine severity
of infection incrensed mt this teneer ture fron the lower to the higher
soil moistures. In the 80 per cent setursted soil severe infection ey-

. . , eio .. _ . .
peered to be restrictee to 20 C., While at the lover sell moistures sev-

ere infection occurred over a wider range of temger tures.

Infection of Onions Seeded in Naturally Infested Soil

The materials end netlods used in this exgerinent were identi-
cal with those used in studying the infection of onion transgltuts exceot
that the onions were seeded directly in n turelly infested soil and grown

for e neriou of 69 days. The reletion of soil temper ture and soil mois-

‘r

ture to the infection of onions grown from seed in naturally infested gin

root soil 18 shown in Table 4.
The results of this experiment corroborrte those on onion trans-

. o 0 fl. 1 ‘,,.0
plant infection and innicete that no

C. is the ontfnwn soil temperature for
the develoyment of pink root in neturelly infested soil. it this tenpersture

100 per cent of the onions were infected in the 70 per cent seturtted soil,

 

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- 18 -

and more than 90 per cent were infected in the 80 per cent saturated
soil. In contrast to this only 55 to 60 per cent of the glents were
infected at 24° C. At 34° and 280 C. the average dry weight per plant
was from £5 to 45 per cent greater then at 260 C.

v

A further examination of Table 4 reveals the relative amount
of root infection. At 20° C. less than 6 per cent of the total dry
weight of the roots was disezsed, st 220 C. less then 8 per cent, and at
240 C. 1953 than 9 per cent. At 26°, 23°, and 30° C., however, more than
17 per cent of the roots were diseased in the 8 per cent saturated soil
and more then 22 per cent in the 70 per cent saturated soil.

The effect of gink root infection on onion roots is illustrated
in Plate 2. This clearly shows the reduced number of roots on the plants
grown in soil maintained at 260 and 280 C.

In this experiment infection was most severe in the plants
growing in the 70 per cent saturated soil. In the grevious experiment
using onion transplants infection appeared to be slightly nore severe
in the 80 per cent than in the 70 per cent saturated soil, although the
differences were sli ht. This was the only major difference in the re-

\1

sults obtained in this and the previous exoeriment.

A

Infection of Onion in Artificslly Infested Soil
The muck used in this experiment was obtained from an seperently
pink root-free onion field neeriKelsmezoo,Michi5en. I was steamed 8-10
hours and stored for a month before it was used. Oat cultures of a very
pathogenic isolste of P. terrestris were used for rsoil infestation and the
onions were seeded directly in this soil. The glents were harvested 68

days after seeding. The results of this experiment are given in Table 5.

‘ F931. IE Il'illi.
, . . o > .

 

 

- 19 -

TnBLE 5. The relation of soil temperfiture and soil moisture to the in-
fection of onions seeded directly in nrtificnlly infested soil and

grown for a period of 68 days.

 

 

 

 

 

 

 

TSEP° no. of plants Average dry wt. of Per cent of
tOPS.P€T4P1hnt -.EES- plants dead in
Infested Noninfested Infested Noninfested infested soil
soil soil soil soil
60 per cent saturated soil
2O 24 2 .058 .069 O
22 25 2 .059 .056 O
24 24 2 .056 .055 0
2 25 25 .017 .045 12
28 26 26 .008 .026 58
50 16 22 .008 .018 50
70 per cent saturated soil
2O 25 25 .086 .085 0
22 26 25 .079 .085 O
2 25 25 .049 .061 O
26 25 25 .021 .051 12
2 25 25 .015 .048 55
5O 24 25 .005 .050 75
80 per cent saturated soil
2O 25 24 .105 .120 0
22 25 25 .105 .088 O
2 25 25 .076 .090 0
26 25 25 .022 .059 10
28 26 25 .014 .057 44
50 27 25 .000 .057 100

 

The fungus use most destructive in soil held at 30° C. At this
temperature the largest number of plants were killed by pink root. it and
below 24° C. there were no plants killed by the disease. At 26° C., lO-l2
per cent of the plants were destroyed by the funius; at 28° C., 55-44 per

cent were killed; and at 50° C., 50 - 100 per cent were killed.

- 20 -

The plants growing in the 80 per cent saturated soil were
more severely damaged than those at 70 per cent, and the glarte at 60
per cent saturation were the least damaged. Indicrtions were, honever,
that the amount of soil moisture influenced the critical temperature at
which infection became serious. In the 60 per cent saturated soil the
effects of the fungus were evident in the plants growing at 22° C. In the
70 per cent saturated series the effects did not become noticeable until
the soil temgeratures reached 24° C. In the 80 per cent saturated series
the effects of the fungus infection did not becomeeyident until the soil
temperature was 26° C. There were indications of infection at 24° C., but
these were very slight as compared to those in the 70 per cent saturated
series at this same temperature. The effects of pink root infection were
visible 45 days after the onions were seeded at all soil temgeratures above
24° C. At this time all of the plants growing in the soil maintained at
50° C. and 80 per cent saturation had succumbed to the disease. The ef-
fects of these soil maistures and soil temperatures on the development of

the disease are clearly illustrated in Plate IV.

TABLE 6. Analysis of variance of pink root infection in onions grown at

. nno
$011 temperatures of 24Pand 20 C.

 

 

Source of variation Degrees Sums of Mean F
of squares square value
Freedom
Between temgeratures (T) 1 1.81 1.81 78.7*
Between infested and
noninfested soil (1) 1 1.51 1.51 65.6*
Between soil moistures (fl) 2 1.5 0.70 51.6*
T x I l 0.47 0.47 :0.4*
T x e 2 0.09 0.30 12..*
I x % 2 0.04 0.02 0.9
T x I x % 2‘? an on
Within 12‘; '““ 0'0“”
Total 25 6.15

* Statistically significant at 5% level of F.

Table 6 is an analysis of Variance showing the significance of
the various factors which entered into this experiment. The analysis is
limited to the 24° and 26° C. soil temperatures. These soil temgerstures
were used because the experiments indicated they were the critical temper-
atures for infection. This analysis shows there is a significant differ-
ence between the results obtained at the two soil temperatures. The dif-
ferences between the plants growing in the infested and noninfested soils
are also significant. The difference between the infested and noninfested
soils at 26° C. was so great that there is no doubt about its significance.
On the other hand, the difference between these two factors was not as great
at 24° C., but a test of significance of the means at this taupereture in-
dicated tzat the difference in weights of the plants is significant. In
other words, the fungus does enough damage at this temperature to be im-
portant.

The analysis also shone that the interaction between the two
soil temperatures (24° and 26° 0.) and between the infested and noninfestod
soil is significant. This is not true for the interaction between the in-

fested and noninfested soil and the various soil noistures.

DISCUSSI§§_

The results obtained in the exgeriments just described indicate
considerable dijference in severity of infection of plants growing in
naturally infes ed soil and artifically infested soil. In the naturally
infested soil the plants were considerably stunted in growth at 260, 280,
and 500 0.; but there were no plants killed directly by the fungus. 0n
the other hand, several plants were killed at these tenoeretures in the

artificially infested soil. It is possible that there would have been

some mortality at these temocrstures in the naturclly irfested soil had

the experiment been continued for a longer period. This was evident
from an examination of the root system. The roots on naiy of the plants
grown at a soil temperature of 260 C. were completely disintegrated a
the time the plants were h rvested.

It is very difficult to find an eXplsnetion for the differences
in optimum soil tenperetures for the infection of onions in naturally
and artifically infested soil. In steamed soil‘artifically infested,the
optimum was 50° C., and in natur lly infested field soil it was 26° C.

The studies on the relation of temperature to the growth of Phone terres-

 

tris indicated that the differences in the growth rate of the nycelia of

 

the fungus were very slight at 26°, 330, and 30° C. On two kinds of media

the aversge radial growth was the same at 26° and 30° C. This would in-
dicate that plants growing at soil temoeratures of 26° and 300 C. should
be equally susceptible to the disease providing other conditions are the
same. There was, however, a difference in the growth and devalogment of
the onion at these two soil temperatures. The average dry weight of the

. . . . . o . 0
onions groning 1n steamed 5011 was conSiderably less at 30 than at 26 C.

d

It is possible that onion plants growing under the more unfavorable con-
ditions (500 C.) are'more susceptible to pink root than those growing under
conditions more favorable for growth (260 C.). If this is so, then 50° C.
would be the optimum soil temperature for the develOpment of pink root in
onion. This was true for the plants growine in the artifically infested
steamed soil. The results obtained in the naturally infested soil do not
comply uith this hypothesis. In that case the competition among the soil
microorganisms, which was prrctically eliminated in the artifically in-
fested soil by steaming, may have been capable of limiting the activity

of P. terrestris st the higher soil terperetures.

- 02
kfl -

the eXperiment been continued for a longer period. This was evident
from an examination of the root system. The roots on many of the plants
grown at a soil temperature of 260 C. were completely disintegrated at
the time the plants were harvested.

It is very difficult to fin an eXplenetion for the differences
in Optim‘m soil tenperetures for the infection of onions in naturally
and srtificelly infested soil. In steamed soil‘srtificelly infested,the
Optimum was 30° C., and in natur:lly infested field soil it was 26° C.

The studies on the relation of temperature to the growth of Phone terres-

 

Egg§_indicated that the differences in the growth rate of the mycelie of
the fungus were very slight at 26°, 330, and 30° C. On two kinds of media
the average redial growth was the same at 26° and 30° C. This would in-
dicate that plants growing at soil temperatures of 26° and 30° 0. should
be equally susceptible to the disease oIoviding other conditions are the
same. There was, however, a difference in the growth and develogment of
the onion at these two soil temperatures. The average dry weight of the
onions growing in steamed soil was considerably less at 30° the at 26° C.
It is possible thet onion plants growing under the more unfavorable con-
ditions (1300 C.) are more susceptible to pink root than those growing under
conditions more favorable for growth (260 0.). If this is so, then 30° 0.
would be the optimum soil temperature for the development of pink root in
onion. This was true for the plants growing in the artificelly infested
steamed soil. The results obtained in the naturally infested soil do not
comply with this hypothesis. In that case the competition.emon3 the soil
microorganisms, which was pr cticelly eliminated in the artificelly in-
fested soil by steaming, may have been capable of limiting the activity

of‘gg terrestris at the higher soil temperatures.

I
5‘3
(,0.

I

The effect of the fungus on plsnt prowth was much nore evident
at the lower soil temperatures in the srtificnlly infested soil than in
the naturally infested soil. In the natu'elly 'nfested soil the effects
of the fungus were not evident below 26° C., while in the ertifically
infested soil they were visible at 220 C. This noticeable effect at the
lower temperatures in the artificslly infested soil may be because of the
presence of P. terres ris in the soil WithJUt s grest deal of competition
from the soil microflora, the soil microflora having previously been re-
duced in number by thoroughly steaming the soil.

The effects of P. terrestris upon onion develOpment are summer-
ized in Figure 1. This chart shows graphically the relation of soil tem-
perature and soil moisture to the growth of onions in noninfested soil,

and also the relation of these factors to infection in artifically in-

m

fest d soil. The one thing that is especially noticeable on this chart
is the sudden increase in the amount of pink root infection at 26° C.
This is further illustrated by a comparison of the plants shown in Plate
III and IV. These two plates are directly comparable.

This sharp line of demarcation in the amount of pink root in-
fection at soil temperatures between 24° and 26° C. can be partially ex-
plained on the basis of different Optimum temperatures for the fungus and
for the host. The onion plant grows well at or below 24° C. It is hind-
ered in its development by hiéher soil temperatures. Phone terrestris
made its best growth at 260, 280, and 30° 0. (Plate I). Below 260 0.
its growth rate was retarded by the lower temperutures. The difference
between the optimum temperature for the growth of the fungus and the }ost

o . . . , .,
was from 6-8 C., dependins upon the $011 conditions under whicn the plants

‘4

were growrng. It is highly probable thet onion giants growing under favor-

..
A

able environmental conditions are less susceptible to disease than those

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growing under unfavorable conditions. It was shown in the exyeriments
on environmental relations that P. terrestris we more infectious when
growing under ottimum conditions for its development than when growing
under unfavorable conditions. Therefore, a legicel exhlanetion for this
phenomenon can be based on the interaction between two different Optimum
temperatures.

It is evident from the results obtained in the experinents on
the relation of environment to the disease that pink root does not be-
come serious until the soil temperatures approach 260 C. This would in-
dicate that pink root may becone epidemic in any region where the causal
fungus is present in the soil, yrovided the soil tenperatures have remained
favorable for infection over an extended period. In.Michigen this occurs
nearly every year because hot, dry weather is experienced during the later
part of July end the early part of August when the late onion crop is set-
ting bulbs.

The summer of 1940 was no exception. .Pink root was epidemic in
the older onion gTJWing areas and caused serious losses. At Kalamezoo,
Michigan, the minimum temperatures from July 18 to August 18 rarely fell
below 15.50 C., and the lowest maximum temgerature for any day during this
same period was not below 26.60 C. Because of the unseasonably high tem-
peratures, few onion fields infested with the pink root fungus escaped
injury from the diseas .

The condition of two large adjacent fields near Eaton Rapids,
illustrates the seriousness of pink root during an egidemic year. The
fields were similar excegt that pink root was found in only one. Both
were adequately fertilized. The field free from the disease we still
green at the end of the first week in September. .At that time the tops
were rolled down to hasten maturity of the plants, a common commercia

fractice. The bulbs were large and were held firmly in the ground b*

J

1'0

5-

a healthy root system. At harvest time this field yielded apbroximately
700 crates to the acre, and if the onions had been allowed to mature

naturally the yield would probibly have been much greater. On the other
hand, the crop on the diseased field had ripened prematurely by the last

week in August. The bulbs were smell and it was practically inyossible

5

to find a healthy root on then. This field yielded aporoximntely 300
crates of onions to the ecre. Figuring the Value of onions per crate

:"- C'

at $1.00, the loss per acre was at least oo00.00.

Evidence has been presented to show that P. terrestris grow

 

 

well at temperatures from.26° to 50° C. with en ogtinum at 28° C. The
maximum temperature was between 330 and 34° C., and the minimum was

slightly below 100 c.

The radial growth of the mycelium of P. terrestris on culture

 

plates was not greatly influelced by different h‘drouen-ion concentra-

tions. The fungus 5

ran well within the range of pH 4 an‘ pH 8, with the
optimum between pH 5 and pH 6.

The Downing Yellow Globe onion made its best growth and devel-
opment at soil temperatures from 180 to 243 C. in 70 and 80 her cent
saturated soil.

Onion plants grown directly from seed in naturally infested
soil developed pink root most rapidly at 26° C. when the soil moisture
content was maintained at 70 per cent of its water—holding capacity.
Onion transplants did not show a comparable amount of infection until
the soil moisture was brought up to 80 per cent of its water-holding

cagacity. In steamed soil infested with P. terrestris the optimum soil

 

 

 

 

 

; .Jfl.-.1ll.',. ; . .. . .a 3: H.v.....er!.ri«lShm.a
. ‘

temperature for infection of the onion roots was 300 C., and the Optimum
soil moisture content was at 80 per cent of its water-holding capacity.

The marked increase in the amount of infection in plants grow-
ing at a soil temperature of 260 C. can be iertially exgleined on the basis
of different optimum teegeratures for the growth of the fungus and of the
host.

The disease is likely to reach epidemic QTOgortions in any field
where the fungus is already GStLbliShC , if the soil temperatures agproech

o . . . .
26 C. ano remain here for an extended yeriod of time.

 

10.

I
rs
a)

I

LITERATURE CITED

Davis, Glen N. and W. J. Eenderson. The interrelation of the
pathogenicity of e Phone and a Fusarium on onions. PhytOQLth.
325 765-772. 1937.

Du Plessis, S. J. Pink root and bulb-rot of onions. Farming in
So. firica _9_: 70. 1954. (.abst. in Rev. Appl. L-Lyc-ol. .3: 558.

Hansen, E. N. "Pink-root" of onions caused by Phone so. Science
N. S.'gg: 525. 1926.

Etiology of the pink root disease of onion.

 

Phytopath. 19: 691-704. 1929.
Phone ter estris, n. Sp., es the cause of Line
of onions. (Abst.) Phytopeth. 19: 1135-1136. 1929.

A

Kowitt, J. E. Two diseases new to Ontario. Sci. egr. a: 189.
1923.
Sideris, C. P. S>ecics of Fusarium isolated from onion roots.

Phytopeth. 161.: 211-216. 1924.

The effect of the E-ion concentration of the culture

 

solution on the behavior of Fusarium cromvophthoron and Allium

ceoa and the develogment of pink root disease symgtoms. Phytopath.

l

w-

Teubenheus, J. J. end A. D. Jonnson. Pink root, a new disease of
onions in Texas. (Abst.) PhytoPeth, Z} 59. 1917.

and F. W. Melly. Pink root disease of onions and

 

its control in Texas. Texas Agr. Exp. Sta. Bul. 273. 1921.

11.

Thornberry, H. H., and H. R. hnderson.

United States Department of Agriculture.

I
{0
(O

I

Pink-root disease of onions

on tomatoes. U. S. Dept. Agr., Bur. Plant Indus. Plant Dis. Betr.

24: 383-384. 1940.

Grog Eeyortin; Board.

Acreage and production of commerciel truck croys. December 1940.

1L.L..L11£nmb - _ ‘5.-. L.

in“. 3-5.0}: 1513-!- " '

 

PLATE I.
The relation of teneerwture to the grofth of Rhoma terrestris.

Phone terrestris grown on cornLeel egvr for 11 days at 10°, 14°,

t“ .‘q 5‘. P '1 f7.‘ . ' ,_ .., n
"0 “4°, no“, Loo, LOO, PRO "30 C. The LCXllom growth occurred

 

 

PLATE I

 

. . .3. s In. 41?! 7 ~01 fl .
.. ‘ L «w ' Y ,

 

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iafl ‘4‘" m.‘-2‘.fl"-—v -l‘l-'vilu

EWJIPE II.

The relation of soil temperature and soil moisture to the in-

fection of onion roots by P. terrestris.

 

The roots are from plents grown from seed in naturally infested
field soil for 69 days at 20°, 22°, 24°, 26°, 29°, and 30° C. with mois-
ture contents of 60, 70, and 90 per cent of its Ester-holding ccoecity.
Each moisture series shows one root system from each of the soil tempera-

o n this soil the

O
o
l“!

tures. Note the reduced root svstems at 260 end 28

d

O

O
o

optimum temperature for infection on onion roots was 26

 

 

 

PIA‘I‘E II

 

. , ‘ n......a."’ L§:_mm—.L.—‘—.A._.:_J-c ‘.

PLATE II.

The relation of soil temperrture and soil moisture to the growth

and development of the onion.

The plants were seeded directly in the soil cens and grown for
8 days. The soil was thoroughly steamed a month before using and was
well fertilized prior to seediz

1930

The plants were grown at the same
3011 temperatures end soil moistures u

1

GESCTibCQ for Plate II. The
best growth occurred in the soil maintained at 80 per cent saturation

and at temperatures from 20° - 24° C., inclusive.

 

 

 

 

 

 

 

 

PLATE III

 

i’IuZTE IV .

The relation of soil temperature end soil moisture to the de-

veIOpment of pink root in onions grown in artificslly infested soil.

The plants were brown directly from seed in soil infested
with out cultures of a pathogenic isolate of P. terrestris. The plents
were grown under the same environmental conditions as those shown in
Plete III. The only difference between he two sets is that the soil
in one (Plate III) was not infested with the fungus. Heavy infection
occurred at soil temper:tures from 260 to 30° C., inclusive, with the

heaviest infection at 30° c.

 

 

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