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not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
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site maintained by the Florida
Cooperative Extension Service.
Copyright 2005, Board of Trustees, University
Bulletin 197 May, 1928
UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
SOIL TEMPERATURE STUDIES
By M. N. WALKER
III. Relation of Soil Temperature and Soil Moisture to the
Soreshin Disease of Cotton.
Bulletins will be sent free upon application to the
Agricultural Experiment Station
BOARD OF CONTROL
P. K. YONGE, Chairman, Pensacola E. L. WARTMANN, Citra
E. W. LANE, Jacksonville J. T. DIAMOND, Secretary, Talla-
A. H. BLANDING, Leesburg hassee.
W. B. DAVIS, Perry J. G. KELLUM, Auditor, Tallahassee
STATION EXECUTIVE STAFF
WILMON NEWELL, D. Sc., Director ERNEST G. MOORE, M. S., Asst. Ed
JOHN M. SCOTT, B. S., Vice-Director IDA KEELING CRESAP, Librarian
S. T. FLEMING, A. B., Asst. to Di- RUBY NEWHALL, Secretary
rector K. H. GRAHAM, Business Manager
J. FRANCIS COOPER, B. S. A., Editor RACHEL MCQUARRIE, Accountant
MAIN STATION-DEPARTMENTS AND INVESTIGATORS
AGRONOMY BRUCE McKINLEY, B. S. A., Asst.
W. E. STOKES, M. S. Agronomist M. A. BROOKER, M. S. A., Asst.
W. A. LEUKEL, Ph. D., Asso. ECONOMICS, HOME
C. R. ENLOW, M. S. A., Asst.* OUIDA DAVIS ABBOTT, Ph. D., Chief
FRED H. HULL, M. S. A., Asst. L. W. GADDUM, Ph. D., Asst.
A. S. LAIRD, M. S. A., Asst. C. F. AHMANN, Ph. D., Asst.
ANIMAL INDUSTRY ENTOMOLOGY
JOHN M. SCOTT, B. S., Animal J. R. WATSON, A. M., Entomologist
Industrialist A. N. TISSOT, M. S., Asst.
F. X. BRENNEIS, B.S.A., Dairy H. E. BRATLEY, M. S. A., Asst.
R. W. RUPRECHT, Ph.D., Chemist A. F. CAMP, Ph. D., Asso. Hort.
R. M. BARNETTE, Ph. D., Asst. M. R. ENSIGN, M. S., Asst.
C. E. BELL, M. S., Asst. HAROLD MOWRY, Asst.
H. L. MARSHALL, M. S., Asst. G. H. BLACKMON, M. S. A., Pecan
J.. M. COLEMAN, B. S., Asst. Culturist
J. B. HESTER, B. S., Asst. PLANT PATHOLOGY
COTTON INVESTIGATIONS G. F. WEBER, Ph. D., Asso.
W. A. CARVER, Ph. D., Asst. K. W. LOCKS, B. S., Asst.
M. N. WALKER, Ph. D., Asst. ERDMAN WEST, B. S., Mycologist
E. F. GROSSMAN, M. A., Asst. VETERINARY MEDICINE
RAYMOND CROWN, B.S.A., Field Asst. A. L. SHEALY, D.V.M., Veterinarian
ECONOMICS, AGRICULTURAL D. A. SANDERS, D. V. M., Asst.
C. V. NOBLE, Ph. D., Ag. Economist E. F. THOMAS, D. V. M., Lab. Asst.
BRANCH STATION AND FIELD WORKERS
W. B. TISDALE, Ph. D., Plant Pathologist, in charge, Tobacco Experiment
Ross F. WADKINS, M. S., Lab. Asst. in Plant Pathology (Quincy)
JESSE REEVES, Foreman, Tobacco Experiment Station (Quincy)
J. H. JEFFERIES, Superintendent, Citrus Experiment Station (Lake Alfred)
W. A. KUNTZ, A. M., Assistant Plant Pathologist (Lake Alfred)
R. L. MILLER, Assistant Entomologist (Lake-Alfred)
W. L. THOMPSON, Assistant Entomologist (Lake Alfred)
,GEO. E. TEDDER, Foreman, Everglades Experiment Station (Belle Glade)
R. V. ALLISON, Ph. D., Soils Specialist (Belle Glade)
J. H. HUNTER, M. S., Assistant Agronomist (Belle Glade)
J. L. SEAL, Ph. D., Assistant Plant Pathologist (Belle Glade)
H. E. HAMMAR, M. S., Field Assistant (Belle Glade)
L. O. GRATZ, Ph. D., Associate Plant Pathologist (Hastings)
A. N. BROOKS, Ph. D., Associate Plant Pathologist (Plant City)
A. S. RHOADS, Ph. D., Associate Plant Pathologist (Cocoa)
STACY O. HAWKINS, M. A., Field Assistant in Plant Pathology (Homestead)
D. G. A. KELBERT, Field Assistant in Plant Pathology (Bradenton)
R. E. NOLEN, M. S. A., Field Assistant in Plant Pathology (Monticello),
FRED W. WALKER, Assistant Entomologist (Monticello)
E. D. BALL, Ph. D., Associate Entomologist (Sanford)
*In cooperation with U. S. Department of Agriculture.
SOIL TEMPERATURE STUDIES WITH COTTON
III. Relation of Soil Temperature and Soil Moisture to the
Soreshin Disease of Cotton.
By M. N. WALKER
The "soreshin" or Rhizoctonia disease of cotton has- been
known for a number of years, though it was not until compara-
tively recently attributed to its true cause; and even now its
injuries are often attributed by cotton growers to bad seed, cold
weather, or careless hoeing and cultivation. It is due to this
fact that a satisfactory estimate of the importance of the dis-
ease is difficult. "The Plant Disease Reporter" (9), however,
states that "in South Carolina, Mississippi, Louisiana, Arkansas,
Texas, and Arizona, considerable trouble from this disease re-
sulted [during 1926]. In Louisiana, Arkansas, and Arizona par-
ticularly, collaborators remarked that wet and cool weather in
the early part of the season caused much rotting of young plants,
necessitating a great deal of replanting." There can be no doubt
that the disease is a frequent cause of poor stands and replant-
ing during weather favorable to it, and it was in an effort to
more closely define the factors involved in the term "favorable
weather" that the present work was initiated. A thorough under-
standing of the environmental factors favorable to the "sore-
shin" disease is necessary in interpreting results in the field and
in working out control measures.
The soreshin disease of cotton has been reported from every
cotton growing state (9, 21) as well as from foreign countries,
as Egypt (3) and India (24). It is probable, however, that the
disease occurs in all countries where cotton is grown (although
no reports are available), since the causal fungus, Rhizoctonia
solani, is one of the most widely distributed of fungi.
Although there is rather an extensive literature available on
Rhizoctonia diseases, the greater part of it is concerned with
*Figures in parentheses refer to bibliography, page 370.
346 Florida Agricultural Experiment Station
the disease of potatoes, and the literature on the disease of cot-
ton and other crops is somewhat meager.
As the greater part of the literature on the Rhizoctonia dis-
ease of cotton is of a general nature it will not be discussed here.
Only a brief summary of the history of the disease and of the
determination of the causal organism is given under this sec-
tion. Other literature dealing with the more specialized phases
of the work will be given later under the different sections.
The term soreshin was used earlier than 1855 by planters and
in that year Glover (16) reported it as caused by careless hoe-
ing and cold, cutting winds when the plants are young. It was
not, however, until 1892 that soreshin or damping-off was first
adequately described by Atkinson (1) of Alabama, who was able
to isolate and culture the causal organism, and to prove the
pathogenicity of the fungus by inoculations. Atkinson did not
identify the causal fungus as Rhizoctonia, but called it "the
sterile damping-off fungus." Atkinson (2) later, working at
the Cornell Experiment Station, found the same "sterile damp-
ing-off fungus" associated with the damping-off of various vege-
Duggar (10) isolated a fungus from sugar beets affected with
a root rot and identified the fungus as Rhizoctonia betae Kuihn.
After inoculation trials with the beet fungus on hosts used by
Atkinson in his experiments with "the sterile damping-off fun-
gus", Duggar stated that the two fungi were apparently iden-
In 1909 Duggar (11) lists the damping-off of various plants,
including the soreshin disease of cotton, as caused by Rhizoc-
tonia solani Kuihn (Corticium vagum B. and C.). In a still later
paper, Duggar (12) reviews very carefully the literature extant
on R. solani Ktihn and R. Crocorum Pers. and explains the ori-
gin of the binomial R. betae Kuihn, to which he attributed the
root rot disease of the sugar beet. This name, Duggar suggests,
probably originated with Eidam rather than with Kihn and he
believes it is unquestionably the same. fungus now generally
known in this country as R. solani Ktihn. In this paper Duggar
also states more definitely the conclusions reached in his earlier
work as to the probable identity of R. betae and "the sterile
damping-off fungus" of Atkinson.
Balls (3, 4, 5) in Egypt has probably done more with the sore-
shin disease of cotton than any one else, having worked on prac-
Bulletin 197, Soil Temperature Studies With Cotton 347
tically every phase of the problem from cause to control. Balls
was the first man to suspect the probable importance of soil
temperature in relation to the disease and carried on some work
of this nature which will be discussed later.
Rhizoctonia injury to cotton is manifested in three ways: by
reducing germination, by causing a damping-off of the seed-
lings, and by causing a boll rot. The latter injury is rare, occur-
ring only on bolls near the soil and as it is of no practical import-
ance it will not be further discussed. The other two injuries,
however, are extremely common and are of decided practical
importance during favorable weather conditions, when they may
cause a large reduction in stand or even necessitate wholesale
Defining germination for practical purposes as the appearance
of the seedling above the soil, Rhizoctonia may be considered as
causing reduction in germination by attacking the plant be-
fore it reaches the surface of the soil. It will be seen that this
type of injury is the most serious, for even a relatively slight
attack of the fungus at this time may be sufficient to kill the
growing point and thus prevent further growth from taking
place. While the plant is underground any part of it may be
attacked and often the radical is attacked as soon as it emerges
from the seed coat. The fungus then enters the seed coat and
rots the cotyledons before they begin to unfold. Later attacks
may .cause a general soft rot of the radical and cotyledons after
they are well out of the seed coat.
After the cotyledons have reached the surface of the soil the
only area attacked is that portion of the stem just at or immedi-
ately below the soil surface as this area seems to be the region
presenting conditions most favorable to the fungus. Attack at
this time presents two types of injury, damping-off and the true
soreshin. The two types of injury are different only in degree
and all gradations between the two may be found. Damping-off
is the complete girdling of the stem by a soft rot just at or below
the soil level, thus causing the plant to wilt and fall over. This
injury involves a deep penetration of the fungus which reaches
the phloem and destroys it. The term soreshin designates a less
severe attack of the fungus or an early stage of damping-off,
in which a canker or a mere superficial browning appears on one
348 Florida Agricultural Experiment Station
side of the stem. Recovery of the plant often follows this type
of injury and even when the plant appears to be completely
girdled recovery is often observed. This injury involves only the
cortex and is often stopped by the formation of cork on the part
of the host. There are a number of factors which allow the host
to delimit diseased areas by a cork cambium, one of which is
temperature. Some stunting may accompany this type of injury,
but this is a minor phase of Rhizoctonia injury.
A superficial browning that is very similar to the browning
A B C D
I r i
Fig. 147.-Various effects of Rhizoctonia on young cotton plants. A, plants
from control pots; B, soreshin type of injury; C, a more serious type
of soreshin injury; D, plants "damped-off" by Rhizoctonia. About twice
Bulletin 197, Soil Temperature Studies With Cotton 349
caused by Rhizoctonia is very common in the field during the
summer months. Much of this browning is probably caused by
excessive soil temperatures, 390 C., or above, in the surface inch
or two of soil. It is distinct from the browning caused by Rhizoc-
tonia early in the season, which apparently sloughs off and dis-
appears as the plant grows. Stem lesions and browning may be
caused by other. fungi and Shapovalov (23), recognizing this
suggests that the term "soreshin" be used to designate the group
of diseases rather than the disease caused by Rhizoctonia. Since
Rhizoctonia appeared to be the chief cause of damping-off and
"soreshin" early in the season during the past two seasons in
Florida, the term is used here in the specific sense. In figure
147 are shown various types of Rhizoctonia injury.
Rhizoctonia solani Kiihn, the sterile stage of Corticium vagum
B. & C. is the cause of the soreshin disease of cotton. This fun-
gus is practically omnivorous, and attacks a great many differ-
ent plants, both cultivated and wild, 165 of which are listed by
Peltier (21). As Duggar (12) and Peltier (21) have given good
accounts of Rhizoctonia solani Kiihn, only a brief description of
the fungus is given. The description is quoted from Peltier (21)
and agrees in all essential details with the fungus used in the
"The morphological characters of Rhizoctonia solani Ktihn
vary with the age of the mycelium. The young hyphae branch
at an acute angle from the parent hypha, subsequently lying
parallel to it. A constriction is shown at the point of union, and
a septum is generally laid down a short distance from this point.
The threads are colorless and vacuolate. With age the hyphae lie
more at a right angle with the main axis, showing less constric-
tion. They deepen in color into a yellowish and then a rather
deep brown, becoming more or less granular and empty. Fusion
of hyphae is very common and can be observed in any young
culture of the fungus. It occurs either between hyphae of the
same parent mycelium or between hyphae from separate col-
"On many hosts a short tufted or bushy growth of the my-
celium may occur with some strains. This tufted growth is like-
wise present in cultures of the strains that produce such growth
350 Florida Agricultural Experiment Station
on the host plants. The tufts are composed of brown hyphae,
closely septate, constricted at the septa, and often branching in
an irregular manner.
"Sclerotia in cultures first appear as small, soft, white masses
of hyphae. Later they become larger and turn dark and hard.
Study of sclerotia at different ages shows that they are of uni-
form structure composed entirely of masses of irregular and
barrel-shaped cells which break up into sections of one or sev-
eral cells. These shortened hyphal cells function as conidia and
germinate readily under suitable conditions. Germination gen-
erally takes place by the protrusion of a tube thru the septum of
a cell where it has broken away from an adjacent cell. In some
cases the hyphae of the germinating cells pass thru adjacent
cells, which are apparently empty. Occasionally these irregular
barrel-shaped cells germinate equatorially instead of at the
poles. After the germ tube has grown out some distance, it be-
comes narrowed near the germinating cell and a septum is laid
down. The mycelium then develops in the usual manner."
THE RELATION OF SOIL TEMPERATURE TO THE
SORESHIN DISEASE OF COTTON
Very little work has been done on the relation of soil tem-
perature to the soreshin problem. Balls (3, 4) has made field
observations that show the dependence of the disease on favor-
able temperatures. From these observations Balls was unable to
point out an optimum temperature range for the disease, but
states that low temperatures are most favorable.
Jones (18) made a few trials of the effect of the Rhizoctonia
from potatoes on cotton and found greatest injury at about
180C. Practically the same optimum temperatures were found
in work with potatoes, beans, and peas.
The apparatus for the control of soil temperatures used in
this work is fully described in a bulletin of this Station (7). It
consisted, in brief, of an internally balanced series of tanks
regulated to various temperatures, each tank containing 'eight
pots, five inches in diameter and sixteen inches in depth.
The soil used in the experiments was of the Norfolk sandy
loam types found in the vicinity of Gainesville. During the early
Bulletin 197, Soil Temperature Studies With Cotton 351
experiments the soil was screened and then placed in a steam
sterilizer, thoroughly wetted and steamed three times on alter-
nate days at temperatures ranging from 850 to 1000C. The soil
was then brought to a suitable and uniform moisture content
and placed in the pots, 7.5 kilos to each pot. In later experi-
ments a large autoclave was used in which the soil was steril-
ized in the pots for two to three hours at 15 pounds pressure.
The soil was inoculated with flask cultures of the fungus ground
up in a mortar with sterile sand. The cultures were usually
about two weeks old when used. The inoculum was thoroughly
incorporated in the upper two or three inches of the pot. After
allowing the pots to stand for two or three days at the same
temperature to allow the fungus to begin a good growth, they
were placed in the tanks and a day longer allowed before plant-
ing so that the pots might reach the tank temperatures and in
order to make any necessary adjustments of the control appa-
ratus. In planting, four to six delinted seed were used, planted
to a depth of one inch around the edge of the pot to insure uni-
form temperatures for all the seed. The tops of the pots were
then covered with ground cork, the so-called "doll cork," to a
depth of approximately one half inch to reduce evaporation and
to help insulate the surface against heat losses. The plants were
watered by merely bringing the pots up to the original weight,
though during some of the later experiments the pots were
watered by merely adding water to the pots showing a need
for it. No more variation occurred in series watered in this
manner than in others where the pots were brought to weight.
The pots at the higher temperature required water almost
every day, but as the temperatures decreased in successive com-
partments an increasingly smaller amount of water was neces-
Notes were taken each morning on germination and killing.
Temperature records to the nearest quarter of a degree were
taken throughout the day with occasional records taken at night.
An average was taken of these readings for the duration of each
experiment. As the temperature records were taken by three
different persons there was consequently some variation in the
readings, but several checking showed never more than a quar-
ter of a degree difference in readings.
352 Florida Agricultural Experiment Station
The first experiment to determine the relation of soil tem-
perature to the soreshin disease of cotton was run in June 1926,
and no other series was run until fall on account of the high
temperatures prevailing in the greenhouse during the summer
months. In this series four delinted seed of the variety Light-
ning Express No. 3 were planted in each of the eight pots of a
tank. The soil of four of the pots had been inoculated with
Rhizoctonia. The other four pots served as controls. Since the
results of this series differ somewhat from those of other series
with the variety Lightning Express they are tabulated and
charted separately, in Table I and figure 148, which show the
effect of soil temperature on the germination of cotton seed in
both infested and uninfested soil, as well as the rate of killing
of germinated plants in the inoculated pots. No injury, either
by reduction in germination or by killing of germinated plants,
occurred at 36.5 C. or above. Below this temperature germina-
tion decreased very rapidly, much more rapidly than in the con-
Q l O /-
. 30 I
14 16 10 W 22 24 26 Z8 3 3 4 $6 36 40
TEMPERATURE IN DEGREE CG.
Fig. 148.-Soil temperature series with Lightning Express. shows
percentage of germination in uninoculated pots (controls); - shows
percentage of germination in inoculated pots; -.-.-. shows percent-
age of killing of germinated plants in the inoculated pots. No killing
occurred in the control pots. In this chart failure to germinate below-
30C. is taken as 100 percent killing.
Bulletin 197, Soil Temperature Studies With Cotton 353
trol pots, and at 300C. no plants appeared above the soil, al-
though control pots at the same temperatures showed a decreas-
ing, yet appreciable germination. Killing increased rapidly below
36.50 C. reaching 100 percent at 300 C. In this case the lack of
germination was considered as killing of all viable seeds.
TABLE I.-SUMMARY OF RESULTS OF A SOIL TEMPERATURE SERIES WITH
Controls Soil Inoculated with Rhizoctonia
Average $ 1 1 1 g .
Tern- M w S
perature r 'g. g g g +
S o $ o.S oS o. S S^ o^
40C. 16 0 ------ -----------16 0--
36.5 16 15 93.75 0 16 15 93.75 0
33.5 16 15 93.75 0 16 7 46.66 0
30.0 16 12 75.00 0 16 0 0 ...........
26.5 16 10 62.50 0 16 0 0 ........-
23.0 16 11 68.5 0 16 0 0 -......
19.0 16 7 43.75 0 16 0 0 ........
From these data it would appear that the disease is equally in-
jurious at all temperatures below 30C. It should be kept in
mind however, that these temperatures are fixed and in no way
approximate field temperature conditions, where a fluctuation
of many degrees may occur in a single day.
After running one other series using Lightning Express seed
an effort was made to find a lot of seed showing a higher per-
centage of germination. Three other series with different lots
of Lightning Express seed showed no improvement; the germi-
nation of one, in fact, being so poor and so variable in the dif-
ferent pots of the same tank that the results were discarded.
Another series with Cook 307-6 seed showed even poorer germi-
nation and the results were discarded. The results of the two
series from which the data were saved are given in Table II,
and figure 149.
The curve of killing in figure 149, is almost identical with that
of figure 148, in that 100 percent killing occurred below 300 and
354 Florida Agricultural Experiment Station
o10 / /
14 16 18 20 22 24 26 28 30 52 34 36 58 40
"TEMPE1ATUm E IN PEGREE5 C.
Fig. 149.-Results from two soil temperature series with Lightning Ex-
press. shows average percentage of germination in uninoculated
pots (controls); - shows average percentage of germination in in-
oculated pots; -.-.-. shows percentage of killing of germinated
plants in the inoculated pots. No killing occurred in the control pots.
TABLE II.-SUMMARY OF RESULTS OF TWO SOIL TEMPERATURE SERIES WITH
Controls Soil Inoculated with Rhizoctonia
Tem- cc U) .. .-
pertaure J g
25.0 22 14 63.63 0 38 8 21.05 8 100.00
22.5 22 14 63.63 0 32 4 12.50 4 100.00
19.0 22 14 63.63 0 32 0 0 ......................
16.5 10 6 60.00 0 15 0 0 ..................
Bulletin 197, Soil Temperature Studies With Cotton 355
31C. However, in the first case all the killing below 300 was
due to failure of the seed to germinate, whereas in the other such
a stage was not attained until the temperature of 190C. was
reached. The prevention of germination would appear to be the
more serious type of injury, although the final results were the
same in both cases-100 percent killing. Alone, the first lot of
data would indicate a wide optimum range for the disease below
30C., considering as optimum the range of greatest injury. In
the second case, the optimum would appear to be under
20C. Such a variation of results with the same variety of cotton
grown under the same conditions of temperature and moisture
in soil inoculated with the same fungus, a Rhizoctonia isolated
from cotton, demands an explanation which will be attempted
later, after the data from other experiments are presented.
After the preceding experiments a lot of seed of the variety
Express 432 was found which gave a very high percentage of
germination, consequently it was used in all subsequent soreshin
experiments. The data from six soil temperature series are given
in Table III, and figure 150. These data show several differences
14 16 18 20 22 24 Z6 28 30 83 34 56 38 40
TEMPEeATURPE IN DEG.EE5 C..
Fig. 150.-Results from six soil temperature series with Express 432.
shows average germination in uninoculated pots (controls); - -
shows average percentage of germination in inoculated pots; -.-.-.
shows average killing of germinated plants in inoculated pots. No kill-
ing occurred in the control pots.
356 Florida Agricultural Experiment Station
from those reported above. In the first place germination in the
control pots was much higher and much more uniform at the
different temperatures. In the second place the germination in the
inoculated pots showed a slower rate of decline and no tempera-
ture at which no germination took place. In the third place the
curve of killing showed a less steep incline and only at one tem-
perature did 100 percent killing consistently occur, 22.50C. These
data by themselves would indicate a definite optimum tempera-
ture of 22.5C. for both decreased germination and killing of
germinated plants, but variations from series to series would in-
dicate that there is a range of temperatures rather than a defi-
nite temperature, although it is also possible that slight varia-
tions in the surface inch of the soil due to the wide range of
daily temperatures that occurred in the greenhouse might have
accounted for these minor variations.
TABLE III.-SUMMARY OF RESULTS FROM Six SOIL TEMPERATURE SERIES
WITH EXPRESS 432.
Controls Soil Inoculated With Rhizoctonia
Average | |) 2
Tempera- M %
Ture og C
38.5C. 72 68 94.44 0 169 160 94.97 0 0
37.0 90 90 100.00 0 132 131 99.24 0 0
34.5 72 70 97.22 0 138 134 97.10 13 97.00
31.5 66 66 100.00 0 120 88 73.33 49 55.68
28.5 66 64 96.96 0 120 47 39.16 33 70.21
25.5 66 64 96,96 0 120 41 34.16 40 97.55
22.5 66 65 98.48 0 120 14 11.66 14 100.00
19.0 60 55 91.66 0 120 16 13.33 14 87.5
15.0 42 40 95.24 0 72 20 27.77 14 70.00
An attack of cotton seedlings by Rhizoctonia under the soil
surface results in death to a larger percentage of the seedlings
attacked than when seedlings are attacked after they appear
Bulletin 197, Soil Temperature Studies With Cotton 357
above ground. This is more or less obvious, since a relatively
slight attack of the fungus might be sufficient to kill the growing
point and thus preclude the possibility of further growth. Later,
when the seedling is up, only a relatively small area of the host
is attacked, and this being just at or below the surface of the
soil is subject to greater fluctuations in temperature. As a re-
sult a soil showing an optimum temperature for the fungus a
short distance under the soil might be several degrees higher
during a shorter or longer period during the day. In Balls' (5)
experiments a few hours' exposure to a temperature of 33C.
or a much shorter one to a temperature of 370C. was found suf-
ficient to stop infections that had started and to so attenuate
the fungus that a period of several hours was necessary for the
fungus to resume growth. This would, no doubt, explain the fre-
quent recovery of plants in the field and a lower percentage of
killing than occurs in greenhouse experiments where the tem-
peratures are maintained at a constant point. Several experi-
ments along this line, in which pots were changed from one tem-
perature to another, showed some agreement to Balls' results but
differed in that higher temperatures and longer periods of ex-
posure were necessary to cause a reduction in the injury from
Rhizoctonia. The results of these experiments are as yet not
complete enough for publication, and will be reported elsewhere.
The first series of soil temperature experiments with Light-
ning Express seed showed 100 percent killing of viable seed be-
low 310C. as indicated by total failure of germination. Two
other series with the same variety run by the writer also showed
100 percent killing below 31C., but in this case total failure of
germination did not occur until the temperature of 19C. was
reached. This variation is probably due to a variation in the lot
of seed used, as great variations were observed in the percentage
of germination of the seed and the vigor of the seedlings of the
same variety of cotton. This point is discussed at 'ome length in
a paper by Toole and Drummond (24). The difference is indi-
cated by the more rapid germination of the seed of the second
two series. Table IV and figure 151 show the length of time nec-
essary for 90 percent germination to take place ih the different
lots of seed used in these experiments. These figures show that
below 30C. the seed of the second two series with Lightning
Express consistently germinated one day earlier) than those of
the first series. The one day longer exposure of the seedling tc
358 Florida Agricultural Experiment Station
>- I2 0
S6 + X o
+ y x 0 o X
S4 + + +
14 16 18 20 22 24 26 Z8 S0 52 35 36 38 40
TEMPERATURE IN DEGREC5 C.
Fig. 151.-Number of days required for different lots of seed to reach 90
percent germination at different soil temperatures. The O indicates the
results from the first lot of Lightning Express seed; the X shows the
average of results of two experiments with another lot of Lightning
Express seed; the + shows the average of results of three experiments
with a lot of Express 432 seed.
TABLE IV.-AVERAGE NUMBER uF DAYS FOR GERMINATION OF DIFFERENT
LOTS OF COTTON SEED.
T eraure Lot 1 Lot 2 Lot 3
C3ntigrd6 e Lightning Expre6 Lightning Express Express 432
38.5 5 .................................... 5 .4
340 5 5 4
310 6 5 4
28 .............................. ...... 5 4.5
26 7 6 5
22.50 8 7.5 6
19 12 10.5 8
16o .................................... 17 15
Bulletin 197, Soil Temperature Studies With Cotton 359
Rhizoctonia below the soil is probably sufficient to account for
the more rapid killing shown in the first series. In any case, the
optimum temperature for killing of Lightning Express must be
determined from the results of the two later series, since there
is no basis for differentiation in the results of the first series.
From these results it would seem that the optimum range for
killing lies below 22.5C.
The results from the experiments with Express 432 would
indicate that this lot of seed was more vigorous than the two
lots of Lightning Express seed used in the earlier experiments.
These results also indicate a definite optimum for infection at
22.50C. from both the standpoint of reduced germination and
increased killing. It is not believed that such a definite point ex-
ists, however, in view of the observed variation in the behavior
.of seed of different varieties and of different lots of seed of the
same variety. It is suggestive that this temperature is the same
as that at which soil temperature begins to be a decided factor
in the growth of the host (7). Another factor that probably
plays a part in variations of results from such experiments is
the existence of strains of the fungus; a point discussed at
greater length elsewhere. Considering the results from all the
soil temperature experiments it would appear that the optimum
range for soreshin attack lies between 17 and 230C. Although
it is difficult to distinguish between reduced germination due to
Rhizoctonia attack and to low temperature, it is believed that
there is a slight reduction in the virulence or the vigor of the fun-
gus at temperatures below 17C. A high percentage of injury to
cotton may result from constant temperatures below 300C., how-
ever, and a day or two of cloudy, cool weather at any time dur-
ing the time that the plants are small may result in severe in-
jury. Judging from the results in all series the maximum tem-
perature for infection would appear to be at 33 or 340C. Some
infection occurred at temperatures as high as 350C. but as the
thermometers were at a depth of about three inches it is prob-
able that surface fluctuations accounted for this, as the house
was rather cool and the higher temperatures naturally showed
greater surface fluctuations than the lower.
As it is planned to determine the relation of changes in soil
temperatures to the Rhizoctonia disease, a correlation of the
360 Florida Agricultural Experiment Station
present work with soil temperature records from the field will
be postponed until the completion of that work.
EFFECT OF SOIL MOISTURE ON THE SORESHIN DISEASE
To test the importance of another environmental factor which
with temperature has been reported (9, 14) as contributing to
the severity of the soreshin disease and on which there is no
specific information, a few soil moisture experiments were run.
The results of these experiments seemed so conclusive that few-
er tests were conducted with soil moisture than with soil tem-
Soil moisture is much harder to control than temperature, and
as a consequence considerable time was used in trying various
methods for maintaining a uniform moisture content in the soil
pots. After a number of trials a method was devised which
seemed to serve the purpose fairly well, though it is doubtful
whether it would be of value except for use with seedling plants.
The variation in the moisture content was attained by varying
the height of the water table. This was accomplished by inserting
sections of four-inch galvanized iron drain pipe in the soil pots
and maintaining varying heights of water in the pots. After
placing a small wad of excelsior in the bottom of each pipe to
prevent the sand from washing out, the pipes were filled with
dry, sterile quartz sand. They were allowed to stand for a few
days, long enough to permit the capillary water to reach the top
of the driest pot. Quartz sand was used because water rises
most rapidly in coarse sand and in preliminary experiments it
was found that the limit of rise was higher than the height
of the pots, 16 inches. Half of the pots were then inoculated
with boiled rice cultures of Rhizoctonia ground up in a mor-
tar with sterile sand. Two days longer were allowed for the
fungus to resume growth, after which time the pots were all
placed in a tank maintained at a temperature of 22.50C., a tem-
perature within the optimum range of the fungus and one at
which seeds of the host germinate fairly well. Two soil mois-
ture determinations were made of the top two inches of soil in
each can and were averaged for use in the table.
Bulletin 197, Soil Temperature Studies With Cotton 361
The average of three soil moisture series are given in Table
V. These data show practically 100 percent injury in the inocu-
lated pots at all the soil moistures tried, which ranged from two
percent to saturation at 20 percent of the dry weight of the
soil. The range was sufficient to materially reduce the germina-
tion in the control pots on the dry side and to completely prevent
germination on the wet side. The germination of three seed in
the driest inoculated pots would indicate some reduction in viru-
lence of the fungus. The germination of two seed in the next
to the wettest inoculated pot might indicate an attenuation of
the fungus due to deficient oxygen as demonstrated by Balls
(5), though the data on this point are insufficient. The experi-
ments show that any soil moisture at which cotton plants will
grow is sufficient to allow the fungus to attack the plants, pro-
viding that the soil temperature is favorable.
TABLE V.-SUMMARY OF THE RESULTS OF THREE SERIES TO DETERMINE THE
RELATION OF SOIL MOISTURE TO THE SORESHIN DISEASE OF COTTON.
Controls Soil Inoculated with Rhizoctonia
Average Q 'o
Moisture o' OQ
Content 10 H. 4 .
2.01% 18 13 72.72 0 18 3 16.66 ..-------i----
4.17 18 17 94.44 0 18 0 0 -.-------- ----
7.43 12 12 100.00 0 18 1 5.55 0 0
11.53 18 16 88.88 0 18 0 0 ...... ........
18.82 18 11 61.11 0 18 2 11.11 1 50.00
20.30 18 0 0 0 18 0 0 .......
EFFECT OF TEMPERATURE ON THE FUNGUS
Balls (3) states that the optimum temperature for continued
growth for Rhizoctonia in culture is about 230C., although the
length of time grown was not specified nor was the criterion for
comparison mentioned. The maximum temperature given was
33C. and it was stated that fairly good growth occurred at 150C.
362 Florida Agricultural Experiment Station
The temperature range found by Richards (18) in his work
with the Rhizoctonia from potatoes and which he tried on cot-
ton, was from 6C. to 35C. with an optimum at about 27"C.
In determining the optimum temperature for the growth of
the fungus in culture, potato dextrose agar was used as the
medium. The formula for the medium used was 200 grams of
potatoes, 20 grams of dextrose and 25 grams of agar to 1,000
c. c. of distilled water. The plates contained about 20 c. c. of the
medium and all the medium used in any one series was from the
same lot. Transfers were made from vigorous flask or tube cul-
tures of the organism two weeks old. Two-millimeter squares of
the mycelial weft were transferred to each plate. The cultures
were then left at room temperature for six to 12 hours after the
transfer was made and were then observed for growth. Cultures
showing no growth were discarded. The others were placed in
sterilized one-pound coffee cans, five or six plates to a can, and
immediately suspended in a tank can at each temperature. After
a specified number of hours the cans were removed and the
growth in diameter of the cultures was measured in millimeters,
two measurements being made in each plate an average of the
two being used in the table. On account of the risk of contamina-
tion it was difficult to make successive measurements on any
one culture, but in successive series different periods of time
were allowed to obviate this difficulty. This did not give growth
increments for an individual culture for increasing time periods
but did show that there was little variation in the optimum tem-
perature after different periods of exposure to different tem-
peratures up to 72 hours. This statement, however, is based on
only one point-diameter of mycelial weft. In the case of some
of the longer periods where the mycelial weft covered the en-
tire plate, merely general appearance was used as a criterion.
This was very definite in some cases where the mycelium had
grown up the side of the plate and onto the cover of the plate.
One such clear-cut case is indicated in Table VI, by a small
In certain experiments lactic acid was used to reduce bacterial
contaminations, and not to determine the relation of the fungus
to H and OH ion concentrations. In cases where the acid was
Bulletin 197, Soil Temperature Studies With Cotton 363
U2 / l \
5 4 / 4\
/ \ \ \
- .., / \, \
IZ. 14 16 16 ZO ZZ 4 26 z 30 3 2 54 36 38 40
TEMPE2ATUEE IN DEGREES C,
Fig. 152.-Growth at different temperatures of a strain of Rhizoctonia
solani from cotton grown on potato agar. cultures exposed to vari-
ous temperatures for 30 hours, - for 48 hours, -.-.-. for 72 hours.
The cross over the 72 hour curve represents the probable optimum tem-
peratures, the fungus having grown entirely out of the plates at this
)L 14 16 18 2ZO Z 24 Z6 Z8 0Jo 34 36 15 4o
TEMPE2ATUEE IN DEGR" E C.
Fig. 153.-Growth at different temperatures of a strain of i',.i. :,,'.i.i r
solani from cotton. Grown on potato agar acidified with five drops of
25 percent lactic acid to each plate. -- cultures exposed to the various
temperatures for 48 hours, --- for 72 hours.
364 Florida Agricultural Experiment Station
used 5 drops of 25 percent lactic acid were added to the plates
when they were poured.
The results of several series of petri plate cultures grown at
different temperatures for varying time periods are tabulated
in Table VJ, and shown graphically in figures 152 and 153. From
these data it will be seen that the optimum temperature is close
to 280C. for exposures up to 72 hours, with an optimum range
between 27 and 290C. There appears to be no decided shifting
of the optimum with changes in the time of exposure to the dif-
ferent temperatures, since no marked changes occurred at any
of the time intervals tried. The few experiments with acidified
TABLE VI.-SUMMARY OF RESULTS OF SEVEN TEMPERATURE SERIES WITH
CULTURES OF Rhizoctonia solani FROM COTTON.
Number of Hours at Different Temperatures.
30 Hours 48 Hours 72 Hours 48 Hours** 72 Hours**
Ave. Ave. Ave. Ave. Ave.
Ave. Diam. Ave. Diam. Ave. Diam. Ave. Diam. Ave. Diam.
Temp. in mm. Temp. in mm. temp. in mm. Temp. in mm. Temp. in mm.
39C. 0 (2)
38.6 3 (6)*138 1 (5) 38 14 (1)38.9 0 (6) 38 3 (2)
37.0 8.3 (6) 37 7.8 (6) 37.3 20 (1) 37.6 7.6 (3) 37.3 20 (1)
34.7 16 (6) 34 44.2 (13) 34 90 (2) 34.7 10.1 (4) 34 37 (2)
32.8 43 (5) 31.5 68.6 (12) 30.8 90 (1) 31.9 33 (3) 30.8 60 (1)
29.7 51.5 (5) 28 75.1 (10) 27.8 90t (2) 29.4 54 (3) 27.9 67.5 (2)
26.7 48.2 (6) 25 67.2 (10) 24.8 90 (2)25.4 50 (4) 24.9 57.5 (2)
23.6 48 (6) 22 55.9 (10) 21.3 90 (2) 23.1 37.3 (2) 21.4 57.5 (2)
20.8 38 (5) 18.5 43.5 (10) 18.2 80 (1) 19.4 38.6 (3) 18.3 53 (2)
16.6 29.5 (6) 15.5 28.7 (10) 14.6 65 (1) 15.1 15.5 (4) 14.6 20 (2)
11 3.2 (7) 11 9 (5) 11 12 (1) .... ...... 11 6 (2)
S...... 7 0 (2) .. ..... ....... ..
"*The figures in parentheses indicate the number of plates from which
the average diameter was taken.
"**Acidified with 5 drops 25% lactic acid.
fGreatest growth, the fungus was growing out of the plate.
Builltin 197, Soil Temperature Studies With Cotton 365
agar seem to indicate that acidity does not tend to alter the
optimum range for the fungus, although material reductions in
the rate of growth occurred.
From the charts showing growth of the fungus at different
temperatures it will be seen that from the lowest temperature to
the optimum temperature of approximately 280C., growth ac-
celeration follows the Van't Hoff rule for the acceleration of
chemical processes by temperature. Above the optimum tem-
perature some other factor enters to retard the growth of the
fungus. Balls (5) explains this retarding of growth by his theory
of thermotoxy which involves the formation of a toxic substance
"x". This substance is said to form at all temperatures but at
the lower temperatures the rate of diffusion into the substrate
equals or exceeds the rate of formation, consequently no injury
results at the lower temperatures. At high temperatures, how-
ever, the rate of formation exceeds that of diffusion and injury
to the fungus occurs.
In figures 154 and 155, are shown typical series of cultures
grown at different temperatures for different periods of time.
Fig. 154.-Culture series showing growth after 48 hours at different tem-
peratures. The temperatures at which the various plates were grown
are as follows: A, 40 degrees C.; B, 39 degrees C.; C, 35.5 degrees C.;
D, 32.5 degrees C.; E, 29 degrees C.; F, 25.5 degrees C.; G, 23 degrees
C.; H, 19.5 degrees C.; I, 14.5 degrees C.; J, 11 degrees C.
366 Florida Agricultural Experiment Station
Fig. 155.-Culture series showing growth after 72 hours at different tem-
peratures. The temperatures at which the various plates were grown
are as follows: 1, 38 degrees C.; 2, 37 degrees C.; 3, 34 degrees C.; 4,
31 degrees C.; 5, 28 degrees C.; 6, 25 degrees C.; 7, 21.5 degrees C.; 8,
18 degrees C.; 9, 14.5 degrees C.; 10, 11 degrees C.
STRAINS OF RHIZOCTONIA SOLANI KUHN
The difference between 230C., the optimum temperature re-
ported by Balls (3) for the growth of Rhizoctonia from cotton,
and 28C. the optimum temperature found for the fungus in the
present work suggested the possibility of there being two or
more strains of Rhizoctonia solani causing damping-off and sore-
shin of cotton. The existence of distinct strains within the spe-
cies seems definitely established in the papers of Rosenbaum and
Shapovalov (22), Edson and Shapovalov (15), Matsumoto (19),
and Gratz (17). The importance of these strains and their con-
stancy under varying environmental conditions is questioned in
other papers by Duggar (12), Peltier (21), Dahl (8), and Brit-
ton-Jones (6). As it is planned to do further work on this phase
of the problem, only a brief report of the work to date is given.
The optimum temperatures found by Richards (18) and Gratz
(17) for culture of Rhizoctonia solani isolated from potatoes
and cabbage were 270C., and 240C., respectively. As these tem-
Bulletin 197, Soil Temperature Studies With Cotton 367
peratures were much the same as the two mentioned for the cot-
ton Rhizoctonia it was decided to test the pathogenicity of each
to cotton. Cultures of the two strains were obtained through the
courtesy of the departments of plant pathology of the Univer-
sity of Wisconsin and of Cornell University. A few other strains
were also secured for trial from various sources, but they were
not all tried in detail for the problem soon proved to be too
great to include in the present work.
Pots filled with sterilized soil were inoculated with two-weeks
old flask cultures df Rhizoctonia isolated from diseased cotton,
potato and cabbage plants and planted in the manner described
in an earlier section. The pots were then transferred to the soil
temperature tanks. Notes on germination, killing, and tempera-
ture were made in the manner previously described.
Besides the tests in the soil tanks a number of large test tubes
were filled with quartz sand, sterilized, and inoculated with the
various strains of Rhizoctoriia. Two delinted seed were planted
in each tube and the tubes left at room temperature until germi-
nation appeared complete.
Culture series were run with the various strains of the fungus
in the same manner reported in a preceding section.
TABLE VII.-RESULTS FROM THREE INOCULATION SERIES IN SOIL TEMPERA-
TURE TANKS TO DETERMINE THE PATHOGENICITY TO COTTON OF A STRAIN
OF RHIZOCTONIA ISOLATED FROM POTATOES.
Average No. of No. of Percentage No. of Percentage
Temp. C. Seed Seed of Plants of
Planted Germinated Germination Killed Killing
38.50 24 24 100.0 0
34.5 24 24 100.0 8 33.3
31.5 24 21 87.5 11 54.4
28.5 24 19 79.2 18 66.7
25 24 16 66.7 12 75.0
21.5 24 12 50.0 8 66.7
18.5 24 4 16.7 3 75.0
368 Florida Agricultural Experiment Station
The effects of strains of Rhizoctonia isolated from diseased
cabbage and potato plants on the germination of cotton seedlings
are shown in Tables VII, VIII, and IX. For controls on these ex-
periments see Table III. These data show that there was a dif-
ference in pathogenicity of the three strains. The cabbage strain
was found to be practically non-parasitic on cotton, only one
plant out of 102 being killed. A slight superficial browning oc-
curred on some of the plants at the lower temperatures. The
strain from potatoes was found to be almost as vigorous in its
attack on cotton as the cotton strain itself.
TABLE VIII.-AVERAGE OF TWO INOCULATION SERIES IN SOIL TEMPERATURE
TANKS TO DETERMINE THE PATHOGENICITY TO COTTON OF A STRAIN OF
RHIZOCTONIA ISOLATED FROM CABBAGE.
Average No. of No. of Percentage No. of Percentage
Temp. C. Seed Seed of Plants of
Planted Germinated Germination Killed Killing
38 12 10 3.3 .0 1
34 18 18 100.0 0 1
31 18 17 94.4 0
28 18 18 100.0 1 5.55
24.5 18 17 94.4 0
21 18 15 83.3 0
TABLE IX.-RESULTS OF AN INOCULATION SERIES TO DETERMINE THE
PATHOGENICITY TO COTTON OF DIFFERENT STRAINS OF RHIZOCTONIA.*
Source of Strain 7. z ' o "4S m 0
S0 0 Oa
Cotton (Fla.) ...... 28 16 1 6.25 1 100
Cabbage (N. Y.) .... 24 10 10 100 0
Potato (Wis.) ........ 27 16 7 43.75 7 100
*Grown in large test tubes at room temperatures ranging from 20V to
Bulletin 197, Soil Temperature Studies With Cotton 369
Cultures of the cabbage and potato strains were then grown
at different temperatures and their optimum temperatures were
found to be approximately the same as reported by Gratz and
Richards, 24 and 280, respectively. This in itself would point to
the constancy of the strains in culture as the cabbage strain
had been in culture for at least five years. No information is at
hand on the length of time the potato organism had been in cul-
These data show that the two parasitic strains of Rhizoctonia
on cotton have practically the same optimum temperatures,
whereas, the non-parasitic strain from cabbage had a lower opti-
mum temperature. They would also point to the existence of sev-
eral strains of Rhizoctonia, of varying degrees of parasitism to
cotton. These results do not explain the differences between the
present work and that of Balls but would indicate that they are
possibly due to a difference in strains.
Some work with five other strains of Rhizoctonia solani from
other hosts indicate the same thing but the work is not yet com-
plete, and is to be continued in the hope of determining the con-
stancy of various strains of Rhizoctonia solani in culture and
their relation to the soreshin disease of cotton.
1. During favorable weather the soreshin or Rhizoctonia dis-
ease of cotton may necessitate wholesale replanting by reducing
germination and by killing young plants.
2. The optimum temperature range for killing lies between
17'C. and 23C. No minimum temperature for killing was de-
termined, as cotton failed to germinate below 150C. The maxi-
mum temperature at which killing took place was 340C.
3. There appeared to be a variation in the amount of killing
due to variations in the rate of germination of different lots and
varieties of cotton seed.
4. The fungus grew best in culture between 27'C. and 290C.
No growth took place above 380C. and this appears to be the
maximum temperature at which growth can take place. The
minimum temperature for growth lies between 7C. and 110C.
5. Practically all soil moistures at which cotton would germi-
nate and grow were sufficient to allow Rhizoctonia to attack cot-
ton plants, providing the soil temperatures are favorable to the
370 Florida Agricultural Experiment Station
6. It would appear that there are several strains of Rhizoc-
tonia solani, all of which are not capable of attacking cotton with
The author dishes to express his appreciation for help and
criticism by Dr. A. F. Camp, who initiated the work here re-
ported, and to Mr. R. M. Crown, who assisted in certain phases
of the work.
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