Bulletin 242 November, 1931
UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATIONS
Wilmon Newell, Director
BOTTOM ROT AND RELATED
DISEASES OF CABBAGE
CORTICIUM VAGUM B. & C.
By GEORGE F. WEBER
Fig. 1.-Cabbage-heads naturally infected showing bottom-rot in dif-
ferent stages of development. The plant at extreme left shows
Bulletins will be sent free upon application to
the Agricultural Experiment Station,
BOARD OF CONTROL PLANT PATHOLOGY
W. B. Tisdale, Ph.D., Plant Pathologist
P. K. Yonge, Chairman, Pensacola George F. Weber, Ph.D., Associate
A. H. Blanding, Bartow R. K. Voorhees, M.S., Assistant
W. B. Davis, Perry Erdman West, M.S., Mycologist
Raymer F. Maguire, Orlando
Frank J. Wideman, West Palm Beach
J. T. Diamond, Secretary, Tallahassee
EXECUTIVE STAFF NORTH FLORIDA STATION, QUINCY
John J. Tigert, M.A., LL.D., President of the L. O. Gratz, Ph.D., Associate Plant Pathologist
University in Charge
Wilmon Newell, D.Sc., Director R. R. Kincaid, M.S., Asat. Plant Pathologist
H. Harold Hume, M.S., Asst. Dir., Research W. A. Carver, Ph.D., Asso. Cotton Specialist
Sam T. Fleming, A.B., Asst.Dir., Administration R. M. Crown, B.S.A., Asst. Agronomist, Cotton
J. Francis Cooper, M.S.A., Editor Jesse Reeves, Farm Superintendent
R. M. Fulehum, B.S.A., Assistant Editor
Ida Keeling Cresap, Librarian CITRUS STATION. LAKE ALFRED
Ruby Newhall, Secretary
K. H. Graham, Business Manager John H. Jefferies, Superintendent
Rachel McQuarrie, Accountant Geo. D. Ruehle, Ph.D., Asst. Plant Pathologist
W. A. Kuntz, A.M., Asst. Plant Pathologist
B. R. Fudge, Ph.D., Assistant Chemist
MAIN STATION, GAINESVILLE W. L. Thomp3on, B.S., Assistant Entomologist
AGRONOMY EVERGLADES STATION, BELLE GLADE
W. I. Stokes, M.S., Agronomit R. V. Allison, Ph.D., Soils Specialist in Charge
W. A. Leukel, Ph.D., Associate R. W. Kidder, B.S., Farm Foreman
G. e. itche, M..A., Assistant R. N. Lobdell, M.S., Associate Entomologist
Fred H. Hula M.S., Assistant F. D. Stevens, B.S., Sugarcane Agronomist
J. D. Warner, M.S., Assistant H. H. Wedgeworth, M.S., Asso. Plant Path.
John P. Camp, M.S., Assistant B. A. Bourne, B.S., Asso. Plant Physiologist
ANIMAL HUSBANDRY J. R. Neller, Ph.D., Associate Biochemist
A. Daane, Ph.D., Associate Agronomist
A. L. Shealy, D.V.M., Veterinarian in Charge M. R. Bedsole, M.S.A., Assistant Chemist
E. F. Thomas, D.V.M., Assistant Veterinarian Fred Yount, Office Assistant
R. B. Becker, Ph.D., Associate in Dairy In-
vestigations SUB-TROPICAL STATION, HOMESTEAD
W. Neal, Ph.D., Asst. in Animal Nutrition SUBTROPICAL STATION, OMETEA
P. T. Dix Arnold, B.S., Assistant in Dairy In- H. S. WolfePh.D.,Asso. Horticulturist in Chg.
vestigations L. R. Toy, B.S.A., Asst. Horticulturist
CHEMISTRY Stacy O. Hawkins, M.A., Assistant Plant
R. W. Rupreeht, Ph.D., Chemist Pathologist
R. M. Barnette, Ph.D., Associate
C. E. Bell, M.S.. Assistant
J. M. Coleman, B.S., Assistant FIELD STATIONS
H. W. Winsor. B.S.A.. Assistant FIELD STATIONS
H. W. Jones. M.S., Assistant
vECONOMICS, AGRICULTURAL M. N. Walker, Ph.D., Asso. Plant Pathologist
C. V. Noble, Ph.D., Agricultural Economist W. B. Shippy, Ph.D., Asst. Plant Pathologist
Bruce McKinley, A.B., B.S.A., Associate K. W. Loucks, M.S., Asat. Plant Pathologist
M. A. Brooker, Ph.D., Associate C. C. Goff, M.S., Assistant Entomologist
Zach Savage, M.S.A., Assistant J. W. Wilson, Ph.D., Assistant Entomologist
ECONOMICS, HOME Plant City
Ouida Davis Abbott, Ph.D., Head
L. W. Gaddum, Ph.D., Biochemist A. N. Brooks, Ph.D., Asso. Plant Pathologist
C. F. Ahmann, Ph.D., Physiologist R. E. Nolen, M.S.A., Field Asat. in Plant Path.
J. R. Watson, A.M., Entomologist A. S. Rhoads, Ph.D., Asso. Plant Pathologist
A. N. Tissot, Ph.D., Assistant
H. E. Bratley, M.S.A., Assistant Hastings
E. F. Grossman, M.A., Asso., Cotton Insects H. .D., Ao. P t
P. W. Calhoun, Assistant A. H. Eddins, Ph.D., Asso. Plant Pathologist
HORTICULTURE West Palm Beach
A. F. Camp, Ph.D., Horticulturist 'D. A. Sanders, D.V.M., Associate Veterinarian
Harold Mowry, B.S.A., Associate
M. R. Ensign, M.S., Associate Monticello
G. H. Blackmon, M.S.A., Pecan Culturist
C. B. Van Cleef, M.S.A., Greenhouse Foreman Fred W. Walker, Assistant Entomologist
*In cooperation with U.S.D.A. David G. Kelbert, Asst. Plant Pathologist
INTRODUCTION ....----.-.. -----.. .......... ..- --- --. -..-------....-... 5
THE DISEASE ...-..--- ...----- .--...- .....- ........ ---------...---- ........--- 5
Geographical Distribution ------.............--- ... -------------......--.... 5
Economic Importance -------........ ..... ...... --.....- -......... 6
Host Range .--............-- ..----- ------......------..--........ 7
Symptoms --...............- ...--...- ---..........-----.......--.. 7
Damping-off ............ ..... ...---------------- ......----.....--...-. 7
W ire-stem ................. ---............. ------- -- ...........-- 7
Root-rot ....-...........----- ......... ..... ...-...-- .. ........ .. 10
Stem-lesions ...-- ---..................- .......................... 11
Bottom-rot ...............-------------------------........................ 11
CAUSAL ORGANISM --............-......---------------.............----- ............. 15
Taxonomy -----........-...--....--. ---..-- ..--------............... 15
Morphology and Physiology .......-..--------.............. ..................... 17
Temperature Relations --..........-----..........- -........................... 18
Pathogenicity ......--..........----- ---.-.........--------........ 21
Isolations-Imperfect Stage ......-----------........... ---.................-... 21
Isolations- Perfect Stage ...................................... ................... 22
Inoculations-Imperfect Stage ....-....- .................--- ................. 23
Inoculations-Perfect Stage ----.......----..... .---........ ..----...- -... 23
CAUSAL ORGANISM IN RELATION TO THE PRODUCTION OF BOTTOM-ROT...... 25
Seasonal Development ---------..-.. --.......-........... ................... 25
Field Infection ......-------......--- ........................................ .. 26
Dissemination ..---.........-------- ........-..-.....----... ................. 27
CONTROL .....--- ..-- ---.... ... .. ...................................... 28
CONCLUSIONS ............--- ....------ ----- -----------........ ..................... 29
LITERATURE CITED -------.............. ------- ....... ------------ 29
BOTTOM ROT AND RELATED
DISEASES OF CABBAGE
CORTICIUM VAGUM B. & C.
By GEORGE F. WEBER*
During the season of 1929-1930 considerable losses of cabbage
occurred in Florida fields due to a rot of heads caused by the
Rhizoctonia stage of Corticium vagum B. & C. The disease ap-
parently has not been described and few references have been
found in literature concerning the effect of Rhizoctonia solani
Kiihn, the sterile and parasitic stage of the fungus, on cabbage
heads. Damping-off, stem-rot and wire-stem are common names
applied to other cabbage diseases caused by this fungus and a
short description of them will be included in this discussion to
show their relationship to bottom-rot. Bottom-rot is the com-
mon name proposed for this new disease, since the fungus at-
tacks the head from the lower side, climbing up the stem from
the soil. Although the name is common in literature, having
been applied to a similar disease of lettuce caused by the same
fungus, it would not complicate the common nomenclature as
much as the name head-rot, as this term is applied to diseases
of cabbage heads caused by Bacterium campestre (Pam.) E.F.S.,
Sclerotinia sclerotiorum (Lib.) Mass. and to numerous rots oc-
curring in storage.
According to Duggar (7)', Shaw (22) and Peltier (16), dis-
eases of plants caused by Corticium vagum B. & C. are more or
less common in all parts of the civilized world. In the United
States diseases caused by this organism have been reported from
Damping-off of cabbage caused by this fungus was reported
first by Atkinson (2) in 1895 in Alabama, and later by Duggar
*Photos by D. G. A. Kelbert.
'Figures in parentheses (italic) refer to "Literature Cited" in the
back of this bulletin.
6 Florida Agricultural Experiment Station
and Stewart (9) in 1901 in New York and Illinois. In Florida,
Fawcett (10) first reported damping-off of cabbage in 1909
under the common name "stem-rot," and Sherbakoff '(23) (24)
described various symptoms of cabbage diseases caused by
Rhizoctonia solani Kiihn. Dana (6) concluded that the causal
fungus was indigenous to the soils of the Pacific coast. The
writer has observed cabbage diseases caused by the fungus in
almost all trucking sections in Florida during the last few years.
The Plant Disease Reporter (25) shows cabbage diseases caused
by this organism in the following states: South Carolina, Ken-
tucky, North Dakota, Massachusetts, Texas, Illinois, Wisconsin,
Alabama, Louisiana, Virginia, Pennsylvania, Ohio, Washington,
New Jersey, Indiana, Missouri, Florida, Connecticut, New York,
California and Kansas. Thus, the range may be said to extend
from Maine to Texas and California and from Florida to Wash-
ington and North Dakota. Even though the fungus causing bot-
tom-rot has almost a national distribution, reports of this dis-
ease on cabbage, by Beach (3), Ramsey (18), Walker (26),
Weber (27) and Wellman (28) show that it has been observed
only in Pennsylvania, Wisconsin, Illinois and Florida. In Florida
it has been found through the central part of the state and north-
Damping-off, root-rot, wire-stem or stem-cankers cause about
the same percentage losses in Florida as bottom-rot. Walker
(26) reported from 2 to 12% damping-off of cabbage seed-
lings in Wisconsin and Northern Illinois and Wellman (28)
estimated that losses in Washington, Massachusetts and New
York amounted to 1%. Root-rot resulting from infection by this
fungus caused considerable stunting on the Pacific Coast, accord-
ing to Dana (6) and United States Department of Agriculture
reports (25). Wire-stem as described by Gratz (12) was im-
portant because of stunted plants which were usually discarded
at planting time. Stem-lesions have been reported and illus-
trated by Gloyer and Glasgow (11) as being of considerable im-
portance on plants that were older than those upon which wire-
stem occurred. Bottom-rot was first reported by Beach (3)
from Pennsylvania in 1923 where he considered the losses in one
county amounted to 7%. Ramsey (18) reported the occurrence
of this trouble in Florida where he found it on old plants left
after harvest. Walker (26) stated that a few heads were at-
Bull. 242, Bottom-Rot and Related Diseases of Cabbage 7
tacked in fields in Wisconsin and Illinois and that foliage leaves
touching the soil were often infected. He also observed the per-
fect stage (Corticium vagum B. & C.) of the fungus under plants
in different fields. Wellman's reports (28) appeared to be identi-
cal with those of Walker. Weber (27) reported this disease of
cabbage plants in the field from Florida.
Bottom-rot was first observed in 1922 in Florida and has
been more or less prominent annually since that time.. In 1930-
31 losses in certain fields resulting from bottom-rot amounted
to 4%. Often areas on moist ground varying in size from 1 to 2
acres were a complete failure. The probable losses of cabbage
in Florida caused by this fungus during the past two years
might be divided as follows: Damping-off 2%, wire-stem and
stem-lesions 2%, bottom-rot 4%, totaling a loss of between
$50,000 and $75,000 calculated on the production of 1929.
The host range of Rhizoctonia solani Kiihn is not completely
known; however, approximately 200 species of plants have been
reported by Rolfs (21), Peltier (16), Pethybridge (17), Gratz
(12), Dana (6), the United States Department of Agriculture
(25), and others. The hosts observed in Florida by the writer
number 54. They include all of the cultivated cruciferous plants,
most of them developing wire-stem and stem-cankers, while chi-
nese cabbage and lettuce develop a characteristic bottom-rot
quite similar to that disease on cabbage.
Symptoms of the various diseases of cabbage caused by Rhiz-
octonia solani are given in order to show the characteristics of
each disease with special emphasis on "bottom-rot."
Damping-off :-This is a disease of cabbage seedlings in which
the stems show a lack of turgidity and suddenly collapse and
topple over. Closer observation of recently affected plants often
reveals slightly water-soaked areas several millimeters in ex-
tent on the stem at the soil line. The affected portions dry out
very rapidly during the day and the plants die. Fine hyphae of
the fungus may be seen connecting the soil and the stem lesion.
Wire-stem:-A typical symptom of this disease is a mature
or "hardened" appearance of the seedlings. Further examina-
tion shows a darkened portion of the stem often 1 to 3 inches
8 Florida Agricultural Experiment Station
in extent originating at the soil line. (Fig. 2.) The discolored
area in most cases covers the stem between the topmost fibrous
root to the lowest node and leaf scar of the stem. This disease
2.-Wire-stem of natural infection.
Fig. 2.-Wire-stem of cabbage seedlings, natural infection.
Bull. 242, Bottom-Rot and Related Diseases of Cabbage 9
may be considered more or less associated with damping-off and
differs from it primarily in maturity of the stems when attacked
and in their response to attacks of the fungus. Due to the hard,
Fig. 3.-Root-rot of cabbage plants, showing the absence of the cortex
on the lower root resulting from infection of Rhizoctonia solani Kihn
in wet soils.
woody condition of the stems the attacked plants do not fall
over but assume an unhealthy appearance and may be badly
stunted. Such seedlings often develop and produce an average
10 Florida Agricultural Experiment Station
crop when transplanted. Usually, however, the most severely
stunted plants are discarded at planting time.
Root-rot:-In Florida this disease has been found only on
Fig. 4.-Cabbage plants in the field showing wilt because of root-rot.
Fig. 5.-Corticium vagum B. & C. on the lower surfaces of the foliage
leaves of a cabbage head.
Bull. 242, Bottom-Rot and Related Diseases of Cabbage 11
plants in the field in extremely wet soil. The first indication of
the trouble is wilting. After this the lower leaves turn yellow
and shed rapidly. Examination of the lower stem and root in
the early stages of wilting show a girdled stem at or slightly
Fig. 6.- Typical bottom-rot of cabbage head, natural infection. Fol-
iage leaves have been broken down in foreground to show infection
below the soil line. The cortex is killed and sloughs off, leaving
only the central woody tissue. (Fig. 3.) This condition blends
into the following disease.
Stem-lesions:-This type of injury varies from small, shallow,
discolored areas of the stem cortex to those several centimeters
in length. These lesions usually originate on the stem just above
the soil line or at the lower leaf scars. It is not common in the
Bottom-rot:-This disease has been reported as occurring in
the United States by Beach (3), Ramsey (18), Walker (26),
Weber (27), and Wellman (28), but has not been described. The
12 Florida Agricultural Experiment Station
early stages of infection and the subsequent development of the
disease are extremely inconspicuous. In most cases the fungus
has invaded the lower portion of the head and killed portions of
the leaf blades before its presence can be detected by casual
observation. (Fig. 6.) The
outer foliage leaves hide the
diseased portions of the
heads. (Fig. 7.) The foliage
leaves are usually not se-
verely affected themselves
St in the early stages of the
disease except at their bases
Where the fungus invades
b oand kills tissue of the leaf
S blade on either side of the
midrib, extending up the
margins of the blade for
distances of from one to
several inches. The outer-
[ most leaves are usually af-
fected less than the inner
ones. Where the foliage
leaves closely enclose the
head the invasion of the
head leaves is more com-
plete than where the foli-
age leaves spread out. The
fungus grows up the main
stem, passing between the
leaf petioles. The outside
headleaf is always the most
severely affected. The lower
portion of the blade is killed
and the fungus invades the
Fig. 7.-Cabbage plant which has shed petioles, forming deep le-
the foliage leaves and shows typical sions and finally destroying
bottom-rot of the head. them entirely. This causes
the uninvaded area of the blade covering the top of the head to
die and wither. The head leaves are successively involved in
like manner, although to a slightly lesser degree. As the head
leaves are killed they are abscised at the base of the petioles and
dry rapidly. They are usually held in place mechanically by the
Bull. 242, Bottom-Rot and Related Diseases of Cabbage 13
margin of the blade that folds over the top of the head. They
are also held in place by the hyphae of the fungus that grows
rapidly over the surface of the leaf when it is killed. The foliage
leaves gradually succumb to the attacks of the fungus and when
abscised are shed. In the final stages of the disease all the foli-
Fig. 8.-Last stages of bottom-rot showing completely involved heads
covered with fungus mycelium and numerous sclerotia.
14 Florida Agricultural Experiment Station
age leaves are shed. (Fig. 8.) The affected plants stand erect,
consisting of a main stem terminated by a capitate knob, com-
posed of dead leaves detached at their bases from the stem but
held together by the fungus
and in place by their over-
lapping margins. The outer
head leaves are brown in
color, wrinkled and more or
less wet below and often
dry and parchment-like
above. Over the whole sur-
face fungus hyphae are eas-
ily observed and extensive
mats of sclerotia are not
uncommon. These plants
usually remain upright in
this condition until the
preparation of the soil for
the following crop.
The perfect stage of the
fungus Corticium vagum B.
& C. was observed on nu-
merous cabbage plants in
the fields. But close exam-
ination was necessary in
every instance to detect the
plants which bore it. The
fungus hyphae were always
conspicuous on the main
stem (Fig. 9), at the base
of the petioles where the
fine white mycelium ap-
peared and spread fan-like
over the surface of the leaf,
the advancing margin being
Fig. 9.- Portion of cabbage stem very distinct. (Fig. 5.) The
showing the light colored sporiferous hyphae of the perfect stage
stage of Corticium vagum B. & C. of the fungus apparently did
not penetrate the host tissue, except on a few isolated specimens
where small areas were dead and brown. The sporulating hy-
phae were matted closely together and this mat was easily lifted
Bull. 242, Bottom-Rot and Related Diseases of Cabbage 15
with forceps and removed in strips. This fruiting mat covered
the external surfaces of the stems and leaves and produced
spores abundantly over these areas. Spores from stems and
leaves were collected on poured-agar petri-dish plates and on
glass slides and used in obtaining cultures for studying charac-
teristics of the fungus.
Rhizoctonia solani Kiihn is the name applied to the sterile
stage of the fungus in its parasitic role, whereas Corticium
vagum B. & C. is the binomial designating the sporiferous stage.
The former has been known to investigators for more than 200
years, according to Peltier (16).
Duggar (7) gave the following synonymy under R. solani
Kiihn, the form commonly found in this country and to a less
extent in Europe, and which is the name generally used by
Rhizoctonia betae Eidam (non Kiihn) (1887)
Rhizoctonia napaeae West (1846)
Rhizoctonia rapae West (1852)
Hypochnus solani Prill. & Del. (1891)
Peltier (16) stated that Webber first reported Rhizoctonia on
alfalfa in the United States in 1890 in Nebraska and listed it as
Rhizoctonia medicaginis DC. Duggar (7) reported that Pammel
was the first American pathologist to report in this country a
disease now known to be caused by Rhizoctonia solani. Pammel
(15) however recognized the fungus causing the trouble of beets
as one related to Rhizoctonia betae Kiihn, but further than that
did not attempt to identify it, although he gave an account of
the disease. Atkinson (1) observed a damping-off of cotton and
later of a number of other seedlings and in that connection iso-
lated a sterile fungus which he used in pure culture to repro-
duce the disease. He (Atkinson (2)) kept the fungus in culture
for more than three years and was perplexed because no fruit-
ing structures or spores were produced. His account of this
fungus attacking cabbage is the first on record. This fungus
later became known as Rhizoctonia solani Kiihn. It is not clear
whether he referred to "damping-off" or "stem-rot" but the
former is suspected. In addition to cabbage he listed as hosts
16 Florida Agricultural Experiment Station
radish, lettuce and eggplants. Duggar (8), who had been study-
ing the disease, reported that the same fungus was causing at
least three types of disease, namely, damping-off of seedlings,
root-rot, as on the beet, and stem-rot, as on the carnation. Dug-
gar and Stewart (9) recognized the fungus as causing damping-
off of a number of seedlings including cabbage and recorded the
receipt of specimens of diseased cabbage seedlings from Cairo,
Illinois, in 1898. They noted that the fungus caused damping-
off on extremely young cabbage seedlings and that it was com-
mon on plants somewhat older that had developed two or more
true leaves. In this case the lesions often appeared below the
soil surface. This description of a disease of the stems of older
plants is similar in essentials to the disease described by Gratz
(12) as wire-stem.
Rolfs (9) described and illustrated Rhizoctonia solani Kuhn,
the sterile parasitic form of the fungus, on potatoes in Colo-
rado. He made further studies and reported (20) the discovery
and described the perfect stage of the fungus. He was not suc-
cessful in developing the imperfect stage from basidiospores
but grew this stage from the aseptical plantings of hyphae of
the mycelial layer from which the basidia arose. In main charc-
ters this fungus agreed with Corticium vagum B. & C. as de-
scribed and published by Berkeley (4). However because of
slight differences in spore form and in its parasitic mode of life,
it was suggested that it should be given varietal rank. Accord-
ingly Corticium vagum B. & C. var. solani Burt was applied to
it. Later Burt (5) dropped the varietal rank and thus the fun-
gus became known as Corticium vagum B. & C. Rolfs (21) fur-
ther reported this perfect stage on lettuce in Florida and de-
scribed the disease caused by the imperfect stage as "bottom-
rot" of this host. In addition to lettuce he listed 17 hosts of the
perfect, stage of the fungus.
Fawcett (10) reported a stem-rot of cabbage seedlings from
Florida for the first time and the fungus was identified by Orton
of the United States Department of Agriculture as Corticium
vagum B. & C. var. solani Burt. Sherbakoff (23) (24) described
two types of disease on cabbage caused by this fungus; the first
a damping-off by which the seedlings were killed outright and
the second where they were infected, stunted more or less but
recovered. He collected the perfect stage of the fungus and
considered it the same as identified by Orton for Fawcett.
Bull. 242, Bottom-Rot and Related Diseases of Cabbage 17
Morse and Shapovalov (14) in Maine and Pethybridge (17)
from Ireland reported the perfect stage of the fungus on pota-
toes. Pethybridge not only obtained Rhizoctonia in pure cul-
ture from the Corticium mycelium and actually followed an un-
broken hyphae strand from sclerotium to basidium, but obtained
pure cultures of Rhizoctonia from the basidiospores of the Cor-
ticium stage. Matsumoto (13) studied this fungus in numerous
isolations from various sections and concluded that there may be
physiological strains but did not specifically designate them.
Dana (6) reported the fungus indigenous to the Western states
and stated that it caused damping-off and stem-rot of cabbage in
Washington. Gratz (12) recognized two distinct stages of the
disease, namely damping-off and stem-rot; the latter trouble he
designated as wire-stem. Damping-off and stem-rot or wire-
stem occur throughout Florida wherever cabbage is grown. A
short description of them has been given so as to show the con-
nection and association with bottom-rot, the disease described
in this paper.
MORPHOLOGY AND PHYSIOLOGY
The general morphological characters of this fungus have
been described and illustrated by a number of writers including
Rolfs (20) (21), Peltier (16), Duggar (7), Gratz (12), Dana
(16) and others. The mycelium of the fungus causing bottom-
rot of cabbage isolated in pure culture at various times conforms
in general characteristics with Rhizoctonia solani Ktihn. The
color, shape, size and growth habits of the vegetative hyphae,
the barrel-shaped sclerotial cells, the basidia and basidiospores
agree entirely with earlier descriptions and for that reason
will not be given here. However, the sterigmata found on the
fungus fruiting on cabbage plants are much longer and larger
than those in any of the illustrations shown in literature. (Fig.
10.) The basidiospores were obtained in abundance and 200
measurements averaged 9 x 12g. They are hyaline and in other
ways agree with the original description by Rolfs (20). Pure
cultures of Rhizoctonia solani Ktihn obtained from diseased cab-
bage plants and of Corticium vagum B. & C. obtained from ger-
minating basidiospores were not entirely comparable, although
in the important details they were essentially the same. The
variation, however, between these cultures was no greater than
that between separate isolations of Rhizoctonia from different
18 Florida Agricultural Experiment Station
Fig. 10.-Basidiospores, basidia and sterigmata of Corticium vagum B.
& C. from cabbage. (Camera lucida drawings.)
RELATION OF TEMPERATURE TO GROWTH OF THE
CABBAGE RHIZOCTONIA IN CULTURE
The cultures derived from the sterile and perfect stages of
the fungus showed approximately the same limitations in rela-
tion to growth at various temperatures. These cultures at dif-
ferent temperatures showed 5"C. as the minimum, 250C. as the
optimum and 340C. as the maximum temperatures for growth.
The organism used in these temperature studies was isolated
from heading cabbage plants and had been grown in pure cul-
ture on potato-dextrose agar. A four-day old potato-dextrose
agar culture of the fungus in a petri dish was used to inoculate
the series of poured plates. The medium containing the myce-
lium was cut into pieces about 2 mm. square. One of these pieces
was transferred to the center of each poured-agar plate. Four
plates were then placed in incubators at each of the following
temperatures, designated in degrees Centigrade: 5, 7, 8, 10, 12,
13, 14, 18, 20, 24, 25, 27, 29, 30, 34, 35, 40, and 41. After 72
hours the cultures at optimum temperatures had extended to
the edge of the culture dish. Consequently, the data were taken
Bull. 242, Bottom-Rot and Related Diseases of Cabbage 19
on all cultures after that period. The colonies were measured
and the diameters of the cultures at each temperature were
averaged and shown in Table I.
TABLE I.-THE RELATION OF TEMPERATURE TO THE GROWTH OF Rhizoctonia
solani Kihn ON POTATO-DEXTROSE AGAR.
Temperature in de-
grees C .............. 7 8 1012 13141820 24 252729 30
Diameter of culture
in cm. .............Slight 2 2.5 3 3.5 4 5 6 8 10 11 9 2.5 slight
The mycelial mat on the medium at the lower temperatures
was extremely thin. At 5 to 100C. the fungus strands radiated
from the planting and were very few but profusely branched.
At 12 to 180C., these strands were much more numerous but
still one was impressed with the thinness of the mat. From
180C. up to the optimum temperature the growth was dense,
whitish, radiating from the transfer with an even margin, the
Fig. 11.-Pure culture on potato dextrose agar of Rhizoctonia solani Kiihn
isolated from bottom-rotted cabbage plants. Top view left.
whole culture becoming brown and dotted with sclerotia with
age. (Fig. 11.) Above 250 the growth was reduced very rapidly
up to 300 above which no growth occurred. The mycelial mats
were thick and the knotting of hyphae representing the begin-
nings of sclerotia were numerous. The mycelium in the cultures
at the lower temperatures was characteristically effused, while
at the higher temperatures it was noticeably more aerial.
20 Florida Agricultural Experiment Station
Examination showed that no growth took place above 340 and
that very slight growth was evident at 300 and 50 (Fig. 12).
The wide, 20-degree, range for growth between the minimum
and optimum is very contrasting when compared to the narrow,
five-degree, range above the optimum.
The fact that growth took place at and probably somewhat
below 50C. will account for the development of this fungus and
resulting diseases of plants during the winter months in this
State. The mean minimum temperature of this section of Flor-
Fig. 12.-Series of pure cultures of Rhizoctonia solani Kihn growing
on potato-dextrose-agar at different temperatures Centigrade as des-
ignated. Minimum 5C., optimum 25C., maximum 30C.
ida for the past 10 years is considerably above 50C. The maxi-
mum temperature (300C.), at which this fungus grew, is lower
than the mean-maximum Florida air temperatures. These tem-
peratures agree in the main with those reported by Gratz (12),
the exception being a slightly lower minimum than he showed.
The summer vegetation which grows extremely rank in aban-
doned fields in Florida during this high temperature period un-
doubtedly protects the soil and this fungus so that the maximum
temperature is attained in the soil seldom or possibly only for
Bull. 242, Bottom-Rot and Related Diseases of Cabbage 21
The fungus may be dormant during this high temperature
period and survive in the sclerotial stage. Organisms survive
cold periods in dormant conditions and it is not difficult to
imagine that they might possibly survive high temperatures in
a similar manner, provided the temperature was not too high
for a long period.
The cultures derived from Rhizoctonia and Corticium were
also found to respond in very much the same way when grown
on media adjusted to different hydrogen-ion concentrations.
These cultures grew throughout the range of pH 2.5 to pH 10
with an optimum between pH 6.5 and pH 7 at room temperature.
Isolations-Imperfect Stage: -The imperfect stage of the
fungus (Rhizoctonia solani Kiihn) was isolated many times from
cabbage plants affected with bottom-rot. This process consisted
usually of placing a small portion of unsterilized infected plant
material removed from protected leaves of the head, on hardened,
poured-agar plates. The affected material used in making these
plantings was obtained by making deep incisions into the head
with a sterile scalpel and removing a piece of head leaf approxi-
mately an inch square. The diseased portions of the leaf immedi-
ately beneath, exposed by removing the top leaf, were used in
these plantings. Very seldom were contaminations obtained by
this method. The fungus grew rapidly in culture, showing char-
acteristic branching and coloration. The hyphae gradually be-
came yellowish and later changed to various shades of brown.
Sclerotia developed in these cultures in considerable numbers.
At first they were merely aggregates of mycelium, whitish and
more or less raised above the surface of the medium but they en-
larged later and changed in color to yellow and then brown and
averaged in size from mere discernible knots to a half centimeter
Cultures of the fungus were also obtained from cabbage
plants affected with damping-off, wire-stem, root-rot, and stem-
lesions. These various strains of the fungus were grown in cul-
ture and studied as to their rate and type of growth as well as
coloration and sclerotial formation. The general conclusions
reached from these studies were that the same organism was
22 Florida Agricultural Experiment Station
the causal agent in the production of all the phases of the dis-
ease previously discussed.
The fungus was increased in culture for inoculation purposes
by placing small portions of hard potato-agar upon which the
fungus was growing luxuriantly onto the newly cut surfaces of
fresh cabbage heads quartered longitudinally and enclosed in
large moist chambers. The fungus grew rapidly on this medium
at room temperature and in four or five days completely cov-
Isolations-Perfect Stage:-The perfect stage of the parasite
Corticium vagum B. & C. was collected in nature on living cab-
bage plants intermittently throughout the winter and spring of
the past two years. The basidia-bearing mat of mycelium most
often developed on the surface of the stem of the plant from 1
to 3 inches above the soil line. Close examination, with a low
powered lens, revealed mycelial strands connecting the soil and
the sporiferous mats. This mycelium was yellowish-brown and
indistinguishable from mycelium of Rhizoctonia solani Kiihn
isolated in pure culture from bottom-rotted plants. Large areas
of the mat were readily removed, almost intact with a scalpel or
tweezers. The mat was always more dense over the surface of
old leaf scars on the stem than elsewhere on living cabbage
plants. Cultures were obtained from the Corticium stage of the
fungus, by placing on the poured agar plates small portions of
the fruiting fungus which readily developed in culture and was
easily included within the varying range of different strains
of Rhizoctonia from cabbage in pure culture.
Portions of cabbage stems, leaf petioles and blades covered
with the spore-bearing hyphae were collected. Then sections of
host tissue bearing this fruiting fungus were removed and pins
were inserted into them at oblique angles to act as legs to ele-
vate them several millimeters above the plane upon which the
"pin-legs" rested. These mounted sections, fungus surface down,
were then placed in sterile petri dishes over glass microscope
slides or hard poured agar. They were left in this position from
4 to 18 hours during which time the basidiospores were natu-
rally shed, falling on the glass slides and agar. The basidio-
spores on the glass slides were mounted in water and their
measurements taken while those on the agar were left to germi-
nate. Germination on potato agar was slow and included less
than 5% of the total number of spores, while germination on
Bull. 242, Bottom-Rot and Related Diseases of Cabbage 23
cabbage agar was more rapid and included 20% of the spores.
The mycelium developed rapidly in both instances and was com-
parable to Rhizoctonia solani cultures obtained from bottom-
rotted cabbage plants.
Inoculations Imperfect Stage: Healthy cabbage plants
were transplanted from the field into pots, and grown in the
greenhouse. These plants were inoculated with the fungus
obtained in pure culture from diseased heads and propagated
on cabbage heads. Portions of cabbage leaves inoculated in
this way were dropped into the growing plants so that they
lodged between the petioles of the oldest foliage leaves and the
main stems. These inoculations made without injury to the
plant produced the disease in a fashion comparable to the dis-
Fig. 13.-Cabbage plants showing check at left and bottom-rot thirty
days after artificial inoculation with Rhizoctonia solani KUhn.
ease under natural conditions in the field. The fungus attacked
the lower portion of the leaf blades first, then gradually grew
up into the more compact portions of the heads. The foliage
leaves were shed and the plant became a typical bald-headed
plant so characteristic of the disease in the field. (Fig. 13.) The
outer leaves of the head dried out and became covered with
masses of sclerotia. The fungus was reisolated from these dis-
eased heads, and in pure culture it was identical to the original
Inoculations-Perfect Stage: Potted plants in the green-
house were inoculated with water suspensions of basidiospores
previously shed on glass slides. The uninjured plants were
atomized with the inoculum and incubated 30 hours in a moist
chamber, after which they were set on the greenhouse bench.
They remained under humid environmental conditions for six
24 Florida Agricultural Experiment Station
weeks but no symptoms of the disease developed. Germination
experiments paralleling the inoculation in which spores were
used from the same collection of basidiospores showed good
germination in 24 hours at room temperature. Other cabbage
plants were inoculated with the mycelium developed in culture
from germinated basidiospores in a series parallel with those
inoculated with mycelium obtained in culture from Rhizoctonia
solani Kiihn. Inoculated plants in both series developed the dis-
Fig. 14.-Cabbage plants showing check (left) and bottom-rot produced
by artificial inoculations with mycelium obtained from basidiospores
of Corticium vagum B. & C. (center) and mycelium of Rhizoctonia
solani Kiihn (right).
ease characteristically, while the checks remained healthy. (Fig.
14.) One of the plants inoculated with mycelium originating
from germinated basidiospores developed the perfect stage of
the fungus in characteristic form on the upper surface of sev-
eral of the innermost foliage leaves in addition to bottom-rot.
In another instance (Fig. 15) Rhizoctonia-like mycelium, typi-
cal Rhizoctonia sclerotia and the basidiospore-bearing mycelium
appeared near the base of a cabbage leaf on a living plant. Care-
ful examination under a low power lens on a microscope showed
characteristic Rhizoctonia-like mycelium connecting the killed
leafblade tissue with the sclerotia and the basidiospore-bearing
Bull. 242, Bottom-Rot and Related Diseases of Cabbage 25
Fig. 15.-Cabbage leaf showing mycelium, sclerotia at lower left on mar-
gin invaded by Rhizoctonia solani Kiihn, and Corticium vagum B. &
C. in top center, resulting from artificial inoculation with mycelium of
Rhizoctonia solani Kiihn originally from bottom-rot.
THE CAUSAL ORGANISM IN RELATION TO THE
PRODUCTION OF BOTTOM-ROT
Bottom-rot of cabbage has been found in Florida fields from
November until June, probably being most prevalent during
the latter part of March or at other times during the cabbage-
growing season when there were excessive rains. Moisture was
undoubtedly the most important single factor. The disease ap-
peared in the late fall and early winter only when there were
wet periods. At the beginning of the season only the most
mature plants showed the trouble, as most of the plants were
26 Florida Agricultural Experiment Station
still very young and were not beginning to head. The disease
was very common in low places in fields throughout the season,
probably because of moisture and accumulated vegetative debris.
This was especially true in the Gainesville area. The manifes-
tation of the disease on the plants was erratic and difficult to
find during the above mentioned period, especially when there
was very little precipitation, as during April and May of most
years. On the other hand, when there was considerable rain-
fall it became common and destructive. Generally, diseased
plants were widely scattered over the fields but the losses were
unimportant except in the low places where large percentages
of plants were affected. During the early part of the season the
fungus attacked the cabbage seedlings and caused other diseases
as previously mentioned. In the latter part of the season the
mean temperature was higher and secondary organisms fre-
quently followed after the initial advent of Rhizoctonia, causing
rapid decline, rot and drying out.
The regular growing season is usually concluded in the latter
part of May or early in June; consequently, the fungus survived
until seedbeds were planted in August and September by other
means than on cabbage plants. The fungus attacked the seed-
ling plants when they were small, causing damping-off and wire-
stem. Later, when they began to head, bottom-rot appeared.
During the period from June until the latter part of August
the fungus survives as a saprophyte in the soil or as a parasite
on cabbage plants left in the field or on wild plants and weeds
and as sclerotia which were developed abundantly on the cul-
tivated crop during the previous growing season. This period
almost coincides with the summer rainy season during which
the average mean rainfall for the past 20 years at Gainesville,
Florida, has been as follows: June, 6.57 inches, July, 7.32 inches
and August, 6.75 inches, or 20.64 inches for the three-month
period. During this period the fields become overgrown with
grass and weeds and the soil is almost continuously wet, thus
supplying the most favorable environment not only for the
survival of the fungus but for its continuous growth and spread.
The source of inoculum for infection in the field is principally
from infected plants in the seedbed which are taken to the fields
at transplanting time or contaminated soil in the fields where the
Bull. 242, Bottom-Rot and Related Diseases of Cabbage 27
plants are set. Infested soil is the source of infection for seed-
lings in the seedbed, as the disease is not seed transmitted.
Thus, infested soil appears to be the actual source of the inocu-
lum. New soil becomes inoculated by washed or windblown soil
particles carrying the fungus, by the movement of infected plant
parts by the same means, by the dissemination of hibernating
sclerotia and by the transplanting of diseased seedlings from in-
fested seedbeds to uninfested fields. Infection occurs when en-
vironmental factors, especially temperature and moisture, are
favorable for growth of mycelium which comes in contact with
the host. This contact is made by the mycelium growing up
the stem of the plant or by growing onto the lower foliage leaves
that touch the soil. Bottom-rot is initiated when the fungus in-
vades the leaf-blade tissue on either side of the leaf petiole.
The invaded tissue is killed rapidly and turns brown. Por-
tions of the mycelium grow over the surface of the blades and
continue up the stem of the plant, involving the leaves suc-
cessively. When the foliage leaves were wide-spread below the
head only limited areas of the lower blades on each side of the
petiole were invaded and killed. This condition was probably
influenced more by humidity and moisture supply to the fungus
than any other factor. When the foliage leaves were closer to-
gether, the fungus killed larger areas of the successive leaf
blades. The first head-leaf was usually the most seriously and
completely involved. The successive leaves under it were af-
fected less and less until no disease was evident. The fungus
gains entrance to the covered head-leaves by growing up the
stem among the leaf petioles, entering the existing humid cav-
ities and spreading out in the spaces around the stem onto the
The method of spread of the disease in the field from foci of
infection has not been observed with the exception of the trans-
portation of diseased seedlings from infected seedbeds. In a
certain instance there was an increase of 6% of diseased plants
in a field row set from a seedbed affected with wire-stem when
compared to the adjacent row planted with seedlings from a
seedbed free of wire-stem. Such comparisons have not been
common because most seedbeds were not disinfected and con-
sequently showed considerable wire-stem. The importance of
the disease depended on moisture and temperature conditions.
28 Florida Agricultural Experiment Station
The infected refuse left in cabbage fields played an important
role in the survival of the fungus and probably to some extent
aided in dissemination because most of the infected plants be-
come heavily laden with sclerotia. The sclerotia vary consider-
ably in size and may be washed by rains and running water con-
siderable distance across fields, especially during rainy seasons
on sloping land.
The basidiospores produced throughout the season were prob-
able factors in the spread of the disease. They were pro-
duced by the perfect stage of the fungus found on lower por-
tions of the stems, leaf petioles and blades of plants in the fields
in winter or spring, especially following rainy spells. The basid-
iospores were small and easily carried by the wind; their role
in the spread of the disease has not been studied but the pro-
duction of them did not appear to be necessary for the propa-
gation of the fungus in Florida.
The absolute control of this disease, even though possible, is
not practical in Florida. The principal reason is that the fun-
gus is well distributed in the soils in the state. Soil sterilization
in seedbeds will prevent losses of seedlings from early infection
and also insure disease-free plants for use in transplanting to
the field, thus preventing distribution of the disease. Young or
immature plants have not always become infected when planted
in infested soil, especially if the soil is not heavily infested.
Young healthy plants have a better chance of maturing when set
in infested soil than an infected plant set in the same kind of
soil. Sanitation should be practiced even though it is expensive.
Careful cultivation should be practiced so that the top soil
is prevented from resting in contact with the foliage or too close
around the stems of the plants. More than 80% of the infected
plants were banked too high with soil. High humidity aids the
growth of the fungus and when aeration is prevented by banks
of soil the environment is made more favorable for the develop-
ment of the parasite. The fungus usually did not noticeably in-
jure the woody stem above ground in its progress up to the fol-
iage, while on the other hand it attacked and killed areas of the
leaves where they came in contact with the soil.
Bull. 242, Bottom-Rot and Related Diseases of Cabbage 29
1. Bottom-rot of cabbage heads is a disease caused by Rhizoc-
tonia solani Kihn.
2. The description of this disease, apparently new to litera-
ture, has been given in detail and its relations to other diseases
of cabbage caused by this parasite have been pointed out.
3. Loss of cabbage because of this fungus in Florida dur-
ing the two seasons 1929-31 approximated 4 to 5% annually,
or $50,000 to $75,000.
4. The perfect stage of the fungus, Rhizoctonia solani Kiihn,
has been collected in nature and reproduced by artificial inocu-
lation experiments under controlled conditions.
5. Basidiospores of the perfect stage have been germinated
in pure culture and the imperfect stage of the fungus produced.
6. Cultures obtained from Rhizoctonia solani Kiihn and from
the basidiospores of Corticium vagum B. & C. were indistin-
guishable and produced bottom-rot comparable to the disease in
7. Corticium vagum B. & C. is the perfect stage of the sterile
fungus Rhizoctonia solani Kiihn which causes bottom-rot of cab-
8. Losses from the disease may be reduced by seedbed steril-
ization and care in cultivation so as not to bank soil too close
to the plants.
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