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JSARIUM BLIGHT OF THE SOY BEAN
AND THE RELATION OF VARIOUS
FACTORS TO INFECTION

By RicHarp O. CROMWELL

A THESIS

PRESENTED TO THE FACULTY OF
THE GRADUATE COLLEGE IN THE UNIVERSITY OF NEBRASKA IN
PARTIAL FULFILLMENT OF REQUIREMENTS
FOR DEGREE OF DOCTOR OF PHILOSOPHY
DEPARTMENT OF PLANT PATHOLOGY AND PHYSIOLOGY

LINCOLN, NEBRASKA
May, 1918

Reprint from Nebraska Agricultural Experiment Station
Research Bulletin No. 14

FUSARIUM BLIGHT OF THE SOY BEAN
AND THE RELATION OF VARIOUS
FACTORS lO INFECTION

By RICHARD O. CROMWELL

A THESIS
PRESENTED TO THE FACULTY OF
THE GRADUATE COLLEGE IN THE UNIVERSITY OF NEBRASKA IN
PARTIAL FULFILLMENT OF REQUIREMENTS
FOR DEGREE OF DOCTOR OF PHILOSOPHY
DEPARTMENT OF PLANT PATHOLOGY AND PHYSIOLOGY

LINCOLN, NEBRASKA
May, 1918

Reprint from Nebraska Agricultural Hxperiment Station
Research Bulletin No. 14

THE OFFICIAL ROSTER OF THE STATION

THE GOVERNING BOARD
(THE REGENTS OF THE UNIVERSITY )
HON. EDWARD P. BROWN, President, Davey,
Term expires January, 1921
HON. JOHN E. MILLER, Vice-President, Lincoln
Term expires January, 1921

HON. PHILIP Lk. HALL, Lincoln-.:.-2...... Term expires January, 1923
HON. HARRY D. LANDIS, Seward......... Term expires January, 1923
HON. JOHN R. WEBSTER, Omaha......... Term expires January, 1925
HON. FRANK D. JUDSON, Omaha......... Term expires January, 1925
SAMUEL AVERY, Ph. D., LL. D., Chancellor
J. S. DALES, M. Ph., Financial Secretary 2) \ \

THE STATION OFFICERS
BH. A. BURNETT, D. Sc., Director Est f
W. H. BROKAW, Director of Extension Service { ao
Cc. A. LEWIS, B. Sc., Bulletin Editor ,

THE WORKING STAFF
. W. CHaseE, M. E., A. E., Agricultural Engineering
. W. SJOGREN, B. Se. in A. E., Agricultural Engineering
. W. Burr, B. Sc., Agronomy
. A. KIESSELBACH, PH. D., Agronomy
. J. GRAMLICH, B. Sc., Animal Husbandry
. VAN Es, M. D., V. S., Animal Pathology and Hygiene
. Gain, M. D. C., Animal Pathology and Hygiene
. Upson, Pu. D., Chemistry
et FRANDSEN, M.S. A., Dairy Husbandry
AWRENCE BRUNER, B. gen Entomology
. H. Swenk, A. M., Entomology
F. Howarp, A. M., Horticulture
A. LOVELAND, A. M., LL. B., Meteorology
Mrap WIitcox, PH. D., Plant Pathology and Physiology
EK. MUSSEHL, B. Sc., Poultry Husbandry
. C. Fititey, A. M., Rural Economics
. P. SnypDER, M. S., Superintendent Experimental Substation,
North Platte
. BrousE, B. Sc., Superintendent Experimental Substation, Valentine
HOLDEN, B. Sc., Superintendent Experimental Substation, Mitchell
. CALVIN, B. Sc., Associate in Agricultural Chemistry
. LOEFFEL, B. Sc., Assistant in Animal Husbandry
. SHEDD, B. Sc. in A. E., Assistant in Agricultural Engineering
. Gappis, A. B., B.Sc., Assistant in Agronomy
KEIM, B. Sc., Assistant in Agronomy
. MarTIN, V. M. D., Assistant in Animal Pathology and Hygiene
. HENDRICKSON, A. M., Assistant in Dairy Husbandry
LUITHLY, B. Sc., Assistant in Dairy Husbandry
. WIGGANS, PH. D., Assistant in Horticulture
. WERNER, B. Sc., Assistant in Horticulture
rian. A. M., Askistuit in Rural fea s

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AUG 2/ 1920

CONTENTS

nitROdiiChiOnte ws wee: ei emer eee el eens Sy Wann eter ee he AOD Need 5
INooravouoauye Ion ovorenaysy @it Wovey Stony IEEE Yooacsacuactoden coeds sneaks ae 6
Orhers Soy. Beam lDISSASES# karen erases ae Ie cine ee eas eee cd
History, Occurrence and Importance of the Disease ................... 8
SHAMAN ON AOVTMIS VE sige os rs AAs eRe oe oe oe aes RD ra eee aa gre we Ae ae 10
HGLOlO Rea rachae cea Es Fs EERO Decne POR OO See CE oy DEER RE NCEE oe I oa a 13
Comparison of the Soy Bean Species of Fusarium with Other Wilt-Pro-
CUCITE ES DEClESwOR LHC MGOMUS | aracmnceterrs qe te ofots ele stu eiale sists cela ote bse 16
AS Source of Cultures and: Methods-ofisolation: .°....0....+.5... 16
B. Culture Media and Their Various Effects on Species of
US OTUULM sats cnc, Cotteov eer nie ate tees eae eS eae Re Oe es 18
Ca -Methodseor study ands Pressmtations . .9s.eeoe ee oe oe 19
D. Results of the Comparison of the Soy Bean Fungus With other
Membersmotathen SeeuloneoH LEG Qs) enn cme chee Cen 20
Morphological and Cultural Comparison of the Fusariwm Species on Soy
IB GEN MUO JI5 IMR COMO ob oma OSG nemo MODs Do cob Se bas ome dae 23
InrOCUlALION VEX PEEVE M US ar cis seneac tara oariere, cae, ohare Bee ere al 25
Experiments on the Relation of Various Soil Factors to Infection of
SOV CANS) Dyan EU iOGHCUDIU UTI ie aan Rot esaes miaicketeio el oneness 30
At hee InnuveEncemoOfes Ollie Typ CSatcis «<0 crise cats oe coos Reo: 30
Bee ehhesiniivenceroL Actditya ands Alkalinity cm eesce is seinen 33
C. The Influence of the Nematode (Heterodera Radicicola) ..35
Dynes inniiuence Of Sollee Rem pecatill: crus sei tercnacie tiercioneetee ne ene 37
He hheeinniwrencesore Other OreaniSiicerdasrm costs ascii 38
Field Experiments to Determine the Susceptibility of Varieties ....... 3
SS UDELNITL ED Tay eter wer scigeech Menta oy ated Seis Sicuctich st SPOONS sd stata ors misisde Souresee PS coke eRe caters 41
ILaieveees Uy RSS COU eR le Anaemia ed ad Nae ns oe a eo ees MRA Mi eae ae Be Cat oa 42

FUSARIUM BLIGHT OF THE SOY BEAN AND
THE RELATION OF VARIOUS FACTORS
TO INFECTION

BY RICHARD O. CROMWELL
Extension Plant Pathologist,
Iowa State Coilege

During the summer of 1915 and each succeeding summer,
packages of diseased plants of the soy bean Soja max (L.) Piper
(20)? 3 were received at the North Carolina Experiment Station
from several correspondents. A large number of plants in the fields
from which these specimens were taken had become stunted or
chlorotic, or were dead. The plants received were still green and

‘in good condition for examination. The evidence obtained from
a preliminary inspection indicated that the diseased condition
was due to the presence of a fungus belonging to the genus
Fusarium. Furthermore nearly all of the isolations from this
material gave apparently pure cultures of a species of Fusarium.

Because of the importance of legumes in the cropping systems
of the Piedmont and Coastal Plains sections, and because of the
seriousness and extent of Husarium diseases of members of this
and thirteen other plant families,’ an investigation was outlined
(1) to determine the parasitism of this species of Fusarium on
soy bean, (2) to establish its relationship to /usaria of the section
Hlegans in so far as a comparison of the cultural characters per-
mitted, and (3) by means of cross inoculations and field studies
to determine the relationship of this disease of soy beans to the
wilt disease of cowpeas (Vigna sinensis Hassk.) caused by
Fusarium tracheiphilum Smith.

The results of these investigations up to the close of the sum-
mer of 1916 have been reported by the writer (6). The studies
were continued at the North Carolina Experiment Station until

_7Formerly assistant plant pathologist, North Carolina Experiment Station. The
writer is indebted to the North Carolina Experiment Station for leave of absence in
order that full time could be given to these studies. Submitted for publication June, 1918.

?Reference is made by number to “Literature Cited,” pp.

®Piper (20) gives the following as the full synonomy of the soy bean:
Phaseolus max 1
Dolichos soja UW.
Soja hispida Moench
Soja japonica Savi
Glycine soja Siebald and Zuccarini
Soja angustifolia Miguel
Glycine ussuriensis Regel and Maack
Soja max (L.) Piper
*Wollenweber (31, p. 35)

6 Agricultural Kaperiment Station Research Bulletin 14

the fall of 1917 and then at the University of Nebraska. <A re-
vised report of them is given in this paper. Additional studies of
the soy bean blight, the results of which are also reported here,
were planned to determine the effect of various factors on the
amount and severity of the disease.

The writer wishes to express herein his sincere thanks to
Doctors F. A. Wolf and E. M. Wilcox for their assistance and
criticism during the time these studies were being conducted in
connection with their departments.

ECONOMIC IMPORTANCE OF THE SOY BEAN

The soy bean is a native of tropical Africa, Asia, and Australia
(26, p. 860-361; 20, p. 76) and was introduced into Europe by
Kampfer about 1690 (21, p. 9). At the present time it is the
most important legume grown in Japan, China, and Manchuria.
The soy bean is the chief source of protein in human food in
Japan, where very little meat, except fish, is eaten as compared
with the amount of meat consumed in this country. Its culture
in England was begun in 1790. The plant was introduced into
the United States from Japan in 1860. Since that time its culti-
vation as a soil-improving and a forage crop has been confined
for the most part to the Southern States. North Carolina is
probably foremost among these States in the production of soy
beans. ‘The yield in 1909 was only 13,313 bushels (29, p. 632),
and in 1915 was estimated! as approximately 1,000,000 bushels.
Within the last three or four years, and especially since the war
began, this crop has become increasingly important because of
the large variety of products manufactured from the oil and meal
and because of its introduction in the United States as a human
food.

The following is a list of the most important products
obtained from soy beans or in which soy beans enter: Soy bean
milk, vegetable cheese, meal or flour, macaroni preparation, soups,
pork and beans, meat substitutes, toilet powder, fertilizer, and
cattle feed from the meal, and high explosives, soaps, linoleum,
rubber substitutes, margarine, Japanese sauce, paints, varnishes,
water-proof cloth, salad oil, lubricants, and lard substitutes from
the oil.

The grain is more valuable as a supplementary feed than
cottonseed meal for the production of pork, mutton, beef, wool,
milk, and butter. The seed contains 34 per cent protein and
47 per cent fat. A bushel contains more than three times the
amount of digestible protein, fat, and ash that is contained in a

1Estimate furnished by the North Carolina Experiment Station.

Fusarium Blight of the Soy Bean t

bushel of corn. Soy bean hay contains 2.48 per cent nitrogen,
0.40 per cent phosphoric acid, and 1.32 per cent potash.

It has been found in most of the soy bean growing sections of
the South that an acre will produce on the average something
like two-thirds to three-fourths as many bushels of soy beans as
of corn and the price brought by soy beans has always been
from 50 to 100 per cent greater.

During 1915, $9,000,000 worth of oil alone was imported.
Cottonseed oil mill owners have been induced, however, partially
by the efforts of members of the staff of the North Carolina Ex-
periment Station, to crush soy beans during their otherwise idle
season. The few mills in the State which have done this have
found a ready market for the oil and meal.

OTHER SOY BEAN DISEASES

Soy beans are very generally observed to be quite free from
disease, and no very seriously destructive parasites of this host
appear to have been reported in the literature at hand. Of those
reported, a detailed study has not been made, except in the case
of Bacillus lathyri Manns and Taubenhaus (16, 17). The accounts
of the other diseases consist of brief fragmentary mycological
notes and mention of their place of collection or of their appear-
ance. Since any of them may appear on plants affected with
blight or wilt, it is deemed advisable to call attention to the pub-
lished accounts of these diseases and the appropriate bibliography.

Septoria sojina v. Thiimen (on living or declining leaves) (27).

Phyllostica sojaecola Massalongo (18, p. 688).

Aecidium glycines P. Henn. (8, p. 52).

Uromyces sojae (P. Henn.) Sydow (25, p. 429).

Bacillus sp. (on leaves)—Heald (11, 12), Smith (24), and Clinton (4).

Bacillus lathyri Manns and Taubenhaus (on leaves and pods) (17),
and Manns (16).

Heterodera radiciola—Scofield (22, p. 9), Gilbert (10, p. 9), Bessey
and Byars (2, p. 8). (These authors merely mention the soy bean
as a host for this parasite.)

Chlorosis and crinkling (cause?). (Description of the disease in the
field.) Clinton (5).

Septoria glycines T. Hemmi (comparison with S. sojina above) (13).

A disease dué to Sclerotium rolfsii is the only one not re-
ported which the writer has observed to seriously injure the crop.

It is not believed that the presence of any of these organisms
would lead to confusion in the diagnosis of blight caused by the
species of /usariwm under consideration.

8 Agricultural Kxperiment Station Research Bulletin 14

HISTORY, OCCURRENCE AND IMPORTANCE OF THE DISEASE

No published report of a disease of soy beans caused by any
species of Pusarium and one account only of attempts to produce
a disease of this host with the cowpea wilt organism have been
brought to the writer’s attention. Orton (19, p. 16-19) conducted
these tests at Edisto Island, §. C., in 1900, and at Monetta, S. C.
He says (p. 18):

“Eight varieties (soy beans) were tried on ten plats. All
proved to be immune to the wilt disease, but none of them was
adapted to the local conditions. The growth was very small, the
plants averaging from 8 to 14 inches high, tho most of the
varieties bore a “good crop of seed for such small plants. All
suffered from much drought in midsummer and all were badly
injured by the root nematode. On examination of the roots a
moderate number of bacterial tubercles were found. * *. *
They (soy beans) were at a considerable disadvantage in this test
on account of the late date of planting and the ensuing dry
weather.”

The varieties tested were Tokio, Buckshot, Yosho, Ito San,
Manhattan, Guelph, and Ambherst.t Orton reported that at
Edisto Island the soy bean made a heavy growth, 3 or 4 feet high,
and was free from the wilt disease. It may be said that a very
considerable proportion of the several varieties of cowpeas grown
in adjacent plots succumbed to wilt. The results of these tests
accord with the observations of others who have had opportunity
to observe these crops when they were grown on soil known to be
infested with cowpea wilt.

A limited number of careful observations have therefore been
made during 1915 and 1916 to determine whether the /usariwm
diseases of these two hosts are coextensive in range and thus to
furnish evidence of the identity of the two. Two 5-acre fields on
widely separated parts of the North Carolina Experiment Station
farm, in which cowpeas and soy beans were grown in alternate
rows, showed a very considerable proportion of the former host
affected, whereas the latter remained entirely free from disease.
In other localities of the State, soy beans growing on soil infested
with the cowpea-wilt organism have remained disease-free.

Observations differing from these were made in the case of
soil brought from another part of the Station farm. When this
soil was used to grow soy beans in pots out of doors, it was found
to be infested with the soy bean-blight organism, as shown by the
development of the disease in 33 of the 80 jars (Plate 95, D and

1The names in use for these varieties in 1890 were respectively as follows: Best
Green, Early Black, Yoshoka, Rokugatsha, Gosha, Black Round, Green Medium, and
Bakaziro.

Fusarium Blight of the Soy Bean 9

E). Wilt of cowpeas and bight of soy beans were present on the
farm of one of the correspotidents previously referred to, at Red
Springs, N. C. Many of the soy bean plants in this field were
killed and many only stunted, so that a decrease in yield of 60 per
cent during the season of 1946 is probably a correct approxima-
tion of his loss. Blight of soy beans has also been found to occur
at Exum and Belhaven, N. C., and was the cause of considerable
loss in both locations. The first of qaece soils occurs in the eastern
edge of the Piedmont and the others in the Coastal Plains section
of the State.

Dr. W. H. Tisdale, in conversation with the writer in 1917,
said that while at Madison, Wisconsin, his attention was called
to diseased soy beans growing in experimental plots which seemed
to be infected with a species of Kusarium. Upon being shown
specimens of the soy bean blight, he stated that the diseased
plants looked very similar to those he had previously seen.
Dr. G. L. Peltier wrote from the Alabama Experiment Station in
the fall of 1917: “It (soy bean blight) was quite common here
on the station farm, and I isolated a Fusarium from the infected
material.”

Cowpea-wilt has been found in many localities in parts of
the United States. It is also entirely probable, if we judge from
the results to be presented subsequently, that the soy bean-blight
may appear more or less generally wherever the soil is infested
with Fusarium tracheiphilum. Records received from the office of

|
5

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aN
Pil: |

{|

|

rill |

Fig. 1—The ruled area indicates the states that have reported the presence of
Fusaium trackeipnium.

10) Agricultural Kaperiment Station Research Bulletin 14

Plant Disease Survey show that, up to January 1, 1918, F.
tracheiphilum has been reported as being productive of losses to
cowpeas ranging from 2 to 100 per cent in Indiana, Missouri,
Mississippi, Louisiana, Texas, Oklahoma, Georgia, Florida, North
Carolina, South Carolina, Virginia, Arkansas, and Tennessee.
‘These states are blackened in the accompanying map (fig. 1).

SYMPTOMS

In 1916, soy beans were planted during the last two weeks in
May. This is somewhat later than usual, being due to the late
season and a period of drought. When the plants were 4 weeks
old, they had attained a height of 2 to 3 dm. and were apparently
still free from disease. The disease was first observed on July 25,
when the affected plants were about 8 weeks old. Symptoms of
the trouble could probably have been found a week or two earlier.
Affected plants, all of the same age but varying in height from
2 dm. to 1 meter, were observed on the 25th. The fungus is
believed to have stunted these small plants. In no case has the
disease been observed to occur on seedlings under field conditions.
In sand inoculated with pure cultures, however, a number of
seedlings became diseased as described later in this paper.

Tn 1917, soy beans were planted in the same field on April 26.
The weather was cool with considerable rain for the following
week or ten days so that on May 27 the majority of the plants
had only just broken thru the surface of the soil, some were not
yet up, and some were from 10 to 12 cm. in height. Examination
of a few of the plants from a number of the rows did not show
injury that could be attributed to Fusarium. On June 12 some
of them were 15 to 25 cm. in height and infected plants were
found in many of the rows. On June 26 the plants were 8 weeks
old and from 3 to 5 dm. in height. Many were stunted by this
time, partly because of the action of /usariwm and partly because
of nematodes, Rhizoctonia, and other causes, so that only by
removing suspected plants could it be certain that they were
diseased and that /usarium was quite generally present thruout
the field. Plants were found without any of the external symp-
toms described below, except the dwarfing, the xylem areas of
which were browned well up the stem. By July 20 the disease
was present thruout the field and many plants were in advanced
stages of the disease.

Comparing the conditions in 1917 with those of 1916 in the
same field, one finds that at the end of 8 weeks the plants were
smaller in 1917 but the disease was more general and more ad-
vanced in its injury to the individuals.

Fusarium Blight of the Soy Bean Li

The contrast in appearance of five healthy and five diseased
plants is shown in Figure 3, D. E. The same type of sandy loam
soil was used in both jars and the plants in each were grown out
of doors under the same conditions. The plants shown in figure
E were naturally infected from naturally infested soil and were
typical of the diseased plants in 32 other jars of the 80 in the
test. A considerable number of the leaves have fallen from the
diseased plants, a portion of the petioles persist without leaflets,
the plants are dwarfed, and there is no evidence of wilting in
any part of the plants. The foliage which persists on these plants
is yellow as contrasted with the normal leaf green of healthy
plants.

Pig. 2—A. A diseased stem of soy bean, showing the roughened appearance caused
by the irregular covering of sporodochia.

B. Interior of healthy (unstained) stem of soy bean.

C. Interior of diseased (discolored) stem of soy bean.

The occasional absence of a definite wilting of the leaves
has been noted in other wilt diseases. Orton (19, p. 10), in speak-
ing of the cowpea disease caused by /. tracheiphilum, says: ‘The
term ‘wilt’ is somewhat misleading, as the leaves usually drop off
before there is any conspicuous wilting. The name was applied

1200 Agricultural Reperiment Station Research Bulletin 14

because of its relationship to the wilt of cotton and watermelon.
where this symptom is very prominent, and it seemed desirable to
retain it for the cowpea disease.”

In the case of the soy bean disease, wilting is a less prominent
symptom than in cowpeas, and is seldom present at any stage of
the disease. The plants, as a rule, drop all of their leaves and die
without any evidence of wilting. Wilting has been observed
in a very few instances in the field in the case of young plants.
The woody nature of the stem and petioles probably accounts
for the general absence of wilting in them, and the presence of
well-developed mechanical tissues in the leaflets may account for
their failure to manifest wilt. The possibility exists, also, that the
physiological interaction of parasite and host differs from that
exhibited by wilted cotton and watermelons infected with
Fusarium spp. If potted soy beans which have never been ex-
cessively watered are allowed to remain without water they do
not wilt but the leaves finally curl as the tissue becomes dry and
crisp. Neither do the leaves wilt if the stem is cut to the center.

_ Fig. 3—D. Soy bean plants grown out of doors in the same type (Cecil) sandy loam
soil; D, healthy; E, diseased thru the naturally infested soil.

Fusarium Blight of the Soy Bean 13

Instead of applying the name “wilt,” therefore, to the soy
bean trouble, it is thought desirable to call it “blight.” This
word describes the most prominent symptom on the fohage.

That plants are often almost indifferent, for some time, to the
fungus which may even be abundantly present within it, is shown
not only by the absence of wilt but also by the fact that many of
the plants mature a reduced crop of beans in spite of the disease.
Affected plants in such cases are stunted and mature earlier than
healthy plants. In contrast to this, 100 per cent of the cowpeas
in rows in different parts of the same field are infected, most of
them die before reaching a height of 2 dm., and the scattered
plants then remaining may all die before blooming.

Perhaps the most prominent symptom is a browning of the
interior of the stems and roots. By the time the lower leaflets
or leaves begin to drop, this discoloration is evident well up into
the stem and, if necessary, by removing the petioles, infected
plants may be noted from the brown color of the bundle scars
when no other positive symptom is to be observed. As the dis-
ease progresses, the discoloration extends in some cases to the tip
of the stem and into the bundles of the leaflets. The tracheal
tubes of affected stems when cut obliquely show as brown specks.
The relative amount of discoloration in general and the depth
of color in affected xylem portions is less in soy beans than in
cowpeas. Healthy and diseased stems are shown in Figure 2, B
and C, respectively.

The surface of stems of plants in advanced stages of the dis-
ease in the field generally have salmon-colored spore masses,
sporodochia, thickly and irregularly distributed over them.t This
character is shown by the roughened appearance of the stem in
Figure 2, A. The spore masses are composed of macroconidia of
the fungus and are frequently found to occur on plants, the upper
leaves of which are still healthy in appearance. Sometimes they
are formed only in more advanced stages of the disease.

ETIOLOGY

Sterile seedlings had been grown in test tubes by the method
described later in this paper for use as a culture medium to main-
tain the virulence of the organism. In 1915 the roots of such
seedlings, inoculated after the development of the first true leaves,
were found in a few days to be penetrated by the fungus thru
stomata and epidermis. The roots were mounted directly on slides
in a glycerin-eosin water solution and examined under the micro-

1Sporodochia on stems of cowpeas are reported by Orton (19, p. 9) to appear after
the death of the plants.

14. Agricultural Fxperiment Station Research Bulletin 14

scope. Tisdale describes practically the same method in a recent
paper (28, p. 576). Under such unfavorable conditions, however,
the host was at a disadvantage, and since a number of other
species of Fusarium penetrated the plants in the same way, no
significance is given to the observations.

In order to determine the relation of the organism within the
various host tissues, a large number of stained free-hand and
microtome sections were made of stems and roots at various stages
of development of the disease. A number of attempts to obtain
pieces of roots at the time of infection were, however, unsuccess-
ful. In woody stems, in an early stage of the disease, only the
xylem tubes nearest the pith were found to contain the fungus
filaments. The pith had disappeared in both normal and diseased
plants of moderate size. Later, other of the tubes thruout the
xylem area were penetrated and had become filled to a large extent
with a network of fungous filaments. In still more advanced
stages, all of the xylem elements (fig. 4, H) were found to contain
the fungus, and in addition the cortical parenchyma was invaded.

Many of the fibrous roots were destroyed, and figure 5 shows
how the disease progresses from the smaller root branches into
the main root. A and C represent the cortex and pith, respec-
tively, and are, at this stage of the disease, seen to be free from
discoloration due to the fungus. B indicates the xylem region,
which is discolored in areas ‘beginning at the point of origin of
lateral roots and extending mostly upwards. Later the browned
areas become continuous and the xylem is found to be in this con-
dition thruout the stem and root (fig. 2, C). New roots form,
but often of insufficient number to maintain the life of the plant.
In other cases the plants subsist with a reduced supply.

It seems, therefore, that the symptoms produced result not
simply from (1) a mechanical clogging or (2) a slow appropria-
tion of food and water by the fungus, as others have previously
stated, but that (3) a considerable destruction of the root system,
and, perhaps, (4) a reduction of the activitv of the protoplasm
due to the possible presence of toxins secreted by the fungus, also
aid in this.

That other organisms may often facilitate the entrance of
Fusarium is given “special consideration in another part of this
paper.

Fusarium Blight of the Soy Bean 15

Fig. 4—A-c, Types of macroconidia of the species of Fusarium on soy bean. H,
Cross section of the xylem portion of a diseased soy bean stem, showing the invasion of
the medullary rays (a) and the xylem vessels (b) by mycelia of the species of Fusarium
on soy bean.

16 Agricultural Experiment Station Research Bulletin 14

Fig 5—Diagrammatic drawing of a longisection of the main
root of the soy bean to show the entrance of the fungus from
the lateral roots. A and C indicate uninvaded pith and cortex,
respectively. B represents the discolored xylem in an early
stage of the disease.

COMPARISON OF THE SOY BEAN SPECIES OF FUSARIUM WITH
OTHER WILT-PRODUCING SPECIES OF THE GENUS

SOURCE OF CULTURES AND METHODS OF ISOLATION

Tsolations were made from the interior of stems of freshly
wilted soy bean and cowpea plants. The stems were first thoroly
washed in water and allowed to remain wrapped in cotton mois-
tened with 0.1 per cent solution of mercuric chlorid for 15
minutes. They were then split open so that the diseased interior
was exposed. Fragments of diseased tissue were removed with

Fusarium Blight of the Soy Bean abi ¢

a sterile scalpel and transferred to cooled poured plates of string-
bean agar (8 c.c. per plate), to each of which four drops of 20
per cent lactic acid had been added. After several days, a micro-
scopic examination was made of the conidia and mycelium to
determine whether other organisms were present. Eight trans-
fers to test-tube slants were made from the margin of several
plantings and kept for comparison and for indications of con-
tamination. It may be noted that a large percentage of pure
cultures was obtained by this method. From the cultures that
Were pure, single-spore cultures were obtained according to the
method described by Sherbakoff (23, pp. 102-103; p. 104, ‘footnote
8). Stock cultures were made from these single-spore cultures and
repeatedly repoured to protect from subsequent contamination.

Several species of /usarium were secured, in order to com-
pare them with the /usarium sp. from the soy bean and the one
from the cowpea, isolated as described above. The following
species, subcultures from Wollenweber’ s authentic cultures, were
obtained thru the courtesy of Mr. C. W. Carpenter, of the Bureau
of Plant Industry: Fusarium oxysporum (Schlecht.), 7. vasin-
fectum (Atk.), F. Tyc opersict Sace., fF. niveum Smith (members
of the section Vegans), and F. discolor, var. sulphureum
(Schlecht.) App. and Wollenw. (1, pp. 115-118), (section
Discolor ).

These species were studied in culture, in order to determine
their morphological and cultural characters, since such a study
is considered of primary importance in their differentiation. The
species mentioned were chosen because all except one belong to the
section Hlegans, the section which contains the known wilt- -pro-
ducing species, and because, according to Wollenweber, they are
the most difficult to separate by this method. F, conglutinans
Wollenw., 7. redolens Wollenw., and F. orthoceras App. and
Wollenw.., ., of the same section are included in the comparisons.
They are so different from the others, as indicated by the original
descriptions, that the writer soon realized that there was little
probability of confusing them with the soy bean strain. Wollen-
weber (31, 32) and Sherbakoff (23) have described other species
and varieties of the section Hlegans, which are not, however, 1n-
eluded in this study, because they occur on hosts widely separated
genetically from the soy beant and because the authors have not
had opportunity to make a sufficient number of infection experi-
ments to establish them as wilt producers.

1Wollenweber, H. W. (31, p. 37) says, “The parasite from one host has not been
found on living organs of another host. In pure culture the parasite from one host
did not cause wilt in any other host as a result of inoculation experiments.”

18 Agricultural Kxperiment Station Research Bulletin 14

CULTURE MEDIA AND THEIR VARIOUS EFFECTS ON SPECIES OF
FUSARIUM

In making a cultural study of these fungi much care was
taken to follow the suggestions of Appel and Wollenweber (i),
Wollenweber (81, 82), and Sherbakoff (23), in order to determine
what criteria to employ in judging normal growth characters. Ut
is generally believed that standardization of cultural methods is
highly essential in the comparative study of so difficult a group
of fungi.

The writer has kept the soy bean and the cowpea strains
under constant observation for three years and other strains for a
part of this time, on various kinds of “natural and _ artificial
media” and under widely variable physical conditions. He is
therefore familiar with the possible variability of members of this
genus.

Since a large number of the media used did not prove to be
of. special diagnostic value, they are not discussed here. Among
the media most commonly employed and serving some particular
purpose were oat, potato, and string-bean hard agars (3 per cent
agar), which, because of the paucity of moisture (23, p. 106),
give all forms of fructification with “normal” spores. Five to 10
per cent of dextrose was added to agars to favor the production
of pigment. The addition of this sugar, however, favored the
development of mycelium at the expense of macroconidia, and
when from 8 to 10 per cent was added these spores were often
absent. Growth on steamed rice in test tubes from weighed
quantities of rice and measured amounts of water to obtain uni-
formity also results in the formation of pigment and sometimes
an odor that is typical for certain related species of Fusarium.
Herbaceous and woody stems, string-bean pods, and potato plugs
give the best development of sporodochia and pionnotes.t Potato
plugs also serve for the proper development of sclerotia and
colors, both of which may be reduced or absent from stem plugs
when there is a minimum development of mycelium.

According to Wollenweber (31, p. 87), virulence is commonly
maintained on stem plugs. Living sterile soy bean and cowpea
seedlings grown in 6-inch test tubes were also used and are
thought to be a better medium for maintaining virulence in the
strains from the respective hosts.

In order to obtain sterile seedlings for this purpose the seeds
were first washed for 5 minutes in tepid water and were then
placed in concentrated sulphuric acid for 20 minutes. Formalin,
mercuric chlorid, both in aqueous and alcoholic solution, and

1For a discussion of these terms, see Wollenweber (31, p. 24).

Fusarium Blight of the Soy Bean 19

other disinfectants were employed with much less success. After
washing off the acid in three or four changes of sterile water, the
seeds were transferred into sterilized moist chambers in the bot-
toms of which several layers of moist filter paper had been placed.
Germinated seeds on which there was no evidence of contamina-
tion after a day or two were transferred to sterile test tubes! the
bottom of each of which contained a wad of moistened filter
paper.” If, during germination or transfer, contamination occurs,
it generally becomes evident on the seedlings or white paper,
especially if the seedlings are set aside until they have grown to
a height of 3 or 4 inches.*

More recently, however, such precaution to maintain virulence
was found to be unnecessary because the age of cultures seemed
to have little effect upon their virulence. Old cultures gave as
high a percentage of infection, if grown on proper media and
transferred frequently, as they did when first isolated.

METHODS OF STUDY AND PRESENTATION

All transfers of different strains in a set for comparison were
made to a certain medium on the same day and to additional
media to provide the necessary cultural characters. When species
were compared, they were always of the same age and were grown
on the same medium. As many comparisons could be made on
the same day as there were species and kinds of media in the set.
If sufficient data had not been obtained, if certain cultures were
abnormal, or if other species or media were to be used, new sets
were prepared of all of the species using the desired media and
comparisons were again made thruout the series.

Cultural differences also arise as a result of the employment
of spores or a bit of mycelium in inoculation. In the former case
the young cultures quickly produce spores with a scant mycelial
growth, while in the latter the mycelial growth is abundant and
there is a paucity of spores. For this reason spores from sporo-
dochia, when present, were used, and in all cases, in so far as was
possible, the same kind of inoculum was transferred for all cul-
tures of a set. When the production of spores becomes subnormal,
as it often does in cultures, considerable time and patience may be
required to bring the strain back to a “Normkultur.” This was

*For making this last transfer, dip the ends of long tweezers into 95 per cent alcohol

and ignite in the flame. This sterilizes instruments, burns off the excess of alcohol,
and leaves them dry and cool enough for immediate use.

*The use of agar as a substratum for this purpose (Garman and Didlake, 9), and
Sphagnum moss, did not prove to be satisfactory. Soil, too, has a disadvantage in that
it does not show the contaminations as readily as filter paper or agar.

%An oat sprouter with glass front, heated by a kerosene lamp and costing about
$10, makes a good light incubator for such purposes when the greenhouse is not con-
veniently located or the temperature suitable. This sprouter is unsuited, of course, to
cultures or material requiring a constant temperature.

20 Agricultural Fxeperiment Station Research Bulletin 14

accomplished by transferring a small portion of mycelium to a
variety of media until a medium was found on which spores
were again obtained.

All cultures were kept in the laboratory at room temperature,
12° to 26° C., and in diffused daylight, so that they were sub-
jected alike to any change of environmental Scene

In all cases’ 10 cultures of a species were made on each
medium. Different forms of fructification which normally appear
on a certain medium may not do so in every tube. For example,
in a species in which sporodochia are not abundant, they may
perhaps form on only 2 or 3 of the 10 stem plugs; or if the form
produces green sclerotia, they may develop on not more than 5 of
the 10 potato plugs. In some instances as many as 8 to 10 sets of
10 tubes each of a particular species were made.

In making the microscopical examination, note was taken of
the size, septation, abundance, and type of conidia (fig. 1, A-G),
chlamydospores, and conidiophores. In measuring spores, "several
fields were first examined to fix in mind the prev -ailing type and
an average of 10 or more of these typical spores was made. Care-
ful note was taken also of extreme types.

In the macroscopic study of the cultures, the nature of the
stromata, the pionnotes and sporodochia, the character of the
aerial mycelium, the color of spore masses, aerial and submerged
mycelium, and substratum, and the production of sclerotia were
considered.

RESULTS OF THE COMPARISON OF THE SOY BEAN FUNGUS WITH
OTHER MEMBERS OF THE SECTION ELEGANS

The first sets of parallel cultures were intended to serve in
the separation of any or all of the species of Fusarium causing
wilt from the soy bean fungus. /. discolor, var. sulphureum,
F. owysporum, F. vasinfectum, FP. lycopersici, FP. niveum, FP. tra-
cheiphilum, and Fusarium sp. from soy bean were therefore
grown on the following media, several sets of 10 cultures of each
species being used on each medium: Potato plugs, steamed rice,
cotton stems, potato hard agar, and string-bean hard agar. The
cultures were examined when 8, 15, 19, 30, and 50 days ‘old. The
results are noted in Table 1. Only those characters are recorded
that are necessary for the separation of the species.

Fusarium Blight of the Soy Bean

21

Taste 1.—Characters which separate a number of the wilt-pro-
ducing specics of Fusarium from F. tracheiphilum and
the soy bean fungus.

Species Sclerotia Sporodochia | Pionnotes | Chlamydospores
. discolor........| None Numerous Perfect Intercalary; no
measurements.

F. vasinfectum....| Green and do do Interealary and

flesh-colored terminal; no
measurements.

F. oxysporum..... do Few Reduced | Interealary and
terminal; 6 to
12 wu.

F. lycopersici..... Flesh-colored | Numerous Perfect Interealary and
terminal; no
measurements.

1B 5 TUTGONTD so 0 BSB Large green do Reduced | Same as for F.
lycopersici.

F. tracheiphilum...| Green and Few None Intercalary and

flesh-colored terminal; 6 to
ili
Fusarium sp. on | Mostly green; do do Same as for F.

SOv- Deanery aa oe

some flesh-

colored

tracheiphilum.

22 Agricultural Kxperiment Station Research Bulletin 14
Taste 1 (Continued).—Characters which separate a number of
the wilt-producing species of Fusarium from F. tra-
cheiphilum and the soy bean fungus.

Maer<conidia
Species a Odor
Size of 3-septate Type
PRSCISCOL Ole No data Discolor; mostly _ None.
5-septate
F. vasinfectum..... Same as in F.| Elegans; mostly | Strong lilac onrice.
oxysporum 3-septate
F. oxysporum..... VAY Ma KOO OM ON'4 do Often none, some-
SeOnOn 4s lar times seant lilac.
F. lycopersici......| Abnormal do None.
F. niveum.........| Abnormal; (orig- do do
inal description
gives larger than
F. oxysporum).
F. tracheiphilum...| 23.6 to 41.0 by do do
3.9 to 4:1 py
Fusarium sp. on | 24.6 to 35.8 by do do
SOVsbeaneyce ciel fos) (HO) GIL yun

From the data in Table 1 it is important to observe that
F. tracheiphilum and the species of Fusarium on soy bean belong
to the section Hlegans, as established by Appel and Wollenweber
(1) and modified by Wollenweber (31) in a subsequent study.
They are themselves very similar in cultural characters, but can
be quite sharply separated from the other species included in the
tabulation. When the characters of the species of /usartum on
the cowpea and soy bean noted in this table are compared with
those in the original descriptions of certain other members of the
section Hlegans—namely, F’. redolens, F. orthoceras, and F. con-
glutinans—there is plainly no chance of their confusion. Ff.
redolens (31) produces no blue sclerotia, and its conidial masses
are brownish white; /’. orthoceras (25) possesses neither sclerotia,
sporodochia, nor pionnotes; and 7’. conglutinans (381) is distin-
guished because of the absence of sclerotia, sporodochia, or pion-
notes, and the typical wine-red to purple colors of the section.

Fusarium Blight of the Soy Bean 23
MORPHOLOGICAL AND CULTURAL COMPARISON OF THE
FUSARIUM SP. ON SOY BEAN WITH F. TRACHEIPHILUM

Since the studies summarized in Table 1 do not succeed in
distinguishing the species of Fusarium on soy bean and cowpea,
a more extensive cultural study of these two fungi was made.
For this purpose three series of cultures were grown, and the
results have been summarized in Table 2. Each series contained
10 cultures of each fungus on stem plugs, potato plugs, steamed
rice, standard nutrient agar (1.8 per cent agar, 1.0 per cent acid),
string-bean hard glucose agar (3 per cent agar, 1.0 per cent acid,
-and 10 per cent glucose), and oat hard agar (3 per cent agar and
1.0 per cent acid). The cultures were examined when they were

8, 15, 30, 50, and 75 days old.

Taste 2.—A morphological comparison of the species of
Fusarium on soy bean and cowpea.
Fusarium sp. on soy bean.
Medium Macro- |Sporodochia| Sclerotia Color of Character
conidia | mycelium | of mycelium
Standard (No measure-)/Salmon- iNone White Mostly aerial
nutrient ments colored and floccose,
agar becoming ap-
pressed in
old age.
String-bean do Salmon- Green do do
Agar oe ee colored;
generally
present
Oat, hard [26.6 to 38.6|Flesh- Dark-green| Mostly lilae;|Cottony.
glucose by 3.69 to] colored some dark
AC Aes ee AOA Siftins t540) purple
days old
MILE AIMEG LICE ae ic dane eee al alis 3 Rae oll ay eee ISSO joa eelleg oo ude s pe
| lilaes,
purples
Potato plugs|Normal Salmon- Dark-green|Green, near |Floccose.
spores colored; sclerotia
absent generally
present on
sclerotia
Stem plugs.|22.5 to 43.6|Salmon- Green, very|White, i\Floccose;
by 2.87 to| colored; small; sometimes | scant.
4.11 yw, 14] small numerous | green near
days old sclerotia

24-0 Agricultural Kx periment Station Research Bulletin 14
Taste 2 (Continued).—A morphological comparison of the
species of Fusarium on soy bean and cowpea.

F. tracheiphilum.
Medium Macro- |Sporodochia| Sclerotia Color of Character
conidia mycelium | of mycelium
SCAN ards spe aes None Flesh- White Mostly sub-
nutrient colored merged or
AvaALeeene appressed
String-bean |No measure-|Salmon- Mostly do do
agar) ments colored; flesh-
few colored;
some green
Oat hard 22.5 to 36.9/|Flesh- Dark-green|Mostly dark/\Cottony to
glucose by 3.8 to} colored and flesh- | purple; matted and
agar, a. che 4.42 yw 50 colored some lilac | appressed
days old
SLC AIMEG TICE! Se ig tea eer en cage reel | ta et en eet Pinks sr edss)|ireeeacts ieee
lilacs,
purples
Potato plugsi24.6 to 36.9|\Salmon- Flesh- Pinks, lilaes,|Mostly
by 8.28 to} colored; colored; greens appressed
4.42 w 19] often on often none
days old sclerotia
Stem plugs. |No measure-!Sa!mon- Green; very| White; Appressed;
ments colored; small; ? sometimes | good growth.
small; numerous | green, near
sometimes sclerotia
none

No mention is made in Table 2 of pionnotes or odors, as none

was produced in any of the cultures.
noted on steamed rice.

wide

Only color-production was
The macroconidia of both strains show a
variation both in size and in shape, but these differences can
properly be included in the range of variation.
macroconidia of the soy bean (fig.
indistinguishable.

The normal
4, A-G) and cowpea strains are
The chlamydospores of either strain are ter-

minal or intercalary in or on vegetative filaments and average
6 to 10.25 » in diameter. The conidiophores are verticillately
branched when normal. Sporodochia, altho sometimes flesh-
colored, are normally salmon-colored. They are not always present
on all media but are formed by each strain either on sclerotia or
on mycelia as stromatal bases. Green sclerotia are normally
present in both strains. There appear to be some differences in
colors produced in substrata, altho not very consistent ones, a

Fusarium Blight of the Soy Bean 25

difference in the character of mycelium until advanced ages of
the cultures and generally, but not always, an absence of flesh-
colored sclerotia in the soy bean fungus. These differences, how-
ever, are not believed to be of sufficient importance to warrant
regarding the soy bean strain as a distinct species or variety.

In addition to the media employed in Table 2, potato hard -
agar, cornmeal plugs, and string-bean pods were used, but they
showed no additional characters of value.

Perithecia have never been observed on the diseased stems;
neither have they been obtained in cultures from the surface spores,
nor from the diseased internal tissues. In fact, the cultural difter-
ences between the Fusarium sp. on soy bean and Neocosmospora
spp. are as striking as between NMeocosmospora spp. and the
several species of Fusarium causing wilt studied by Higgins (14)
and Butler (3).

INOCULATION EXPERIMENTS

From the foregoing morphological and cultural studies, 1t is
evident that the species of Fusariwm on soy bean is not distin-
guished from /. tracheiphilum by any well-defined differences.
Since the possibility existed that they might be separated by
biological differences, reciprocal inoculation studies were under-
taken to secure additional evidence of their identity.t

Plants were therefore grown in pots and flats in the green-
house and in plots in the field for use in inoculations. The soil
used in the pots and flats was a fine, compact, sandy loam, except
in the case of one experiment, and was taken from a field in
which diseases of cowpeas and soy beans caused by Fusarium spp.
had never been observed. In certain of these tests, as an added
precaution, the soil was partially sterilized by the use of a 2 per
cent solution of formaldehyde. The seed were also sterilized in
certain experiments by immersion for 15 minutes in commercial
sulphuric acid. Since uninoculated plants remained free from
disease when these precautions were not employed, their use was
discontinued in subsequent tests, unless otherwise stated.

The pots and flats were of sufficient size to permit the plants
to grow to maturity.

In determining the percentage of diseased plants, count was
made only of those in which it was possible to find discoloration
and invasion of the xylem tissues. In case of doubt in this micro-
scopic examination, planted plates were made from the tissues and
the subsequent growths studied.

The varieties of soy beans and cowpeas planted for the cross-
inoculation experiments were known to be subject in the field to
the species of Husarium on soy bean and cowpea, respectively.

1Wollenweber (31, p. 37) says that a consideration of the biological characters is of
secondary importance in the determination of species.

26 Agricultural Kxperiment Station Research Bulletin 14

EXPERIMENT I.—Twenty-five North Carolina Black cow-
pea and 25 Mammoth Yellow soy bean seedlings, growing in each
of two flats in the greenhouse, were each inoculated when from
10 to 15 cm. high with spores from sporodochia and with
mycelium by introducing the material into incisions in the stems
- at 2 to 4 cm. below the surface of the soil. AJl of the plants in
one flat were inoculated with the soy bean strain of Pusurzwm
and all of those in the other with the cowpea strain. Checks and
all inoculated plants except two cowpeas inoculated with the soy
bean strain and one with the cowpea strain remained healthy.
The test was repeated, using freshly isolated strains of both
organisms; and, since all but one of the plants remained healthy,
this method of inoculation was discarded.

EXPERIMENT II.—In this experiment the soil in two flats,
A and B, in the greenhouse was inoculated with pure cultures of
Fusarium spp. on cowpea and soy bean, respectively. These cul-
tures were then incorporated in the upper 4 inches of soil.

In this and succeeding experiments the organisms had been
grown on pieces of moistened, sterilized cowpea stems until
numerous sporodochia had formed. On April 12, 1916, 20 North
Carolina Black cowpeas and 20 Mammoth Yellow soy beans were
planted in each flat. A third flat, containing uninoculated soil,
was planted as a check.

By June 4a cowpea plant on Flat B was noted to be diseased.
Others had been observed to be affected by June 15, when all the
plants were removed and examined. The results are presented in

Table 3.

Tae 3.—Results of growing soy beans and cowpeas in artificially

inoculated soil.

Total Diseased plants

Flat Organism Host number |— ———

of plants} No. | Percentage
A | F. tracheiphilum on cowpea. .| Cowpeas.... 20 6 30
Soy beans... 20 3 6s
B HIND 5 on soy bean...| Cowpeas.... 20 10 50
Soy beans... 20 7 35
Co PNonen(controll) is sere Cowpeas.... 20 0 0
Soy beans... 20 0 0

EXPERIMENT III (Series 1).—Since the percentage of
diseased plants in Experiment II is relatively small, the test was
repeated, using another strain of each organism and Clay cow-

Fusarium Blight of the Soy. Bean Xu

peas instead of North Carolina Black variety. The roots of each
plant in this test were injured during the process of cultivation.
The period of growth of these plants extended from June 29 to
September 1, at which date the plants were fully matured. The
results of this series are recorded in Table 4 (a).

EXPERIMENT III (Series 2).—The test in series 1 was
duplicated between September 7 and November 20, with no re-
sultant increase in the percentage of infections.

EXPERIMENT III (Series 3).—This test was in duplica-
tion of the other series in this experiment except that the soil
consisted of a mixture of six parts of coarse sand, one part of
fine sandy loam, and one part of stable manure. The results
obtained between September 7 and November 20 are included in
Table 4 (b), because they show considerable increase in the per-
centage of infection even tho the cultures used were transfers from
cultures nearly 3 months old.

Tape 4 (a) and (b).—esults of growing soy beans and cowpeas
in artificially inoculated soil, the plants having been
(a) wounded below the surface of the soil.

Total Diseased plants

Flat Organism Host number = a
of plants| No. | Percentage
D | F. tracheiphilum on cowpea. .| Cowpeas....| ° 20 3 15
Soy beans... 20 3 15
E | Fusarium sp. on soy bean...| Cowpeas.... 20 6 30
Soy beans... 20 5 DAS:
None (controls. e: - 2 -| Cowpeas..:: 20 0 0
Soy beans... 20 i) 0
(b)

Total Diseased plants

Flat Organism Host number
of plants| No. | Percentage

G | F. tracheiphilum on cowpea. .| Cowpeas... 20 16 80
Soy beans... 20 12 60
SF Fusarium sp. on soy bean...| Cowpeas... 20 13 65
Soy beans... 20 WZ 60
a INonex(CONtTON)po.iesrnee isis Cowpeas.... 20 0 0
Soy beans... 20 0 0

ee

28 Agricultural Kxperiment Station Research Bulletin 14

EXPERIMENT IV.—Since it was thought that the strains of
Fusarium on soy bean had to a degree lost their virulence by
‘growth in culture, soy bean stems bearing an abundance of sporo-
dochia were macerated and mixed with the soil in two flats. Seed
of the Mammoth Yellow variety were planted on May 25. When
the experiment was concluded, August 10, only 8 of the 80 soy
bean plants in these two flats were found to be infected.

EXPERIMENT V.—This experiment was designed to con-
firm the results of inoculations in the greenhouse by inoculations
under partially controlled field conditions. Four small plots
(Nos. 26, 27, 28, and 29) on wilt-free soil of the station farm
were inoculated with the /. tracheiphilum from soy bean; two
others (Nos. 59 and 60) with this organism from cowpea, and two
(100 and 101) were left untreated as controls. Thirty cowpeas
and thirty soy beans were planted in each plot on June 10, and
the final results noted in Table 5 were obtained on September 4.

TABLE 5.

Results of cross-inoculations in the field.

Total | Diseased plants
Plot; Organism Host number ———
No. of plants| No. | Percentage
26 | Fusarium sp.| Clay cowpeas.............- : 30 al 56.6 iT
on soy bean| Haberlandt soy beans...... 30 4 13.3
Pat do Clava cowMeaseen its ease 30 10 33.3
Molders oy Weasel ie 30 0 0.
28 do Clayvacowil Casa see ae 30 10 33.3
28 do Mammoth yellow soy beans. 30 8 26.6
29 do ClayicOWPCaSan osteo 30 15 50.0
_| Tar Heel Black soy beans... 30 3 10.0
59 | Fusarium sp.) Clay cowpeas.............. 30 26 86.6
on cowpea.| Tokio soy beans.. ........ 30 6 20.0
60 do ClavacOwleaSetee scents 30 iT 56.6
60 do Mammoth Yellow soy beans. 30 6 20.0
100 | None ClayicOWwReaS sa 1 ree soe 30 0 0.0
(control). ..| Mammoth Yellow soy beans. 30 0 0.0
101 do ClayecowPeases saosin 30 0 0.0
Mammoth Yellow soy beans. 30 0 0.0

EXPERIMENT VI.—On May 25, 1916, two 100-foot rows
of each of the soy bean varieties Tokio, Haberlandt, Mammoth

Fusarium Blight of the Soy Bean 9

bo

Yellow, Medium Yellow, and Virginia were planted in a field
which produced a large percentage of wilt in cowpeas in 1914.
Two rows of cowpeas were planted in the same plot. By Septem-
ber 1, when all the plants had fully matured, a small percentage
of wilted cowpeas had been noted; but no blighted soy beans were
found. ;

Similar data were obtained from observations on cowpeas and
soy beans grown in the experimental plot devoted to plant breed-
ing. In this 4-acre plot, three or four rows of soy beans were
alternated with three or four rows of cowpeas thruout the field.
Some wilt occurred in practically every row of cowpeas in the
plot, but careful examinations during the season failed to reveal
a single soy bean blighted with Fusarium sp. among 17 standard
varieties and 50 other unnamed selections. :

DISCUSSION OF THE RESULTS OF INOCULATION EXPERIMENTS

In inoculation experiments soy beans and cowpeas, from the
time of germination until 4 or 5 days after their appearance above
the surface of inoculated soil, were often killed by an organism
which invaded the cotyledons and the growing tips. This was
especially true if nearly pure sand was used instead of soil. It
was not definitely proved that Fusarium was the cause of this
condition, however, and no record of these cases was made in the
results given above.

In the results recorded, the cowpeas after 4 to 6 weeks were
generally invaded well up into the stem and the plants were often
killed after a period in which they showed, except for sporo-
dochia, the striking symptoms commonly known to appear in
connection with this disease in the field. On the other hand, the
affected soy beans have shown symptoms only on the roots. Some
of these were found to have typical discoloration in the xylem
areas but the root systems were never invaded to the extent that
the plants showed the effects above the ground. <A lack of vigor
was apparent in many soy beans but it was uncertain without
an examination of the roots whether this was due to the action of
the organism or to more or less unfavorable conditions for plant
growth.

That reciprocal inoculations were successful in a number of
cases can be seen from the results of certain of the above experi-
ments in which plants of both hosts became infected by both
strains of Fusarium. Certain other attempts were made, how-
ever, in which all soy beans remained free from disease. Contrary
to this, the cowpeas in the same flats always showed at least
several plants typically diseased, regardless of whether they

30 3» Agricultural Fxperiment Station Research Bulletin 14

were growing in soil that had been inoculated with the cowpea or
with the soy bean strain of Fusarium.

EXPERIMENTS ON THE RELATION OF VARIOUS SOIL FACTORS TO
INFECTION OF SOY BEANS BY F. TRACHEIPHILUM

THE INFLUENCE OF SOIL TYPES

Since artificially inoculated soy beans have not always
developed the disease, nor developed it to the same degree of
severity that cowpeas have under the same conditions, nor as
severely as naturally infected soy beans in the field, a number of
experiments were planned to determine the factor or factors
which seemed to be responsible for the limitations. At the outset
possibly all of the factors of the air and soil that influence the
health of plants might be concerned. The effects of certain of
these have been under consideration in the following experiments
in which, with the exception of that on Norfolk soils, all of the
plants were subjected alike to those factors which it was impossi-
ble to control. In this way evidence was obtained as to the effect
produced by certain factors by varying one, under control, in
each experiment.

The relation of conditions above the ground, such as tem-
perature, humidity, and light, to the susceptibility of plants to
parasitic diseases is often an important one, but a study of them
in connection with the disease at hand has not yet been made
because a more direct relation probably exists between soil fac-
tors and infection. In consideration of the soil, attention has
first been given to the effect of variation in texture which is
limited by the size of soil particles and by organic and inorganic
materials which further influence such factors as temperature and
water holding capacity. The United States Bureau of Soils has
divided soils into types, classes, and series.

Soil class—“Soil types, which constitute the units of soil
classification, may be grouped in different ways. As soils are
made up of particles of different sizes, they may be grouped
according to the relative proportions of the particles of different
sizes which they contain. This grouping is known as soil class
and is based on texture.” (30, p. 16.)

Soil series—“‘It has been found that in many parts of the
United States a given set of soil classes are so evidently related
thru source of material, method of formation, topographic posi-
tion and coloration that different types constitute merely a grada-
tion in the texture of an otherwise uniform material. Soils of
different classes that are thus related constitute a series. A com-
plete soil series consists of material similar in many other charac-

Fusarium Blight of the Soy Bean dl

teristics but grading in texture from stone and gravel on the
one hand, thru sand and loams, to a heavy clay on the other.”
(30, p. 19.)

In North Carolina, Fusarium tracheiphilum occurs mostly
in the Coastal Plains or eastern one-third of the state and in this
section the Norfolk soils series is the most important one, not
only because of its percentage of area but also because of its
agricultural value. These soils are characterized by the hght
eray to grayish-yellow color of the surface soils and by the yel-
low color and friable structure of the subsoils. They occupy
nearly level to rolling uplands thruout the Atlantic and Gulf
Coastal Plains, and have been derived mainly from Piedmont and
Appalachian material.

The writer has observed soy bean blight in the field on sand,
fine sand, sandy loam, and fine sandy loam soils, but not on those
with a higher (Mao Se of the finer particles such as silt, silt
loam, clay loam, or clay.t| Inoculations in the greenhouse thru
mixed soils to which a large amount of coarse sand had been
added also resulted in a higher percentage of infection. Wollen-
weber (31, p. 46) concluded, from observations made during his
inoculation experiments, that light sandy soils? favored the de-
velopment of Fusarium spp. inhabiting the soil and causing wilt
cliseases.

An experiment was conducted in which soy beans were grown
in eleven types of soil of the Norfolk series which were collected
with considerable care from typical localities in the Coastal
Plains with the assistance of Mr. C. C. Logan of the North
Carolina Station who has had considerable experience in making
soil surveys. That there are no well-defined limits to individual
types, and that different survey parties often disagree in classifi-
cation and hmits of areas, was kept constantly in mind. Conse-
quently soil maps were used only to assist in the general location
of several examples of a type from which an average could be
selected. Furthermore, as nearly as it was possible, soils were
selected which contained a normal amount of humus for the type
and to which fertilizers had not been added since the previous
crop had been harvested but to which they had been added in
the form of complete commercial fertilizers for the benefit of that
crop. So far as known neither soy beans nor cowpeas had ever
been grown on these soils.

Each type was obtained in quantities of 600 pounds. ‘Two
hundred pounds of the first six inches (surface), 200 of the second

1The soil referred to previously by the writer (6, p. 424) as a clay was instead Cecil
sandy loam.

“By this term it is supposed that he referred to soils with a larger percentage of
coarse than of fine particles.

32, Agricultural Experiment Station Research Bulletin 14

six (subsurface), and 200 of the third six (subsoil) were placed
in separate sacks, transported to the station at West Raleigh, and
replaced at their original depths, in wooden frames sunk to the
level of the surrounding soil. These types were arranged in a
sequence according to the increase in the percentage of fine par-
ticles. The types used were as follows and were arranged in the
order given: Coarse sand, sand, fine sand, very fine sand, coarse
sandy loam, sandy loam, fine sandy loam, very fine sandy loain,
loam, silt loam and clay (30).1 ‘When ‘arranged in this way,
variation in the sequence from type to type was evident. They
were each artificially infected with 7. tracheiphilum from soy
bean and the nematode (/eterodera radicicola). A liberal num-
ber of nematode galls from the roots of plants not susceptible to
Fusarium and cultures of the fungus on cut stems were incor-
ner ated into the upper six inches of soil. Soil acidity tests indi-

sated that the different lots ranged from approximately neutral to
signe acid.

At best it was hoped to obtain, quite approximately, a series
each part of which should vary from the others in its mechanical
analysis but as little as possible in all other respects, and from any

variations that might appear in the number and severity of result-
ing infection to eet some indication of the cause for the same.
If the results should warrant it, a careful physical and chemical
analysis could be made from samples of each type that had been
set aside for this purpose before the seed were planted.

Soy beans and cowpeas were planted on July 3, 1917, and the
cowpeas were removed after the disease occurred on several of
them in each flat. The soy beans were harvested on September 26,
at which time the plants were mature. The results are presented
in Table 6.

_1For the mechanical analysis of these types see 30, pp. 46-54, and soil surveys ot
various regions containing these types.

Fusarium Blight of the Soy Bean 33

Taste 6.—Influence of soil types on percentage of infection by
Fusarium spp. in the presence of the nematode

(Heterodera radicicola).

Type came of Nae ree Ne
plants | nematodes | nematodes | Fusarium
Norfolk coarse sand......... 25 4 16 0
Norfolk sand............... 30 8 26.6 0
Norfolk fine sand). s...¢-...2. 34 8 23.5 0
Norfolk very fine sand....... 34 6 17.6 0
Norfolk coarse sandy loam... 33 5 Is ,Il BS 0
Norfolk sandy loam......... 33 | 8 24.2 0
Norfolk fine sandy loam..... Bil 4 12.9 0 pe,
Norfolk very fine sandy loam. 25 a 28.0 0
Norfolk loam............... 15 12 80.0 ies
Norfolk silk loam......... att, 1 5.8 ones
INorfolkwclaye sa) Gees. 30 0 0.0 0

None of the plants were infected by the fungus and conse-
quently the original purpose, for which the experiment was
planned, failed. The results, however, are included since they
furnish some evidence that previous failures of a similar nature
were not due primarily to the use of soils of unsuitable type,
water holding capacity, or humus content. The percentage of
infection of cowpeas, however, seems to be increased when grow-
ing in inoculated soils containing an excessive amount of humus.

THE INFLUENCE OF ACIDITY AND ALKALINITY

No definite experiments have yet been undertaken to deter-
mine the influence of soil acidity on the development of the dis-
ease, but field observations indicate that it is not a factor of pri-
mary importance. They have shown that the cowpea wilt is
destructive on soils varying considerably along the plus and minus
scale of acidity.

A similar conclusion can be drawn from the following cul-
tural studies. Two strains of F. tracheiphilum, one from cowpea
and one from soy bean, were grown on a culture medium whose
reaction was varied from +40 to —40 (Fuller’s scale) by the
addition of standard solutions of NaOH and HCl to a standard

84. Agricultural Experiment Station Research Bulletin 14

nutrient agar, the original acidity of which was +8. Phenol-
phthalein was used as an indicator. The results presented in
Table 7 do not include the measurements of colonies on cultures
the acidities of which were above +25, for the reason that the
medium was liquefied by so large an amount of acid. Fairly good
growth was obtained thereon, however, in 4 or 5 days.

Taste 7.—Growth of F. tracheiphilum at varying degrees of

acidity.

Age of Diameter of colonies in mm. at various degrees of acidity?

eo ony el -26|4-20\416\410145| 0 |—s\—10\—16\—20|—25| sol ssl —a0
24 9710 eos oe) 9 | ul 10140 | on eae ns ca
“a2....| 26 | 25 | 22 | 22 | 24 | 21 |21| 20 | 18 | 19 | 18 | 18|....]....
“68....| 43 | 42 | 41 | 42 | 37 | 33 |32| 30 | 29 | 27 | 24 | 24 | 22 | 22
feo vaall eae Bee 4g | 43 |40| 37"| 34 | 36 | 36 | 36 | 34 | 34.
ie 66 | 64 | 66 | 66 |....|....|...| 44"| 42 (aaa ae
140....| 77 | 78 | 74 | 72 | 63"| 60 |60| 53 | 50 | 53 | 52 | 53 | 48 | 49°
165....| 83 | 83 | 80 | 80 | 69 | 67*|66| 60 | 67 | 63 | 63 | 62 | 62 | 62.

The strain from soy bean

Age of Diameter of colonies in mm. at various degrees of acidity?

eooné | 425|4201415|410| +5| 0 |—s|—10l—15|—20l—26|—30|—s6|_40
yin koe cn ee mech Ole les toes ee
“42....23 | 24118 20 | 28 | 22 |21| 19 | 18] 17|17/181|....)....
68 40 | 41 | 38/39 | 35 | 34 |33| 32 | 31 | 28 | 28 | 28 | 25 | 25°
9635 |Saae “471 46 |44| 39 | 38 | 39 | 39 | 40 | 36 | 35.
115....| 60 | 62 | 62 | 64 alert a fees me ene See
140....| 69 | 73 | 70 |72 | 66 | 64 |10| 55 | 55 | 55 | 51 | 57 | 50 | 47.
165....| 83 | 83 | 79 |80 | 76 | 75 |68| 68 | 63 | 67 | 68 | 67 | 60 | 57

The strain from cowpea

1Contaminations. : oe
°The figures are approximate to within 2 or 3 mm., and are an average of the meas-
urements from ten plates.

Fusarium Blight of the Soy Bean 35

From an examination of the table as a whole it is evident in
the case of both strains of the organism that there was better
erowth in the presence of various amounts of acid than in the
presence of alkali, but that even on a strongly alkaline sub-
stratum the colonies required only 2 or 3 days longer in which
to extend themselves over the entire surface of the medium in a
petri dish.

Edgerton (7, p. 12) reports field tests with /’. lycopersicé in
which tomato wilt was only temporarily checked by the applica-
tion of lime. He says, “The heavy application of lime (10 tons
per acre) decreased the wilt and the plants produced a larger
yield of tomatoes. * * * As the season advanced, however,
most of the plants in the treated plot also died with the disease.”

THE INFLUENCE OF THE NEMATODE (HETERODERA RADICICOLA)

As noted in the above experiment with the eleven types of
the Norfolk series of soils, nematodes had been introduced with the
Fusarium cultures into each flat. This experiment differed from
others in which nematodes were present in that the conditions
were those of the field under slight modification. The plants
were grown to maturity and only a few nematodes were present
on the plants indicated as affected with nematodes. Twenty-three
per cent of the total number developed galls, however, but none
showed symptoms of the blight, altho the cultures were known to
be virulent for the reason already stated.

Taste 8.—/nfluence of nematodes on the percentage of infection
by F. tracheiphilum.

|
Total | No. with ; No. with

Organism number | nematode | Fusarium
plants galls | sp.
F. tracheiphilum from cowpea and nematodes. . 10 10 2
F. tracheiphilum from cowpea without a
TFAXSTRRE REO C Veh ee, oy epee Ree Oe eens ho Geen Oe 10 0 0
F. tracheiphilum from soy bean and nematodes . 10 10 3
F. tracheiphilum from soy bean without
MEMLACOCCS HME ree tee etait cieeekenen Siarricns = 10 0 2
INemeatodestomnlyesergsss seiko cia ots seacl cols 10 10 0
INGE. (Goto) pe bodeuepep mccacesDecdeaur 20 0 0

ne

386 Agricultural Rxperiment Station Research Bulletin 14

A previous test had been made with soy beans, between
September 26 and December 1, 1916, in an attempt to determine
whether the presence of nematodes increases the number of in-
fections. The nematodes were introduced into the soil of large
buried pots in root galls from living soy beans free from infection
by Fusarium spp. ‘The results are presented in Table 8.

At Lincoln, on December 4, 1917, six stone jars of five gallons
capacity were filled with nematode infested soil from a greenhouse
bench in which badly nematode-infected tomatoes were growing.
Four other jars were filled with nematode-free potting soil. Cul-
tures of Fusarium growing on pieces of sweet clover (Meléiotus
alba) stems, from two 1 liter flasks, were incorporated into the
soil of each jar. Three Clay cowpeas and three Mammoth Yellow
soy beans were grown to maturity in each jar in a greenhouse
kept at approximately 28° C. during the day and 22° C. at night.
On February 16, when the plants had nearly matured seed pods,
they were removed and examined. Table 9 shows the number of
plants affected with nematodes and with Fusarium.

Taste 9.—/nfluence of nematodes on infection by
F. tracheiphilum.

Total number | Per cent affected | Per cent affected
Jar| Organisms of plants with nematodes with Fusarium
noe Soy bean| Cowpea |Soy bean} Cowpea |Soy bean Cowpea
1 | Fusarium and
nematodes... 3 3 100 100 0 100
2 do 3 3 100 | 100 0 100
2 do se 3 100 | 100 0 | 100
4 | do 3 3 100 | 100 0 100
5 do ae lea 100 | 100 0 100
6 do aes cae 100 | 100 0 | 100
7 a Fusarium..... 3 3 0 0 0 ie 331
8 tee lee cree eke 0 0 663
soe donee s 3 0 0 0 662
10 do 3 pace 0 6. | 3a

Fusarium Blight of the Soy Bean 37

It is to be noted that all of the plants in the last test were
infected with nematodes but that the cowpeas were more severely
affected, the galls being somewhat larger and more numerous.
The cowpeas s generally showed SV mptoms of the fungus whether
the eelworms were present or not. The soy beans reniained free
from the fungus in spite of nematode injuries. The galls on
the soy beans did not reach a diameter of more than 1 to 2 mm.
whereas in the fields where the blight developed they were
commonly 8 to 10 mm. in diameter. The presence of the galls
even tho small, and the absence of the fungus on the roots of
plants in soil infected with both organisms in this and the two
other tests mentioned, is evidence that the presence of nematodes
under conditions which favor the development of the fungus on
cowpeas does not supply the conditions that obtain in the field,
which allow the development of this fungus on soy beans.

THE INFLUENCE OF SOIL TEMPERATURE

tecent reports of various investigators point out the relation
of temperature to diseases caused by soil inhabiting fungi espe-
cially species of Fusarium. Jones (15) emphasizes the impor-
tance of this factor by summarizing the results of these investiga-
tions and correlating them with his own field observations. In
main the results with Fusarium spp. show a minimum tempera-
ture for infection around 15° to 17° C. and a rather broad
optimum of about 25° to 30° C. As far as the writer is aware, no
data on maximum temperatures have been reported.

Before attempting to determine the influence of certain tem-
peratures on soy bean blight, the organism was tested in culture
at constant temperatures of 5 , 8°, 12°, 16°, 20°, 28°, and 33° ©.
After 10 days at 5° there was ” practically no erowth, at 8° the
colonies averaged 1 or 2 mm. in diameter, at 12° they were about
5-7 mm., at 16° about 18-20 mm., and with a rise in temperature
to 28° a corresponding increase in size of colonies. At 33° the
growth was somewhat less than at 28°. Cultures of the other
wilt producing species of Fusarium reported by others correspond

rather closely in their growth at these temperatures.

The optimum condition for infection in the case of soy bean
blight may, however, be entirely different from that which is
favorable to either parasite or host. Experiments are now in
progress in which soy beans are growing in inoculated soil main-
tained at various constant temperatures. Nothing of significance,
however, can at present be reported as to the relation of this
factor, except that the amount of disease has not been increased
at 14, 16, 17, or 24 degrees Centigrade.

38 Agricultural Kuperiment Station Research Bulletin 14

THE INFLUENCE OF OTHER ORGANISMS

Tt is very possible that a larger number of infections and a
more extensive development of the fungus within the host occur
‘in the field than under the conditions of controlled inoculations
because of the presence in the former of associated parasitic
organisms and the injuries caused by them, or because of other
injuries of the roots caused by insects, mechanical tools, or im-
proper culture. This may oftentimes be of especial importance
in connection with Fusarium spp., which are not as strict para-
sites as some and therefore enter more readily thru wounds. Two
such organisms of the soil, namely, Rhizoctonia and Sclerotium
rolfsii, were noticed affecting soy beans in fields where the
Fusarium blight was abundant. The soy bean is more resistant
to Rhizoctonia than most garden and field crops but lesions were
noted on seedlings, young plants, and the small roots of older
plants. Sclerotium rolfsii, however, is very destructive to soy
beans whenever present and kills plants at all stages of their
growth.

Soy beans are now growing in soil inoculated with Husariwm
tracheiphilum and Rhizoctonia, and in another soil inoculated
with Fusarium tracheiphilum and Sclerotium rolfsii, and it is be-
lieved by the writer that either these or other organisms will be
found to play an important part in the development of this dis-
ease. It seems probable from preliminary tests that Husariwm
tracheiphilum is unable to penetrate soy bean roots to the xylem
elements unaided but that, once it gains entrance thereto, it
develops rapidly in them in a somewhat saprophytic manner,
obscures the primary injury, and finally affects the host as
previously described.

FIELD EXPERIMENTS TO DETERMINE THE SUSCEPTIBILITY OF
VARIETIES

Sixty per cent of the Mammoth Yellow soy beans in the field
at Red Springs, N. C., were blighted in 1915. The main part
of this field was planted to the same variety on May 23, 1916;
but in another part reserved for the purpose, one 54-meter row
each of Haberlandt, Mammoth Yellow, Pekin, Black Eyebrow,
Medium Yellow Virginia, and Tar Heel Black soy beans and a
row of Clay cowpeas were planted on June 8. On August 10
the main field and all of the varieties in the test, including the
cowpeas, showed considerable blight or wilt, except the Black
Eyebrow and the Virginia varieties of soy beans. On August 26
the latter of these varieties was apparently free from disease, but
the plants had declined with age to such an extent that the exact

Fusarium Blight of the Soy Bean 39

determination was doubtful. The fact that these varieties were
planted so late that hot, dry weather prevailed during a large
part of their early growth explains why they were so rapidly
forced to maturity. The Black Eyebrow variety remained free
from disease thruout the season. An examination of plants in all
parts of the field showed that the disease was abundantly and
uniformly distributed.

Since the Black Eyebrow variety, which was planted late in
1916, 1. e. June 8, remained free from the disease, it was planted
again at intervals in 1917 in order to observe the effect of seasonal
planting on the development of the disease. The first planting
was made on April 26, another on May 31, and a third on June
21. The ground was hardly suitable for planting between these
dates. Plants from the second and third planting were much
dwarfed because of unfavorable weather, severe nematode infec-
tion, and a lack of cultivation, and for this reason no certain
results as to the amount of infection in the different plantings
were obtained. The most important determination possible from
these observations is that some other variety more suitable to
late planting should be used in future tests for this purpose.
Since the Black Eyebrow variety remained free from the disease
in 1916, it is important to note that a few diseased plants of this
variety were found in the general variety test rows referred to
below where the seed were planted earlier. However, the variety
seems to show some evidence of resistance.

A larger number of varieties were tested in this field in 1917.
Three rows each of the following varieties were planted on April
26: Brown, Black Eyebrow, Virginia, Mammoth Yellow, Early
Dwarf Green, Wilson Black, Barchet, Jet, Austin, Arlington,
Guelph, Chiquita, Auburn, Manchu, Tokio, Peking, Tar Heel
Black, Haberlandt, and Medium Yellow. Every tenth row was
planted to Clay cowpeas, and one row of the One Hundred Day
Speckle velvet bean (M/ueuna utilis) was planted around two sides
of the field. By July 20 the disease was abundant in all of the
varieties of soy beans except the Black Eyebrow discussed above.
The cowpeas were so badly diseased that all died before blooming.
The velvet beans were entirely free from nematodes or Fusarium.

The Brown variety, altho as badly infected by the nematode
and Fusarium as any of the other varieties, deserves special men-
tion because of its tolerance to these parasites. In spite of the
presence of a large number of nematode galls, varying in diameter
from 1 to 15 mm., and the presence of Fusarium thruout the xylem
area of the roots and for some distance up the stem, there was
absolutely no wilting, no chlorosis, nor any external evidence of
any infection whatsoever. The plants were from four and one-

40 Agricultural Kaperiment Station Research Bulletin 14

half to five and one-half feet in height, they stood six inches to a
foot above any other variety and more than that above the Mam-
moth Yellow; they remained green and healthy in appearance
thruout the season and produced. a good crop of beans which
were about mature on September 8, when the field was pastured
to hogs. Perhaps the size of these plants was somewhat reduced
by the action of the two organisms. Unfortunately there were
no check plants with which these could be compared since the
entire field was infected. Affected plants of this variety, how-
ever, yielded as well as the average healthy Mammoth Yellow
plants in nearby fields.

The Brown soy bean is identical with the Mammoth Yellow
in habit-type and is very similar to it in other respects. The color
of the seed is the only apparent difference. This variety has been
grown but very little in North Carolina, but tests have shown that
it is as desirable in every respect, if not more so, than the present
favorite variety, the Mammoth Yellow, which suffers greatly
from Fusarium blight. Mr. Walter White at Edenton, N. C., says
that he prefers the Brown to the Mammoth Yellow because it
produces more forage and more seed and can be grown wherever
conditions are favorable to the Mammoth Yellow.

The Haberlandt variety, which is also suitable to conditions
in North Carolina, develops well in spite of rather severe
Fusarium and nematode infection.

The Brown and Haberlandt varieties are preferable to the
Black Eyebrow for planting in infected soil, especially if nema-
todes are present, even tho the latter should remain free from
Fusarium infection.

Fusarium Blight of the Soy Bean 41

SUMMARY

I. A disease of the soy bean has been studied during the past
three years. The first report of this disease appeared in a publi-
‘ation by the writer in 1917.

If. The disease is characterized by a chlorosis and shedding
of the leaves or leaflets, followed by the death of the plants, and
is herein called “bhght.”

Ill. Soy bean bhght has been observed in several localities
within North Carolina on soils infested with cowpea wilt. What
is probably the same disease has been recently observed by others
in Alabama and possibly in Wisconsin.

IV. A species of Fusarium belonging to the section Hlegans
is the causal organism.

V. Cultural and morphological studies which are regarded
as of primary importance in distinguishing species of Fusarium
show that the strain of Fusarium on soy bee in is identical with the
organism producing the wilt of cowpeas

VI. Reeiprocal imoculation eepccinent with the strains
from soy beans and cowpeas show that cross-inoculations can be
made. These experiments were conducted in the greenhouse and
under field conditions. Pure cultures of the two strains were used
in certain of the experiments and inoculum from the natural
host in others.

VII. Bhght of soy beans is therefore due to Fusarium
tracheiphilum.

VIII. Physical structure and acidity of the soil under
natural conditions are not the limiting factors in infection, but
acidity under certain conditions may have some influence.

TX. Infection occurs thru the roots, but nematodes appear
not to increase the percentage of blight mate srially. Other organ-
isms such as Rhizoctonia and Sclerotium volfsii and other ‘root
injuries are believed to materially increase the percentage of dis-
eased plants in the field.

X. The Black Eyebrow variety of soy beans shows some
evidence of resistance. The Brown variety, while not resistant,
is tolerant and seems to develop remarkably in spite of numerous
fungous filaments and nematodes within the roots. Fifteen other
varieties tested are severely affected. Velvet beans are not sub-

ject to infection.

42

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

(11)

(12)

(13)

(14)

(15)

(16)

Agricultural Experiment Station Research Bulletin 14

LITERATURE CITED

Appel, Otto, and Wollenweber, H. W.
1910. Grundlagen einer Monographie der Gattung Fusarium
(Link). Arb. K. Biol. Anst. f. Land-u. Forstw. 8:1-207.
pl. 1-8. Figs. 1-10.
Bessey, EH. A., and Byars, L. P.
1915. The control of root-knot. Farmers’ Bul. U. S. Dept. Agr.
648:1-19. Figs. 1-20.
Butler, E. J.
1910. The wilt disease of pigeon-pea and the parasitism of Neo-
cosmospora vasinfecta Smith. Mem. Bot. Ser. Dept. Agr.
India, 2:1-64. pl. 1-6. (2 colored.) .
Clinton, G. P.
1916. Bacterial leaf spot of soy bean. Rpt. Conn. Exp. St.
1915:444-446. Fig. 1.

1916. Chlorosis and crinkling of the soy bean. Rpt. Conn. Exp.
Sta. 1915: 446-447.
Cromwell, Richard O.
1917. Fusarium-blight, or wilt disease of the soy bean. Jour.
Agr. Research 8:421-440. pl. 95. Fig. 1.
Edgerton, C. W.
1918. A study of wilt resistance in the seed bed. Phytopathology
8:5-14. Figs. 1-4.
Engler, Adoif.
1895. Die Pflanzenwelt Ost-Afrika und der Nachbargebiete.
Teil C. Berlin.
Garman, Harrison, and Didlake, Mary.
1914. Six different species of nodule bacteria. Bul. Ky. Exp. Sta.
184: 343-363. pl. 1-7.
Gilbert, W. W.
1914. Cotton wilt and root-knot. Farmers’ Bul. U. S. Dept. Agr.
625:1-21. Figs. 1-15.

Heald, F. D.
1906. New and little-known plant diseases in Nebraska. Science
23:624.

1906. Report on the plant diseases prevalent in Nebraska during
the season of 1905. Rpt. Nebr. Exp. St. 19-1905:29-81.
Hemmi, Takewo.
1915. A new brown-spot disease of the leaf of Glycine hispida
Maxim. caused by Septoria glycines sp. n. Trans. Sapporo
Nat. Hist. Soc. 6:12-16.
Higgins, B. B.
1911. Is Neocosmospora vasinfecta (Atk.) Smith, the perithecial
stage of the Fusarium which causes cowpea _ wilt?
Rpt. N. Car. Exp. Sta. 32-1908-1909:100-117. Figs. 1-16.
Jones, L. R.
1917. Soil temperature as a factor in phytopathology. Plant
World. 20:229-237. Figs. 1-2.
Manns, T. F.
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