‘UDIES ON FUSARIUM DISEASES OF
POTATOES AND TRUCK CROPS
IN MINNESOTA

A THESIS SUBMITTED TO THE FACULTY
a OF
THE GRADUATE SCHOOL
OF
THE UNIVERSITY OF MINNESOTA
3 BY
: G. R. BISBY
‘IN PARTIAL FULFILMENT OF THE REQUIREMENTS
| FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
JUNE 1918

STUDIES ON FUSARIUM DISEASES OF
POTATOES AND TRUCK CROPS
IN MINNESOTA

A THESIS SUBMITTED TO THE FACULTY
OF
THE GRADUATE SCHOOL
OF
THE UNIVERSITY OF MINNESOTA
BY
G. R. BISBY
IN PARTIAL FULFILMENT OF THE REQUIREMENTS
FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
JUNE 1918

et Sag Ud gt <6 P ee. : . 4
ey Mie ae (4 > ue gh Fae

v eat

j
ya A Lt
ra é
t ae bs ic!
-
i ‘er
i ?
y 5
.
e
uy Se
CDK i Be
co G
Cie
Sac
-
\
a
a *
i
aa
a
r ]
‘
> a
es
a ¥
‘

CONTENTS

Creatine slcats .0'.°3 cic SR pn ET i
Pimeniaissandameriods......cutaeger tas eas. ee
AOPAR OM WE oR is. sc. . 5p sce ig 1a AS Ta Oe Rea err
JSS BOTS rete ae EDN CIEE a er
Symptomology of potato wilt conditions in Minnesota..................
Bielory of wilt or potato im, Ninuesotae, 800s). t. esos... .:.
BiimagveGrnhoot rOl.:.-..... ce cee Meas ee
Occurrence of Fusarium oxysporum in potato plants....................
Artificial inoculations with F. oxysporum on potato ROUEN es... he
Field studies with seed tubers from wilted iD BNE ol aah
Hasaniunedry Tot ol potato tubers: =. os. ae eee eee ee...
HA oGical Marne tae Jus shes saan Maes ee MR ef ..
LET 7 LYE TG 01 Ro Re Woe eee icine le gta Ian he eat
‘S TELTE SIEING NG A em man pi fh na N Ses aa a A inet a
HSULOLC CR ek ah Ho nee Nee ie ae eet aR aint ht ane So te At ee
Beaperimte mitten tei. <2 a: Fin Pe oe Se WOME,
Bucauiim ciseases Of certains tuckicrops... 2-12-4805. Cee cs...
Wilt and rooterots of Pisum-satioum... 250.2 inal ee
Root rots of the bean (Phaseolus vulgaris) .......000c0ccecccccccccee.
Fusarium diseases of other truck crops in Minnesota....................
iy HVT) 21) LOG Ce em ye oe eR ears ek ol cr
ctomereveretables cj. a nh oe ei ROE ek
Bicaringineat Cots Olconsnete 65. b a oe | wee Oh kk
Exicet ot temiperature-on varieuseb uSaria-c!.c0/. 4: ok, chee heck. ss.
Etecemot amoistute, loht) asemfoods./...1.0 4:0 eee. ks
PelALIONIGE LOO MOIStILbex see memes aes coe ea ee,
SDR Se NON aioe. Ce ok aaa ae ea |
IEEE OR RON RMR Eres SoG aioe mentee Soe
LP GTO RYE AOS ie ONS OTR ASN.2 Oa A cae ge rr
CART SISTERS 7 ETO) SSM Raa Egy | Oa Rep hay Steg in 2 cul 2
Does the substratum alter the pathogenicity of Fusaria?..................
The production of “toxic substances” by Fusaria...................0.0005.
wultxedmenitiie ‘relationshipsemee. ee. eek eta ee... on
Sees IS CUISSLOI.\ 0% xR ra oe nia y ee
SS GEER CE EHICAS TIRES Ns:..4. 3. <M RAN re a Ua MAM RC MRA Se Sic
OBA IE Res. 7.7./5 eee ER ee
EOLA GMURV EGE a. «2 5.. -ac een eee I ae ee ene
SUD ENTE 8 GAR ee ge rece 5 |) 3 Ceo ware eR ye ee et
[EVI SIROCAREIT) AM GAG eam pak <2 URE ey ee he a er

15

20

STUDIES ON FUSARIUM DISEASES OF POTATOES
AND TRUCK CROPS IN MINNESOTA

By G. R. BisBy

INTRODUCTION

Fusarium wilt was reported (72) as causing a loss of more than
twenty-five million bushels, or 4.54 per cent of the potato crop of the
United States in 1917. Despite the large damage due to Phytophthora
infestans in this country the same year, the total loss reported from
Fusarium wilt was greater. Besides the injury from wilt, Fusarium
tuber rots in the field, in storage, and during transportation may de-
stroy from 10 to 50 per cent of the crop (37, 43, 72, 75).

Minnesota is one of the states in which typical Fusarium wilt has
been serious. Certain symptoms atypical of wilt have also been under
observation for some time, particularly in the Red River Valley. The
study of this rather anomalous disease has received particular atten-
tion. Fusarium dry rot was also found to present, in Minnesota,
certain phases not emphasized heretofore. The writer has also studied
certain Fusarium diseases of other truck crops as well as those of
the potato.

The genus Fusarium was established by Link in 1809 (34). Var-
ious changes in the use of generic and specific names for the fungi in
question were made during the succeeding century; the species added
were often imperfectly described, and the host or substratum served
frequently as the chief distinguishing diagnostic character. Smith
and Swingle in 1904 (63) were forced to revert to the oldest avail-
able name to designate the Fusarium on potato, viz., F. oxyspor.m
Schlechtendal, 1824. Appel and Wollenweber in 1910 (2) published
a monograph of the genus Fusarium, and were able accurately to
define several species. The literature to the year 1910 is also sum-
marized. Wollenweber (76), Lewis (32), Sherbakoff (59), and others
have also worked intensively on the Fusarium problem and described
several new species. The name Fusarium oxysporum is, however,
still applied to the fungus commonly causing wilt of potatoes.

MATERIALS AND METHODS

Isolations were made during the summers of 1916, 1917, and 1918
from potato plants showing various wilt symptoms. The plants were
obtained from sections of Minnesota north of St. Paul, particularly

6 MINNESOTA BULLETIN 181

the Red River Valley region. Several cultures of Fusaria isolated in
1914 and 1915 were furnished by A. G. Tolaas. During the winters,
isolations were also made from rotted potato tubers. Isolations were
made from garden beans and peas, sweet corn, cucurbits, and toma-
toes. Several hundred cultures were studied and numerous inocula-
tions were made in the laboratory, in the greenhouse, and in the field
in 1917 and 1918.

Various culture media were used, particularly rice and potato
plugs, sweet clover stems, the common agars for dilutions, and 5 and
10 per cent dextrose agar for color reactions. The ordinary methods
of technique were used unless otherwise stated.

The writer wishes to express his thanks particularly to Dr. E. C.
Stakman and Dr. E. M. Freeman, under whom the work was done,
for suggestions and supervision. The writer is also indebted to A. G.
Tolaas and Dr. W. A. Orton for cultures and other help, and to Dr.
C. D. Sherbakoff for tentative corroboration of some determinations.
The writer is particularly grateful to Dr. H. A. Edson of the United
States Department of Agriculture who in his visits to Minnesota has
freely given information and ideas.

The writer has submitted cultures of the various unidentified Fu-
saria to Dr. Sherbakoff for such taxonomic disposition as he sees fit.

POTATO WILT

HISTORICAL

Smith and Swingle (63) made the first detailed study of the wilt
of potato caused by Fusarium oxysporum. The dry rot of tubers
discussed by them is now generally considered to be caused chiefly
by other species of Fusarium. They described in detail the effects of
the wilt fungus on the plant and its entrance into and spread within
the tuber. They studied the behavior of the fungus on various media.
Control methods for wilt were suggested. While the earlier publica-
tion of Stewart (65) on “Another ‘stem blight of potato” deals with
a disease similar to wilt, Stewart (66) decided in 1898 that. the blight
was not communicable and “not caused by any vegetable organism,”
and recently stated, in letters dated Nov. 18 and 30, 1918, “While
the symptoms point to Fusarium wilt, I doubt that it was actually
that disease.” However, “If it is true that tubers showing pronounced
discoloration of the fibro-vascular bundles, owing to the infection
with Fusarium wilt, do not usually produce affected plants, then there
is some reason for believing that my Long Island stem-blight was in
reality Fusarium wilt. The tubers which were planted in my experi-
ments were all very definitely affected by the stem-end browning.

FUSARIUM DISEASES IN MINNESOTA 7
IXvery piece planted showed the stem-end browning. Accordingly,
it seems to me that more diseased plants should have resulted.”
Clinton’s description in 1895 (11) of a “Bundle blackening of tubers”
may have been of the ring discoloration caused by F. oxysporum. He
wrote in a letter dated Dec. 3, 1918, “While the tubers mentioned may
quite likely have been On with such a wilt, I have no positive
information that they were.’

Orton in 1909 (40) reported that the accumulation of F. oxysporum
and other fungi in the peat soils of sections of California soon made
the growing of potatoes unprofitable. Manns (36), a8 a result of his
work, recommended clipping the stem ends of infected tubers. This
is now a commonly used control method. Orton in 1914 (42), in
comparing wilt due to F. oxysporum with leaf roll and other diseases,
considered that wilt was “apparently a disease of warmer climates,”
altho he recognized that “in Minnesota wilt appears to be present in
the older communities.”

Discussing the occurrence of this disease in Europe, Appel (1, p.
143) states, “The [wilt] disease occurs in Germany also, but is of
much less importance.” Nicholls (38) reported the presence of F. O.ry-
sporum in Tasmania, and Carpenter (10) found this fungus in potato
vines and tubers in Hawaii. Reports of F. oxysporum from other
countries are doubtful, since this name has been loosely used.

Jones (27) found potato wilt especially in the older communities
in Wisconsin. Milbrath (37) noted its seriousness in North Dakota,
and its importance in Minnesota has been recognized for some time
by Stakman and Tolaas (64). Kohler (30) may have referred to the
stem end browning caused by F. oxysporum, tho it may be inferred
that dry rot of tubers was also involved in the rot he attributed to
“an undetermined species of Fusarium.”

Carpenter (8), Link (33), and others have shown that F. oxys po-
rum can produce a rot of potatoes. This is not in agreement with
Wollenweber’s (76) conclusion that members of the Elegans section
of the genus Fusarium cause wilt but not rot. F. eumartii Carpenter,
belonging to the section Martiella (76, p. 30), has been found by Has-
kell (20) and C. R. Orton (39) to cause a stem rot and wilt of potato
plants, as well as a rot of the tubers. “Potato wilt” may, therefore, be
due to more than one species of Fusarium, possibly following certain
geographical limits. Orton (42) reported the symptoms of Verticil-
lium wilt to be similar to those of Fusarium wilt and stated that the
distribution of the former was restricted more particularly to the
northern states. Verticillium wilt is reported (72) to be especially
serious in Oregon. Appel (1) has noted (referring presumably par-
ticularly to Minnesota) symptoms atypical of the common potato wilt.

8 MINNESOTA BULLETIN 181

SYMPTOMOLOGY OF POTATO WILT CONDITIONS IN MINNESOTA

The symptoms have been fully described by other writers, and
in general agree with those found under Minnesota conditions. Coons
(13) recently noted that in Michigan the disease may exhibit two
aspects; one, a rapid wilting in which the vine dies when the tubers
are about half grown; and another characterized by the dying of the
plants “at the close of the growing season.” He found these symptoms
to depend perhaps on whether the infection is from the seed piece
or from the soil.

Figures 1 and 2 show the wilt symptoms common in Minnesota
fields. Except in more severe cases, the plants do not begin to wilt
until about blossoming time or later. The symptoms on the upper part
of the plants are apparently those resulting from a considerable reduc-
tion in water supply. A cross-section of the lower stem reveals the
browning of the vascular system and often of the other tissues as well.
This browning may extend to the tips of the plants, tho the bundles
are often free from hyphae in these upper discolored areas. The roots
are usually affected seriously. The tubers, which have ordinarily had
an opportunity to develop considerably before the wilting of the plant
stops their growth, may be affected at the stem end, as fully described
in the literature.

Atypical wilt symptoms such as those mentioned by Appel (1, p.
147) have received particular attention. Other observers had noticed
these atypical symptoms, particularly in 1914 and 1915 in the Red
River Valley, and had considered that they might be caused by the
blackleg organism or some species of Fusarium. For convenience the
term “foot rot’ will be used to indicate the condition in question.
The writer found some of this disease in 1916, practically none in 1917,
but in August, 1918, it was found in Polk and Clay counties in the
form more characteristic of that seen by Appel, Edson, Stakman,
Orton, and others in 1914 and 1915.

Plants affected with foot rot are shown in Figures 3, 4, and 5.
There is a dark brown or almost black discoloration of the lower and
underground portions of the stem. These discolored areas are often
rotted. When secondary organisms are present there may be a typical
soft rot. While the symptoms resemble those of blackleg somewhat,
there is not the inky black, slimy rot characteristic of blackleg. The
disease is, however, confused with blackleg by growers and others.

There is a more abundant development of hyphae in the primary
vessels and other tissues of the stem than in stems affected with
ordinary wilt. The effect on the roots and stolons is similar to that
on portions of the lower stem (see Figure 5). The stem end of the

FUSARIUM DISEASES IN MINNESOTA 9

tuber may be attacked, and the way paved for invasion by secondary
rotting organisms. The above-ground portions of the plant succes-
sively wilt, die, and eventually collapse. Fortunately this foot rot oc-
curs more particularly late in the season, as is also ordinarily the case
with wilt in Minnesota, so that a considerable crop of tubers may
already have been produced. These tubers are, however, liable to suf-
fer considerable injury before or during storage from the invasion of
Fusaria and other organisms through the injured point of attachment
of the tubers to the affected stolons.

The relation of this foot rot in Clay County, Minnesota, to the
weather (United States Weather Record, Moorhead Station) during
the 5 years this condition has been under observation is shown in
Dablesl.

TABLE I
RELATION OF WEATHER TO THE DEVELOPMENT OF Foot Rot

Precipitation Average temperature
Year Notes on the
| disease
May June July |August] May June July |August
Inches | Inches | Inches | Inches | Degrees] Degrees] Degrees! Degrees
1914 1.47 8.92 3.65 2.89 57.4 64.8 [fie 1! 65.0 Abundant

1915 3.93 9.13 Deez, 1.05 SiaT 59.2 65.2 65.2 | Present
1916 3.76 4.28 5.30 2.87 53.0 60.3 75.9 67.2 | Present
1917 0.38 i o2 0.81 Odili 53.6 61.3 75.2 66.4 | Absent
1918 Da df) 1.79 2.68 4.90 55.0 64.4 67.7 69.4 | Present late in
season
Normal] 2.95 4.13 3.74 3.10 54.8 64.14} 68.7 65.9 ay

More than double the normal precipitation occurred in June, in
1914 and 1915. The rainfall was especially heavy in July, 1916. The
season of 1917 was very dry, while in 1918 it was dry until late Juiy
and early August, when there was considerable precipitation. Moder-
ately high temperature is also undoubtedly a factor in producing Fusa-
rium wilt, altho, as shown by the temperature in July, 1917, the atyp-
ical foot rot does not occur as a result of high temperature without
abundant rainfall; and as indicated in 1915, these symptoms may ap-
pear in a year of high precipitation even with temperatures consid-
erably below normal. Observations indicate further that foot rot
attacks the plants seriously only later in the season, even tho weather
conditions from planting time on have been favorable to its develop-
ment. Kohler (30) described Fusarium diseases of potato in Minne-
sota, and the foot rot condition may have been involved. He stated
that “This disease does great havoc in wet years.” Poor yields were
obtained from planting tubers showing rot.

10 MINNESOTA BULLETIN 181

ETIOLOGY OF WILT OF POTATO IN MINNESOTA

The fungi isolated from various parts of wilted plants, particularly
the interior of the stem near the surface of the soil, from several
regions in Minnesota, especially the Red River Valley, were predom-
inantly Fusaria. Verticillium was obtained in only a very few cases,
and then in association with other organisms, indicating that it was
only saprophytically or accidentally present. There was no evidence
that Verticillium wilt is important in Minnesota. Most frequently the
cultures obtained were determinable as Fusarium oxysporum by the
character of their conidia, the salmon to lilac color of the medium
(potato or rice), the dark bluish green sclerotia, and the buff sporo-
dochia. As was to be expected, contaminations were sometimes pres-
ent, and other Fusaria than F. oxysporum developed occasionally.
Sometimes the difficulty in obtaining a “high culture’ (Appel and
Wollenweber 2, p. 22) of the Fusarium rendered identification some-
what less certain, owing to the paucity of macroconidia produced, or
to the suppression of some other distinguishing character. The cul-
tures were, however, run along with authentic F. oxysporum obtained
originally from Wollenweber’s laboratory (Nos. 3315 and 3394)
through the courtesy of Dr. W. A. Orton. Specimens were also sub-
mitted to Dr. C. D. Sherbakoff for identification.

Ordinary wilt of potato in Minnesota appears, then, to be due, at
least predominantly, to Fusarium oxysporum. This fungus has also
been isolated several times from tubers showing brown ring discolora-
tion. It was thus obtained from tubers grown as far north as Kittson
County, in the extreme northwestern corner of the state.

ETIOLOGY, DE FOOT ROT

Isolations were made from numerous wilted plants showing atyp-
ical wilt symptoms in the expectation that organisms other than F. oxy-
sporum were the causal agents. Some isolations obtained by A. G.
Tolaas from atypically affected plants in 1914 and 1915 were identified
by the writer. The fungus obtained from plants showing foot rot
symptoms was found in the majority of cases to be F. oxysporum and,
as already indicated, the unusual appearance is attributed particularly
to the heavier precipitation resulting in a watersoaked condition of the
soil. This is most likely to occur in a heavy soil such as that in the
Red River Valley. Other fungi and several bacteria were also isolated,
but all the evidence indicated that they were merely saprophytes.

OCCURRENCE OF FUSARIUM OXYSPORUM IN POTATO PLANTS

In the course of development of the wilt or foot rot disease, con-
siderable amounts of the infecting fungus are of course accumulated
in the tissues of the potato stems, roots, stolons, and even in the tubers.

FUSARIUM DISEASES IN MINNESOTA 11

The following observations indicate that the fungus may grow on
other parts of the plant also, and develop in greater abundance on
those parts mentioned. ;

On vines affected with wilt in the field and placed two or more
days in a moist place, a luxuriant growth of fungus may develop.
(See Figure 4.) From the surface and the interior of these vines,
F. oxysporum was isolated. Not infrequently the mycelium and spores
of F. oxysporum may have developed abundantly in the somewhat
hollow areas within the stem of plants affected in the field. Plants
affected with wilt or foot rot may thus cause heavy contamination
of the soil.

Isolations were made on September 10, 1917, to determine if F.
oxysporum might be present more or less saprophytically in the stems
of plants late in the season. This.was shortly after a frost had prac-
tically destroyed the leaves. These plants had been grown at Univer-
sity Farm, part of them from northern grown seed, had not shown
signs of wilt, and had produced a good crop of healthy tubers. Below
the surface of the soil the inside of these stems was browned, and
from some such stems “high cultures” of F. oxysporum were readily
obtained. Similar isolations were made later in 1917, and several on
October 1 and. 2, 1918. The isolations made in 1918 were from the
old stems of normal plants which had been killed by frost. They were
taken from a field in Hennepin County which had been sprayed
with bordeaux mixture, and which had yielded 214 bushels per acre.
F. oxysporum was obtained consistently from this material.

The “dry stem rot” of potatoes with which Rhizoctonia is asso-
ciated is common in Minnesota. That Fusarium oxysporum may occa-
sionally be a factor in causing this condition is indicated by the fact
that it was isolated from the external stem lesions of plants affected
with “stem rot,” as well as from the interior of such stems. The
interior of potato stems affected with dry stem rot is often browned,
especially near the base. Edson and Shapovalov (15) have shown
recently that various fungi, including F. oxysporum, may cause stem
lesions. Rhizoctonia hyphae may of course be present even if they
are not the primary cause of the lesions.

The seed piece under the growing plant is often rotted. If the rot
is caused by bacteria it is soft and foul smelling. Species of Fusarium
may cause a dry rot. The rot of the seed piece may be soft and
without a foul odor. Isolations were made in the season of 1917
from several such cases as the last two. The specimens were obtained
from University Farm and other parts of the state. F. oxysporum
was often obtained from seed tubers affected with soft rot. From
tubers affected with dry rot, F. discolor sulphurewm (Schl.) App.

12 MINNESOTA BULLETIN 181

and Wr. and other Fusaria were obtained. Bacteria and other fungi
were of course commonly present as secondary organisms. No diffi-
culty was experienced in securing a more or less soft rot of potato
tubers with F. oxysporum by artificial inoculation.

Considerable mycelium of F. oxysporum may occur in and on the
leaves of plants growing under moist conditions, even when the lower
stem does not show the presence of the fungus. Such leaf infection
may presumably result from inoculum carried by insects or spattered
by rain. Milbrath (37) reports that leaves may be affected, altho he
may have meant only internally. (See also 15.) Cases of external as
well as internal infection of leaves and petioles have been secured
from artificial infection in the greenhouse.

The relation of F. oxysporum to the soil is discussed in another

section. :
ARTIFICIAL INOCULATIONS WITH F. OXYSPORUM ON POTATO
PLANTS

Many preliminary experiments in the greenhouse and in the field
to secure infection and wilt of potato plants by artificially inoculating
F. oxysporum into the seed piece planted, or into the soil, were unsuc-
cessful. An examination of the literature indicates also that other
workers have not had great success in securing infection of potato
plants with the wilt organism under ordinary conditions. It is evident
that F. oxysporum is not vigorously parasitic to actively growing potato
plants.

Sometimes such results as shown in Figure 6 were obtained under
greenhouse conditions. Rotting of the seed piece, browning of the
stem, and death of the leaves ensued from inoculating the seed tuber
with F. oxysporum. This is hardly characteristic of Fusarium wilt,
however, tho resembling the foot rot condition.

In view of the possibility that the average temperature in the
greenhouse during the winter months was not sufficiently ‘high for
good infection, the cage shown in Figure 7 was constructed, and
heated with two carbon electric light bulbs. A soil temperature of
from 20 to 30 degrees could thus be maintained. The humidity was
of course also high. Figures 8 and 9 show a type of injury resulting
from inoculating sterilized soil heavily with F. oxysporum under these
warm and damp conditions. This injury was caused several times
with F. oxysporum, and F. radicicola Wollenw. caused a similar injury
in one trial. Fitch and Bennett (17) illustrate a somewhat similar
condition as found in the field. Link (33) also secured stem rots in
the laboratory with F. oxysporum. Injuries such as are illustrated

FUSARIUM DISEASES IN MINNESOTA 13

in Figures 8 and 9 are considered entirely comparable with the natur-
ally occurring foot rot condition illustrated in Figures 3 and 4.

Figures 10 and 11 show two infected plants resulting from a lighter
infection of the soil, and are believed to represent a fair greenhouse
manifestation of Fusarium wilt. It is to be noted that the upper
leaves show the characteristic rolling (see 1, p. 143). The higher
temperatures in the warm chamber, while allowing infection, were un-
favorable to the potato. Plants placed inside the chamber died sooner
than corresponding plants left outside.

FIELD STUDIES WITH SEED TUBERS FROM WILTED PLANTS

Wilted plants do not result from planting infected seed, unless
conditions are favorable to the development of the fungus. These
conditions, particularly a high temperature, are often at the same
time unfavorable to the potato. Seed from vines wilted in the field,
showing more or less of the bundle blackening, usually produced plants
in the greenhouse similar to those from normal seed. Such seed
planted in the field in 1917 in not seriously infected soil gave no more
wilt than several plots from ordinary seed.

A fairly extensive study of the effect of planting tubers produced
under wilted vines was made in the field in 1918. Late in the summer
of 1917 several Green Mountain potatoes were dug by hand from
under badly wilted vines in Clay County, Minnesota. There was no
marked amount of stem end discoloration of the tubers at digging
time, nor did this vascular browning increase appreciably through the
winter. Through the courtesy of Dr. G. H. Coons, a half bushel of
tubers was obtained in the spring of 1918 from a field in Michigan
which had shown from 30 to 40 per cent of wilt. Plantings were
made in the field at University Farm. The tubers from Clay County
were planted whole, and those from Michigan were divided into two
lots. Several isolations were made from one lot to determine the
fungi present in the browned vascular tissue of the stem end of the
tubers. F. oxysporum and various other Fusaria were obtained. The
other lot was used for planting, and the tubers were sorted into two
groups according to size. The smaller tubers were halved to give eye
and stem ends, and the larger tubers were cut longitudinally through
the former point of attachment of the stolon, then cut transversely,
to give two each of approximately equal eye ends and stem ends.
These were planted in two places on University Farm. The stand of
the potatoes obtained from Michigan was poor, owing particularly
to frost necrosis of the tubers (29) and to the fact that the “seed”
had been obtained from seriously affected plants. It was also neces-
sary to plant the tubers rather late in the spring. The seed pieces were
planted 1614 inches apart in rows 3 feet apart.

14 MINNESOTA BULLETIN 181

The average yield of the tubers from Clay County was slightly
more than one pound per hill (2914 pounds from 25 hills) or at the
rate of 180 bushels per acre. The plants were not wilted. The yield
indicates that the seed was not affected; indeed, it is possible that the
greater immaturity of such seed resulted in added vigor of the progeny.

The results with the seed from Michigan are summarized in

Table II:

TABLE II
RESULT OF PLANTING TUBERS FROM BADLY WILTED VINES

Character of Date Area of No. of wilted Rate per
seed piece planted plot* plants Yield acre
Sq. Ft. Pounds Bushels
Eye quarters June 4 268.5 0 32.0 86.5
Stem quarters June 4 268.5 2 23.0 62.2
Eye halves June 4 148.5 2 12.0 58.4
Stem halves June 4 148.5 1 14.5 70.9

* Including proper marginal area abouw plot.

In 1918 a plot of the eight standard varieties (6) was planted,
and a considerable amount of fungus from cultures of F. oxysporum
introduced into the soil beside each seed piece at planting time. Here
again only healthy plants were produced, indicating that none of the
varieties is particularly susceptible to the fungus, unless other factors
are conducive to the development of wilt.

The data presented in Table II indicate that serious disease does
not necessarily follow from planting seed from wilted vines, and that
no more wilt may result from the use of the stem ends than from
the use of eye ends. Other observations support this view. Wilted
plants do not, of course, produce tubers of as good quality as healthy
plants, and it can not be denied that infected tubers may introduce
more of the disease into the soil. Such seed is considerably less desir-
able than seed from healthy plants, and plants affected with wilt
should be rogued from plots to be dug for seed. Selecting seed or
clipping the stem ends is, however, not alone sufficient to avoid loss
from wilt. The considerations involved in the use of affected seed
from the north for planting in the southern states require further
attention.

FUSARIUM DRY ROT OF POTATO TUBERS

HISTORICAL
Some of the earlier literature regarding Fusarium rots of potato,
both American and European, is summarized by Smith and Swingle
(63) and in part by Manns (36), altho these authors did not distin-
guish between the Fusaria causing dry rot and those causing wilt.

FUSARIUM DISEASES IN MINNESOTA 15

The monograph by Appel and Wollenweber (2) made it possible to
distinguish between species of Fusaria. Jamieson and Wollenweber
(25) reported F. coeruleum (Lib.) Sacc. and F. discolor sulphureum
to occur in Germany as wound parasites, and the American F. tricho-
thecioides Wollenw. was described and reported from Washington,
Minnesota, Iowa, Nebraska, and South Dakota. Inoculation studies
were described. F. tuberivorum Wilcox and Link (75) was consid-
ered a synonym of the previously established F. trichothecioides.
Orton (41) in 1913 gave a brief description of this “powdery dry
rot” and suggested methods of control. Wollenweber (76) distin-
guished sharply between wilt- and rot-producing Fusaria. Carpenter
(8), besides showing that this sharp distinction did not hold for tuber
rots, described F. ewmartu as a new species of Fusarium causing dry
and wet rot of tubers. He also reported F. radicicola as producing
tuber rot through wound infection. Pratt (49, 51, 52) showed that
_ F. radicicola and F. trichothecioides were apparently weil distributed
through the western desert soils, and suggested disinfecting the stock
before storage or the use of cold storage, as a control measure against
rot. Link (33) has shown that F. trichathecioides can cause wilt as
well as rot, and also that F. oxysporum can cause rot as well as wilt.
Sherbakoff (59) stated that the Fusarium most commonly producing
potato rot in the eastern United States is F. coeruleum. Pethybridge
(46, 47, 48), in Ireland, performed experiments with dry rot of pota-
toes which he considered due to F. coerulewm. Orton (39) and Has-
kell (20) have found that F. ewmartii can cause, besides a tuber rot,
a wilt or stem rot of the potato plant. Milbrath (37) reported dry
rot to be serious in North Dakota, causing a loss of “‘over 20 per cent
in all storehouses in the Northwest” in 1914. Altho he did not specify
which Fusarium was responsible, it is noteworthy that Carpenter
mentions having isolated F. discolor sulphureum from tubers sent in
by Milbrath, as well as from tubers obtained from South Dakota.
Other references to F. discolor sulphureum (2, 25, 59, 76) mention
its presence in Germany, and nowhere has the writer seen it referred
to as being serious in the United States.

DISTRIBUTION
In the United States, Fusarium dry rots appear to be widely dis-
tributed east and west, but the north central part of the country has
not been very critically surveyed. In Minnesota, isolations have been
made from tubers grown in Kittson, Pennington, Polk, Norman, Mah-
nomen, Clay, Wilkin, Otter Tail, Bigstone, Swift, and Lincoln coun-
ties, along the western side of Minnesota, and from Brookings County,

16 MINNESOTA BULLETIN 181

South Dakota. Some have also been made from the region of the
Twin Cities and from Crow Wing and Kanabec counties.

SYMPTOMOLOGY

The Fusarium dry rot of potatoes found in Minnesota is a brown,
compact, firm rot, without the foul odor of bacterial rots. Cavities
are often present in the tissues. These cavities and the tissues con-
tain considerable mycelium which develops readily and abundantly
when the tuber is placed in a damp chamber. From the edges of the
rotted areas, pure cultures of the fungus may usually be obtained
directly from tissue cultures. The skin of the potato is often wrin-
kled. Figures 12, 13, and 14 show the appearance of this rot as found
in storage. The rot starts at any point on the potato, and in the case
of stored potatoes usually from a wound. It is more abundant as the
winter advances. It does not have the powdery appearance charac-
teristic of the rot caused by F. trichothecioides, because the spore
masses when present are more compact and less dry.

Sections of rotted potato show that the fungus grows through
the cells in considerable abundance. The observation of Orton (39)
and Pratt (49) that a dry rot fungus has a tendency to follow the
vascular system can be confirmed in tubers rotted by F. discolor sul-
phureum. ‘The writer’s experience in general corroborates Carpenter’s
observations (8) that there is no real distinction between the effects
of Fusaria causing dry and soft rots, altho F. discolor sulphureum
under ordinary conditions produces a dry rot.

ETIOLOGY
F. discolor sulphureum was obtained readily from affected tubers
grown in many parts of Minnesota. Altho the fact that this Fusarium
is the cause of a dry rot of potatoes has not been emphasized, it is
one of the most common causes of rot in Minnesota, particularly in the
Red River Valley. The ability of this fungus to cause dry rot has
been demonstrated frequently.

EXPERIMENTAL

Efforts to determine varietal differences in susceptibility were un-
successful. The eight standard varieties for Minnesota (Brown and
Wellington, 6) were used, and rot developed from wound inoculations
in each variety.

A series of experiments was made to determine the relations of in-
jury to the tuber and of moisture and temperature to the development
of the rot caused by F. discolor sulphureum. Tubers were inoculated
on the uninjured epidermis, on the surface after slight wounding with

FUSARIUM DISEASES IN MINNESOTA 17

a sterile scalpel, and in deeper cuts into the tuber. Sets of inoculated
tubers were kept at different temperatures under damp conditions,
and similar sets in dessicators containing calcium chloride. The re-
sults are summarized in Table III. (See Figure 15.) The extent and
rapidity of the rot is proportional to the seriousness of the injury to
the tuber, tho the fungus may sometimes enter through uninjured
surfaces, probably through lenticels. The later series of inoculations
(December, 1918), incubated for 13 days (see Table III), resulted in
less infection than in the previous experiments. A less vigorous
“strain” of the Fusarium may have been used. There are character-
istic differences in the rot developed at different temperatures. Under
cooler conditions, the tissues are darkened and contain few “pockets”
and few spores. It is evident that the fungus can rot tubers readily
under dry conditions, especially if it gains entrance through wounds.
The absence of wounds appears to retard the development of F. dis-
color sulphureum more than dryness or storage temperature, except
‘in the case of cold storage.

TABLE III
EFFECT OF INJURY, TEMPERATURE, AND MoIstuRE Upon THE - OCCURRENCE OF THE Rot OF
PoTATOES CAUSED BY F. discolor sulphureum

Character of Tubers
injury Moisture Temperature| inoculated Time Results
Degrees Days

None Saturated 1.1-1.7 4 30 No rot
Saturated 8-10 4 12 No rot
Saturated 8-10 9 13 No rot
Dessicator 8-10 4 12 Slight rot in some cases
Dessicator 8-10 8 13 No rot
Saturated Room 4 12 Slight rot in some cases
Saturated Room 8 13 No rot
Dessicator Room 6 12 Slight rot in some cases
Room humidity Room 4 12 Slight rot in some cases
Saturated 25 6 13 No rot
Dessicator 25 6 13 No rot

Slight Saturated 1.1-1.7 4 30 Trace rot
Saturated 8-10 4 12 Moderate rot on all
Saturated 8-10 9 13 Slight rot on 3 tubers
Dessicator 8-10 4 12 Moderate rot on all
Dessicator 8-10 8 13 Slight rot on 4 tubers
Dessicator Room 6 12 Moderate rot on 4 tubers
Saturated Room 4 12 Moderate rot on all
Saturated Room 8 13 Slight rot on 2 tubers
Saturated 25 6 13 Slight rot on 2 tubers
Dessicator 25 6 13 Slight rot on 3 tubers

Considerable | Saturated 1.1-1.7 8 30 Slight rot
Saturated 8-10 6 12 Much rot on all
Dessicator 8-10 6 12 Moderate rot on all
Dessicator Room 4 12 Much rot on all
Saturated Room 4 12 Much rot on all
Room humidity Room 4 12 Much rot on all
Saturated 25 5 12 Much rot

18 MINNESOTA BULLETIN 181

Pethybridge (47) has reported that young sprouts of uninjured
tubers may be killed by heavy inoculations with F. coeruleum. F. dis-
color sulphureum likewise injures young sprouts if present in |
abundance. i

Sherbakoff (59) and Pethybridge (47) have found that potato
tubers rot more readily after sprouting. To determine the relative
susceptibility to rot of old and new potatoes, several inoculations were
made October 16, 1917, on recently harvested tubers and on tubers
of the 1916 crop kept in cold storage for more than a year. The latter
had sprouts only about fifteen millimeters long at the beginning of the
experiment. At room temperature under a bell jar, the tubers grown
in 1916 showed, October 26, about twice as large an area of rot as did
those of the 1917 crop. The difference was due partly to greater
shrinkage of tissue in the older potatoes. Nevertheless the newer
potatoes had developed a considerable amount of rot. Additional
tests with sprouted and non-sprouted tubers grown the same year
indicated that while sprouted tubers usually rotted more extensively,
sprouting was not at all a controlling factor in the development of the
rot. In sprouted tubers there is a marked shrinkage of the tissue.
Naturally infected tubers frequently rotted before the appearance of
any sprouts.

Experiments to determine the effect of the fungus on tubers show-
ing frost necrosis (Jones and Bailey, 29) as compared with healthy
tubers, were made by inoculating, at the same time, both kinds of
tubers. These experiments failed to show that the injury by frost had
increased susceptibility to rot. Likewise, it was found that the tubers
from “constitutionally degenerate” plants which had shown the so-
called curly dwarf symptoms were no more susceptible to the rot
caused by F. discolor sulphureum than were normal tubers. Indeed,
the degenerate tubers often showed smaller rotted areas than did the
healthy tubers.

No characteristic wilting of the foliage resulted on potato plants
grown from tubers infected with F. discolor sulphureum. Several
trials for the purpose of determining the effect of planting diseased
tubers under field and greenhouse conditions gave the following results:

1. If the tuber or seed piece were badly affected at planting
time, the continued rotting frequently resulted in the destruction of
the sprout. Sometimes this destruction of the seed piece and the sprout
ensued even when only a small amount of rot was present at planting
time. : :

2. If the sprout were well started before the seed piece was com-
pletely rotted, it usually continued to grow, altho the resulting plant
was unthrifty, owing to the loss of the reserve food in the seed piece,

FUSARIUM DISEASES IN MINNESOTA 19

and also perhaps in part to the presence of “toxic substances” (see
below) in the rotting tissue in contact with the base of the sprout.

3. The rot might not develop rapidly enough to affect the sprout
or growing plant. (Figures 16, 17, and 18 show examples of cases
2 and 3.)

Fusarium trichothecioides Wollenw. has been reported from St.
Paul (25,8). The writer is uncertain as to whether the tubers referred
to were grown in St. Paul or collected there. At any rate, he has
never isolated F. trichothecioides from a potato grown in Minnesota.
This, of course, does not mean that it does not occur, since the whole
state has not as yet been thoroly surveyed for tuber rots, but this
Fusarium is apparently not abundant. It has been isolated several
times from potatoes shipped in from western points, including one
lot from North Dakota.

BUSARIGM: DISEASES OF CERTAIN =ERUCK CROPS

Fusarium injuries may be of considerable importance to various
truck crops in the United States (71), even tho a definite wilt is not
produced. Root rots and stem injuries due to Fusaria are rather com-
mon on several crops. Members of the Leguminosae (see 60) such
as cowpea, pigeon pea, and soybean, are seriously affected.

WILT AND?ROOT ROTS OF PISUM- SATIVUM

‘Fusarium vasinfectum pisi was established by Van Hall (73) as
the cause of St. John’s disease of the garden pea. The Fusarium
which Schikorra (60) assigned to the same species was determined
by Appel and Wollenweber (2) to be identical with their species F. fal-
catum, which was reported to occur on garden peas in Germany, and
on tomato fruit in Germany and the United States (76, 59). Lewis
(32) isolated a Fusarium from diseased Pisum sativum in Maine,
which Wollenweber determined as F. orthoceras App. and Wr. Wol-
lenweber (76) also described a new species, F. redolens, with the
following notes: “Vascular parasite, cause of wilt and foot disease
of Pisum sativum. Distribution unknown.” This author also con-
sidered that ‘““More than one species, differing both in size of conidia
and color of conidial masses, may cause the St. John’s disease of the
garden pea.”

Little information is as yet at hand regarding the distribution or
seriousness of Fusaria affecting the garden pea in the United States.

The first report of a serious outbreak of this disease in Minnesota
came in late June, 1916, from Le Sueur. The disease caused con-
siderable damage in a field of about 16 acres. A wilt of garden peas
was reported from near Kasson in 1917.

20 MINNESOTA BULLETIN 181

Species of Fusarium have been found (4) associated with the
diseased condition of roots and stems of the garden pea in Minnesota.
One species, evidently belonging taxonomically in the section Martiella
Wollenw. (76) has been found to be particularly pathogenic. The
stem and root injuries resulting in wilt of the pea plants have been
obtained from infecting the soil or sterilized seeds when planted in
either sterilized or unsterilized soil. If considerable inoculum be ap-
plied, the seeds may rot before sprouting or shortly after (Figure 19).
With a less heavy infection the plants may grow to a considerable size
before the general rotting of the roots and lower stem results in
wilting and death.

Studies of this disease are being made by Dr. F. R. Jones, of the
United States Department of Agriculture, with whom the writer is
cooperating. Cultures of the Fusarium have been submitted to Dr.
Sherbakoff for taxonomic consideration. The writer has used this
Fusarium in some comparative studies with other Fusaria, as reported
later in this paper.

ROOT ROTS OF THE BEAN (PHASEOLUS VULGARIS)

Burkholder (7) reported Fusarium root rots of the bean to be
serious in New York State. Reddick (55) reported that Burkholder
found the fungus to be similar morphologically to F. martu, but differ-
ent physiologically ; he called the fungus Fusarium mariu phaseoli, and
described experiments indicating important relations between temper-
ature and the development of bean plants and the “hemi parasite.”
Several pathologists have reported (71, p. 8) troubles from root rots
due probably to Fusarium, from various sections of the United States.

Rots of the roots and lower stem of bean plants have been noted
in Minnesota, particularly in the spring while the plants are still small
and the ground cool. From such injured roots a Fusarium was iso-
lated. Inoculation experiments demonstrated the pathogenicity of this
fungus to bean plants. This Fusarium has been utilized in some tem-
perature studies, as noted under a subsequent heading. Upon sub-
mission of the fungus to Dr. Burkholder, he pronounced it to be prob-
ably different from his F. marti phaseoli.

FUSARIUM DISEASES OF OTHER TRUCK CROPS IN MINNESOTA

Muskmelon wilt—A Fusarium was isolated by G. R. Hoerner, of
the Section of Plant Pathology, in 1916, from wilted muskmelon vines.
The fungus has not been found to agree with either F. niveum E. F.
Smith or F. vasinfectum Atk. (see 61, 71, 72). Inoculation experi-
ments did not demonstrate that it was particularly parasitic to musk-
melons or cucumbers. In 1918, two reports of non-bacterial wilt were

FUSARIUM DISEASES IN MINNESOTA 21

received from the region of the Twin Cities, and from one field Fu-
saria somewhat similar to the one isolated in 1916 were obtained.
The trouble did not become serious in the field in 1918, and the writer
considers the Fusaria to have been present semi-parasitically, gaining
entrance when the plants were in a nonvigorous condition.

Rots of vegetables.—Fusaria causing rots of cucumber fruits have
been isolated, and are not uncommon, affecting either green or ripe
cucumbers. In view of the inoculation experiments reported later,
the writer regards these Fusaria as acting semi-parasitically, not as
specific parasites restricted to the cucumber. Lewis (32) obtained
rots of cucumber fruits with several different Fusaria.

Wollenweber (76) has described Fusarium sclerotium as causing
a rot of tomato fruits, and has found that F. falcatum also causes a rot
of tomatoes. He named a fungus obtained by Lewis (32) from tomato
fruits, F. citrinum. The writer also has isolated Fusaria from the
tomato fruit. A wilt of tomato such as is caused by F, lycopersict
Sacc. in the south and F. oxysporum and F. orthoceras App. and Wr.
in the west (24) has not been definitely found in Minnesota.

Rots of carrot and other vegetables due to various Fusaria are
quite common, particularly in storage and following wounds. The
rots may be soft or dry. No specificity appears to exist between these
fungi causing various fruit and vegetable rots and the hosts on which
they may be found. This is also indicated by the inoculation experi-
ments recorded later.

Fusarium ear rots of corn (Zea mays).—Pammel, King, and Seal
(44) have summarized the literature of Fusarium diseases of corn.
They found that roots, stalks, and ears were attacked, but the Fusaria
isolated were not named. Sheldon (58) described Fusarium monili-
forme as the cause of moldy corn. Hoffer and Holbert (22) have
recently called attention to injury to corn plants by Fusaria and
bacteria.

The symptoms considered by the writer have been particularly
rots of the ear and cob, ordinarily pinkish or reddish in color. Such
rots were widely distributed in Minnesota in 1917. As a result of
early frosts that year, much immature corn was gathered.

Fusaria were isolated from field corn in the crib, but more par-
ticularly from sweet corn in the field. While inoculations have not
been made to determine the pathogenicity, it was soon suggested from
laboratory studies in 1917 that the Fusarium from some isolations from
corn (both sweet and field varieties) were identical morphologically
with F. culmorum (W. Sm.) Sacc., the wheat scab organism. Hoffer
has been working upon this problem, and with others has published
(23) results of cross-inoculations.

22 MINNESOTA BULLETIN 181

EFFECT OF TEMPERATURE ON VARIOUS FUSARIA

The relations of temperatures affecting the development of host
and parasite are highly important. Considering Fusaria, the work of
Humphrey (24), Link (33), Tisdale (69), Gilman (18), and others
is summarized by Jones (28). The papers of Reddick (55) and of
Wollenweber (76) also deal with this question.

Several of these authors have emphasized the fact that infection
by the Fusarium is more serious at, or even dependent upon, a tem-
perature near the optimum for the fungus; in the case of flax wilt,
there appears to be a definite temperature below which the plant is not
affected (Tisdale, l.c.). The suggestion of Reddick (l.c.) that the
fungus may develop upon the host when unfavorable temperature has
lowered its vitality, is important and has perhaps been partially over-
looked.

Several experiments were begun in 1917 to test the relation of
certain Fusaria to temperature. While the relation of the host plants
to the different temperatures was not critically determined, considerable
is already known in a general way.

The low temperature used in the experiment (1.1 to 1.7 degrees
C.) was practically constant. The temperatures of 25, 30, and 35
degrees were fairly constant. The medium used of course strongly
affects the rate of growth of the fungus. In these experiments, potato
dextrose agar was employed, and since the four Fusaria were sub-
jected in each case to the same conditions, the data are comparable
at each of the different temperatures. More than one set of cultures
was run at most temperatures, and from three to eight measurements
were made at different periods of time. A partial series run later
and not included in the table gave figures somewhat different, tho
a similar relation existed between the rates of growth of the four
Fusaria at each of the temperatures utilized.

Analysis of Table IV shows that the Fusarium from the bean can
make a good growth at 1.1 to 1.7 degrees C., and at temperatures of
20 degrees and below grows somewhat more rapidly than does the
Fusarium from pea, while at 25 degrees and above the reverse is true.
The growth of each Fusarium is comparatively more favorable at the
temperature more unfavorable for its host. This supplements Red-
dick’s (55) observations. F. oxysporum grows well at temperatures
unfavorable for the potato plant. F. discolor sulphureum makes but
slight growth at 1.1 to 1.7 degrees, but is able to cause a slight amount
of rot at this temperature (see Figure 20). At 8 to 10 degrees, this
fungus rots tubers readily as shown in Figure 21.

FUSARIUM DISEASES IN MINNESOTA 23

TABLE. IV
THE EFFECT OF TEMPERATURE ON THE RATE AND’CHARACTER OF GROWTH OF FUSARIA

Av. daily | No. days | Character of Macroconidia or
Temperature Fusarium growth measured mycelium sporodochia
: in radius
. Degrees, C. mm.
1.1-1.7 From bean 1.4 14 Loose aerial No sporodochia
From pea None NAR eats eters rallies o\'sve. scalars Sveti onanie Tow
F, oxysporum None DAs | re eae Mn eee | ays Cave, aoa “a ois Seley oncuelers
F. discolor sul-
phureum Trace Arye Ohl tee vena shatetcertersescn Kile! Ge alles etd cle el. wat earace
8-10 From bean 2.4 13 to 20 | Loose aerial No sporodochia
From pea .0 13 to 20 | Close to med. | Few macroconidia
F. oxysporum ilove 13 to 20 | Thickset aerial! No sporodochia
F. discolor sul-
phureum 3.4 13 to 20 | Loose aerial No sporodochia
14-16 From bean 4.5 6 to 13 | Loose aerial No sporodochia
From pea 4.2 6 to 13 Close to med. | No sporodochia
F. oxysporum 4.5 6 to 13 | Lvose aerial No sporodochia
F. discolor sul-
phureum 6.6 6 to 13 | Loose aerial Some macroconidia
Room temper- | From bean 6.6 4to6 Loose aerial No sporodochia
ature From pea 9.0 4to6 Close to med. | Few sporodochia
F. oxysporum 12.0 4to6 Loose aerial Few macroconidia
F. discolor sul-
phureum 13.0 4to7 Close to med. | Many sporodochia
25 From bean 6.6 4 to 6 Loose aerial Some sporodochia
From pea 9.0 4to6 Rather loose Some sporodochia
F. oxysporum 12.0 4to6 Loose acrial Few sporodochia
F. discolor sul-
phureum 13.0 4 to 6 Close to med. | Pseudopionnotes
30-31 From bean 4.7 4to6 Loose aerial No sporodochia
From pea 9.5 4to6 Rather loose No sporodochia
F. oxysporum 9.6 4to6 Rather close Few macroconidia
F. discolor sul-
phureum 6.0 4 to 6 Very close Abundant pseudo-
pionnotes
35-36 From bean Trace Shape eaeg| |r ev Peppered Sa o>. cer seive, atin shave. ene ca oe
From pea 4.3 8 Loose No sporodochia
F. oxysporum aiev) 8 Close to med. | No sporodochia
F. discolor sul-
phureum Trace S.- <allhoeodos eno 20 SEBO DOO mor coro o.c

From about 8 to 15 degrees C., F. discolor sulphureum develops
a loose vegetative mass of mycelium without sporodochia, whereas at
about 20 degrees and above macroconidia are produced, more abun-
dantly as the temperature rises, until at 30 degrees a dense pseudo-
pionnotes is produced, with mycelium close to or sunken in the agar.
Removal of cultures of this fungus from higher or lower temperatures
to room temperature allows again the development of the growth char-
acteristic in the new temperature. (Figures 22 and 27.) The abundant
spore production of this fungus at higher temperatures has a bearing

24 MINNESOTA BULLETIN 181

on the accumulation of inoculum in storage houses, and perhaps fields, ©
during the summer months.

Freezing would hardly be expected to injure Fusaria. Bartram
(3) reported, however, that a Fusarium obtained from conifers suc-
cumbed to temperatures occurring in winter at Burlington, Vermont.
Cultures of F. oxysporum exposed to the outside temperature from
December 21, 1917, to February 11, 1918, began growing again when
brought indoors, and transfers developed normally. This exposure not
only involved at times temperatures far below freezing, but, since the
cultures were placed on the south side of the building, exposure to
the sun and to alternate freezing and thawing.

Similarly, cultures of F. discolor sulphureum were uninjured after
exposure out of doors for more than a month during the winter.
Wilcox, Link, and Pool (75) found that freezing did not injure F.
irichothecioides. The frequent observation that Fusaria, and various
other fungi as well, can overwinter in the soil shows quite clearly
that low temperatures exert no serious deleterious effect upon them.

EERECT OF MOISTURE, LIGHT, AGE stOOD

Relations to moisture—Fusaria grow readily in culture both on
rather dry substances such as clover stems, and when submerged in
liquid media. Possible oxygen relations involved have not been
tested by the writer. That these fungi withstand dry conditions well
is indicated by the fact that more than a year after inoculation test
tube agar cultures of F. oxysporum were still viable; F. trichothecioides
was still viable after 25 months. The tubes were exposed all this
time to the dry and often warm conditions of the laboratory.
Humphrey (24, p. 15) reports viability of cultures containing chlamy-
dospores after two years’ laboratory dessication in a test tube.

Light—Cultures grow almost equally well in light or dark, altho,
as frequently observed, the colors produced are much more vivid in
rather bright light; sunlight on the other hand, is unfavorable.

Age.—That cultures of Fusaria may lose their virulence after
some period of time on culture media is suggested as a possibility by
Sherbakoff (59) and Link (33). The writer has not found that this
necessarily holds true. Cultures of F. oxysporum obtained as men-
tioned from Wollenweber’s laboratory on February 8, 1915, and which
had of course been isolated some time previously, were still able to
cause infection of potato stems and rot of tubers about three years
later. Appel and Wollenweber (2) note that cultures were still viru-
lent after two years; Edson and Shapovalov (15) found that age did
not lessen pathogenicity. It is of course true that cultures may cease
to be “high cultures” and produce fewer macroconidia if transferred,

FUSARIUM DISEASES IN MINNESOTA 25

for example, only at long periods. While such cultures may not be
as actively virulent as “high cultures,’ a ready way sometimes to bring
about a high culture is by inoculation into the proper host and by
subsequent reisolation.

-Food.—While the writer has not endeavored to determine specifi-
cally which enzymes are produced by certain species of Fusarium, he
has grown these fungi on various media, both synthetic and complex ;
it is obvious that they are not restricted in their saprophytic develop-
ment as to the food used. The work of Hawkins (21) showed that
sucrase, maltase, xylanase, and diastase were secreted by both F. oxy-
sporum and F. radicicola. He found these two fungi to have prac-
tically the same effect on the potato.

The situation with regard to the use of starch by various Fusaria
requires special consideration. Smith and Swingle (63) noted that
the starch grains in a rotted potato (causative Fusarium not certainly
F. oxysporum) were not corroded, altho they found some change as
evidenced by the staining reaction with iodine. Hawkins (l.c.) ob-
served that starch was not used by the Fusaria with which he worked
unless first gelatinized. Hawkins sought an explanation in the slow-
ness of action or diffusibility of the enzyme. It may be noted, how-
ever, that many writers consider the outer layer of the starch grain
to be not homogeneous with the interior. Shapovalov (56) translates
Naumov and Pomasski as finding, however, that F. roseum Link and
F, subulatum App. and Wr., which caused “intoxicating bread,” dis-
solved starch in the seeds of cereals.

The writer has investigated the effect of F. discolor sulphureum
on starch, with results similar to those reported by Hawkins: starch
grains in a rotted potato are intact, and stain as darkly with stronger
iodine solutions as grains from normal potatoes. The appearance of
less blue (more purplish or reddish) staining with dilute iodine is
sometimes to be noted with starch from such rotted potatoes, and
is of uncertain significance. On gelatinized starch, that is, starch
paste made by boiling starch with distilled water, F. discolor sul-
phureum and several other species of Fusarium grew fairly well and
produced normal spores. It would seem, however, that, barring a pos-
sibly less ready separation from the tissue, commercial starch should
be procurable from dry rotted potatoes.

To test the effect of prolonged action of fungi and bacteria caus-
ing rot of potato tubers, a number of tubers seriously affected with
F. discolor sulphureum were placed on March 1, 1918, in a jar, and
this was covered and set away to allow the continued action of the
Fusarium as well as any other organisms present. From time to time

26 MINNESOTA BULLETIN 181

samples were removed for examination of the starch grains, the mass
being then stirred and set aside. The last examination was made
December 24, 1918, at which time, after nearly 10 months of “rotting,”
the mass still contained entirely normal starch grains. Whether the
number was reduced can not be stated, but no grains were found show-
ing partial erosion. The rotting of potato tubers does not necessarily
affect the starch present. Edson (15a) has recently published in some
detail on this point.

CROSS-INOCULATIONS

Table V shows the results of some of the cross-inoculations at-
tempted. The data are not presented unless the lesions produced
were fairly definite. The rots reported were all obtained at room
temperature. The plants inoculated were kept at a greenhouse tem-
perature of about 18 to 24 degrees C.

The evidence presented in Table V seems to indicate that various
Fusaria may cause rot on certain fruits, such as cucumber, apple, or
tomato, the host serving as hardly more than a “culture medium,”
in these cases, for the development of the Fusarium. Potato tubers
may also be rotted by several species of Fusarium, altho it was found
that with certain Fusaria, rot was obtained more readily after the
potatoes had been dug some little time. Sprouting did not seem to be
a necessary corollary. Such forms as F. trichothecioides and F. dis-
color sulphureum, could of course produce rot at any time. While it is
evident that certain forms, including those just noted, are, under nat-
ural conditions, the chief producers of injury to potatoes, it is not
apparent that any certain species of Fusarium causes rot on tomato,
cucumber, and other vegetables.

Cross-inoculation experiments are being continued, since it is evi-
dent that the effect of Fusaria on different hosts is important from
the standpoint of crop rotation.

a

FUSARIUM DISEASES IN MINNESOTA 27

TABLE V

RESULTS OF CROSS INOCULATIONS WITH FUSARIA

Fusarium

F. oxysporum

F. discolor sulphureum

F. trichothecioides

F. culmorum

Fusarium from bean

Fusarium from pea

F. lini

F. lycopersici

Host tried

Orange fruit
Tomato fruit
Potato tuber

Potato plants
Cucumber fruits
Apple Fruit
Bean plants
Pea plants

Cucumber fruits
Bean plants

Pea plants

Potato plants
Potato tuber

Orange fruit

Lemon fruit

Apple fruit

Sweet potato

Cucumber fruit

Tomato fruit

Carrot

Year old pota-
to tuber

Newly dug po-
tato

Rotted potato
tubers plant-
ed

Apple fruit

Potato tuber

Cucumber fruit
Bean plants

Pea plants
Potato tuber

Bean plant
Pea plant

Potato tuber
Pea plant
Bean plant
Potato tuber

Cucumber fruit
Cucumber fruit

Development

Injury

Soft rot

Rot

No effect noted

Slight root in-
jury

Soft rot

No wilt or rot
noted

No wilt or rot
noted

No “wilt’’

Rot, usually
dry rot

Rather soft rot

Rather soft rot
Rather soft rot
Slight rot

Soft rot

Soft rot

Dry rot

Dry rot

Dry rot

No wilt
Slight rot
Rather soft rot

Soft rot

No injury not-
ed

No injury not-
ed

Rot in some
cases

Root rots

Slight root in-
jury

Rot in some
cases

Root rots and
wilt

Trace root in-
jury

Some rot

Rot

Rot

Extent of
injury 3 or 4
weeks
VY fruit
4 fruit
Whole tuber

Whole tuber
¥ fruit

Y fruit

Vg fruit
25mm

¥% fruit

¥% fruit

34 carrot

1% tuber

VY tuber

le, 00 0 « ve peice » @

20-40 mm
Y% fruit
VY fruit

Usually a soft rot.

See previous data

Sterilized soil used

Abundant rot

Light and heavy in-
oculations made

Light and heavy in-
oculations made

See previous data

See previous data

Rind and core par-
ticularly attacked

See previous data and

Fig. 21

See previous data

Injury occasional

28 MINNESOTA BULLETIN 181

DOES THE SUBSTRATUM ALTER THE PATHOGENICITY
OF FUSARIA?

Carpenter (8) has reported several Fusaria as able to produce
rot in potatoes. Sherbakoff (59, p. 100) noted that “Several series
of inoculations of potato tubers showed (a) that a considerable num-
ber of Fusaria can cause more or less rapid decay of the tubers, and
(b) that most of the Fusaria readily produce rot only after the tubers
begin to sprout.” Wollenweber (76, p. 37) considered that in general
the wilt parasite of one host was not found on living organs of another
host, and that “the possibility of the adaptation of the parasite de-
creases proportionately to the taxonomic distance of the host.” He
states, however, that “whether such [gradual to other hosts] adapta-
tion occurs and causes changes in the nature of the parasite, indicated
in pure culture by differences in general appearance, production of
color, etc., has not been determined.” Sherbakoff (1. c. p. 103) noted
cases of possible mutations or fluctuations and of temporary changes
in morphological characters.

Sherbakoff also reported that he had isolated F. culmorum from
rotted potato both alone and in association with other Fusaria. Wol-
lenweber (1. c. p. 45) stated similarly that F. rubiginosum App. and
Wr. (a probable synonym of F. culmorum) caused rot of potatoes at
higher temperatures, but irregularly. The writer has isolated organ-
isms similar morphologically to F. culmorum several times from rotted
potatoes. In an endeavor to determine whether the morphological or
physiological nature of these fungi might be altered by continued
development on a host other than their characteristic habitat, inocu-
lations were made with F. lini, F. culmorum, and the Fusaria men-
tioned above as pathogenic to peas and to beans. Some rots of potato
tubers were secured with all these forms, particularly with F. culmo-
rum (see Figures 23 and 24). As yet these Fusaria have not been
noticeably changed in morphology or pathology, but experiments
should be continued for a much longer time.

THE PRODUCTION OF “TOXIC SUBSTANCES” BY FUSARIA

Lutz (35) has tested the effect of used nutrient solutions, includ-
ing old Fusarium (“F. solani’) solutions, upon the germination and
development of certain fungi. He found that such fungi produced,
after a period of growth upon a medium, substances which retarded
the germination or growth of fungi grown subsequently in the same
medium, even tho more nutrient substances were added; other fungi
produced substances acting as accelerators rather than retarders.

FUSARIUM DISEASES IN MINNESOTA 29

Sometimes both types of substances were produced by the same fungus.
The effect of these substances was usually destroyed by boiling, or even
by lower temperatures. He was, however, unsuccessful in certain
other attempts to demonstrate an enzymatic nature of these substances.
Old Fusarium solutions which had been boiled and exposed to the light,
allowed in general a larger growth of the fungus subsequently intro-
duced than did the unheated solutions. He found also that for some
of his used solutions, filtration through a clay filter removed the
accelerating or retarding substances, altho this filtration did not alter
the solutions in other instances. Lutz concludes that “Die von bestimm-
ten Pilzen produzierten wachstumshemmenden resp. fordernden
Stoffwechselprodukte, welche durch Kochen zerstort werden, haben
keine spezifische Wirkung in dem Sinne dass sie immer nur auf Kei-
mung und Wachstum derselben Pilzspezies Einfluss hatten; ste wirken
auch auf die Sporen anderer Pilze.”

On Currie’s (14) solution the writer grew F. oxysporum, F. dis-
color sulphureum, the Fusarium injurious to peas, Rhizopus nigricans,
and other fungi. After the fungi grew for different periods of time,
these solutions were filtered carefully through filter paper, since a clay
filter may, according to Lutz, absorb the products in question. The
results of preliminary germination tests made with spores of F.
oxysporum and F. discolor sulphureum, agreed in general with Lutz’s
results, and indicated that substances were produced by these fungi
which were inhibitory to the subsequent germination and early devel-
opment of the two Fusaria in the same solution. Boiling the solutions
destroyed this inhibitory action.

Coons (13) reported work showing that F. oxysporum produced
substances filterable through a Berkefeld filter, which caused early
wilting of cuttings from potato vines when immersed in the filtered
solution. Lathrop (31) found aldehydes to be produced by F. cubense
E. F. Sm. Peltier (45) determined that a Botrytis produced a “harm-
ful substance” that “may be some inorganic acid other than oxalic, or
it may be a toxin of some kind, which, however, is not destroyed by
heating to 100 degrees C.” Graves (19) found that Rhizopus nigri-
cans produced substances that exerted a negatively chemotropic effect
upon the fungus greater than the positive chemotropic effect of certain
food materials.

The solutions mentioned above, on which the Fusaria and Rhizo-
pus had grown in Erlenmeyer flasks closed with cotton plugs for
different lengths of time, were filtered, and leaves of potato, coleus,
ragweed, and other plants, all cut off under water, were introduced
(Table VI).

30 MINNESOTA BULLETIN 181

TABLE VI
EFFECTS OF SOLUTIONS IN WHICH FuNGcI Hap GRown, ON THE WILTING OF EXCISED LEAVES
Approximate”
Fungus which had Time of Treatment of solution Plant from | time before
grown in the solution growth in after filtration which leaves consp.
solution were taken wilting
Hours
F. oxysporum 2 months | None Potato 2*
F. oxysporum 2 months | Boiled Potato 2
F. oxysporum 2 months | Diluted half with water Potato 4
F, oxysporum 2 months | Diluted and boiled Potato 4
F. oxysporum 2 months | None Coleus 12
F. oxysporum 10 days None Potato 24t
F. oxysporum 10 days None Lamb’s
quarters 4t
F. oxysporum 42 days None Potato dona
F. oxysporum 42 days Diluted half with water Potato 8
F. oxysporum 42 days Filtered through diatoma-
ceous earth Potato 10
F. oxysporum 42 days None Ragweed 7
F. oxysporum 42 days Diluted half with water Ragweed 7
F. oxysporum 42 days Filtered through diatoma-
ceous earth Ragweed 8
F. discolor sulphureum 2 months | None Potato 2
F. discolor sulphureum 2 months | Boiled Potato 2
F. discolor sulphureum 42 days None Potato 7
F. discolor sulphureum 42 days Boiled Potato 8
F. discolor sulphureum 42 days None Ragweed 6
F. discolor sulphureum 42 days Boiled Ragweed 6
Fusarium from pea 2 months | None Potato 3
Fusarium from pea 2 months | None Coleus 12
Fusarium from pea 2 months | Diluted half with water and
neutralized Potato 4
Fusarium from pea 2 months | Diluted as above and boiled] Potato 4
Fusarium from pea 2 months | Diluted with 3 vols. water
and neutralized Potato 4
Fusarium from pea 2 months | Diluted as above and boiled} Potato 4
Fusarium from pea 42 days None Potato 7
Fusarium from pea 42 days Made slightly alkaline Potato at
Fusarium from pea 42 days Diluted with 3 vols. water Potato 8
Fusarium from pea 42 days Boiled Potato 7
Fusarium from pea 42 days None Ragweed 4
Fusarium from pea 42 days Made slightly alkaline Ragweed 4
Fusarium from pea 42 days Diluted with 3 vols. water Ragweed 5
Fusarium from pea 42 days Boiled Ragweed 63
Rhizopus nigricans 2 months | None Potato 1144
Rhizopus nigricans 2 months | None ~ Coleus 5
Rhizopus nigricans 42 days None Potato 7
Rhizopus nigricans 42 days Boiled Potato 6
Rhizopus nigricans 42 days Boiled Ragweed 6
Rhizopus nigricans 42 days None Ragweed 6
None None Curries, freshly made Potato 24+
None None Curries, freshly made, boiled} Potato 24+
None None Curries, 42 days old Potato 2 16
None None Curries, 42 days old Ragweed 10
None None Curries, 42 days old, boiled | Potato 14
None None Curries, 42 days old, boiled | Ragweed 10
None None Tap or distilled water Potato 48+
None None Tap or distilled water Coleus 48+
None None Tap or distilled water Ragweed 24+

* Potato leaves for tests at any one time were taken from plants of the same age and in similar
condition. For the two-months-old solutions, the leaves were from full-grown potato plants.

¢ Tests after ten days reported in only this case, since with all the solutions it was evident
that no particular development of ‘‘toxic substance’’ had ensued.

}{ Wilt less pronounced than in preceding case.

FUSARIUM DISEASES IN MINNESOTA 31

Tests were also run with other Fusaria, and with Rhizoctonia and
Penicillium. Wilting of excised leaves of various plants ensued more
rapidly in old solutions. Wilting occurred even after considerable
dilution. It is not to be explained on the basis of acidity. It is to be
noted that no specific action is evident between the fungi tried and
any one plant; potato leaves wilt as readily in old Rhizopus solutions
as in solutions in which F. oxysporum had grown. This is in agree-
ment with Lutz’s results in growing fungi in old solutions. A differ-
ence exists, in that boiling the solution exerts no evident effect upon
the action of old solutions on the leaves. In certain cases leaves
took on a crinkled, distorted, or mosaic appearance, resembling some-
times the condition obtained by Smith (62, pl. 63).

“MIXED CULTURE” RELATIONSHIPS

Nature seldom works with pure cultures. The interrelationships
of various organisms forming the mixed cultures of nature have re-
ceived little study (see Rahn 54, p. 181). In view of the frequency
with which various bacteria may be associated with Fusaria in wilt
diseases and tuber rots, the writer undertook tests to ascertain some
relations between certain bacteria and Fusaria.

It is a matter of common observation that fungi belonging to the
genus Fusarium grow vigorously on any of the common culture media.
Indeed, Fusaria are often troublesome as saprophytes in isolation,
dilution, and other cultures of various organisms, on account of the
vigor and rapidity of their growth. The writer has observed Fusaria
to grow over and “swamp” colonies of Penicillium and other fungi.

When, for example, two colonies of the same or of different fungi
develop in a Petri dish, there is often a mutual cessation of growth
at about the point where the colonies meet. Aside from the possible
presence of any growth-arresting substance, there may be a lack of
food, or possibly some mechanical obstruction of growth from the
presence of hyphae, in the case of fungi. With a bacterial and fungous
colony, however, the former should offer less mechanical impediment
to the growth of the latter.

Rahn (53) and others have shown that bacteria may produce
growth-arresting substances, inhibiting more especially the further
growth of the same organism. Elliot (16) has emphasized the changes
in the mycelial characters of some species of Alternaria due to con-
tact with colonies of certain bacteria. Sherbakoff (59, p. 214 f.)
found chlamydospores especially abundant when Fusaria grew in the
presence of bacteria.

32 MINNESOTA BULLETIN 181

In the writer’s experiments, Petri dishes of potato dextrose agar
were used, inoculated at the center with the Fusarium, and midway
on the radii with bacteria at the same time, then incubated until the
colonies reached each other. In other cases the bacteria were first
inoculated in the center and, since the Fusaria usually grow more
rapidly than the bacteria, after incubation from one day to three days
the Fusaria were inoculated on the radii. F. oxysporum, F. discolor
sulphureum, and the Fusaria from the bean and the pea were employed.
Bacillus atrosepticus v. Hall, obtained through the courtesy of Dr.
Morse, was used, since the blackleg organism is often found in both
the stems and the tubers of potatoes. B. carotovorus Jones, certain
undetermined species of bacteria isolated from rotted potato tubers
and stems, Pseudomonas phaseoli E. F. Sm., and some common sapro-
phytes such as Bacillus subtilis (Ehr.) Cohn and B. prodigiosus (Ehr.)
Fleug., were also employed. Figures 25 to 30, with explanations in the
list of plates, show in detail characteristic results. These experi-
ments, which were duplicated several times, showed that in general
a colony of bacteria which exerted a retarding influence on one species
of Fusarium, exerted a similar influence on the other three species.
Here again no specificity of “toxic substance” for any certain species
of fungus was noted. Some bacteria exerted no observed influence,
some accelerated, and some retarded growth of the fungus. The
production of mycelium was sometimes changed in quantity, or the
color reaction upon the medium was altered. On the whole the Fusaria
were very tolerant to the presence of bacteria. No marked alteration
of the mycelium or spores was found as a result of the action of the
bacterial colonies on the fungus. While the writer has no reason to
doubt the authenticity or vigor of the bacterial cultures used, he has
not checked this point. Table VII summarizes the observations.

TABLE VII
EFFECT OF BACTERIA ON CERTAIN FUSARIA

From From
ips rotted rotted

Bacillus atrosepticus phaseoli potato seed B. subtilis
stem piece

F. oxysporum |Slight alteration of growth;/Retarded |Retarded |/Retarded

aerial mycelium marked growth growth growth
medium
colored No change
F. discolor sul-|No effect noted Retarded |Retarded Marked
phureum growth growth retardation|No change
F. from bean |Growth somewhat accelerated,|/Retarded |Retarded |Retardation |Acceleration*
or no change* growth growth or no change
F. from pea No effect noted Retarded |Retarded
growth growth.” |icicte sue oe 5.0500 No change

* Acceleration of growth did not ensue in every trial. In general, however, the same results
were secured in the different tests.

FUSARIUM DISEASES IN MINNESOTA 33

GENERAL DISCUSSION

In considering Fusaria and the diseases they induce, we may first
consider these fungi as vigorously growing saprophytes. Their longev-
ity in the soil is a matter of prime importance.

Bolley, in 1901 (5), showed that soil became “flax sick” because
of an accumulation of F. lini; he stated that when once serious in the
soil, “It can live from year to year upon the humus of the soil....
The fungus is able to live in the soil for many years without the
presence of a flax crop to feed upon.” Orton (40), referring to F.
oxysporum in the San Joaquin Valley, California, stated that the fun-
gus “may be present in nature in some of these alluvial soils” and at
any rate soon accumulated sufficiently in the soil to render potato
growing unprofitable. Jensen (26) reported the isolation of F. oxyspo-
rum from soil from the eastern part of the United States.

It is significant that Pratt (49,50,51,52) found F. trichotheci-
oides, F. radicicola, and apparently also F. oxysporum, in virgin west-
ern soils. Werkenthin (74) found in Texas “that the virgin soil
contained fungi which are known to be parasitic to cultivated plants,
e.g., Fusarium Solan (Mart). Sacc., Fusarium oxysporum Schlecht.,
and Fusarium radicicola Wollenweber.” These fungi he considered
“true inhabitants of the soil.” Taylor (68) found Fusarium spp.
to a depth of 24 inches, in Rhode Island. Coons (13) obtained what
was apparently F. oxysporum from native Michigan soils.

There is evidence, then, that F. oxysporum may be present in
many soils, and may become of considerable importance as succeed-
ing crops of potatoes are grown; it must increase greatly from its
growth in roots and stems of parasifized plants, and especially from
its development on the dying potato stems and their débris. Such
saprophytic fungi are able to withstand various unfavorable environ-
mental conditions and persist in the soil through the production of
microconidia and macroconidia, chlamydospores, or “perennating my-
celium.” In their growth, some Fusaria at least are able to compete
successfully with various bacteria and other organisms with which
they come in contact.

While Fusaria are active saprophytes, there can be, on the other
hand, no question as to their seriousness as plant parasites; their
abundant saprophytic growth only renders their control in some re-
spects more difficult. Despite their semi-parasitic nature, many Fu-
saria, such as F. oxysporum, exhibit what amounts to a considerable
specificity of parasitism to certain crops. F. oxysporum, however,
can attack any part of the potato plant; stem, stolon, root, tuber, or
even leaf. If the fungus is present in abundance, it can cause a com-

34 MINNESOTA BULLETIN 181

plete rotting off of the stems. It is not surprising, then, that from
plants showing atypical symptoms of wilt in the field, PF. oxysporum
should be isolated, especially when the soil and weather conditions are
propitious. The Early Ohio variety has been found to be commonly
affected, particularly in the Red River Valley. This may be correlated
with the fact that the Early Ohio remains through a considerable
period in late summer in a condition of slow maturity and lessened
vigor.

In regard to the cause of wilting in potato plants into which
F. oxysporum has gained entrance, a common explanation is that of
mechanical vascular clogging. Link (35) considers the killing of
the root system to be as important as this clogging, and Coons (13,
p. 302) would add also the systemic poisoning from the production
of substances by the fungus. The writer’s experiments indicate that
the fungus does produce toxic substances, but that various other fungi
produce substances equally toxic, the only specificity being in the
fact that the other fungi tried are ordinarily unable to gain entrance
into the tissues of the plant. It would seem, however, that the three
factors mentioned may operate together, with the addition in cases
of foot rot of a considerable rotting of the underground portions of
the potato plant.

The association of injury to the potato stem from Rhizoctonia
or Colletotrichum atromentarium (Berk. & Br.) Taub. (67) and of
F. oxysporum within such stems, and the occasional coincident occur-
rence of bacteria, Verticillium, or other fungi with F. oxysporum in-
dicate that Fusarium wilt ensues more readily when the plant is weak-
ened, and that other organisms may follow or aid the Fusarium in
causing injury to the potato plant.

Tisdale (70) has shown that the method of infection by F. lini
is through root hairs, stomata, or epidermis; in resistant flax the
plant was enabled to cork out the perhaps weakened hyphae, which
could, however, gain preliminary entrance into the plant. He found
further that F. conglutinans could penetrate the root hairs of flax, as it
normally penetrated cabbage, but in flax it did not develop far. F. lini
could also probably penetrate the young root hairs of cabbage.

While rots of potato tubers are attainable in the laboratory with
various Fusaria, in Minnesota the economically important Fusarium
causing rot of tubers is, as far as the writer’s evidence goes, F. dis-
color sulphureum. F. oxysporum may injure the tuber somewhat by
development at the stem end or considerably in the vascular system,
or occasionally by causing a rot; other Fusaria more rarely cause dry
rot alone or in association with other organisms. F. discolor sul-
phureum evidently lives over especially in storage houses; the writer

FUSARIUM DISEASES IN MINNESOTA 35

has observed it in the fall growing luxuriantly, particularly on dirt
floors and walls and on débris in potato houses that had held potatoes
the previous year.

Infection of the tuber may sometimes apparently ensue from con-
tamination with the organism from the field. Once this fungus gains
entrance it can develop at ordinary temperatures regardless of the
humidity in storage, tho lower humidity obviously lessens the lability
of infection. Relatively low temperatures, particularly cold storage,
(1 to 3 degrees C.) allow but slight progress of the disease.

While F. discolor sulphureum ordinarily gains entrance through
wounds, it is worthy of note as reported above that it may sometimes
evidently infect through lenticels. Jn this connection it may be noted
that Pratt (49) found that F. radicicola might infect the tuber through
the stem end, lenticel, or eye; Wilcox, Link, and Pool (75) and Pratt
(51) found that F. trichothecioides, on the other hand, infected only
through bruises or other injury. Experiments and observations indi-
cate that tubers become naturally infected with F. discolor sulphureum
principally through wounds.

Tomato, cucumber, and some other fruits and various vegetables,
especially when mature, may be rotted by several Fusaria. Num-
erous other fungi, such as Penicillium spp., may also rot these plant
parts; the action is hardly more than saprophytic growth upon easily
available food material. While various fungi such as Penicillium spp.,
Aspergillus spp., Stysanus stemonitis, Verticillium sp., Alternaria sp.,
are often found on or in rotted tubers or on healthy tubers, inoculation
experiments failed to show any noteworthy ability of these fungi to
rot the potato. The normal tuber is not an available source of food
for them. Certain Fusaria are also unable to utilize readily the potato
tuber as a food supply.

CONTROL MEASURES

POTATO WILT

The methods of control ordinarily recommended are clipping the
stem ends and rotation of crops. The former method, while of un-
doubted value in removing some infection as well as the somewhat
weaker eyes near the stem end, is not effective in seriously infected
soils. Whether or not F. oxysporum occurs naturally in Minnesota
soils, it is now widely distributed in the potato growing regions. Ob-
servational: evidence has failed to show that this fungus seriously
attacks other crops in the state. It undoubtedly remains in some
abundance in Minnesota soils for a considerable time.

36 MINNESOTA BULLETIN 181

It seems to the writer that the observation that the Fusarium
causing potato wilt in Minnesota attacks the plants more especially at
the time when blossoming, tuber setting, and hot weather have reduced
the vigor of these plants, offers considerable hope in the development
of control measures. From this standpoint the utilization of more
vigorous strains of potatoes, rotation of crops, improvement of the
seedbed, clean culture, and other factors tending to. produce more
vigorous plants likewise lessen the liability to attack by FP. oxysporum.

The writer is uncertain as to the interpretation to place upon the
data presented by Manns (36, p. 317-319) and considered as tending
to show that the “fungus will average in sick fields as great a percent-
age in reduction under favorable conditions as under drouth.” Manns
evidently bases this conclusion on the fact that a three-year rotation
plot at the Ohio station yielded in 1909 only 69 bushels per acre,
whereas the county averaged 186 bushels per acre. It would seem,
however, that throughout that county, in which the wilt had presum-
ably been present previously (l.c., p. 311), it could not have greatly
reduced the yield in 1909 despite the supposed higher percentage of
seed infection in 1908 (l.c., p. 319; see also yield of spray plot, as
noted below). Of course this does not explain the low yield in the
rotation plot at the Ohio station in 1909.

The work of Manns with bordeaux mixture is also significant.
He found that despite the fact that “the only active factor at work
in 1909 in reducing the yield on the area plotted for spraying was
the work of the Fusarium blight, which was very prevalent
the growth in all sprayed plots continued from one to three weeks
longer than in the unsprayed,” with an average yield of 170.36 bushels
per acre in the unsprayed and 181.72 bushels per acre in the sprayed
plots. He adds, “The writer is satisfied that spraying heavily four
times during the season does somewhat retard the action of the Fu-
sarium fungus. Just how the results are brought about can not be
satisfactorily explained.” It would seem that the explanation may
lie in the increased vitality of plants which are sprayed, and which
can thus resist the action of the semi-parasitic F. oxysporum. Stew-
art (66) had previously in New York State obtained a yield of 266
bushels per acre from tubers obtained from wilted vines and in which
“when cut at the stem end, blackened fibers are seen penetrating the
flesh to a considerable distance.”’ This plot was sprayed thoroly eight
or nine times with bordeaux mixture. While it is not certain that
Stewart was dealing with F. oxysporum wilt, the results obtained are
comparable to those secured by Manns.

FUSARIUM DISEASES IN MINNESOTA 37

The writer has obtained as yet only empirical and fragmentary
evidence as to the effect of spraying upon the occurrence of wilt in
Minnesota. In the northeastern states, where spraying is commonly
practiced, wilt is not prevalent. It must not be forgotten, however,
that in this region cool weather and other conditions are more favor-
able to the production of healthy and vigorous plants than in warmer
regions.

The results secured in Minnesota by A. G. Tolaas and certain
county agents in the use of seed-plot methods, including selection,
treatment, rotation, and good cultural conditions, indicate that wilt
may be lessened by methods which tend to add vigor to the plants.
A. G. Newhall, in 1918, found a case in point: A field in Cass County,
a portion of which had received some care, had 15 per cent of wilt,
whereas in another portion in which negligence had allowed weeds to
develop and the potato plants to become less thrifty, 30 per cent of wilt
occurred.

Removal of débris from a field that had grown potatoes would
Jessen considerably the amount of culture medium for the Fusarium.
The consideration involved as to fungi in returning such débris to the
field after a period of rotting, is undetermined.

POTATOCDRY, ROU

Control measures that may be used against the rot caused by F.
discolor sulphureum have not been found to be different from those
recommended by various writers against other fusarial dry rots.
Highly important is more careful handling of potatoes during and
after digging to avoid cuts, bruises, and injuries, since the fungus
attacks the tubers ordinarily and most easily through wounds. Stor-
age cold enough to prevent absolutely the development of this rot
is hardly attainable in any storage facilities possessed by the average
grower, except possibly in the use of pits in the field. Considerably
less infection would probably result, however, if the storage rooms
were thoroly disinfected before potatoes were put in, and cleaned out
carefully after the potatoes were removed. A disinfection of the
tubers before storage would probably be commercially profitable, at
least in the case of seed potatoes.

Control measures against root rots of truck crops are indicated
in the rotation of crops and the most favorable growing conditions
for the crop. Careful handling and clean cool storage of fruits and
vegetables subject to Fusarium rots will reduce the injury.

SUMMARY

1. Fusarium oxysporum Schl. is the cause of one of the most
serious diseases of the potato plant in Minnesota.

38 MINNESOTA BULLETIN 181

2. This fungus characteristically produces the symptoms known
as wilt. It attacks the roots and lower stem of the potato plant,
particularly during the blossoming and tuber setting periods, when
the weather is likely to be unfavorable to the potato, tho not to the
fungus. F. oxysporum can moreover attack any part of the potato
plant, and under certain conditions, particularly in wet soil, causes
darkening and rotting of the stem and other symptoms not typical of
wilt. It may rot the seed tuber under field conditions.

3. As a saprophyte, F. oxysporum grows vigorously on the af-
fected potato plants, accumulates in considerable abundance-in the
soil throughout the season, and persists for some time. In the fall
it may attack plants which have previously produced a normal crop
of tubers.

4. The strains of F. oxysporum used were not, under ordinary
conditions, sufficiently active parasites to cause infection of younger
potato plants from artificial inoculations of the soil or seed tuber.
At higher temperatures, symptoms of disease may occur. If the
soil is inoculated heavily, rotting of the seed tuber and of the sprout
or stem may result.

5. Wilted plants do not necessarily result from planting seed
tubers from affected plants. While such “‘seed” is less satisfactory
than tubers produced under healthy vines, other measures in addition
to seed selection or clipping off the stem ends are necessary to avoid
wilt.

6. While F. oxysporum is largely confined to the potato in Minne-
sota, its habits are for the most part hemi-parasitic.

7. The danger of serious infection by the wilt Fusarium is lessened
by measures tending to add to the vigor of the plants, particularly
during the latter part of the season.

8. Fusarium discolor sulphureum is the common cause of storage
dry rot of potato tubers in Minnesota.

9. This fungus gains entrance commonly through wounds, tho
the rot may sometimes be induced by applying the fungus to the unin-
jured surface of the tuber.

10. Tubers from normal potato vines rot as readily as those
from’ “constitutionally degenerate” plants, and as readily as tubers
showing frost necrosis. None of the varieties of potatoes tested was
found to be resistant to this tuber dry rot.

11. Rot may develop on unsprouted tubers, and under dry condi-
tions. Very slight rot may develop even at temperatures below 2 de-
srees C.

FUSARIUM DISEASES IN MINNESOTA 39

12. At temperatures below about 16 degrees C., F. discolor sul-
phureum produces more abundant aerial mycelium; at temperatures
of from 20 to 30 degrees C., a dense pseudopionnotes.

13. The starch grains in the tubers affected with dry rot are
not appreciably affected.

14. F. discolor sulphurewm does not naturally cause a wilt of
potato plants, but infected seed tubers may produce less vigorous
sprouts, or even no sprouts.

15. While other Fusaria, such as F. oxysporum and F. culmorum
may cause rot of potato tubers, such rots have been found to be of
little economic importance in storage.

16. Careful handling of tubers and the maintenance of clean
cold storage conditions, are important prophylactic measures against
the storage rot caused by F. discolor sulphureum.

17. Fusarium root rots of Pisum sativum and of Phaseolus vul-
garis are of importance in Minnesota.

18. Ear rots of Zea mays due to Fusaria, probably including
F. culmorum, are common in the state.

19. Cross-inoculations indicate that wilt or root rot producing
Fusaria may exhibit a selective tendency in their more common oc-
currence on certain species of host plants, altho hemi-parasitic in that
their action may be more distinctly influenced by conditions unfav-
orable to the host.

20. A temperature at which the host develops poorly may allow
an active development of the attacking Fusarium.

21. Isolations and cross-inoculations demonstrate that no single
species of Fusarium is chiefly responsible for the common storage
rots of vegetables and of cucumber and tomato fruits.

22. Fusaria produced substances in old solutions that inhibited
the germination of spores of the same or other fungi. After boiling,
such old solutions allowed normal germination.

23. Substances detrimental to such plants as potato, coleus, and
ragweed, as shown by the wilting of excised leaves when placed in
solutions, were also produced by Fusaria and other fungi in cultures.
This injurious effect persisted after boiling, neutralization, or some
dilution of the solutions. Specific fungi did not produce substances
selectively injurious to any one or more plants.

24. Fusaria are, in general, little influenced by bacteria, tho some
bacteria may influence the rate of growth of Fusaria.

25. The Fusaria examined could withstand considerable dessica-
tion, exposure to low temperatures or to alternate freezing and thaw-
ing, and can utilize a wide variety of food substances. Altho im-
portant parasites, Fusaria are efficient saprophytes.

TS:

BIBLIOGRAPHY

. Appel, O. Leaf roll diseases of the potato. Phytopath. 5: 139-

148. 1915.

and Wollenweber, H. W. Grundlagen einer Mono-
graphie der Gattung Fusarium (Link). Arb. Kais. Biol. Anst.
Land- und Forstw. 8: 1-207, fig. 1-10, pl. 1-3. 1910.

. Bartram H. E. Effect of natural low temperature on certain

fungi and bacteria. Jour. Agr. Res. 5: 651-655. 1916.

. Bisby, G. R. A Fusarium disease of garden peas in Minnesota.

Abs. in Phytopath. 8: 77. 1918.

. Bolley, H. L. Flax wilt and flax-sick soil. N. Dak. Agr. Exp.

Sta, Ball, 50: 27-58. 1O0r.

. Brown, C. E., and Wellington, Richard. Standard potato varie-

ties for Minnesota. Minn. Agr. Ext. Div. Spec. Bull. 5: 1-8.
pl. 1-8. 1916.

. Burkholder, W. H. Some root diseases of the bean. Abs. in

Phytopath. 6: 104. 1916. See also Phytopath. 7: 61. 1917.

. Carpenter, C. W. Some potato tuber rots caused by species of

Fusarium. Jour. Agr. Res. 5: 183-209. pl. A, B, and 14 to
19, F905.
Wilt diseases and the Verticillium wilt problem.
Jour. Agr. Res. 12: 529-546. pl. A and 17 to 27. 1918.
Report of the plant pathologist. Hawaii Agr.
Exp. Sta. Rept. 1917: 33-42. 1918.

. Clinton, G. P. Fungous diseases of the potato. Ill. Agr. Exp.

Sta. Bull. 40: 136-140. pl. I. 1895.

. Coons, G. H. In Report of the botanist. Rept. Mich. Bd. of Agr.

1916: 270. 1916.
Notes on Michigan plant diseases in 1916. Rept.
Mich. Gd: of Agr. 19172302, 312. 1917.

. Currie, J. N. The citric acid fermentation of Aspergillus niger.

Jour Biol. Chem,31> 15-37. ple 1. 1917.
Edson, H. A., and Shapovalov, M. Potato stem lesions. Jour.
Agr. Res. 14: 213-220. pl. 24-26. 1918.

15a. Edson, H. A. The effect of frost and decay upon the starch in

16.

potatoes. Jour. Ind. Eng. Chem. 10: 725-726. 1918.
Elliot, John A. Taxonomic characters of the genera Alternaria
and Macrosporium. Am. Jour. Bot. 4: 439-476. pl. 19, 20, 1917.

ny.

18.

£9:

20.

Zils

25.

26.

27.

28.

AS),

30.

ail:

oa)

33.

FUSARIUM DISEASES IN MINNESOTA 41

Fitch, C. L., and Bennett, E.R. The potato industry of Colorado.
Colo. Agr. Exp. Sta. Bull. 175: 1-80. pl. 1-23. 1910.

Gilman, J. C. Cabbage yellows and the relation of temperature
to its occurrence. Ann. Mo. Bot. Gard. 3: 25-84. fig. 1-21. pl.
We 1916,

Graves, A. H. Chemotropic reactions in Rhizopus nigricans.
Mem. N. Y. Bot. Gard. 6:.323-331. 1916.

Haskell, R. J. Potato wilt and tuber rot caused by Fusarium
eumartu. Phytopath. 6: 321-327. fig. 1-3. 1916.

Hawkins, L. A. Effect of certain species of Fusarium on the
composition of the potato tuber. Jour. Agr. Res. 6: 183-196.
1916.

. Hoffer, G. N., and Holbert, J. R. Results of corn disease investi-

gations. Science n.s., 47: 246, 247. 1918.

. Hoffer, G. N., Johnson, A. G., and Atanasoff, D. Corn root rot

and wheat scab. Jour. Agr. Res. 14:611, 612. 1918.

. Humphrey, H. B. Studies on the relation of certain species of

Fusarium to the tomato blight of the Pacific northwest. W ash,
MereExp. Stas Bulk 115: 1-22. pl. 125,. 1914;

Jamieson, C. A., and Wollenweber, H. W. An external dry rot of
potato tubers caused by Fusarium tricothecioides Wollenw.
Jour. Wash. Acad. Sci. 2: 146-152. 1912,

Jensen, C. N. Fungous flora of the soil. N. Y. Cornell Agr.
Exp. Sta. Bull. 315: 414-501. fig. 100-134. £912.

Jones, L. R. Potato diseases in Wisconsin and their control.
Wass Nec Exp Stom@ir. 36::1-105/1912. )See-also:Cir. £2: 1-19.
1914.

Soil temperature as a factor in phytopathology.
Plant World. 20: 229-237. fig. 1,2. 1917.
—and Bailey, Ernest. Frost necrosis of potato tubers.
Abs. in Phytopath. 7:71, 72. 1917.

Kohler, A. R. Potato experiments and studies at University
Farm. Minn. Agr. Exp. Sta. Bull. 114: 287-333. 1909.

Lathrop, E.C. The generation of aldehydes by Fusarium cubense.
Phytopath. 7: 14-16. 1917.

Lewis, C. E. Comparative studies of certain disease-producing
species of Fusarium. Me. Agr. Exp. Sta. Bull. 219: 203-258,
fig. 86-118. 1913.

Link, G. K. K. A physiological study of two strains of Fusarium
in their causal relation to tuber rot and wilt of potato. Bot.
Gaz. 62: 169-209. fig. 1-13. 1916. Also Neb. Agr. Exp. Sta.
Res. Bull. 9: 1-45. 1916.

42

34.

Sa

36.

37.

38.

ao:

40.

41.

42.

43

44,

45.

46.

MINNESOTA BULLETIN 181

Link, H. F. Observationes in Ordines Plantarum naturales. Dis-
sertatio I. Magaz. Ges. Naturf. Freunde. Berlin. III. p. 3-42.
1809.

Lutz, C. Ueber den Einfluss gebrauchter Nahrlosungen auf Kei-
mung und Entwicklung einiger Schimmelpilze. Ann. Myc. 7:
91-1382 41909.

Manns, T. F. The Fusarium blight (wilt) and dry rot of the

potato. Ohio Agr. Exp. Sta. Bull. 229: 299-337. pl. 1-15. 1911.

Milbrath, D. G. Potato diseases in North Dakota. N. Dak.

Farmers Inst. Monthly 14: 81-95. fig. 1-8. 1914.

Nicholls, H. M. Plant diseases in Tasmania. Agr. and Stock
Dep. Tasmania Rep. 1915-16: 18-20. 1916. Original not seen;
abs. in Exp. Sta. Rec. 36: 846. 1917.

Orton, C. R. The diseases of the’ potato, -Pa.. Aer: Exp: -Sta:
Bull. 140: 1-37. fig. 1-23. 1916.

Orton, W. A. Potato diseases in San Joaquin County, California.
Un Seept. of Agr By Plier 2aai- 14 aie

Powdery dry-rot of the potato. U. S. Dept. Agr.
BoPeeCir. 110293 - ors:

Potato wilt, leaf-roll, and related diseases. U. S.
Dept. of Agr. B. P. I. Bull. 64: 1-48. pl. 1-16. 1914.

_—————— and Link, G. K. K. Powdery dry rot of potato (Fu-

sarium). U.S. Dept. of Agr. Cotton, truck and forage crop
diseases, Cir. 1: 1-4. fig. 1. 1918.

Pammel, L. H., King, C. M., and Seal, J. L. Studies on a Fusa-
rium disease of corn and sorghum. Iowa Agr. Exp. Sta. Res.
Bull. 33: 115-136. fig. 1-15. 1916.

Peltier, G. L. A consideration of the physiology and life history
of a parasitic Botrytis on pepper and lettuce. Ann. Rept. Mo.
Bot. Gard. 23: 41-74. pl. 1-5. 1912.

Pethybridge, G. H. Dry rot of potato tuber. Econ. Proc. Roy.
Dublin Soc. 1: 547-558. pl. 1-48. 1908.

Investigations on potato diseases. Sixth Rept. Dept.
Agr. and Tech. Instr. Ireland, Jour. 15: 491-526. 1915.

Investigations of potato diseases. Eighth Rept. Dept.
Agr. and Tech. Instr. Ireland, Jour. 17: 595. 1917.

. Pratt, O. A. A western field rot of the Irish potato tuber caused

by Fusarium radicicola. Jour. Agr. Res. 6: 297-309. pl. 34-37.
1916. '

Experiments with clean seed potatoes on new land in
southern Idaho. Jour. Agr. Res. 6: 573-575. 1916.

51.

52.

aS)

54.

5D:

56.

nye

58.

a9:

60.

61.

62.

63.

FUSARIUM DISEASES IN MINNESOTA 43

Control of the powdery dry rot of potatoes caused
by Fusarium trichothecioides. Jour. Agr. Res. 6: 817-832. pl.
108. 1916.

Soil fungi in relation to diseases of the Irish potato
in southern Idaho. Jour. Agr. Res. 13: 73-100. pl. A and B.
fig. 1-4. 1918.

Rahn, O. Ueber den Einfluss der Stoffwechselprodukte auf das
Wachstum der Bakterien. Cent. Bakt. II Abt. 76: 417-429.
609-617. 1908.

In Marshall, Microbiology: 81-184. P. Blakiston’s Son
& Co. Philadelphia. 1911.

Reddick, D. Effect of soil temperature on growth of bean plants
and upon their susceptibility to a root parasite. Am. Jour.
Bot. 4: 513-519, 1917.

Shapovalov, M. Intoxicating bread. [Review of papers of Nau-
mov, N. A., and Pomasski, A.] Phytopath. 7: 384-386. 1917.
Shear, W. V. Potato growing in the San Joaquin and Sacramento
deltasiof Galiforma.. Cali Acrvrxp) Sta, Cir) 120: 1-17. fig.

1-7. 1914.

Sheldon, J. L. A corn mold. Neb. Agr. Exp. Sta. Rept. 17:
23-32. 1904.

Sherbakoff, C. D. Fusaria of potatoes. N. Y. Cornell Univ. Agr.
Exp. Sta. Memoir 6: 87-270. fig. 1-51. pl. 1-7. 1915.

Shikorra, G. Fusarium-Krankheiten der Leguminosen. In Appel,
Beitrage zur Kenntnis der Fusarien und der von ihnen hervor-
gerufenen Pflanzenkrankheiten. Arb. Kais. Biol. Anst. Land.
Forstwirtsch. 5: 157-188. 1906.

Smith, E. F. Wilt disease of cotton, watermelon, and cowpea.
U. S. Dept. Agr. Div. Veg. Phys. and Path. 17: 1-72. pl. 1-10.
1899.

Mechanism of tumor growth in crowngall. Jour. Agr.
Res. 8: 165-186. pl. 4-65. 1917.

and Swingle, D.B. The dry rot of potatoes due to
Fusarium oxysporum. U.S. Dept. Agr. B.P.I. Bull. 55: 1-64.
pl. 1-8. 1904.

. Stakman, E. C., and Tolaas, A. G. Potato diseases. Minn. Agr.

Eext, Bully35.: 1-15: hee 1-7. 1912:

. Stewart, F. C. Another stem-blight of potatoes. N. Y. Geneva

Agr. Exp. Sta. Bull. 101: 83-84. 1895.
The communicability of potato stem-blight. N. Y.
Geneva Agr. Exp. Sta. Bull. 138: 632-634. 1898.

67.

68.

69.

70.

76.

MINNESOTA BULLETIN 181

Taubenhaus, J. J. A contribution to our knowledge of silver scurf
(Spondylocladium atrovirens Harz.) of the white potato. Mem.
N. Y. Bot. Gard. 6: 549-560. pl. 41-43. 1916.

Taylor, Minnie W. Preliminary report of the vertical distribu-
tion of Fusarium in soil. Phytopath. 7: 374-378. 1917.

Tisdale, W. H. Relation of temperature to the growth and in-
fecting power of Fusarium lim. Phytopath. 7: 356-360. fig. 1.
pide 1917.

Flax wilt: A study of the nature and inheritance of

wilt resistance. Jour. Agr. Res. 11: 573-606. fig. 1-8. pl. 44-46.
1917.

. U.S. Dept. of Agr. B. P. I. Plant Disease Survey. Plant Disease

Bull. 1 Nos. 1-7: 1-131. 1917..

. ——— 2: 1-226. 1918.
. Van Hall, C. J. J. Die Sankt-Johanniskrankheit der Erbsen,

verursacht von Fusarium vasinfectum Atk. Ber. Deutsch. Bot.

Gesells. 21: 2-5. 1903.

. Werkenthin, F. C. Fungous flora of Texas soils. Phytopath. 6:

241-253. 1916.

. Wilcox, E. M., Link, G. K. K., and Pool, Vi W..-A dry sot/of the

Irish potato tuber. Neb. Agr: Exp. Sta; Res, Bull) 1: 4-88:
fig. 1-15. pl. 1-28. 1913.

Wollenweber, H. W. Studies on the Fusarium problem. Phyto-
pathoj3;-24-50, fig. 1. ply S913:

EXPLANATION OF PLATES

Figure 1. Plant showing typical wilting. Illustration by the courtesy of H. A.
Edson of the United States Department of Agriculture. Taken in a field in
Clay County, Minnesota, August 11, 1917.

Figure 2. Rather early stage of wilting. Taken by Dr. Edson, also in Clay
County, August 11, 1917.

Figure 3. Plants collected August 23, 1918, from Clay County, illustrating the
browning and rotting of the lower stems and of the roots. One plant also
injured by stalk borer. Isolations yielded Fusarium oxysporum from these
and similar plants.

Figure 4. Plants showing similar and serious injury from foot rot, collected
August 22 and 23, 1918, from Polk and Clay counties. The large plant illus-
trates also the external production of fungus after having been in a damp
place about two days.

Figure 5. Tubers from plants showing foot rot, collected in Polk County,
August 22, 1918. F. oxysporum and secondary fungi and bacteria present,
causing a rather soft rot of the tubers. This rot was not ordinarily foul
smelling. The blackening shows some tendency to follow the fibro-vascular
bundles.

Figure 6. Seed piece inoculated with F. oxysporum, received February 8, 1915,
from W. A. Orton. (No. 3394 from Wollenweber’s laboratory.) Inoculation
September, 1917. The seed piece had rotted, the fungus was present in the
stem. Reisolations yielded F. oxysporum.

Figure 7. Cage heated by carbon electric lamps to secure higher temperature.

Figure 8. Results of rather heavy inoculation of sterilized soil with F. ory-
sporum in the warmed cage. Seed piece rotted, one stem rotted off, other
injured at the base. March, 1918.

Figure 9. A case similar to Figure 8. Stems rotted off or seriously injured at
the base. March, 1918.

Figure 10. On the left, plant growing in the warm chamber in sterilized soil
infected with F. oxysporum. Moist conditions did not allow a serious wilt-
ing, but the plant is affected, particularly as indicated by the upper leaves.
On the right, check grown from the same seed in sterilized soil. February,
1918.

Figure 11. Affected plant growing in artificially infected soil. The lower leaves
have fallen and the plant is unthrifty. February, 1918.

Figure 12. Surface view of tubers affected with F. discolor sulphureum from
Beardsley. The wounds from which infection occurred can be seen on the
surface. January, 1918.

Figure 13. Longitudinal sections of the tubers shown in Figure 12. The rotted
tissue is dark brown or Dlackish, containing some “pockets” filled with
mycelium and sporodochia of the fungus.

Figure 14. Stem and eye end infection of tubers from Clay County and char-

acteristic of the rather early stage of a considerable infection in that region.
Received December 10, 1917.

46 MINNESOTA BULLETIN 181

Figure 15. Effect of injury, moisture, and temperature on the development of
rot by F. discolor sulphureum. Figures A to E, inclusive, no injury to the
surface; inoculum applied to the uninjured epidermis. Figures F, G, and H,
slight injury to the surface before inoculation. Figures I to L, considerable
wounding of surface previous to inoculation. Figures A and B, room tem-
perature, damp. Figures C and D, room temperature, in a dessicator.
Figure E, icebox (8 to 10 degrees C.), damp. Figure F, room temperature,
damp. Figure G, room temperature, dessicator. Figure H, icebox, damp.
Figure I, room temperature, damp. Figure J, room temperature, dessicator.
Figure K, room temperature and room humidity. Figure L, icebox, damp.

Figure 16. Weak plant secured from planting seed partially rotted with F. dis-
color sulphureum. March, 1918.

Figure 17. Healthy plant from seed tuber planted at same time as that of plant
shown in Figure 16. Some rot on seed when planted. The rot did not,
however, progress much. March, 1918.

Figure 18. At left, base of plant shown in Figure 16, seed rotted; center, base
of plant shown in Figure 17, seed healthy at insertion of stem. At right,
another plant similar to the one on the left. March, 1918. .

Figure 19. Pea seeds rotted and roots and lower stems of young plants affected
with Fusarium isolated from pea plants. ‘Greenhouse inoculations, Sep-
tember, 1917.

Figure 20. Four tubers at left show slight rot, with F. discolor sulphureum
developed at 1.1 to 1.7 degrees C. Plugs cut out of potatoes in inoculating.
The browned vascular ring in some of these tubers is due to frost necrosis,
which had developed prior to the subjection to cold storage. Previous
experiments demonstrated that this slight necrosis had no influence on the
rate of rotting. At the right, a tuber almost wholly rotted when placed in
cold storage. The rot progressed little at the temperature mentioned. This
tuber was cut before being put in cold storage and shows the development
of some mycelium on the cut surface. Duration of experiment, 31 days,
March 16 to April 16, 1918.

Figure 21. Rot of potatoes from F. discolor sulphureum at 8 to 10 degrees C.,
artificial inoculation, two weeks’ development.

Figure 22. F. discolor sulphureum: center of plate, mycelium produced at 8 to
10 degrees C.; area of less abundant mycelium ‘produced at room tempera-
ture, containing many small sporodochia not shown clearly; circumference,
mycelium produced again at 8 to 10 degrees C.

Figure 23. At the right, tuber rot secured at 25 degrees C. with F. culmorum
from wheat; at left, rot by same fungus at room temperature (about-18 to
20 degrees C.). Time, two weeks.

Figure 24. Rot started by F. lint on potato tuber. Time, two weeks.

Figure 25. F. oxysporum inoculated January 25, 1918, in the center. The
stained area (dark red in natural color) shows the area occupied by a colony
of bacteria obtained originally from a rotted seed piece and as yet unidenti-
fied, over which the fungus grew slowly, as indicated by the lines marking
dates. Opposite this a colony of Bacillus atrosepticus was present, but
exerted no influence on growth or production of color. A colony of Asper-
gillus at the margin opposite the stained area checked the growth of the
Fusarium. View from lower face of Petri dish.

FUSARIUM DISEASES IN MINNESOTA 47

Figure 26. View from above, showing mycelium of F. oxysporum growing
over a colony of B. subtilis: aerial mycelium marks the margin; no pause
in the growth. The radii, etc., on the opposite side are due possibly to
shrinkage of the medium.

Figure 27. F. discolor sulphureum retarded by a colony of bacteria (the same
species of bacteria mentioned for Figure 25, obtained. from a rotted seed
tuber). The fungus eventually grew completely over this colony; the conidia
and mycelium produced thereon appeared normal microscopically. Opposite,
a colony of Bacillus atrosepticus had exerted no influence upon the growth.
This figure illustrates the ample macroconidial production at room tempera-
ture. View from above.

Figure 28. Fusarium from bean plant. The irregular bacterial colony, checking
growth somewhat, is Pseudomonas phaseoh. (The fungus finally grew en-
tirely over this colony, but more slowly.) Opposite roundish colony is
B. subtilis. The growth of the colony was noticeably accelerated when this
colony was reached, just as the growth has been accelerated on the lower
side, where the fungus has pushed out over a colony of B. atrosepticus.
“Growth arresting and accelerating” substances.are evidently produced. The
organisms shown in Figures 25 to 28 grew on potato dextrose agar under a

bell jar at room temperature. Inoculations January 25, 1918, photographs
February 5, 1918.

Figure 29. At right, relation between bacteria from a soft-rotted potato and
(1) F. oxysporum, (2) F. discolor sulphureum, (3) Fusarium from pea, (4)
Fusarium from bean. Bacteria inoculated in center November 9, 1918, fungi
inoculations November 12, photograph November 15. The growth of the
fungi was somewhat retarded, and the bacteria tended to grow between the
fungous colonies. At left, B. atrosepticus in center. Fusaria numbered as at
right, inoculations and photographs same date.

Figure 30. At right, B. subtilis in center, exerting little influence on the Fusaria.
At left, a colony of bacteria isolated from a potato stem has diffused sub-
stances through the medium checking equally the growth of the four Fusaria.
Reciprocally, the bacterial colony ceased to enlarge. JInoculations~in both
plates: bacteria, November 9, 1918. Fusaria, November 14, photograph
November 25.

48

49

50

51

52

53

54

55

56

57

58

LIBRARY OF CONGRESS

OT es

0 015 793 611 6
rR RESALE ARENSE