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UNIVERSITY OF ILLINOIS 

Agricultural Experiment Station 



BULLETIN No. 133 



EAR ROTS OF CORN 



BY THOMAS J. BURRILL AND JAMES T. BARRETT 




URBANA, ILLINOIS, FEBRUARY, 1909 



SUMMARY OF BULLETIN No. 133 

At husking time or before, certain ears of corn (maize) are found in the 
field covered with and penetrated by a whitish, or sometimes a pinkish, mold. 
Affected ears become very light in weight and present all the evidences of dry 
decay. This state of things has long been known and observed thruout the corn 
growing regions of- the United States and probably elsewhere. There does not 
seem to be much variation in the occurrence or amount of infection due to soil, 
date of planting, variety of corn, etc., except that there is more of it in fields 
continuously devoted to this crop. Pages 65-69 

Though not usually accounted serious, the losses are far greater than are 
commonly supposed, and vary in different years and in different fields up to 
ten or even more percent of the entire crop, or up to at least $5,000,000 for one 
year in the State of Illinois. Pages 69-70 

The active agents of the destruction are several species of parasitic fungi, 
among which one does by far the most damage probably 90 percent of the 
whole amount. This is botanically known as Diplodia Zeae (Schw.) Lev. It 
lives over winter on old infected ears and stalks, from which there are sent out 
the following season myriads of spores which are widely distributed by the 
wind. Under favoring conditions (mainly the presence of moisture at the right 
date) these spores start new infections in the green ears.. Of this fungus see: 
Life history on the ears, page 73; Life history on stalks, page 74; Growth 
in cultures, page 76; Effects of acids and alkalis, page 78; Germination of 
spores, page 80 ; Distribution of spores, page 81 ; Inoculation experiments, page 
83; Synonomy, page 94. Pages 70-85 

At least three other species of fungi, all belonging to the genus Fusarium, 
attack, with somewhat similar results, the developing ears of corn in the field. 
Their full life histories in the field have not been worked out, but infection 
originates from wind-borne spores. No ears become diseased except from 
spores reaching them from an outside source ; that is, the ears are never affected 
by means of anything working up through the stalk. Pages 85-91 

Ears in the field are sometimes injured by one or more species of bacteria 
but this kind of loss from these minute organisms seems to be comparatively 
slight. Pages 91-92 

So far at least as the Diplodia fungus is concerned, the disease is certainly 
subject to control. Since the spores come from old infected ears and stalks 
their destruction must reduce at least the loss for the new crop, and a system 
of rotation which excludes corn for two years from or near the given plat of 
ground will assuredly help to prevent infection. Pages 92-94 



64 



EAR ROTS OF CORN 

BY THOMAS J. BURRILL, CHIEF IN BOTANY, AND 
JAMES T. BARRETT, FIRST ASSISTANT IN BOTANY 

GENERAL OBSERVATIONS 

APPEARANCE Every one who has had anything to do with harvesting 
corn has noticed at least an occasional ear that differed 
remarkably from the normal ones in being more or less covered with 
and penetrated by mold. In many cases the husks and silk are also 
involved and appear cemented together and to the ear by a mass of 
white, cobwebby filaments. (PI. I.) . At the same time the parts affected 
have lost their substance, are light in weight and brittle in texture. 
Sometimes such diseased ears are seldom found at the time of husking, 
often they are not uncommon. 

Upon closer study it soon becomes apparent that there are several 
kinds of these ear rots, or at least that there are differences which seem 
fairly constant when numerous specimens are carefully examined. It 
is thus possible to divide the affected ears into several groups, four of 
which are described in this paper. They are discussed Under the names 
of the parasitic fungi to which the effects are attributed, as follows: 
(1), Diplodia; (2), Fusarium I. ; (3), Fusarium II. ; (4), Fusarium 
III. These names are defined further along and each form of rot is 
described later under its own heading. 

Some of these ear rots are so similar that the casual observer 
rarely entertains any suspicion of there being but one form. The 
resemblances are so complete in some instances that the removal of the 
husk and sometimes a microscopical examination are needed for the 
classification of the variety. Commonly, however, in fairly advanced 
stages of the disease one or more characteristic differences are apparent. 
The two forms most likely to be confused, and the only ones which as 
a rule involve the husks, may be distinguished by the color of the mold- 
like growth. In the case of the Diplodia disease this is white, while in 
that of Fusarium II. it is pink to red. 

The first indication that ears of corn are diseased is a fading of 
the bright green of the husks to a pale yellowish green color. In the 
Diplodia disease this change goes on gradually, and under favorable 
conditions quite rapidly, until the entire ear has an appearance of pre- 
mature ripening. While this change of color on the outside is pro- 
gressing one finds that the inner husks have not only lost their normal 
color, but are more or less tinged with brown, particularly along the 
advancing margin of the diseased area. (PI. I.). This condition is 
much more striking in some ears than others. With the advance of the 
disease the outer husks grow darker and darker, frequently becoming 
dirty to sooty black in appearance, when they present a striking con- 
trast to those of normally ripened ears. 

This description also applies to the disease produced by Fusarium 
II., although no entirely decayed ear due to this organism has been 

65 



66 BULLETIN No. 133 [February, 

found. In this case infection always begins at the tip and proceeds 
downward, rarely involving more than half the ear. In both forms 
badly diseased ears are tightly clasped by the dry, brittle husks except 
in cases where infection by Diplodia takes place in the base of the ears 
too late in the season for the entire ear to become diseased. Many of 
the badly diseased ears on account of their lightness in weight remain 
upright. 

The diseased ears shrivel up more or less, become darker in 
color and lighter in weight. The kernels are also shriveled, are very 
brittle, and are loosely attached to the more or less rotten cob. The 
silk is moldy and adheres by the mass of fungous threads to the inner 
husks and corn. Under the microscope the starch is seen to be variously 
corroded and notched, and it is frequently discolored. The germ por- 
tion of the kernels is most frequently killed, or if not is always injured. 
Microscopical examination shows that the fungus penetrates all parts 
of the ear, sometimes extending into and badly injuring the shank. 
No ill effects on other parts of the corn plant have been observed. 

The other Fusarium diseases mentioned produce very different 
effects on the ears and are commonly not detected in the field until the 
husks are removed. Fusarium I. attacks only those husks which come 
into contact with the diseased surface of the ear. The cob is not so 
generally diseased as in the above described forms. A third Fusarium 
species, Fusarium III., attacks the ends of scattered individual grains, 
causing them to crack open and the starchy contents to become crumbly. 
Mycelium and spores are found in this crumbly starch which is con- 
siderably corroded. (PI. III., Fig. I.). 

SEASONAL The premature yellowing of the husks on plants other- 

OCCUREENCE wise healthy is, as previously stated, an indication that 
a diseased condition exists which is usually attributa- 
ble to infection by some one of the field rot organisms. This condition 
in the case of the Diplodia disease may be found in fields soon after 
the fertilization of the corn has taken place, the number of infected 
ears increasing more or less thruout the season. Very little is known 
as to the time of maximum infection by the various species of Fu- 
sarium which cause these diseases. Two of the forms, as previously 
stated, can rarely be detected until the corn is husked and the third has 
not been well studied in the field. 

Infection is certainly in the case of Diplodia and very probably in 
that of the other fungi brought about by means of spores. It is known 
that under favorable conditions Diplodia spores are produced in large 
numbers during the summer and fall in infected fields, and that these 
spores are carried considerable distances by the wind. They are scat- 
tered thruout the fields where they find favorable germinating condi- 
tions, and yet the fungus has not been found on any other plant, nor 
has any other part of growing corn other than the ear and its shank 
been found to be infected. 

The best spore-producing periods seem to follow hot, rainy weather 
preceded by more or less continued dry spells, the reason for which 
will be stated later. 



1909] EAR ROTS OF CORN 67 

Since, then, under favorable conditions the spores are produced 
in such large numbers thruout the season, the matter of little or much 
infection depends in part, at least, on these spore-producing periods 
coming at a time when the corn is in the most susceptible condition for 
infection. Of a large number of inoculations made during the season 
of 1907 the highest percentage of infections was obtained from those 
made on August 31, from a pure culture, when the corn was in the 
thick-milk stage. It is at this period and later, in the development of 
the corn, that the larger percent of infected ears in the field begins to 
show. 

These diseases occur with more or less severity in 
almost every locality in Illinois where corn is grown, 

Ox HJUA.Ll.Lx, . '.. . - ~ . 

SOIL, ETC. an d the same or similar ones have been reported trom 

Nebraska, Arkansas, Iowa, Indiana, Ohio, and North 
Carolina. It \is quite probable that no corn-growing section is without 
at least some of the diseases. Corn grown on the rich, black land of 
our corn belt is more subject, on the whole, to them than that on higher 
and thinner soils, although a few seemingly contrary reports have been 
received. 

A part of the report from Vermilion County is as follows : 
"The field had about 5 acres of what we call low, black land ; this always 
has the best corn and this year we seemed to find the most rotten corn in this 
part of the field. There seems to be less rotten [corn] on high ground where 
plenty of manure had been used. I also noticed in another field containing 
some of the same black soil that the rotten [corn] is thicker than in any other 
part of the field. We do not find it this year in quite the same form as last 
year. You can tell by the looks of the husks if an ear is rotten. Last year 
many rotten ears had just as bright husks as the good ears and you could not 
tell until you had husked an ear whether it was good or bad. This year the 
husks on the rotten ears are black or nearly so." 

The following is from a report from Douglas County: 

"I farmed a 33-acre field belonging to a man who does not sow clover at all 
(this piece being in corn about 13 years). And the amount of rot was large, 
especially on the low ground. I do not know what amount of rot was on the 
field last year. I notice that as a rule the rotten corn appears to be in spots, 
say two or more ears near by, especially in proximity to tiles or drains, our 
tiles and ditches are not working well in this section at present and the low 
ground is wet much of the season when we have a good deal of rain. Of 
course there is some rotten corn on the high ground." 

A report from Wayne County states : 

"Found a larger percent about the old stockyards and heavily manured 
spots." 

The greater the number of old stalks and the greater the supply 
of moisture, the better the opportunity for a continual and rapid propa- 
gation of the most destructive of these fungi, thus subjecting the corn 
grown at such a place to a much greater chance of inoculation. 

EARLY AND There seems to be some difference of opinion as to 

LATE PLANTED the extent of rot on early and late planted corn. This 
CORN difference has been, the past two seasons, in favor of 

the early planted, the majority of the reports stating 
that it showed more rot. Fifty-five percent said that there was more 



68 BULLETIN No. 133 [February, 

rot in the early planted, 33 percent in the late and 12 percent found no 
perceptible difference. In 1906 a very dry summer was broken by 
heavy rains while the early corn was beginning to silk. Everything 
was favorable for the production of Diplodia spores, and as a result 
much corn rotted. Sixty-one percent of all reports for that season 
stated that the early corn was more badly rotted. Such differences 
cannot be attributed to differences in susceptibility of early and late 
corn, only in so far as influenced by weather conditions. Warm, moist 
weather favors the development of the diseases and the production of 
spores, and when these conditions obtain at the most susceptible period 
in the development of the ears everything is favorable for infection. 
Inoculations made late in the season on corn in the right condition 
grew much more slowly than earlier ones, due, no doubt, to CQO! 
weather. 

,T, vn, m From careful data collected by the department and 

UJN UJjU UK .Nx. W , . , . . 

CORN GROUND from reports sent in by corn growers, it is very ap- 
parent that, as a rule, ear rot is more prevalent and 
destructive in fields planted successively to corn than in those on which 
a good system of rotation is practiced. There are, of course, excep- 
tions to this, but they are rare. The old stalks and diseased ears when 
left in the field are known to carry the Diplodia fungus over winter, 
and to offer opportunity for infection the following season. 
A report from Fulton County says: 

"There was about three times as much rot on the fourth crop of corn on 
the same ground as on the first." 

During the fall of 1907 some field counts were made at husking 
time as to the relative amounts of the different forms of rot in fields 
both old and new to corn* on the same farm. The old ground produced 
the most rot in every case. 

Of the reports sent in the past two seasons 65 percent stated that 
more field <rot is found on old corn ground, 16 on the new, and 19 said 
there was no difference. 

Instances are not uncommon where one or more sides of a field 
for a number of rows are much more affected than the interior, indi- 
cating a source of infection without the field. In view of the easy 
transmission of the spores by the wind, this is entirely possible, and 
also accounts for the fact that corn on new ground may become badly 
diseased. 

A report from De Witt County says : 

"The outside of my fields had more rotten corn than the inside, and the east 
sides more rotten than the other sides." 

In May, 1908, a clover field was visited which produced a crop of 
corn in 1906 badly damaged with rot. The field was sown to oats and 
clover in 1907, and in 1908 most of the field planted to corn. Old corn 
stalks were plentiful in the clover field and most of those examined 
were abundantly infected with the Diplodia fungus. The stalks were 
not all covered by earth in the portion of the field planted to corn and 

* "New to corn," meaning not previously in corn for at least two years. 



1909] EAR ROTS OF CORN 69 

these, too, carried numerous spores. The latter were found to be 
capable of germination. 

Even though all stalks in the corn field had been covered, there 
remained abundant opportunity of infection from the clover field. This 
is but one instance of a condition which is not at all uncommon. The 
first requisite of an epidemic of disease is the presence of a sufficient 
number of spores or germs capable of producing it, and their ^absence 
'is a sure prevention. 

A correspondent from Springdale, Arkansas, writing under date 
of October 10, 1908, remarks: 

"Will say that out of 500 ears gathered in a field planted the third straight 
year in corn, 4% were affected by this trouble." 

No definite data have been collected as to the sus- 

. . 

ceptibihty of the various varieties of corn to the rot 
diseases. Of those mentioning the matter in reports forwarded to us 
relative to the 1906 crop, 50 percent said yellow and the other 50 per- 
cent that white was the most susceptible. The reports of 1907 showed 
that some form of rot occurred with six different varieties, but few 
statements as to comparative amounts were made. One who breeds 
and raises corn for seed reported that the rot was much worse on 
certain rows growing directly beside others where each row came from 
a separate seed ear. 

AMOUNT OF INJURY 

Upon careful observation and inquiry it has been ascertained that 
the loss is much greater than is ordinarily supposed and sometimes 
amounts to surprising percentages. In the autumn of 1906 fields were 
examined by the writers in which as high as 10 percent of the ears 
were so attacked, and reports of actual counts were received in which 
as much as 20 percent of rotten ears were recorded. Reports of from 
10 percent to 15 percent were not very unusual. 

Upon the best estimates that could be made with the aid of hun- 
dreds of correspondents in all parts of the state, the conclusion has 
been reached that in 1906 the destruction from the cause in question 
amounted to 4.5 percent of the entire crop, and in 1907 to about 2 per- 
cent of the produce of the state for that year. When the enormous 
total of the corn crop of Illinois is considered, the losses reach magni- 
tudes which necessarily arrest attention and imperatively call for in- 
vestigation. 

The State Department of Agriculture reports the corn crops of 
Illinois in recent years as follows: 

1903 264,087,431 bushels, worth $ 95,071,475. 

1904 344,133,680 " " 134,212,135. 

1905 382,752,063 " " 145,445,784. 

1906 347,169,585 " " 124,981,051. 

Of the crop for 1906 there were, therefore, lost about 15,622,631 
bushels, worth $5,620,147. There was much less of the rot in 1907, 
but the loss figured in a similar way from the best data at hand was 
not less than $2,000,000. These figures at least indicate enormous 



70 BULLETIN No. 133 [February, 

financial damage year by year which has not heretofore been duly 
appreciated on the part of the farmers or of others interested. While 
the rots have long been casually known and the variations in propor- 
tions of affected ears have often been remarked, there is good reason to 
suppose that there has been really considerable increase during later 
years. From the information now gained, further increase is very 
probable upon land persistently devoted to this crop. The amount for 
1906 was undoubtedly far beyond an average ; but this may easily be 
much surpassed some year not now distant, while the general average 
loss, unless wisely prevented, is pretty sure to increase more or less 
constantly. 

If all this is true for Illinois, the figures for the whole country 
must reach enormous proportions. While it is probable that there is 
more absolute loss in Illinois than in any other state, this seems but 
due to the fact that there is more corn produced and that the best land 
is more often continuously planted to corn year after year. Certain 
it is that similar losses are common thruout the area extending from 
Michigan to Arkansas and from Nebraska to North Carolina, as our 
own observations and correspondence prove. While so often consid- 
ered negligible locally, the total loss in the United States must some- 
times amount to at least $25,000,000 in one year. 

CAUSES OF EAR ROTS 

Most people still suppose that molds are the direct results of the 
prevailing conditions.* Dampness and confined space are most fre- 
quently thought of as the causes of moldiness. When a piece of bread 
is shut up in a tin box or when placed in a damp cellar, it soon be- 
comes covered with a cobwebby growth soon taking on a characteristic 
color, as bluish or blackish, and having a musty odor. These molds 
are plants; 1 there are many kinds of them. They reproduce themselves 
and grow when once started after the fashion of the higher, better 
known plants. Instead of seeds they produce spores which differ from 
seeds in being much more simple in structure and in being too small 
to be seen singly by the unaided eye. Sometimes, however, they are 
easily so seen in masses as a cloud of dust arising from a disturbed 
surface. In fact it is mainly the spores which give to any given mold- 
crop its characteristic color. They are produced in enormous numbers, 
absolutely innumerable even from a small area of an infected sub- 
stance; and it is to this abundance of "fruit" and the microscopic size 
of the individual spores, permitting easy and wide carriage by the air, 
that the plants everywhere spring into existence when conditions favor 
germination and growth. Unlike the higher, green-leaved plants, they 
do not require light for development. They grow only on organic 
matter, on food already prepared in this respect like animals. But 



A correspondent says: "I have never considered the loss of corn by the rotten _ ears 
found at husking time due to any other cause than water entering the husk and remaining 
during a warm day or two which seemed to steam the ear and cause it to shrivel and then 
decay more or less, as the case nrght be." Another says: "Mold depends on weather con- 
dit : ons more than anything else." Another, "The prevailing opinion among farmers is that 
dry weather is the cause of dry rot." 



1909] EAR ROTS OF CORN 71 

they are really plants, each producing "seed" after its kind from which, 
and only from which, it continues its existence. Their generations are 
shorter but they have the same round of germination, growth, fruit- 
age and death as do other living beings. Origination, except in this 
method, does not occur. No matter how moist the air or how devoid 
of ventilation the space or how favorable the temperature, a piece of 
bread never can become moldy, indeed can never decay at all, without 
a seeding with spores or their substitutes. And no special kind of mold, 
or other fungous growth can develop, without, to start with, the spores 
of this particular kind or species. 

Molds belong to the great group of plants called fungi a group 
including besides molds and mildews, all such diverse kinds of plants 
as the shelf-fungi on deadwood, puff-balls, mushrooms, toadstools, and 
a host of microscopic forms among which are the rusts and smuts 
upon cereals. The greater number of the thousand and more kinds 
of fungi grow only on dead organic matter. Their function is to induce 
decay, decomposition, putrefaction, etc. These are called saprophytes. 
But some are capable of attacking the living bodies of plants or ani- 
mals. These are called parasites. Again, some of the latter may live, 
either as saprophytes or parasites, while others are strictly limited to 
living bodies and often to a particular species, called the host, for each 
parasite. Thus the large, sooty masses seen on corn stalks or ears is 
made up of the spores of a special parasite which attacks nothing else 
than the maize plant, and develops only on this plant during its life- 
time. The vegetative portion of the fungus answering in some sense 
to the roots, stems, and branches of the higher plants is called the 
mycelium. In molds this constitutes a cobwebby, puffy substance 
which is more often white. The spores (fruit bodies) are borne on 
the mycelium or upon specially modified structures arising from it. 
The latter are of wonderfully varied form and structure, while the 
mycelium itself is characteristically made up of fine filaments or 
threads with comparatively little difference in form for different spe- 
cies. Under the microscope the spores of each kind are usually recog- 
nizable and often are very distinct. 

Now the ear rots of maize are due to definite species of mold-like 
parasites. So far as is known, these grow on nothing but the corn 
plant, though some of them may have wider possibilities. The greatest 
amount of destruction is made by one kind called Diplodia Zeae. There 
are numerous species of Diplodia known on various hosts or sub- 
stances, but this one seems to grow only upon maize. It was first found 
producing its characteristic spores on dead stalks and was then con- 
sidered a purely saprophytic plant. When in recent years the mold on 
many living ears was traced to Diplodia the suspicion was strong that 
it was a distinct species, but our investigations have clearly shown that 
the growth on the green ear and that upon the dead stalks is one and 
the same thing. This fungus is, therefore, a parasite during a part of 
its life and a saprophyte at other times. 

It is evident now how the fungus lives over from year to year, 
and how the growing ears gain infection. As will be fully shown 



72 BULLETIN No. 133 [February, 

later, the spores are produced in abundance during the summer upon 
old stalks, even from those lying on the ground the second year, and 
these spores are readily carried by the wind as dust. Lodging upon 
the developing ear they germinate when the conditions are favorable. 
For this moisture is a necessity ; temperature has something to do with 
it. Given the same distribution of viable spores there will still be much 
seasonal difference in the amount of rot, due to the differences in influ- 
encing conditions, without at all supposing that the conditions originate 
the trouble. The rot could not, does not, occur without the infecting 
spores, no matter what the weather may be, what the soil may be, or 
what state soever the corn plant may be in. Conditions simply favor 
or do not favor the spore growth. With spores capable of germination 
on the green ears, rot is likely to follow moist weather because this 
permits the growth of the fungus. Then the state of the corn plant 
has something to do with it. Undoubtedly a difference exists at differ- 
ent times concerning its power of resistance. It is more susceptible 
to infection at one period than at another, other things being equal. 
The maximum of rot will occur when numerous spores of the fungus 
are deposited on the ears at a time when these are easiest infected and 
when the weather conditions most favor the fungus in its growth. 
Much difference may therefore be anticipated in the amount of rot 
from year to year, due to the coincidence or otherwise of the favoring 
conditions. 

The principal other fungi which have been found as agents of ear 
rots of corn are species of the genus Fusarium. Three of these have 
been distinguished, to be described later. To the casual observer their 
effects on corn are identical with the result produced by Diplodia, but 
on closer comparison differences are discoverable. All show mold-like 
growth. All cause decay of the part of the ear infected silk, kernels, 
cob, husks and sometimes shank causing these parts at length to be- 
come dry, brittle, and light in weight. 

In addition to these fungi certain bacteria sometimes cause a rot 
of the developing ears, producing final results somewhat similar to 
those described. This form does not seem to be very common and has 
not been much studied. Possibly more than one species thus infest 
corn ears. Further investigation must be made before much may be 
known concerning the part played by bacteria in these field rots of 
maize. 

In a word, then, the rots observed upon the ears of corn in the 
field are due to certain parasitic plants, mold-like in appearance, be- 
longing to the genera Diplodia and Fusarium, and to one or more spe- 
cies of bacteria. The amount of destruction at any particular time 
depends upon the varying prevalence of the spores of these parasites 
in association with conditions existing at the given period. It is worthy 
of remark that in no case has natural infection by these parasites been 
discovered upon any other part of the immature corn plant save the 
ears and their belongings. Upon the latter infection always begins 
externally from air-distributed spores. 



1909] EAR ROTS OF CORN 73 

DIPLODIA ZEAE (SCHW.) LEV. 



LIFE HISTORY mycelium of the Diplodia organism, as it occurs 

ON EARS m the active growing condition on the ear and inner 

husks, is white in color and the much branched threads 
are about 4/u,* in diameter. With age and more or less drying up of the 
diseased tissue the size of the newly formed threads become smaller, 
averaging about 2. 5fi. With the exception of a slight darkening in 
color of portions more exposed to the air and the deep coloring of that 
which surrounds and goes to form pycnidia (fruit vessels), the .color of 
the mycelium remains white. 

The slender threads penetrate the young tissue of the grains, cob, 
and husks, progressing from cell to cell and extracting from their con- 
tents whatever is of value for food. After the ear has become entirely 
involved or the growth of the parasite somewhat checked by the ma- 
turing of the corn, the fungus begins to form its reproductive stage. 
This consists of small black bodies which develop in the husks, cobs, 
and more rarely in the grains, and which contain large numbers of 
purplish brown, rather slender, two-celled spores, 25x5.2/x in size. 
(PI. VIII., Fig. 1.). If 4he outer husks of an ear in a well advanced 
stage of the disease are pulled down, the spore cases, or pycnidia, will 
be seen as minute black specks slightly elevated above the surface. 
(PI. IV., Fig. 2.). An examination with a hand lens will reveal emerg- 
ing from the ruptured tissue a short neck which contains a centrally 
located circular pore through which the spores escape. The pycnidia 
usually occur singly on the husks, but several grouped together in a 
mass is not an infrequent thing where conditions have been favorable 
for a luxuriant development of the fungus, as under bell jar conditions. 

The pycnidia which develop in the cob are much more irregular 
in shape. They develop principally on the scales which surround the 
inner ends of the corn kernels, hence are usually not detected until the 
ear is broken, when they are seen forming a concentric ring of black 
specks about the margin of the cob. (PI. VII. , Fig. 1.). They are 
usually not at all or only slightly imbedded in the tissue of the cob, but 
are seated in a rather dense mass of white mycelium from which they 
originate. A longitudinal section of an ear also reveals them very dis- 
tinctly. (PI. III., Fig. 2.). 

Diseased ears left in the field under natural conditions eventually 
develop numerous pycnidia in the grains, giving them a black appear- 
ance. In May, 1907, rotten corn of the 1906 crop was scattered over 
a small plot of ground in an infection experiment. The following 
March some of this corn was collected and was found as described 
above. Many of the pycnidia contained spores, some of which were 
germinated in the laboratory; 'but most of them were old and empty 
and at that time all development of the organism had apparently ceased. 

The pycnidia formed in the cob, as previously stated, are quite 
irregular in shape ; but those found in the badly diseased grains are 
somewhat flask-shaped with the comparatively short neck projecting 

* A M is .001 of a millimeter or .0004 inch. 



74 BULLETIN No. 133 [February, 

thru the testa. (PI. X., Fig. 2.). It will be noticed from the figure 
that the wall of the pycnidium is formed by the interweaving and fusing 
of the hyphae, or mycelial threads, which form a tangled mass between 
the seed coats and starchy portion of the grain. The wall of the tubular 
neck is much thicker than that of the body of the pycnidium and is 
mostly made up of thick-walled cells, with others having thinner walls 
lying toward the outside. Arising from the inner surface of the 
pycnidial wall are numerous simple conidiophores, or spore stalks, on 
which are borne the two-celled, brown spores. Among these are 
numerous paraphyses, or stalk-like forms without spores. (PI. X., 
Figs. 1 and 2.). 

The development of the Diplodia fungus is not confined alone to 
warm summer weather, as is evidenced by an examination of diseased 
ears in the field during the winter and early spring. January 29, 1908, 
a stalk of sweet corn with an ear attached enclosed in the husk which 
had been inoculated with Diplodia spores on August 10, 1907, was 
brought into the laboratory from the field where it had been all winter, 
and at the time was partially covered with snow and ice. On remov- 
ing the husks a mass of white mycelium in an active condition was 
revealed. Pycnidia were present in various stages of development and 
the spores germinated readily. On March 6, 1908, some diseased ears 
of field corn in husks on stalks left in the field in the fall of 1907, were 
examined and were found to be in much the same condition as was 
the ear of sweet corn just described. 



ON STALKS indication of the Diplodia fungus on the 

dead stalks is the appearance of very small dark col- 
ored specks under the rind. In outdoor conditions these may appear 
during late fall and winter but usually develop during the spring and 
summer. An examination of stalks in the field on March 6, 1908, 
revealed very few that showed any developing pycnidia, but in the 
same field and plat on May 14, 1908, many stalks showed numerous 
developing spore cases just beneath the rind, few having broken 
thru. (PI. VI., Fig. 1.). The stalks had been dragged and broken 
off near the ground and most of the fertile portions were at or near 
the breaks. The pycnidia are produced all over the old stalks but are 
usually more abundant about the nodes. This condition is more fre- 
quently found in two or more year old stalks. There is also a tendency 
for them to occur in vertical rows. During the summer the necks of 
the pycnidia begin to break through the rind of the stalks and in favor- 
able weather conditions send out large numbers of spores. Pieces of 
diseased stalks one or two years old have been found in July, August, 
and September almost covered with black tendrils of Diplodia spores 
capable of quick germination. Apparently the spores are slightly coated 
with a gelatinous substance, as in a protected place they adhere to- 
gether in tendrils for some time, but immediately separate on the addi- 
tion of water. (PI. VI., Figs. 2 and 3.). Pieces of stalks almost three 
years old have been found bearing pycnidia and some few of the spores 
found in them were capable of germination. These were .pretty badly 
decayed, however, and the fungus was not in a very active condition. 



1909] EAR ROTS OF CORN 75 

This fungus has not been found growing naturally on the green 
stalks, although, as will be further mentioned, a slight growth was 
produced by artificial inoculation. The green shanks, on the other 
hand, are frequently found badly infected when bearing diseased ears. 

Old stalks may become infected, thru diseased ears and shanks 
left on them in the field, after they are matured and dead. As in the 
ears, there seems to be some growth of the fungus in the stalks in 
rather severe weather conditions. Many stalks are no doubt infected 
in the late fall, the fungus slowly spreading thru them and with the 
advent of spring weather developing its numerous pycnidia and spores. 
Just how long the spores may retain their vitality in the pycnidia after 
being formed is not known, but that they will germinate after remain- 
ing thus for six months is shown by .the following experiment. During 
August, 1907, some infected pieces of old cornstalks were brought into 
the laboratory and kept in a very dry place during the winter. These 
were examined from time to time and there was no appearance of any 
young pycnidia. Most of the old ones were filled with spores. On 
February 25, 1908, some pieces of these stalks were soaked over night 
in water and then placed in a moist chamber. After a few days long 
tendrils of Diplodia spores covered the surfaces of the stalks. (PI. VI., 
Figs. 1, 2, and 3.). The figures show one soaked and one ttnsoaked 
piece from the same stalk. A large percent of these spores were capa- 
ble of germination. After remaining a few days longer in the moist 
chamber these pieces of stalks were washed with a small brush, remov- 
ing all spores, and again allowed to soak in water for a few hours. 
They were then returned to the moist chamber with a new piece of the 
same stalk soaked for the first time. The latter piece was in a few 
days covered with the spore tendrils, but all others even after weeks 
showed no sign of exuding spores from old marked pycnidia. A few 
new ones finally developed which produced spores. Sections made of 
the old pycnidia revealed only a few, mostly collapsed spores which 
evidently failed to get out with the others. This experiment together 
with other observations leads to the supposition and strong probability 
that pycnidia soon reach a mature stage after which no more spores 
are produced. This explains the occurrence of so many tendrils of 
spores on old stalks after rains following dry weather. During the 
dry period the pycnidia come to maturity and are filled with spores. 
As has been seen, moisture causes the expulsion of the spores and their 
abundant appearance after rains. If the season is rather moist thru- 
out, the issue of spores is more evenly distributed, and danger is then 
less than when large production occurs when the corn is most sus- 
ceptible. 

Pycnidia produced on corn stalks are fairly regular in size and 
structure and usually occur singly. Sometimes partitions separate the 
interior into two or more chambers which emit their spores through a 
common opening. Occasionally one may find several pycnidia congre- 
gated together without the presence of a stroma, but this is rare on the 
stalks. Many are vertically compressed and most of them have a 
thicker wall than those found on the corn grains and in cultures. (PI. 



76 BULLETIN No. 133 [February, 

X., Fig. 1.). It will be noted from the figure that the wall of a Pyc- 
nidium is made up of two fairly well marked layers of tissue, an outer, 
composed of rather thick walled threads taking on the nature of cells 
by the short joints, and an inner one made of thinner walled cells 
which form a hymenium or fruiting layer. 

Arising from this layer are seen numerous sphorophores and para- 
physes. The spores become two-celled before leaving the pycnidium. 
Howard* states that in the case of Diplodia cacaoicola, the spores at 
the time of leaving the pycnidium are greyish and unicellular but that 
they soon become dark brown, the septum appearing at the same time. 

The mycelium in the stalks is mostly hyalin, becoming somewhat 
dark about the pycnidia. The beginning of a pycnidium can be seen in 
section just under the rind as a rather closely matted and much 
branched mass of brownish colored threads which finally becomes 
almost black in appearance. The threads of the mycelium penetrate 
the cells of the pith and partially fill them and make their way in the 
woody portions from one element to another by means of the pores. 
(PI. X., Fig. 1.). In some cases one can trace the disease in the pith 
by a slight darkening of that tissue, but this is not an infallible sign of 
its presence. 

The protoplasm of the mycelial threads in the active, growing 
condition is slightly granular and sometimes very much vacuolated, but 
in the older and more matured condition the threads are more or less 
filled with oil globules. 

GROWTH IN A l ar g e number of cultures were made on various 

CULTURE natural and artificial media with the hope of inducing 

the fungus to develop a perithecial stage, but all at- 
tempts to find such, either in culture or in nature, have been without 
success. Perhaps this stage has been entirely lost from the life history 
of the fungus or it may be that the conditions necessary for its forma- 
tion were not found. Although many cultures were made directly 
from diseased tissue, all comparative cultures were descendants from 
a single spore. 

The fungus grows very well on many fruit, vegetable, and arti- 
ficial media, the amount of mycelium and number of pycnidia varying 
considerably. Both solid and liquid cultures were modified in various 
ways as to their reaction and the nature of the carbohydrate present, 
with some striking results. 

The media used most extensively for propagating spores for 
inoculation work and for maintaining a stock of pure cultures was 
boiled rice in tubes in the proportion of 2 grams of rice to 8 cc of dis- 
tilled water. This induced a rapid growth and an abundant formation 
of pycnidia and spores. 

A series of 20 tubes containing boiled vegetables, grains, and nuts 
were inoculated and the resulting growths compared. A number of 
them proved excellent for the development of mycelium but few were 
suited for production of spores. Notes are given as follows : 

* Howard, Albert. On the Diplodia cacaoicola, P. Henri. A parasitic Fungus on sugar 
cane and cacao in the West Indies. Annals of Botany 15:686, 1901. 



1909] EAR ROTS OF CORN 77 

Boiled turnip. A rather dense, white growth, becoming grayish with age 
and covering and surrounding most of the slant. No pycnidia developed. 

Boiled carrot. Good, rather flocculent growth surrounded the slant. Pyc- 
nidia rather sparse. 

Boiled salsify. A very fair growth developed after two weeks or more, 
but no pycnidia were produced. 

Boiled parsnip. Excellent growth of white, rather cottony mycelium sur- 
rounded the slant. A sHght tinge of brown appeared. A good many pycnidia 
were developed. 

Boiled potato, Fair, rather compact growth all about the slant ; cream to 
light brown with age. No pycnidia formed. 

Boiled beet. Growth pretty fair ; but mycelium and liquid at the bottom of 
the tube very brown. No pycnidia found. 

Boiled apple. Growth pure white and very s'ow, becoming fair in six 
weeks. 

Boiled macaroni. Growth pretty good ; white tinged with gray to light 
brown in patches. A good many small pycnidia formed. 

Boiled cabbage. Growth poor. No pycnidia. 

Boiled orange. Growth good ; white, becoming somewhat gray with age. 
A very few small pycnidia developed. 

Boiled onion. Growth good; mostly white. Pycnidia rather abundant. 

Boiled Brazil nuts. Growth fair ; mycelium tinged light brown. No pyc- 
nidia. 

Boiled cccoanut. Rather good growth, turning to dirty cream, almost light 
brown at the lower portion. No pycnidia developed. 

Boiled peanuts. Fair growth developed; white above, becoming light 
brown with age. No pycnidia. 

Boiled green bean stems. Growth fair. No pycnidia. 

Boiled germinated corn. Growth good, filling spaces between the grains. 
Very few pycnidia. 

Boiled soaked corn. Growth good ; white becoming slightly darkened with 
age. Pycnidia rather numerous. 

Boiled corn. Growth much like that of the boiled soaked corn with more 
pycnidia present. 

Cccoanut milk agar. Good growth. A good many pycnidia developed. 

Litmus lactose agar (acid). Growth fair, agar changed to blue at top, be- 
coming brownish later. Pycnidia absent. 

Five cultures were made in liquid media with Diplodia spores from a pure 
culture. 

Uschinsky's fluid*. In one week a thin flocculent growth was present 
thruout the liquid and a week later most of the growth was within 1 cm of 
the surface which was covered by a thin growth. A sparse growth of mycelium 
had extended 8 to 10 mm up the sides of the tube. The growth finally became 
slightly more dense, showed a tinge of brown at one place, and produced a few 
pycnidia at the surface on the sides of the tube. 

Raulin's fluidt. In one week a thin white growth covered the surface of 
the liquid and extended 6 mm up the sides of the tube. A slight submerged 
growth was present near the surface. One week later a dense growth covered 
the surface and the submerged portion for 3 or 4 mm deep had a beau- 
tiful green color. The aerial portion on the sides of the tube showed alternate 
zones of light cream, pink, and brown. Later the growth and the intensity of the 
colors increased. The bright green finally became a dirty green and then almost 
black. A few pycnidia were produced. 



78 BULLETIN No- 133 [February, 

Beef bouillon. In a week's time a slight growth had developed thruout 
the liquid and a rather dense layer of white mycelium covered the surface. In 
two weeks the growth had become more dense on the surface, extending up 
the sides of the tube 6 to 8 mm and thruout the liquid as a light flocculent 
cloud. The growth remained white and but 2 pycnidia were found. 

In a solution containing 2 percent of Witte's peptone, 1 percent dextrose, 1 
percent maltose, and 1 percent mannite, a very dense growth had covered the 
surface of the liquid and a flocculent mass developed all thru it in one week. 
Growth increased rather rapidly, becoming more dense on the surface and ex- 
tending well up on the sides of the tube ; color white, finally becoming tinged 
with brown in a few places. The liquid below the growth became deep orange 
in color. Only a few pycnidia were produced. 

Distilled water with 2 percent of Witte's peptone and 1 percent glycerin : 
In one week the surface was only partially covered with mycelium and but 
little could be seen thruout the liquid. One week later growth was good, a 
dense white mass covering the surface but not extending far up on the sides of 
the tube. Slight growth in the liquid. Very few pycnidia were formed. 

Three series of cultures were made relative to the 

EFFECTS OF ACID n- j- -1 j 11 1- ,1 xi i r 

4-Km ATTrarrw effects of acid and alkali on the growth and fruiting 

AJNJJ A.LK.A.H.N -,, , r i i i 

MEDIA of the fungus. A number of both organic and inor- 

ganic acids were used in the two acid series and one 
alkali, sodium carbonate, in the alkalin series. The medium used in 
all tube cultures was boiled rice, and in plate cultures it was extract of 
corn meal with agar. 

The injurious effect of the alkali was very apparent in cultures 
containing very small amounts as three parts of a normal solution to 
one thousand of media gave no growth, while slightly less amounts 
produced a very weak mycelium and few pycnidia. It should be said 
that boiling rice in the presence of alkali reduces the alkali proportion- 
ally to the amount present, and it was found necessary to prepare an 
extra series of tubes for titration after sterilization in order to be sure 
of the reaction of the media when inoculated. 

As a result of the cultures in acid media it was found that of the 
organic acids used the most injurious were formic and butyric, mem- 
bers of the acetic series, while the best growth and greatest develop- 
ment of pycnidia took place in the presence of oxalic, malic, citric, 
and tartaric, members of the hydroxy acid group. At the strength of 
twenty-five parts normal acid to one thousand of media no growth took 
place in the presence of formic and butyric acids, while in the presence 
of acetic, a member of the same group, there was a pretty fair growth 
of mycelium tho very few pycnidia. This applies also to the growth 
in tartaric and lactic acid cultures. Of the inorganic acids used, hydro- 
chloric, nitric, and sulfuric, the first two were most favofable for 
good development of mycelium, while nitric alone seemed to be favor- 
able for the formation of many pycnidia, there being very few to de- 
velop in either of the other two cultures. Variation of color appeared 
in some of the tubes. In the malic acid culture patches of cream, yel- 
low and orange to brown were present. Similar colors, but less marked, 
appeared in the acetic and citric acid tubes, while that in all others 
was principally white tinged with cream to gray. 

A series of cultures was made in poured plates for determining the 
effects of the acids, alkalis, carbohydrates, and a few other substances 



1909] EAR ROTS OF CORN 79 

on the production of pycnidia. The media to which almost all the 
above were added was extract of corn meal with agar. All acid cul- 
tures were made a strength of -\-2Q, Fuller's scale, and those contain- 
ing alkali 15, same scale.* All carbohydrates except starch were 
used 5 percent strength. 

In two weeks the following condition existed in the plates : 

Formic, acetic, butyric, and oxalic cultures had developed no 
growth, while the colonies in those containing malic, tartaric, citric, 
and lactic acids covered the surface of the plate and extended well up 
the sides with zonation clearly shown. The growth in standard agar 
and standard gelatin was rather dense and covered most of the plate. 
No zonation was present. In the cultures containing glucose, galactose, 
maltose, and cane sugar the growth was rather dense, especially at the 
margin and on the sides of the plate which was entirely covered. In 
litmus-lactose agar, Uschinsky's solution hardened with 2 percent 
starch, and Fermi's solution 1 ' agar the growth was rather poor, particu- 
larly in the last named medium where only a small, thin colony devel- 
oped. The growth in the plates containing sodium and potassium 
hydroxids was very thin, irregular, and almost entirely submerged. 

In one week there was in a few cultures those containing glucose, 
galactose, and maltose an indication of forming pycnidia. They rap- 
idly increased in another week and at the end of the third week about 
all had formed that did appear. None developed in standard agar, 
standard gelatin, Fermi's solution agar, potassium hydroxid, and 
litmus-lactose agar; very few in malic and tartaric acid cultures, and 
only about 50 and 75 in those containing citric and lactic acids. Three 
developed in the sodium hydroxid culture and about 40 in Uschinsky's 
solution plus starch. In the check plate which contained extract of 
corn meal with agar the number of pycnidia was fairly large. The 
cultures producing by far the most pycnidia were those containing the 
sugars in the order of maltose, galactose, cane sugar, and glucose. 
Over 200 were counted in one square inch of surface. Plate IX., Fig. 
1 is a photograph of the galactose culture. 

It will be noticed that most of the pycnidia develop near the mar- 
gin of the plate. If only a very few formed they were almost invariably 
on the sides of the plate or at the very margin. 

By means of the microscope the beginning of the pycnidia can be 
seen in plate cultures as a small clump of irregularly branched and 
darkened hyphae which grow in size quite rapidly with an increase in 
color. Many of them are entirely submerged, form little or no neck, 
and discharge their spores into the medium thru a more or less 
broad opening in the wall. It is not unusual, however, to find per- 
fectly formed pycnidia in such cultures but as a rule the necks are 
shorter than those on the corn stalks. Here, as on the corn husks and 
occasionally on the stalks, may be found pycnidia with the internal 

* That is, plus or minus so many cc of normal sodium hydrate to bring one litre of 
medium to the phenolphthalein neutral point. 

t Fermi's culture fluid is made as follows: Distilled water, 1,000 cc; magnesium sulfate, 
.2 gram; acid potassium phosphate, 1 gram; ammonium phosphate, 10 grams; glycerin, 45 
grams. 



80 BULLETIN No. 133 [February, 

cavity divided by partitions forming somewhat irregular compartments 
communicating with each other toward the orifice. Sometimes more 
than one orifice is present. 

A number of spores from seven of the above cultures were meas- 
ured and the averages taken. The greatest variation was in the length, 
the width being almost constant. The largest were in the check plate, 
the extract of corn meal with agar, and measured 28.5 X5/x and the 
smallest were produced in the same media plus lactic acid and meas- 
ured 22.1X5.2/*. 

Mature spores germinate in from 5 to 8 hours by 

GERMINATION , 11- i r i ,1 r j.t, 

OF SPORES sending out a hyalin hypha from one or both of the 

cells which soon forms septa and branches. (PL XL, 
Fig. 3 and PI. VII., Fig. 2). The protoplasm of the germ tubes is at 
first finely granular, but as they begin to grow more rapidly it becomes 
vacuolated. 

Almost all germinations were made in Van Tieghem cells three- 
fourths Inch in diameter, using various liquid media and spores from 
different sources depending upon the nature of the test. Within three 
or four days a tangled skein of mycelium forms and fusion of hyphae 
is not uncommon. There may be seen here and there small dark 
specks, the beginning of pycnidia. Cell cultures offer a good means 
of studying the first processes in such formations which usually start 
with hyphae in direct contact with the cover glass. These first send 
out short, thickened branches which become gradually darkened and 
usually contain a small, circular, light spot. (PL XL, Fig. 4). They 
increase in number and complexity until a sort of cellular tissue results 
as has already been described. 

In Uschinsky's fluid no germination had taken place in 5 hours ; 
two-fifths of the spores had germinated in 9 hours, and nine-tenths in 
70 hours, at which time the hyphae were considerably branched. 

In Raulin's fluid about 8 percent were germinating in 70 hours. 
The germ tubes were short and unbranched. 

One-third of the spores had germinated in beef bouillon within 9 
hours, three-fourths in 22 hours, and practically all in 70 hours. 
Pycnidia had begun to form in several places. 

In a solution containing 2 percent of Witte's peptone, 1 percent 
dextrose, 1 percent maltose, and 1 percent mannite, germination began 
in 5 hours; in 9 hours about half, and in 70 hours nearly all had ger- 
minated. Pycnidial formations had begun. 

In a solution containing 2 percent of Witte's peptone, and 1 per- 
cent of glycerin only a few spores had germinated in 9 hours. In 22 
hours about one-third had germinated. 

No germination took place in distilled water. 

The following tests were made January 1, 1908, to determine the 
viability -of spores of different ages. Seven cultures were made in 
corn meal extract with spores from the following sources : 

No. 1. Boiled rice tube culture 19 days old. 
No. 2. Boiled rice tube culture 51 days old. 



1909] 



EAR ROTS OF CORN 



81 



No. 3. Surface of pieces of husk which had been in a test tube almost 5 
months. 

No. 4. A diseased ear of corn of the 1907 crop, which had been in the 
laboratory about 3 weeks. 

No. 5. An old corn stalk brought into the laboratory November 15, 1907. 

No. 6. A specimen of corn sent to the laboratory in March, 1907. 

No. 7. Corn specimens collected January 1, 1907. 

The results are shown by the figures tabulated below : 



Date 


No. 


Medium 


Started 


Percent germinated in 




v 






5 hrs 


22 hrs. 


30 hrs. 


46 hrs. 


64 hrs. 




cornmeal 














Jan. 27 


1 


extract 


11:30 a. m. 


60 


90 


95 


95 


95- 




2 


10 


90 


90 


95 


95 




3 







1 


. 1 


1 


1 




4 




8 


33 


40 


40 


45 




5 







40 


43 


45 


45 




6 





















7 






















January 29, 1908, Diplodia spores were taken from an old piece of 
corn stalk which had been lying outside the building and exposed to 
the weather since August, 1908, and sown in corn meal extract in a 
Van Tieghem cell. In 48 hours 10 to 12 percent, and in 96 hours 15 
percent had germinated. 

On February 3, four cell cultures were made with Diplodia spores 
from pieces of old diseased corn stalks which had been in the labora- 
tory since August, 1907, and which 5 days previous had been soaked 
24 hours in water and then placed in a moist chamber where they pro- 
duced numerous tendrils of spores some of which were used in the 
test. The medium used was corn meal extract and the temperature 
was 26 C. to 28 C. 

In 5 hours No. 1 showed a germination of 80 percent; No. 2, 85 
percent ; No. 3, 92 percent ; and No. 4, 90 percent. In 23 hours No. 1 
had germinated 95 percent ; No. 2 about 95 percent ; and No. 4, 92 per- 
cent, j ' 
The field in which this experiment was carried on is 
situated on a rather high knoll on the University south 
farm. In 1906 it produced a crop of corn, 60 bushels 
per acre, 10 percent of which was destroyed by rot. 
The stalks were not cut nor were they pastured. In July, 1907, the 
south half of the field was sowed to cow peas, the north half having 
been seeded to clover earlier in the season. Numerous pieces of old 
corn stalks, some at least two years old, were scattered about on the 
surface of the ground and, being more or less protected by the grow- 
ing cow peas, were producing in many cases an abundance of Diplodia 
spores. Early in September the cow peas were cut and oats were 
sowed as a cover crop to the young apple trees to which the field was 
planted. 

On September 17, three stakes were set up in the field, one on the 
north edge of the recently plowed south half, and the other two toward 



DISTRIBUTION 
OF SPOKES 
BY WIND 



82 BULLETIN No. 133 [February, 

the north edge of the clover field. The entire field was about 25 rods 
wide. To each of these stakes, 5^2 feet long and driven 8 to 10 inches 
into the ground, were fastened 2 glass plates 6 l /2 x 8j/2 inches, one at 
the fop, the other 2 feet below. The plates which faced northeast and 
southwest were smeared on both sides with glycerin and alcohol. The 
surface of the ground was rather dry and a brisk wind was blowing 
from the southwest. After 48 hours the glass plates were removed 
and new ones similarly treated put in their places. The glycerin and 
contents was washed from the sides of each plate into separate watch 
glasses with 95 percent alcohol, and after considerable evaporation the 
spores were counted. It is quite probable that many of the spores were 
not washed from the plate by this method and that the results shown 
below, although strongly convincing, represent only part of the true 
condition. 

Stake No. 1. On plowed ground. Upper plate, 65 Diplodia spores. 

Lower plate, 400 (approximately) spores. 
Stake No. 2. About the middle of Upper plate, 50 spores. 

clover field. Lower plate, 75 spores. 

Stake No. 3. North side of clover Upper plate, 40 spores. 

field. Lower plate, about 40 spores. 

The second set of plates placed on the stakes were not considered 
further, but on October 1, 1907, 4 microscopic object slides, 3 inches 
long by 1 inch wide, were placed on two of the above mentioned stakes, 
two on each, and the south surface of each smeared with glycerin and 
alcohol. These could be examined under the microscope directly and 
more accurate results could be obtained. 

After 3 days, during which time a hard rain occurred, the slides 
were removed and a new set substituted, two on each of the three 
stakes. The count on the 4 slides was as follows : 

Stake No 1 Upper slide, 25 spores. 
Lower slide, 33 spores. 

Stake Nn 2 Upper slide, 2 spores. 
' Z - Lower slide, 9 spores. 

On October 5, after remaining on the stake 24 hours the 6 micro- 
scopic slides were removed and the counts made. They were as fol- 
lows : 

Stake No 1 Upper slide, 24 spores. 
No< L Lower slide, 36 spores. 

Stake No 2 Upper slide, 22 spores. 

Lower slide, 250 spores. A tendril was present. 

Stake No 1 Upper slide, 8 spores. 
Lower slide, 26 spores. 

The following experiment was made to test whether the Diplodia 
spores could be caught from the air at some considerable distances 
from the infected field. Adjacent to this field on the north is a golf 
field which offered an excellent opportunity for making such a test as 
it was very clean and free from trash, and one could feel quite certain 
that most of the spores obtained must have come from the field above 
mentioned. There was a field of corn to the west of the golf field 
but the stakes were kept at least as far from it as from the infected 



1909] EAR ROTS OF CORN 83 

field to the south. Stake No. 1, bearing two glass object slides, was set 
up in^the golf field 50 yards north of the north edge of the clover field 
with the smeared side of the glass slides facing the south. 

Stake No. 2 was similarly set up 75 yards from the same field, 
but on slightly higher ground. 

Stake No. 3 was put 150 yards away. This experiment was started 
October 10, 1907. 

After 4 days, October 14, the above mentioned slides were re- 
moved and the counts made. They were as follows : 

Stake No. 1,-SO yards from infected field Upper slide, 28 spores. 

Lower slide, 37 spores. 
Stake No. 2, 75 yards from infected field Upper slide, 11 spores. 

Lower slide, 6 spores. 
Stake No. 3, 150 yards from infected field Upper slide, 38 spores. 

Lower slide, 47 spores. 

On October 18 at 8 a. m., the above experiment was repeated by 
using greater distances in the same field. Stake No. 1 was placed 150 
yards, No. 2, 250 yards, and No. 3, 350 yards from the infected field. 
In addition to the two glass slides used on each stake as stated above, 
a third was placed at the top of e'ach stake facing the corn field to the 
west. This field was the same distance from each stake about 150 
yards. All surfaces of the slides facing the south and west were 
smeared with glycerin and alcohol. 

The test continued 4 days during which time no rain fell. On 
October 22, the slides were removed and sometime later the count was 
made, the slides in the meantime being carefully protected. The re- 
sulting count was as follows : 

Slide 1 facing corn field, 11 spores. 

Stake No. 1 150 yds. Slide 2 facing infected field. 12 spores 
Slide 3 facing infected field, 6 spores. 
Slide 1 facing corn field, 4 spores. 

Stake No. 2 250 yds. Slide 2 facing infected field. 5 spores 
Slide 3 facing infected field, 7 spores 
Slide 1 facing corn field, 5 spores. 

Stake No. 3 350yds. Slide 2 facing infected field. 6 spores. 
Slide 3 facing infected field, 14 spores. 

These results entirely confirmed the supposition of the transmis- 
sion of Diplodia spores by the wind and furnished the means for the 
explanation of several peculiar things in reference to the distribution 
of the disease. 

TwnpTTT ATTHV It was now desired to perform some infection experi- 

1IV UL/ UJ-.A J.1UJN "'"< /-/ r 1 1 T TT 1 

EXPERIMENTS having been cut off from the sporophore. In Uschin- 
sky's fluid 90 percent germinated in 24 hours and 
oculations were made as follows : 
1. On sweet corn. 

a. On August 10, 1907, a number of well .selected ears whose 
silk was just beginning to dry were inoculated with spores from a rice 
tube culture forty days old, by inserting the spores under the outer 
husk at the base of the ear in some cases, and ;n others by placing them 



84 BULLETIN No. 133 [February, 

well down into the silk at the tip. The same thing was carried out in 
duplicate using exuded spores from an old diseased corn stalk. 

Within five or six days the success of the infections was apparent 
from the small but striking spots of pale yellowish green that appeared. 
These increased rapidly in size, changing to the characteristic brown 
color along the margins. The disease in the majority of cases pro- 
gressed somewhat more rapidly in the ears inoculated at the base but 
no apparent difference could be detected in the final effect. Those in- 
oculated with spores from pure cultures were in appearance in no way 
unlike those that were inoculated with spores from the old stalks, the 
disease in all progressing at the same rate and showing the same symp- 
toms. On August 27, seventeen days after inoculation, pycnidia could 
be seen developing on some of the ears. From this time on the ears 
proper, kernels and cob, became rapidly involved and more or less cov- 
ered with the white mycelium. 

September 3, a stalk bearing two diseased ears was cut and after 
remaining in the laboratory seven days the upper of the two ears was 
photographed. (PL IV., Fig. 2). The great number of pycnidia can 
be seen as black masses towards the base of each ear. 

b. On August 19 some ears of sweet corn in the same plot as 
above were sprayed with spores in suspension and others were inocu- 
lated by inserting spores in the shank a few inches below the base of 
the ear. Three of the sprayed ears developed rot, 7 did not, while but 
1 of the 10 inoculated in the shank was successful. (PL IV., Fig. 1). 

2. On field corn. 

At intervals from August 14, 1908, to September 13, 1908, inocu- 
lations were made in ears, shanks, and stalks of field corn with spores 
from both pure cultures and old diseased stalks. Ears were inoculated 
in the silk, at the base, and by spraying them with a suspension of 
spores in water. Spores were inserted into wounds made in the stalks 
in different places by means of .1 knife or needle after which a few 
drops of distilled water were added. 

At the beginning of the experiment the corn was just silking out 
well and showed no signs of drying whatever, while on September 13, 
the date when the last inoculations were made, some of the husks 
showed signs of maturing and the grains were already quite firm. 
From 40 to 60 ears were used for each method of inoculation and a 
similar number were always left as checks. 

Of all the inoculations made the most successful in all the series 
were those with spores placed in the silk and under the outer husk at 
the base of the ears, the former giving a higher percent of successful 
inoculations than the latter. 

Of those inoculated August 14 from a pure culture, 16 percent of 
those receiving spores in the base were successful, while 59 percent of 
the silk inoculations developed typical cases of the disease. The per- 
cents of diseased ears resulting from the other methods were small ; 
3.3 from spraying, 3.1 from inoculations made in the stalk just below 
the attachment of the shank, and 1.5 percent from the checks. 



1909] EAR ROTS OF CORN 85 

The percent of disease was lower in all cases when spores from 
exuded tendrils on old stalks were used. Of those inoculated on 
August 16 with such spores the results were as follows : In the silk 
27 percent, in the base 14, by spraying 3.6, and in the stalks 1.8 percent, 
which last was just about the same amount of disease as developed in 
the checks. 

The highest percents of diseased ears obtained were the result of 
inoculations made on August 31, as previously stated, when the corn 
was still in the thick-milk stage. 80 percent of silk-inoculated ears 
produced the disease, 71.7 percent of those inoculated at the base and 
48 percent so treated in the shanks were successful, while but 22 per- 
cent of the sprayed ears showed any signs of infection. All later inoc- 
ulations altho fairly successful produced smaller percents of the disease 
than the others. 

Microscopical examination of the tissue of inoculated stalks 
showed some development, mostly slight, in a number of cases. In 
one case the pith was browned below and above the wound, together 
a distance of three feet, and tubes of boiled rice inoculated with bits of 
the tissue developed the Diplodia fungus. There was no direct evi- 
dence obtained that the infected ears on such stalks were a result of the 
inoculations made. 

A number of inoculations made on stalks and leaf sheaths by 
merely applying spores to the uninjured surface of each and in slight 
wounds made by scratching with a needle were entirely unsuccessful. 

INOCULATIONS n September 5, 1907, several stalks of sorghum 
IN OTHER PLANTS were inoculated about two feet from the ground with 
Diplodia spores in wounds made with a pen knife. 
Five weeks later the stalks were harvested, split open and examinations 
made. In most cases there was about the wound in the pith signs of 
infection. The tissue had a deep purplish red color and fermentive 
odor was evident. Mycelium of some kind was present in all cases 
but there was no assurance as to its being of the Diplodia fungus. The 
discoloration in one specimen extended about 14 inches above and 3 
inches below the point of infection. With pieces of this diseased tissue 
2 tubes of boiled rice were inoculated, one piece from near the wound 
and the other from the portion farthest away. Both tubes developed 
impure cultures of the Diplodia fungus and pycnidia were produced. 
Of the several other plants inoculated none became infected. 

SPECIES OF FUSARIUM. 

The species of Fusarium found upon developing ears of corn seem 
to be undescribed, notwithstanding the number of forms which have 
from time to time been described, and the very considerable attention 
that has recently been given to the group on the part of plant patholo- 
gists and other botanists. There are evidently three different kinds on 
corn which are sufficiently distinct to be considered separate species. 
One of these has been studied at length and the others enough to per- 
mit the descriptions which follow below. It has not been considered 



86 ' BULLETIN No. 133 [February, 

best, however, to give names to these fungi in this publication, but 
simply refer to them by number. They are therefore designated 
Fusarium I., Fusarium II., and Fusarium III. It should be said that 
the field loss by all these does not appear to amount to more than about 
9 percent of that due to Diplodia, tho they are parasites in the same 
sense as the latter. They do cause, independently of the Diplodia 
fungus and of each other, a variable percentage of the destruction wit- 
nessed. 

Fusarium I. 

ON THE EASS ^ s t ^ ie ^ un g us grows on the ears of corn it usually 
produces a rather dense, felty mass of white mycelium 
which extends between the kernels to the cob causing it to become more 
or less diseased. (PI. IT., Fig. 1). The threads of the mycelium can 
be detected microscopically all through the diseased grains, corroding 
the starch and destroying the germs. 

In the earlier stages of development on the ears the oval or pear 
shaped spores are rare but in the old advanced cases they are more or 
less numerous. Two types of spores are produced, microconidia, small, 
obovate, single-celled spores, and macroconidia, larger, two to four 
celled ones. The latter are not commonly found in large numbers on 
the ears or in culture. In but one case were they found in sufficient 
abundance to produce a pink color and then on a dried embryo ear 
(that is, an undeveloped branch or ear generally found in the leaf- 
sheath next below that from which the principal ear issues) which had 
been destroyed by the fungus. (PL XI., Fig. 15). Some of both 
forms as taken from an ear of corn are seen in Plate XL, Figure 12. 

OK THE STALKS Very little is known as to the life history of the fun- 
gus on corn stalks. That it does occur there is cer- 
tain from the fact that a culture made in a tube of boiled rice with 
discolored pith from a stalk near a node gave an almost pure culture of 
the fungus. It has been found causing rots of embryo ears and doubt- 
less the mycelium penetrates the stalk as a result, as in the above men- 
tioned cas"e. 

In culture the fungus shows a vigorous vegetative ac- 
tivity and develops a large amount of a white, rather 
dense mycelium on most suitable media. 
On a plate of asparagin-glucose agar, a centrally located colony 
grew to be 25 inches in diameter in less than 4 days the amount of 
aerial growth increasing with age until scarcity of moisture checked it. 
The amount of such growth depends greatly on the moisture content 
of the air as is seen in tubes of rice with various amounts of water 
present. Under favorable conditions it will grow to a height of 20 
mm above the surface of the media. 

The mycelium is made up of large and small filaments interwoven 
and frequently much coalesced, the latter depending largely on the kind 
of media used, and when occurring to any considerable extent the 
growth has a stringy or ropy appearance. The large filaments are a 



1909] EAR ROTS OF CORN 87 

sign of vigorous, active growth and vary in size from 6 to 10/x 
in diameter. Lack of moisture in a culture aids in bringing about the 
formation of the small type of hyphae and a production of conidia. 
These small filaments vary in size from 2 to 4jn in diameter and hence 
are small in comparison with the larger ones. 

In a young culture the hyphae are usually filled with granular 
protoplasm, becoming during the growing period very much vacuo- 
lated. In certain old cultures with the ceasing of the vegetative activ- 
ities, especially on a very starchy media, the minute fatty drops, which 
give the granular or turbid appearance to the protoplasm during the 
active growing period, seem to collect into large, strongly refringent 
drops and occupy the greater part of the cells. 

As seen under the microscope, the microconidia are colorless, obo- 
vate to pyriform, and vary in size, sometimes considerably, with the 
media used. They are produced terminally on simple or much branched 
sporophores. (PI. XL, Fig. 13). The end of a terminal hypha, or 
more frequently a lateral branch, is cut off from the remaining portion 
by a rather narrow constriction. One after another is thus formed 
until a clump of spores surrounds the tip of the branch. 

The macroconidia vary much in form and size, ranging from 10- 
25X4-8/*, the average being about 18-22X5-6^. They are usually 
slightly curved and somewhat constricted at the septa. (PI. XL, Fig. 
15). In cultures they are usually rounded at the distal end and taper 
toward the bluntly acute, proximal end. 

This type of spore is formed in culture in very much the same 
way as the smaller form and sometimes on the same hypha. This was 
observed in both prune juice and Uschinsky's fluid. (PI. XL, Fig. 
16). So far as observations in this connection could be made the 
sporophores producing the large and small spores are little if any dif- 
ferent in appearance. In both cases there is a slightly swollen portion 
in the middle of the branch and a slight constriction at the point of 
attachment to the mycelial filament. 

GERMINATION Both types of spores germinate very readily in many 
different nutrient solutions. In standard beef bouillon 
germination began in 3 hours, and 2 hours later one-third of the spores 
produced germ tubes. In 9 hours all had produced hyalin germ tubes, 
some of which were quite long. In 22 hours many interwoven 
branches had formed. At the end of 48 hours no spores had formed. 
Other tests were made in Raulin's fluid, Uschinsky's fluid, com- 
binations of Witte's peptone, glycerin, etc., prune juice, and distilled 
water. Raulin's fluid induced fair germination, but little growth of 
the hyphae took place. Prune juice proved a rather favorable medium 
but not so good as Uschinsky's fluid. In this solution germination was 
very good but the germ tubes never became very long. In 48 hours 
both kinds of spores were being produced. In no other medium were 
the large type of spores produced in such abundance. In distilled 
water both germination and growth were poor. 



BULLETIN No. 133 [February, 

GROWTH ON fact that a few cases are on record of inducing 

VARIOUS MEDIA the formation of perithecia from the conidial fructi- 
fication of some Hypocreaceous fungi led to the modi- 
fication of media, both natural and synthetic, in various ways in an 
attempt to find such a stage in the life history of this organism. How- 
ever, no indication of perithecia or any other form of fruit than those 
described developed. 

The fungus grows well on many fruit, vegetable, and grain media 
made by boiling in certain amounts of distilled water. At all times 
this organism was- distinguishable from other Fusariums studied by 
the large amount of at first pure white mycelium. On sweet potato, 
carrot, salsify, parsnip, and rice, the growth rises 15 to 20 mm above 
the surface of the medium in a few days. Poor growths take place on 
apple, raw potato, -tapioca, prunes, and cabbage. Macroconidia are 
sparingly produced on some of the media but microconidia are always 
present and usually in abundance. 

That the production of spores is largely influenced by external 
conditions insufficient nourishment, lack of moisture, high tempera- 
ture, and reaction of the medium was strongly brought out in the 
many cultures made. 

The three first named conditions favor the production of spores, 
while the last may be so controlled as to be either favorable or un- 
favorable. Extremes in acids and alkalin reactions retard while those 
of less degree, such as favor good growth, are more or less favorable 
to the production of spores. 

The effect of alkalis in cultures are more injurious than acids. 
Of the three alkalis used potassium hydroxid, sodium hydroxid, and 
sodium carbonate the two former are the most injurious. Growth 
is retarded by the presence of acid above certain small amounts, the 
strength depending largely on the kind used. Liquid media proved to 
be the most useful in determining such effects. Acids of the acetic 
series were found to be the most injurious, growth refusing to take 
place in strengths above -(-6.25 in a liquid medium, while those of the 
hydroxy acid group are least so, permitting growths in strengths of 
-j-25, and in some cases stronger. 

On most media used a pigment varying in color from salmon to 
purple appeared in time, and was found to be artificially more or less 
controllable. It is retarded by weak solutions of alkalis and stronger 
solutions of acids, as a rule, altho weak strengths of malic, tartaric, 
citric, and lactic acids do under favorable conditions intensify colors, 
especially the salmon, pink, and red. High temperature, on the other 
hand. 29C to 30C, favors the production of color, particularly the 
reddish purple hues produced in the substratum. When a still higher 
temperature, as 35C to 37C, is used growth is seriously retarded and 
sometimes the fungus is killed. Color formation is largely favored 
by light, the salmon color increasing rapidly in the aerial mycelium of 
cultures kept in the dark for a time and then submitted to the action 
of the light. 



1909] EAR ROTS OF CORN 89 

Fusarium II. 

GROWTH ON The diseased portion of ears infected with this organ- 

THE CORN ism, as previously stated, have a deep pink to red 

color due to the pigment produced in the hyphae of 
the fungus. When the husks are removed the color is bright, espe- 
cially in the most active stage of the organism. A microscopical ex- 
amination reveals that the pigment is more or less irregularly distrib- 
uted in the rather large mycelial threads, some cells being entirely 
without it. 

Branching is moderately profuse and hyphal swellings are not 
rare. As yet no spores of any kind have been found on diseased ears, 
and for a time the organism was considered sterile and so reported at 
the Chicago meeting of the American Association for the Advancement 
of Science, January 1, 1908.* Later t however, spores were produced 
in culture, which placed the fungus in the genus Fusarium. The felty 
mass of mycelium permeates the inner husks and silk and holds them 
firmly to the ear. (PI. II., Fig. 2). With age the red color fades. 
The kernels are brittle and the starchy contents is very powdery and 
considerably corroded by the action of the hyphae which permeate all 
portions of the grain. (PI. XL, Fig. 7). 

GROWTH IN Fusarium II. was usually grown in petri dishes on 

CULTURE various media and on modifications of the same ones 

to induce the formation of the reproductive bodies. 
All stock cultures were made on boiled rice in test tubes and transfers 
of mycelium were made from these to the plates. A pure culture was 
first obtained from the interior of a sterilized diseased kernel of corn. 

A series of cultures was carried on in plates duplicate to those 
used with Diplodia, the principal medium being extract of corn meal 
agar, to which various amounts of acids, alkalis, and carbohydrates 
were added. 

The fungus grew rapidly on a number of these and in several 
cases soon produced the characteristic purplish-red color, but of more 
brilliant hues than occur on the infected corn. 

In 4 days some growth had developed on all plates except the one 
containing formic acid -{-20 and on a starch medium containing Uschin- 
sky's solution. The colonies on the media containing various sugars 
showed more rapid development and, at first, more color. Density of 
growth, however, was more pronounced in the plates containing tar- 
taric, citric, and lactic acids, where branching was abundant and the 
colors white to orange. The colony in glucose culture was 2.5 inches 
in diameter at this time, the margin having a deep pink color while that 
of the central area was a bright red. Bladder-like swellings which 
gave rise to from 1 to 12 finger-like branches were numerous in the 
substratum. This condition existed to a greater or less extent in all 
plate cultures containing sugar. 

Four days later, or 8 days after inoculation, there was no apparent 
growth in the cultures containing formic, acetic, butyric, and oxalic 

* Barrett, lames '!'., Science N. S. 27: 212. 



90 BULLETIN No. 133 [February, 

acids, while in all others a more or less rapid increase in the amount of 
both submerged and aerial mycelium had taken place. The pigment 
in the malic, tartaric, citric, and lactic acid cultures varied in color from 
brilliant yellow to purplish red. Finally the resulting color became a 
rusty red to brown. The size of the colonies was still small but the 
growth was very dense. In most of the other cultures the colonies 
covered the plates. 

For a time the growth still increased in many cultures and the 
colors grew more and more brilliant, then finally became dull and 
dingy. 

Zonation was apparent in many cultures (PI. IX., Fig. 2), becom- 
ing very marked in certain sugar media where it was due to alternate 
zones of profuse and sparse branchings and to hyphal swellings filled 
with coloring matter. 

Alkalin cultures were, for the most part colorless, but they event- 
ually became a pale yellow often with slight traces of blue. 

Twelve days after inoculation numerous small leather colored 
tufts were apparent on the surface of the growth in the lactic acid cul- 
ture. A microscopical examination revealed them as masses of ma- 
croconidia of a fusarium type. (PI. XL, Fig. 5). They were borne 
on short, much branched sporophores, and were fairly constant in size, 
measuring 50-62X4.5X6/A. Already many had swollen and some had 
germinated. After a careful search in all other cultures they were 
found in large numbers in but one and that the medium made by 
adding agar to Fermi's solution. This colony had the same color as 
that of the lactic acid culture and the tufts of spores were borne in the 
same manner. 

Cultures made in Uschinsky's fluid variously neutralized gave 
different amounts of mycelium and numbers of spores. Macroconidia 
are produced rather abundantly in this fluid. Microconidia have not 
been found. 

GERMINATION Spores germinate readily, frequently very soon after 
OF SPORES having been cut off from the sporophore. In Uschin- 

sky's fluid 90 percent germinated in 24 hours and 
some of the germ tubes were considerably branched. In 48 hours new 
spores had been produced and a few were beginning to germinate. In 
Raulin's fluid germination was very poor, and those that did produce 
germ tubes soon died. In distilled water the percentage of germinated 
was very good but subsequent growth very poor. 

Fusarium III. 

APPEARANCE The f rm f r t caused by this organism is less com- 
ON EARS plete in its clestructiveness of the ear than that of the 

other forms described. (PI. III., Fig. 1). Many of 
the infected ears have only a few scattered diseased grains and, while 
such corn is almost valueless for marketing, it can T)e utilized for feed- 
ing purposes. Under certain conditions, however, most of the kernels 
may become diseased and the cob more or less infected. 



1909] EAR ROTS OF CORN 91 

The mycelium is white, very sparse, and is found principally in 
the ends of the kernels where it feeds upon the starch and produces 
large numbers of spores, mostly microconidia. In old dried specimens 
of corn the hyphae are more or less swollen and slightly constricted at 
the septa, and frequently contain many large globules. (PL XL, Fig. 
10). 

GROWTH IN On boiled rice growth is fairly rapid. The mycelium 

CULTURE is moderately dense and almost immediately begins to 

produce spores and to have a faint pink to salmon 
color. The color never becomes very dense and with age fades some- 
what. The hyphae are fairly constant in diameter in both cultures and 
on the corn, measuring about 4 to 5/x. 

The spores vary considerably in size and are mostly one and two- 
celled, altho those possessing three cells are not rare on certain 
media. Microconidia range in size from 12-15X3. 5-5 p., while the 
macroconidia are 24-30X35-5.5/A. (PL XL, Fig. 9). 

On a plate of agar made from an extract of canned sweet corn, 
made -\-lO with hydrochloric acid, there was a fair growth in 2 days 
and some spores of both kinds had been produced. In one week the 
colony had become 1.5 inches in diameter, growth dense, all submerged, 
and a slight pink color had developed at the center. The protoplasm 
was very granular. The colony finally covered the entire plate. A 
little aerial growth developed at the center and a pink to red color 
was distributed thruout the plate. 

In the same medium, made 10 with sodium hydroxid, growth 
was good from the beginning, becoming 1.5 inches in diameter in 4 
days. Both kind of spores were abundant. The color remained 
white. Some of the hyphae were 5.5 to 6/x in diameter. 

In the check plate, containing sweet corn extract agar alone, a 
rather rapid development took place and both types of spores were 
present in 2 days. The colony finally covered the plate and changed 
from a pale pink to a pale blue color. 

Growth in cocoanut milk agar was very rapid and possessed more 
aerial mycelium than any of the above. The color was white dotted 
with pink tufts of spores. Some hyphal swellings developed and both 
kinds of spores were present. The growth became pale blue, and 
eventually deep purple in color. 

In a few cultures on boiled rice there developed some small rather 
firm bodies of a pink and finally a rusty color, which resembled scle- 
rotia. Some of these were sectioned in paraffin and were found to be 
made up of a mass of hyphae grown closely together. They were 
watched for. some time but never came to maturity. 

BACTERIA 

The corn plant in the field is subject to attack by several kinds of 
bacteria, producing various forms of disease. The developing ears do 
not escape injury from this source, but the loss sp caused seems to be 
small compared with that from the fungi heretofore described almost 



92 BULLETIN No. 133 [February, 

negligible from a practical standpoint. Whether these ear-infections 
are all due to the same species of bacteria has not been ascertained. 

Certain ears when stripped of the husks show grains which are 
evidently diseased, rather uniformly distributed among the sound ker- 
nels or in small groups on some part of the ear. The diseased kernels 
are dark in color, often corroded upon the surface, and are brittle in 
texture. Sometimes a shiny, mucilaginous or gum-like exudate is 
noticeable upon the outer surface of the grains. Upon microscopical 
examination this exudate is found to be made up of a pure culture of 
a medium sized bacillus of short, cylindrical shape and capable of rapid 
ciliate movement. These are present in myriads and what appears to 
be the same organism is found in great numbers in the crumbling, 
starchy portions of the affected grains. A conspicuous characteristic 
of such diseased kernels is the red color taken on by the substance of 
the scutellum. When such grains are divided lengthwise thru the 
flat surfaces the starchy portion is seen to be distinctly white, while 
that known as the chit is as distinctly red. 

The infection seems to begin externally with the silk and the bac- 
teria follow a strand of this to its attached kernel, explaining how it 
comes about that any one of the latter upon the cob may be diseased 
among those adjoining healthy. Where these bacteria otherwise live 
has not been ascertained. 

The bacteria of the growing corn plant is a subject well worth 
special study. 

PREVENTION 

The diseases of corn (maize) described in this Bulletin should not 
be confounded with corn smut which is frequently seen upon the ears 
as well as on other parts of the corn plant. This is easily recognized 
and is well known on account of the large outgrowths of a black or 
sooty substance which when dry readily falls into fine dust. The ear 
rots under discussion are very different and are best characterized as 
moldy in appearance. There is a white -or pinkish, cobwebby, closely 
adherent growth on and in the husks, silk, grain, and cob or any of 
them. The affected ears are never perceptibly dusty, but later become 
brittle or friable and merit the name sometimes applied dry rot. 

The life history of the fungus (Diplodia Zeae) causing most of 
these ear rots (about 90 percent) has now been sufficiently worked 
out, as detailed above, to make it possible to recommend preventive 
measures with confidence in the prescriptions. This fungus lives as a 
parasite on the ears of the corn plant and apparently on no other por- 
tion of the plant. At first it was natural to suppose that a seasonal 
infection must be due to the wintering over on the old diseased ears, 
and that in all probability a careful collection of these at the time of 
husking would do much towards the reduction of the malady in the 
field the following year. This may be true to a considerable extent, 
but the discovery that the same fungus develops abundantly upon the 
dead stalks, even upon those that have lain on the ground two years 
and are therefore much decayed, changed materially conclusions upon 



1909] EAR ROTS OF CORN 93 

the subject. It will not be surprising if it is hereafter found that the 
fungus does sometimes live on other parts than ears of growing corn, 
neither is it impossible that it develops as a saprophyte on something 
besides corn stalks. It can be rather confidently asserted, however, 
that these things if true at all must be rare occurrences in Illinois corn 
fields, and that for practical purposes attention may be centered en- 
tirely upon the facts now made known. 

Little dependence can be placed upon any direct treatment of the 
soil, any outward application to the plant, any variation in time of 
planting, any selection of varieties, or other similar matters, tho 
there may be some difference at different times and under special con- 
ditions on account of any such variations connected with the soil or 
with the plant. A few cases, indeed, have been observed where the 
amount of rot was undoubtedly traceable to some such difference, now 
one thing, now another. But there is not enough of this to alter the 
recommendations that can now be made. 

It is best then to give attention principally if not solely to the 
active agent which causes the destruction. Rot does not occur, as has 
been shown, under any circumstances or condition except as it is di- 
rectly brought about by the fungus, and the fungus cannot start ex- 
cept by its own reproductive methods. Keep the spores away from 
the green ears and the corn will remain sound. Keep the fields free 
from the substance on which spores are produced from the beginning 
of a season for infection, and the crop must remain free from danger 
in this regard. 

Undoubtedly there is some dissemination of spores from the 
earlier affected ears to sound ones of the same season, but here again 
the probable amount of loss so caused is small. Practically the new 
infection comes from the old stalks those one and two years old 
and therefore these must have chief attention in the combat. From 
this it is easy to see what procedure should be adopted in trying to re- 
duce the rot in, or eliminate it from, the field. Stated in a word, it is 
carefully to take out of the field and destroy the rot-infected ears at 
the time of husking, with the view of reducing the amount of the 
fungus later on the stalks; then to remove from badly infected fields 
the stalks by low cutting and hauling away or by burning, or better 
still by such rotation of crops that corn shall not follow corn within a 
period of two years. Care should also be taken not to plant corn by 
the side of an old infected field especially if the latter is upon the side 
from which come the prevailing summer winds the south and west. 

As corn is commonly cut for fodder or for silage, there may be 
stumps enough left to carry over too much of the disease, and old 
stalks may get back again with the manure to a detrimental extent ; 
tho by attention to these matters there must be a possibility of 
causing a decided diminution of the trouble by such early removal of 
the stalks. 

Unless the old stalks zvith their harboring fungus are effectually 
destroyed, corn should not be planted again zvhere there has been much 



94 BULLETIN No. 133 [February, 

of the disease for two years thereafter, nor nearer than 20 to 30 rods, 
especially on the windward side, of an old corn field badly infected one 
or two years before. 

HISTORY AND SYNONOMY (DIPLODIA ONLY) 

Schweinitz in his Synopsis Fungorum Carolinae (1822), number 
79y described a fungus found on old stalks of maize which he called 
Sphaeria Zeae. Later in his Synopsis Fungorum in America Boreali, 
[North American Fungi] page 207, number 1451, he again described 
the same fungus on the same plant under the same name as follows : 

"Omnino tecta, epidermide fusco tincta (ostiolis solis prominulis) satis 
elevata. Seriatim disposita, brevis, utrinque acuminata, subconfluens. Peri- 
thecii binis vel ternis tantum in caespitulo, subdistantibus, primum albofarctis, 
demum evacuatis. Ostiolis latis, umbilicatis, saepe unico." 

This may be translated as follows : 

Entirely covered, epidermis fuscous colored, rather elevated (ostiola alone a 
little prominent). Distributed in series, short, acuminate at both ends, subcon- 
fluent. Perithecia only two or three in a group, subdistant, at first white within, 
at length evacuated. Ostiola broad, umbilicate, often to a marked degree. 

In the latter work, under number 1866, the author refers to num- 
ber 234 of Synopsis Fungorum Carolinae, and classifies what seems to 
be the same fungus as Dothidea Zeae, but there is no mention in either 
case of asci. This was before the day of the compound microscope as 
a serviceable instrument, which sufficiently accounts for the absence 
of finer details in the descriptions. 

In 1847 Berkeley, in Hooker's London Journal of Botany 6:326 
described a fungus from the stalks of maize which he called Sphaeria 
Maydis, and appended the following description quoted in Ellis and 
Everhart, North American Pyrenomycetes page 452 : 

"Spots minute, elevated, often purple-brown, punctiform or subelliptical, 
rarely linear, containing very few perithecia, with a single, broad-conical ostio- 
lum. Sporidia oblong, slightly curved, uniseptate. Habit that of Leptospaeria 
arundinacea* Very different from Sphaeria (Diplodia) Zeae, Schw." 

These descriptions seem to characterize different species and ap- 
parently justify the remark by Berkeley that the fungus at the time in 
his hands was very different from that earlier described by Schweinitz. 

But, probably more from this remark than from anything else, 
most subsequent writers have referred the" fungus observed by many 
on old stalks of corn and identified as a Diplodia to Berkeley's species. 
Thus Saccardo, in Sylloge Fungorum, 3:373, (1884), writes Diplodia 
Maydis (Berk.) Sacc., and quotes Sphaeria Maydis Berk., Lond. Jour, 
of Bot. 6:326, as a synonym, together with in the same way, Diplodia 
Zeae Lev., Ann. Sc. Nat. III. 9 : 258, and Sphaeria Zeae Curr., Simple 
Sphaer. n. 358, f. 128. So far as these references are concerned, Sac- 
cardo properly takes Berkeley's name, for this was published in 1847 
while the dates for the others are respectively 1848 and 1859. Leveille 
however founded his name upon Sphaeria Zeae Schw., which, as 
shown above, dates back to 1822. If, therefore, the plant so called 
is the same as that named by Berkeley Sphaeria Maydis, the latter 
name becomes a synonym. Notwithstanding the statement by Berke- 



1909] EAR ROTS OF CORN 95 

ley that the two plants are very different, there is now much reason to 
suppose they are really the same, or at least that specific distinction 
cannot be maintained. The reference by Saccardo to Currey is based 
upon a paper by the latter in the Trans. Linn. Soc. 22:330 (Simple 
Sphaer.) appearing in 1859 upon the fungi in the Hooker Herbarium 
this particular material undoubtedly coming from America and prob- 
ably collected by Schweinitz. Though finding no asci, Currey retains 
the genus relation and identifies the specimens as Sphaeria Zeae Schw. 
The spores as figured (PI. 59, f. 128) agree very well with those of our 
plant. Moreover reference is made to Fries, Sys. Fung. 2 :527 where 
S. Zeae Schw. is referred to (1823). This can, therefore, be none 
other than the Schweinitzian plant, and if, as Saccardo thinks, the 
name is a synonym of S. Maydis Berk, the two names must apply to 
the same species. 

The exsiccati specimens examined show no differences which 
should indicate specific distinctness. These are: 
Diplodia Zeae Schw. 

Ravenel, Fung. Car. n. 74 (1852) 
Diplodia Zeae Lev. 
Sphaeria Zeae Schw. 

Thiimen, Myc. Univ. n. 1194 (1878) 
Diplodia Zeae Lev. 

Ellis, N. A. Fungi n. 31 (1878) 
Diplodia Zeae ( Schw. ) 

Ravenel, Fung. Amer. n. 393 (1879) 
Diplodia Maydis (Berk.) Sacc. 

Roumeguere, Fung. Gall. n. 5378 (1890) 
Diplodia Zeae Lev. 

Ellis and Everhart Fung. Col. n. 73 (1893) 
Ellis and Everhart, N. A. Pyr. 745 say: 

"The spec, in Herb. Schw. is the same as Diplodia Zeae Lev. in Ell. N. A. 
F. n. 31". 

Assuming that Sphaeria Maydis Berk, is the same as Sphaeria 
Zeae Schw., or that the former name really applies to some other 
plant than that with which we are dealing, there can be no reasonable 
doubt that the fungus described in this Bulletin should be called Diplo- 
dia Zeae (Schw.) Lev., until this form is proved to be genetically con- 
nected with something of higher fruiting. Many surmises of the lat- 
ter kind have been made ; Schweinitz himself made it a species of 
Sphaeria and was followed in this by Berkeley and Currey as noted 
above. The former also identified another specimen as a Dothidea 
(Syn. Fung. Bor. n. 230 (1866) which he subsequently (Am. Sc. Nat. 
III. 9:258) admitted to be the same as the one called Sphaeria. Later 
the name, Sphaeria Maydis Berk, has several times been applied to 
American specimens certainly identical with our plant. Bennett, Cat. 
PI. R. I. 87, (1888), places it in Dothiora, and Ellis and Everhart, N. 
A. Pyr. 452, (1892), assigns it to Diaporthe. But there is no evidence 
that these writers had before them perithecia with asci or that they had 



96 BULLETIN No. 133 [February, 

anything more than is usually to be found in the examination of or- 
dinary specimens. There is no proof known to the present writers 
that a mature or ascus stage exists, though there are such forms not 
infrequently associated with the Diplodia on old culms of maize. Our 
cultures of the latter though both varied and prolonged have not dem- 
onstrated further fruiting. Diaporthe incongma E. & E., and D. Kel- 
lermanniana Winter, are both (if they are distinct) found on decaying 
culms of Zea Mays, N. A. Pyr. 453. 

The first suggestion in print that this fungus works as a parasite 
seems to be the Heald, Science, N. S. 23 :624 (1906), where the follow- 
ing note, under the title, "New and Little-known Plant Diseases in 
Nebraska," is given : 

"Moldy corn due to a fungus provisionally referred to Diplodia Maydis, 
but differing in several points in habit and structure." 

One of us, Barrett, Science N. S. 27:212-213 (1908), describes 
under "Dry Rot of Corn and Its Causes" something of the effects of 
Diplodia, "very probably Diplodia Maydis", as a parasite upon corn 
and briefly relates its life history. Further citation upon the same is, 
Burrill and Barrett, Circ. 111. Ag. Sta. n. 117:1-3, (1908). Here, too, 
mention is made of similar rots due to species of Fusarium and by 
bacteria. 

Heald, Wilcox and Pool, Reprint from the Twenty-second Annual 
Report of the Nebraska Agricultural Experiment Station, distributed 
January 1, 1909, give a good description of the fungus, called by them 
Diplodia Zeae (Schw.) Lev., and of its work as a parasite upon corn. 
Excellent plates accompany the text. 

The fungus must for the present be cited under the genus Diplo- 
dia and the synonomy seems to be as follows : 

Diplodia Zeae (Schw.) Lev. 
Sphaeria Zeae Schw. 1828 
Dothidea Zeae Schw. 1831 
Sphaeria Maydis Berk. 1847 
Diplodia Zeae (Schw.) Lev. 1848 
Diplcfdia Maydis (Berk.) Sacc. 1884 
Dothiora Zeae (Schw ) *Bennett 1888 
Diaporthe Maydis (Berk.) Ell. and Ev. 1892 

Thru the courtesy of Dr. Farlow, Mr. A. B. Seymour exam- 
ined, in the collections of the former, certain of the specimens enum- 
erated above ; and gave from the notes, prepared for publication other- 
wise, citations to literature embracing all the above names. From 
these notes, Mr. Seymour arranged the synonomy as it is above. This 
latter was communicated in a letter dated July 30, 1908. 

It should be said that the manuscript for this Bulletin was prac- 
tically completed during August, 1908, but was not sent to the printer 
untif February 8, 1909. 

* Bennett wrote: Dothiorq Zeae Lcr, 



19*09] EAR ROTS OF CORN 97 

DESCRIPTION OF PLATES 

Plate I. Fig. 1. An ear of sweet corn thirteen days after inocu- 
lating in the tip with spores of Diplodia Zeae. Fig. 2. Another ear 
of the same, inoculation at base. 

Plate II. Fig. 1. An ear of corn infected with Fusarium I. 
Fig. 2. An ear of corn showing the effect of Fusarium II. 

Plate III. Fig. 1. Field corn with scattered individual kernels 
infected with Fusarium III. Fig. 2. A longitudinal section of an ear 
of corn showing the small, black pycnidia in the cob toward the outside. 

Plate IV. Fig. 1. An ear of sweet corn destroyed by Diplodia 
Zeae, spores of which were inserted into the shank bearing the ear. 
Fig. 2. Ear of sweet corn artificially, inoculated and photographed 
after being in the laboratory seven days. The black color about the 
base of the ear is due to numerous pycnidia. 

Plate V. Two shanks of the corn plant bearing numerous pycni- 
dia of Diplodia Zeae as small black specks. These shanks were collect- 
ed in the spring. 

Plate VI. Fig. 1. A piece of old corn stalk showing pycnidia 
of Diplodia Zeae. Fig. 2. Piece from the same stalk as Fig. 1 after 
soaking in water fifteen hours and keeping moist for a few days in 
a damp chamber. The black masses are tendrils of Diplodia spores. 
Fig. 3. A single pycnidium of Diplodia Zeae on a corn stalk show- 
ing the exuded tendril of spores and the internal cavity. 

Plate VII. Fig. 1. A cross section of an ear of corn showing 
Diplodia pycnidia as black specks in the cob. Fig. 2. A photograph 
of germinating spores of Diplodia Zeae. 

Plate VIII. Fig. 1. A photomicrograph of Diplodia spores from 
an ear of diseased corn. Fig. 2.- Diplodia spores from a rice tube 
culture. 

Plate IX. Fig. 1. A petri dish containing corn meal extract agar 
and 5 percent galactose in which are imbedded numerous pycnidia 
of Diplodia Zeae. Fig. 2. A sweet corn agar plate showing zonation 
of Fusarium II. 

Plate X. Fig. 1. A cross section of a pycnidium of Diplodia Zeae 
on a corn stalk. Fig. 2. A cross section of a pycnidium of Diplodia 
Zeae on a kernel of corn. 

Plate XL Fig. 1. Spores of Diplodia from corn. Fig. 2. 
Young spores with sporophores attached. Fig. 3. Germinating Dip- 
lodia spores. Fig. 4. Short, more or less swollen, and darkened 
branches of Diplodia hyphae. This indicate the beginning of pyc- 
nidia formation. Fig. 5. Macrdconidia of Fusarium II., some of 
which are beginning to germinate. Fig. 6. Mycelium of the same 
fungus. Fig. 7. Starch grains from a corn kernel infected with 
Fusarium II., showing the corrosive effect. Fig. 8. Sporophores of 



All drawings and photographs were made by James T. Barrett except Plate I., which 
was executed in colors by Mrs. Flora M. S 4 ms. (The reproduction as Plate 1 is not in 
color, but a colored duplicate accompanies a part of the issue). 



98 BULLETIN No. 133 [February, 

Fusarium II., drawn at 1 1 :30 a. m. and at 1 :30 p. m. to show the 
rate of development of the spores in culture. Fig. 9. Microconidia 
and macroconidia of Fusarium III. from culture. Fig. 10. Mycelium 
of the same from a corn kernel. Fig. 11. Microconidia and macro- 
conidia of Fusarium I. from a prune agar plate. Fig. 12. Same from 
an infected ear of corn. Fig. 13. A spore-producing hypha from a 
young prune juice culture. Fig. 14. Germinating spores of Fusarium 
I. Fig. 15. Spores of Fusarium I. from a dried, diseased embryo 
ear of corn. Fig. 16. A hyphal branch of Fusarium I. producing 
both microconidia and macroconidia. 



1909] 



EAR ROTS OF CORN 



99 
PLATE I. 




FIGURE 1. INOCULATED IN THE SILK FIGURE 2. INOCULATED AT THE BASE 
WITH DIPLODIA. WITH DIPLODIA. 



100 



BULLETIN No. 133 



[February, 
PLATE II. 





FIGURE 1. FUSARIUM I. 



FIGURE 2. FUSARIUM II. 



1909] 



EAR ROTS OF CORN 



101 
PLATE TIT. 





FIGURE 1. FUSARIUM III. 



FIGURE 2. DIPLODIA. 



BULLETIN No. 133 



[February, 
PLATE IV. 





FlGURii 1. DlPLODIA. 



FIGURE 2. DIPLODIA. 



1909] 



EAR ROTS OF CORN 



103 
PLATE V. 




DIPLODIA ON OLD SHANKS. 



104 



BULLETIN No. 133 



[February, 
PLATE VI. 






DIPLODIA ON OLD STALKS. FIGURE 1, DRY. FIGURE 2, AFTER KEEPING MOIST. 
FIGURE 3, EXUDING SPORES (MAGNIFIED). 



1909] 



EAR ROTS OF CORN 



105 
PLATE VII. 








DIPLODIA. FIGURE 1, PYCNIDIA ON COB. FIGURE 2, GERMINATING SPORES. 



106 



BULLETIN No. 133 



[February, 
PLATE VIII. 






DIPLODIA SPORES. FIGURE 1, FROM DISEASED EAR. FIGURE 2, FROM A CULTURE. 



1909] 



EAR ROTS OF CORN 




FIGURE 1, DIPLODIA CULTURE SHOWING PYCNIDIA. FIGURE 2, FUSARIUM II. . 
CULTURE SHOWING ZONATION. 



108 



BULLETIN No. 133 



[February, 



PLATE X. 





PYCNIDIA OF DIPLODIA : FIGURE 1, FROM STALK. FIGURE 2, FROM CORN KERNEL. 



1909] 



EAR ROTS OF CORN 




JTJ3. de(. 
SPORES, ETC.: FIGURES 1 TO 4, DIPLODIA; THE OTHERS FUSARIUM.