Jan. 15,1925 
Ecological Relations of the Smut of Maize 
165 
RELATION OF WEATHER CONDI¬ 
TIONS TO INFECTION 
Inasmuch as the results of seed and 
soil treatments and inoculations have 
disclosed nothing to indicate true 
systematic development of the disease 
under field conditions, a more intimate 
understanding of the relation of 
weather conditions to the smut fungus 
and its ability to infect its host seemed 
necessary to an interpretation and 
explanation of the characteristic nodal- 
bud infection. 
Arthur and Stuart (2) have elab¬ 
orated meteorological observations 
covering a season in an attempt to 
demonstrate the close relationship 
of humid conditions to infection by 
the corn-smut fungus in the field. 
Although Piemiesel (16) has shown 
that the conidia are very resistant to 
desiccation, he seems to have accepted 
the conception of the dependence of 
infection on high humidities. Simi¬ 
larly, MacMillan (18) emphasizes 
moisture as a possible limiting factor in 
arid regions. 
These prevailing ideas are not in 
accord with the fact that the disease 
is not peculiarly prevalent in humid 
areas and under humid conditions. 
According to the writers’ observations 
corn smut appears to be far more 
abundant and destructive in the ex¬ 
treme western portion of the Corn 
Belt, in the dry hot portions of the 
plains of Kansas and Nebraska, than 
it is in the humid districts of the 
Eastern States. Selby and Hickman 
(19) also have observed that “more 
smut is found in dry seasons than in 
wet seasons; the same appears to hold 
as to situations.” While this fact 
does not obviate the necessary relation 
of moisture to infection, it does appear 
to minimize its importance as a limiting 
factor in the distribution and preva¬ 
lence of the parasite under field con¬ 
ditions. 
The observations of Hitchcock and 
Norton (8) on ecological relations 
seem the most adequate thus far 
offered. They conclude, as a result 
of their experiments, that infection 
“does not depend so much on the 
time of the season as on the stage 
of development of the plant.” They 
point out that in seasonal succession 
the leaves, tassels, ears, and lower 
nodal buds become the principal areas 
for smut infection, because in the 
development of the plant they are 
successively exposed in the meriste- 
matic condition. If, then, there are 
successive “outbreaks” of the disease, 
as observed by Arthur and Stuart (2), 
and more recently by Piemeisel, (16), 
it would, perhaps, be more logical to 
attribute these to the effect of such 
conditions upon the development of 
the host rather than to any effect 
upon the parasite, or, perhaps, merely 
to the coincidence of the condition of 
the host and the “frequent rains and 
cooler weather” of late summer (16). 
Such a season came under observation 
in Kansas in 1920 when the cooler 
weather and frequent rains in August 
had a stimulating effect on the growth 
of the corn crop accompanied by an 
apparent late infection of smut. 
To summarize, it appears exceed¬ 
ingly doubtful, particularly as to in¬ 
fection in the ears or nodal buds, 
whether moisture can be considered 
in any material degree a limiting 
factor in smut development under 
such climatic conditions as are re¬ 
quired for the maturity of maize. 
ECOLOGIC STUDIES 
Under conditions generally suited to 
maize culture, mainly at Manhattan, 
Kans., the writers began a series of 
investigations to determine the pres¬ 
ence of the smut organism on the 
maize plant or in its environment, 
previous to the development or ap¬ 
pearance of the smut. These were 
supplemented by attempts to shield 
the plants from infection, including 
the seed and soil treatments and the 
fungicidal sprays herein described. 
Efforts to isolate cultures of Ustilago 
zeae from the cornfield, prior to the 
earliest sporulation, naturally assumed 
three different aspects, namely, cul¬ 
tures from the soil, from the air, and 
from the plants themselves. (See 
Table I.) 
In order to bring the nature of this 
work more clearly before the reader, 
the history of several individual isola¬ 
tions (cultures) which proved virulent 
in the production of the disease are 
traced out in all the details of manipu¬ 
lation. 
EXPLANATORY LEGEND FOR PLATE 1 
A—A plant inoculated with hypodermic needle on June 7, 1918, using culture No. 6c, isolated in 1917 
and carried over on carrot agar until 1918. Smut galls evident June 18, 1918. 
B.—A plant infected from the same culture, showing large smut gall at point of inoculation. 
C—A plant inoculated by means of a hypodermic needle, June 22,1918, with culture No. 79 carried over 
from 1917. Smut galls evident July 2, 1918. 
D.—Pseudosystemic (nodal bud) infection developed on a culm of pod corn (Zeae maydis var. tunicata). 
Some of the (nodal bud) infections do not show in the photograph. Note that neighboring stalks are 
smut-free. 
