Nov. i, 1925 Infection of Wheat Plants by Ophiobolus graminis 
829 
creases had to be made from mycelium. ‘ The New York strain 
produced ascospores rather abundantly at times and these were used 
for making new cultures. 
The parasites were cultured in Erlenmeyer flasks, on a mixture of 
equal portions of barley and oats which had been thoroughly cooked 
and sterilized. The fungus increased rapidly on this medium, and 
the medium did not produce a toxic effect on the wheat plants when 
it was added to the soil, as was the case when cooked wheat kernels 
were used. Inoculations were made by adding to the sterilized soil 
a given weight of the barley-oat medium on which the fungus was 
growing. This was accomplished by first removing the upper 3 inches 
of soil from the containers and thoroughly mixing the inoculum with 
it. The inoculated soil was then returned to the pots and the seed 
was sown immediately. An amount of uninoculated medium equiva¬ 
lent to the amount added to the inoculated series was added to the 
controls, and they always were prepared and sown before preparing 
and planting the inoculated series in order to prevent accidental 
contamination. 
The relative influences of the different temperatures and moistures 
were determined on the basis of the amounts of disease produced. 
The method used for determining the amount of disease was essen¬ 
tially the same as that used in the studies on the Helminthosporium 
disease of wheat ( 12 , p. 199-200 ). However, owing to the fact that 
Ophiobolus graminis is a more vigorous parasite than Helmintho¬ 
sporium sativum , the wheat plants were more severly diseased in the 
experiments under discussion and it became necessary to classify the 
injuries in a different manner than was done in the previous studies 
referred to. 
Disease manifestations were divided into three groups or types— 
(1) leaf and stem blight, (2) infection of tiller bases, and (3) root 
infection. In order that all data should represent the severity of 
infection as well as the number of plants infected, the various 
types of injury were given the numerical ratings shown in Table I. 
Instead of expressing the total amount of disease occurring at a given 
temperature as a single infection rating, the different types of injury 
were kept separate and the infection ratings were calculated for each 
independently. These calculations were made according to the 
method employed in the studies on the Helminthosporium disease 
previously referred to {12, p. 200). 
Table I ,—Method of determining the numerical ratings for healthy and diseased 
wheat plants 
Type of injury 
Class 
Degree and type of injury 
Numeri¬ 
cal 
rating 
T'p-fif fvnfl stem blight _ __ _ _ __ 
1 
None__ 
0 
2 
Leaves yellow-- 
1 
3 
Plant killed. .. _ 
2 
Tnfectinn nf tillp.r-hasas _ _ __ 
1 
None..... 
0 
2 
Slight___ 
1 
3 
Moderate___ 
2 
4 
Abundant--- 
3 
T?nr»t infpptinn __ 
1 
None_ __ _ 
0 
2 
Slight...— 
1 
3 
Moderate_ __ ... 
2 
4 
Abundant.... 
3 
