814 
Journal of Agricultural Research 
Vol. XXXI, No. 9 
inoculated with the different strains of Ophiobolus graminis. The 
soil used was a fine silt loam, as previously described, and was placed 
in an autoclave for 2 hours under 15 pounds steam pressure. Equal 
amounts of this soil were placed in water-tight metal cans 6 inches 
in diameter and 9 Vo inches deep. The upper 3 inches of soil was 
then removed from each can, and kept separate. To each portion 
of this soil was added 100 gms. of inoculum, which consisted of the 
fungus growing on cooked oat and barley kernels, as described pre¬ 
viously. Each portion of soil and inoculum was then mixed together 
very thoroughly and placed in the proper can. The control cans were 
similarly filled with their portions of soil and 100 gms. of the un¬ 
inoculated oats and barley medium. The wheat seed was sown 1 
inches deep in this uniformly inoculated layer. After sowing, all 
the soil cans were immediately placed in constant-temperature water 
baths in a greenhouse. Samples of the seed used in the experiment 
were disinfected with 1 to 1,000 mercuric chloride, washed m sterile 
water, and then placed on agar in Petri dishes. In all cases the 
kernels were found to be free from seed-borne fungi. 
The plants growing in the inoculated soil soon became diseased, 
and later many of them died. In all cases the check plants remained 
healthy and the roots were white and disease-free, as indicated in 
Table VI and Plate 4. Microscopic examination showed the pres¬ 
ence of the fungus in the tissues of the infected plants, and a pure 
culture of the organism was isolated from the attacked seedlings in 
the early stages of the disease. Dark-brown lesions developed on 
the roots and culms of all of the infected plants, and many of the 
leaves turned yellow and died. Several experiments similar to the 
above were performed later in the course of other studies, and similar 
results were obtained. All three strains of the fungus were found to 
be readily pathogenic, but the New York strain was more virulent 
and killed a greater percentage of plants than either of the other 
strains. This was possibly due to the fact that the New York 
strain fruited rather freely, making it possible to use ascospore 
Cultures for transfers. 
Table VI .—Pathogenicity of Ophiobolus graminis on Goldcoin wheat grown in 
steamed soil , inoculated with pure cultures of the parasite 
[The controls were uninoculated] 
Strain of fungus 
Number 
of 
plants 
Condition of plants * 
New York__ 
150 
All plants diseased. 
No disease. 
Control_ __ _; 
50 
Oregon........ 
150 
All plants diseased. 
No disease. 
Control__ _ __ _ 
50 
Arkansas__ __ _ . „ „ _ 
150 
All plants diseased. 
No disease. 
Control__ _ _____ .. 
50 
* The disease was most severe in the pots inoculated with the New York strain. Plants grown in the 
pots inoculated with the Oregon strain showed a less severe attack, but they were more severly diseased 
than the plants grown in the pots inoculated with the Arkansas strain of the parasite. 
It was also proved, under aseptic conditions, that Ophiobolus 
graminis caused the take-all disease of wheat. Wheat plants were 
grown on Crone's agar in glass culture tubes 2 y inches m diameter 
