830 
Journal of Agricultural Research 
Vol. XXXI, No. 9 
RESULTS 
HOST DEVELOPMENT 
The best germination of Goldcoin wheat was obtained at soil tem¬ 
peratures ranging from 12° to 20° C. and at soil moistures ranging 
from 54.4 to 80 per cent of the moisture-holding capacity. As in the 
case of Harvest Queen and Marquis wheats {12) } germination takes 
place first at the high temperatures and it is retarded at the low tem¬ 
peratures. During the periods of the experiments (20 to 31 days) 
the plants produced the greatest dry weight of the aboveground por¬ 
tions at temperatures ranging from 20° to 28° C. and at soil moistures 
ranging from 71.6 to 80 per cent. Root development seemed to be 
stimulated at soil temperatures ranging from 16° to 26°. All of the 
soil moistures employed in these experiments seemed to be about 
equally favorable for root development. 
DEVELOPMENT OF THE PARASITE 
One of the writers (Davis) has studied the influence of temperature 
on the growth of the parasite in pure culture, and the results are 
given in another paper {1 ). It was found that growth took place at 
temperatures ranging from 4° to 33° C. The optimum temperatures 
for growth varied somewhat for the strains of the parasite studied. 
Howevei this variation was within the limits of 19° to 23°. The 
optimum ior the New York strain was rather wide, growth seeming to 
proceed equally well anywhere between 19° and 24°, whereas the 
optimum temperature for the growth of the Oregon strain of the para¬ 
site seemed to be between 23° and 24°. 
DISEASE DEVELOPMENT 
In no case did Ophiobolus infection occur in any of the plants grow¬ 
ing in the uninoculated controls (pi. 1, A). The results obtained in 
all of the inoculated experiments 4 are tabulated in Tables II, III, IV, 
V, VI, and VII, and the data are shown graphically in Figures 1 to 7, 
inclusive. Plate 1, B illustrates the results obtained on a represen¬ 
tative one-tenth of the plants grown in the inoculated soil in Experi¬ 
ment IB. 
♦ In McKinney, H. H. take-all and foot-rot investigations. U. S. Dept. Agr., Bur. Plant Indus., 
Cereal Courier 14: 23-25. 1922. [Mimeographed] the writers reported a preliminary experiment in which 
the greatest amount of injury took place in soil held at 22° to 24° C. The population of this experiment was 
very small and the amount of parasite used was too great for accurate results, as shown by later experi¬ 
ments. Owing to these circumstances and the fact that data were based entirely on top injury, these results 
are not considered significant and are not included among the results of the subsequent experiments. 
EXPLANATORY LEGEND FOR PLATE 1 
Influence of soil temperature on the infection of Goldcoin wheat seedlings and young plants by Ophiobolus 
graminis 
A. —A representative tenth of all the plants ^rown at the various soil temperatures in the uninoculated 
soil of experiment IB. These plants were all free from infection, as was the case with all of the other unin¬ 
oculated plants grown in all of the experiments 
B. —A representative tenth of all the plants grown at the various soil temperatures in the inoculated soil 
of experiment IB. Note the very severe infection in the plants grown at 12° C.; most of these plants died. 
Also note the severe root rotting on plants grown at soil temperatures below 24° C. 
