Mar. 17,1923 Influence of Soil Temperature on Seedling-Blight 857 
phytes, especially bacteria, which often crowded out Gibberella saubinetii 
entirely. 
In corn, infection takes place and blight progresses, then, at all tempera¬ 
tures below 2 4 0 C. The most rapid development of the disease and the 
maximum blighting occur at 12 0 and 16 0 . Below this, namely, at 8°, 
where wheat is entirely resistant to the attack of this parasite, corn 
succumbs entirely (fig. 8 and PI. 4 and 5). 
As the temperature range for the production of blight in this warm- 
climate plant is the reverse of that for wheat, a cool-temperature plant, 
it is only logical to say that this parasite is capable of attacking both 
hosts during their seedling stages when they are subjected to unfavor¬ 
able environmental conditions. This fact is brought out even more 
strikingly in the following combined moisture and temperature studies. 
INFLUENCE OF SOU/ MOISTURE ON THE DEVELOPMENT OF SEEDLING- 
BLIGHT IN WHEAT 
Earlier studies conducted in connection with this problem demon¬ 
strated that the influence of moisture on the seedling-blight of wheat 
was similar to that of temper¬ 
ature, 7 for low soil moistures in¬ 
creased the susceptibility of the 
wheat seedling and thus increased 
the virulence of the attack. The 
influence of soil moisture grad¬ 
ually decreased until at 45 to 50 
per cent of the moisture-holding 
capacity of the soil this factor 
ceased to influence blighting. 
As a consequence all the tem¬ 
perature experiments were con¬ 
ducted with a soil at 60 per 
cent of the moisture-holding 
capacify, assuming that in this 
way moisture could be separated 
from temperature and the critical 
range of the latter be determined. 
In order to study further the 
influence of moisture on the 
host and parasite two different 
temperature series of plants were 
grown at three different soil- 
moisture contents, 30, 45, and 6° per cent of moisture-holding capacity. 
The cans of soil at different moisture contents were prepared, inocu¬ 
lated, and sown as described in the previous experiments. The seed 
was inoculated with the heavy conidial suspension, 325,000 conidia per 
cubic centimeter, in order to get the maximum temperature and moisture 
response. The average percentage results of the two series are given in 
Table 8 and figure 9. 
7 Credit is gladly given to Mr. B. Koehler for conducting the earlier studies on the relation of soil moisture 
to seedling-blight. 
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Fig. 9. —Graph showing relation of soil temperature 
and moisture to the development of seedling-blight 
of wheat. Compare the solid lines with the broken 
lines. Note the abundant blighting at 8* C. in the 
soil with a moisture content of 30 per cent of the mois¬ 
ture-holding capacity. 
