852 
Journal of Agricultural Research voi. xxm, No.« 
materially within this temperature range. At 32 ° and above the reduc¬ 
tion in germination of the inoculated series was less, in many of the 
series the percentage germination being as high as that in the controls. 
At these higher temperatures, 32 0 and 36° C., the germination of 
both controls and inoculated seed was reduced by what was apparently 
Trichoderma, Penicillium, and other soil organisms attacking the endo¬ 
sperm. The germination of the wheat or corn was not indicative of 
the extent of damage done by the organism, since many of the kernels 
germinated and were blighted afterward. 
The emergence of the seedlings, therefore, was a better indication of 
early blighting, although in many cases, especially at soil tempera¬ 
tures of 16 0 and 20° C., 25 per cent of the seedlings blighted after emerg¬ 
ing. The final index, therefore, was the percentage of disease-free 
and blighted plants at the close of the seedling stage, or about the fourth- 
leaf stage. Ater this period little, if any, blighting occurred. 
The seedling-blight of spring wheat did not occur at soil temperatures 
of 8° C. or below unless moisture and other environing factors were 
varied outside of their critical 
range. At 12 0 , which was about 
the critical soil temperature for 
the production of seedling-blight, 
both in the tanks and in the 
field, series grown with a low 
light intensity blighted badly, 
whereas series grown in good 
light showed only a relatively 
medium degree of blight. In two 
series of Marquis wheat the tem¬ 
peratures were set at io° instead 
of 12 0 , with the result that 
seedling-blight was reduced 75 
per cent below that at a soil 
temperature of 12 0 . The blight 
was most severe at soil temper¬ 
atures of 16° to 24 0 . At this 
range the seedlings were blighted 
before emerging and also showed yellowing and wilting during the first- 
leaf and second-leaf stages. At the higher temperatures, 28° and higher, 
the blighting usually occurred after the seedlings had emerged. At these 
temperatures also, as previously stated, the reduction in germination by 
the parasite became less marked. The maximum rate of emergence of 
the seedling occurred at about this same temperature range. In all 
probability, therefore, the seedling developed so rapidly at these temper¬ 
atures that infection did not take place until after emergence (PI. 5, C.). 
The average dry weight per plant, of roots and of tops, was the same 
in the inoculated and uninoculated series at the soil temperature of 
8° C. At soil temperatures of 16° to 28° the weight of both roots and tops 
in the inoculated series decreased several per cent below that in the con¬ 
trols, which indicated the action of the parasite on the roots of the 
remaining plants even though blighting did not occur. 
At the higher temperatures, 32 0 to 36° C., there was considerable 
reduction in the germination and some blighting in both control and 
inoculated series, especially when grown in nondisinfected soil. Isola¬ 
tions from such seedlings gave some Gibberella saubinetii at 32 0 but 
L 
\ 
\ 
’ CHECK 
0. yjnuurni. / n 
1 1 1 
' 12 /6 20 24 26 32 36 
SOIL TEMPERATURE -DEGREES CENTIGRADE 
Fig. 5. —Graph showing relation of soil temperature to 
the development of seedling-blight of Marquis wheat. 
Average of eight experiments. The distance between 
the heavy and light lines shows the percentage of 
seedling-blight. The wheat seedlings blighted at tem¬ 
peratures from about 12° to about 34 0 C. 
