Mar. 17,1933 Influence of Soil Temperature on Seedling-Blight 
861 
Table IX. —Average soil and air temperatures during germination periods of Marquis 
wheat at Madison, Wis., in the spring of 1920 
Duration of germination period. 
Average soil tempera¬ 
tures, 4 inches deep. 
Average air tempera¬ 
tures, 6 inches above soil. 
Num¬ 
Dates. 
ber of 
Mean.o 
Min. 
Max. 
Mean.® 
Min. 
Max. 
days. 
°C. 
°C. 
°C. 
°C. 
°C. 
°C. 
Mar. 31 to Apr. 20. 
21 
4 - 5 
2 - 3 
7-7 
1.8 
-I. 9 
6-3 
Apr. 22 to 30. 
9 
8.9 
6. 2 
12-5 
6.7 
3-2 
IO. 7 
May 1 to 8. 
8 
12.3 
7-4 
17.8 
7.0 
2. 0 
14*5 
May 10 to 16. 
7 
13-9 
9.4 
18.6 
8.9 
4. 1 
14.2 
June 9 to 13. 
5 
26. 2 
20. 7 
3 2 ‘ 3 
22. 7 
17.4 
28. 1 
a Mean temperatures in this and succeeding tables were computed by adding together the temperatures 
recorded at hourly intervals during the germination period and dividing the sum by the number of hours 
in the period. 
Table X. —Relation of date of seeding to the development of seedling-blight of Marquis 
wheat at Madison, Wis., in the spring of 1920 
Date of seeding. 
Average 
number 
of days 
for emer¬ 
gence. 
Average percentage stand. 
Clean seed 
not 
inoculated. 
Clean seed 
inoculated 
With 
GibbereUa 
saubtnetii. 
Naturally 
scabbed 
seed. 
Mar. 31 . 
22 
69. 0 
74.2 
66.5 
Apr. 2. 
8 
8 a. S 
79.I 
72-5 
May . . 
8 
8 a 1 
37*5 
47.O 
May 10. 
7 
74-7 
27-5 
22.3 
Jlllle 9 . . * . r r. 
6 
38.0 
42.0 
The stands of healthy plants from the uninoculated, the inoculated, 
and the scabbed seed were practically the same for the first planting, 
which required 22 days to germinate—that is, the period from March 31 
to April 20. The germination in all seed-lots was lowered by continued 
freezing and thawing during germination, but no blight appeared in any 
of the plots. The stand in the second series of seedings was greatly in¬ 
creased, due to more favorable weather during the germination period 
of 8 days. A limited number of blighted seedlings, however, appeared 
toward the last of the period in both the inoculated and scabbed series. 
The percentage of disease-free seedlings in the next two seedings was 
reduced 43 to 47 per cent, respectively, below the stand in the controls. 
The average mean temperature during the germination period and the 
daily temperature curves in figures 10 and 11 show a soil temperature 
below 12 0 C. for the first two seedings, and above 12 0 for the two May 
seedings. The critical soil temperature for seedling-blight in the field, 
therefore, corresponds very closely with that in the s6il-temperature 
tanks. 
The results from the last seeding, June 9, which was made during the 
extremely high temperatures, also agreed with the greenhouse results. 
That is, while germination was greatly reduced in both control and inocu¬ 
lated plots, no seedling-blight appeared, due probably to high tempera¬ 
tures inhibiting the development of the parasite. 
