Feb. 16,1924 
Physiological Studies on Flag Smut of Wheat 
437 
The percentage of infection decreased from 61.3 per cent in the sowing 
of October 17 to 20.8 per cent in the sowing of October 31. There was no 
infection in the rows sown on or after November 14. These variations in 
the percentage of infection were due probably to soil temperature and 
moisture conditions, which inhibited the germination of the spores at the 
time the wheat was germinating. 
TEMPERATURE AS RELATED TO INFECTION 
A series of experiments was arranged in order to determine the range 
of temperature within which actual infection could occur. On December 
1, 1921, 40 seeds of each of five susceptible varieties of wheat (Bobs, Hard 
Federation, Harvest Queen, Little Club, and White Federation) were 
inoculated heavily with flag-smut spores by moistening the seeds and 
rolling them in dry spores. The seeds were then incubated between 
moist blotting papers in the manner prescribed for standard seed-germi¬ 
nation tests. Through the kindness of W. L. Goss, of the Seed Testing 
Laboratory of the Bureau of Plant Industry, germination chambers 
were secured in which the temperature was controlled within narrow 
limits by electric thermostats and in which a humidity of practically 100 
per cent was maintained. Recording maximum and minimum ther¬ 
mometers were placed in each chamber. The three chambers used had 
average temperatures of 17.8° C., 22.3 0 , and 25.8°, with fluctuations 
between 17 0 and 19 0 , 21.5 0 and 23.5 0 , and 25 0 and 26.6°, respectively, 
during the time the seeds were in the chambers. A fourth lot of seeds 
of the same varieties was placed in an ice box, the temperature of which 
ranged from 6° to 12 0 during the 30 days of the experiment. 
When the seedlings in each chamber had reached the stage where the 
first leaf had pushed through the coleoptile, they were washed thoroughly 
with the aid of a brush until no spores were visible on the seeds. They 
were then transplanted to clean soil in the greenhouse, in December, 
1921, and allowed to grow until flag-smut lesions appeared or, if the plants 
did not become infected, until maturity. The infection percentages 
obtained at each temperature are given in Table VI. 
Table VI .—The effect of temperature on infection of five varieties of wheat by Urocystis 
tritici when inoculated seed was germinated on blotters in temperature chambers , then 
washed and transplanted in greenhouse soil in December , 1921 
Average temperature. 
Variety. 
9° C. 
17.8* C. 
22.3° C. 
25.8* C. 
Total 
num¬ 
ber 
plants. 
Infected 
plants. 
Total 
num¬ 
ber 
plants. 
Infected 
plants. 
Total! 
num- | 
ber 
plants.) 
j 
Infected 
plants. 
Total 
num¬ 
ber 
plants. 
Infected 
plants. 
No. Ip. ci. 
No. 
P. cU 
No. 
P.cL 
No. 
P. ci. 
Bobs. 
30 
5)16.7 
25 
3 
12.0 
* 9 \ 
6 
3 1 - 6 ! 
I 27 
0 
O 
Hard Federation. 
29 
Oj 0 
0 
O 
16 
7 
43*8 
26 
0 
0 
Harvest Queen. 
23 
Oj O 
32 
6 
18.8 
281 
9 
32.1 
3 ° 
0 
0 
bittle Club. 
2 3 
oj 0 
1 
A. 3 
27 ! 
6 
22.2 
31 
0 
0 
White Federation. 
I 
•*0 
l8 
0 
*r* O 
O 
14 
1 
2 
14.3 
0 x 
14 
0 
O 
All varieties. 
105 
Si 4-8 
| 
117 
10 
8-5 
104! 
1 
30 
i 
28.8 
128 
O 
O 
