204 
Journal of Agricultural Research 
Vol. XXVI, No. s 
Table IV .—Effects of soil temperatures on the infection of Hannchen and Hanna barley 
seedlings with Helminthosporium sativum cultures 51a and 350, at Madison , Wis. t 
in 1921 
Experiment 1. 
Experiment 2. 
Experiment 3. 
Summary.^ 
Artificially inoculated 
soil (culture 51a). 
Hannchen barley seed 
used. Started Feb. 7, 
1921; ended Feb. 23, 
Mar. 12 and 18, 1921. 
Soil moisture 44.4 per 
cent of moisture-hold¬ 
ing capacity. 
Artificially inoculated 
Hanna barley seed, 
culture 51a used. 
Started Mar. 3, 1921; 
ended Mar. 21, 1921. 
Soil moisture 43.2 
per cent of moisture¬ 
holding capacity. 
Artificially inoculated 
Hanna barley seed, 
culture 350 used. 
Started Apr. 29, 1921; 
ended May 21, 1921. 
Soil moisture 32.8 
per cent of moisture¬ 
holding capacity. 
Average amount of infec¬ 
tion at each soil tempera¬ 
ture in three experi¬ 
ments with Hannchen 
and Hanna barley seed¬ 
lings. 
Aver¬ 
age 
soil 
tem¬ 
pera¬ 
tures. 
Num¬ 
ber of 
plants. 
Infec¬ 
tion 
rating. 
Aver¬ 
age 
soil 
tem¬ 
pera¬ 
tures. 
Num¬ 
ber of 
plants. 
Infec¬ 
tion 
rating. 
Aver¬ 
age 
soil 
tem- 
pare- 
tures. 
Num¬ 
ber of 
plants. 
Infec¬ 
tion 
rating. 
Average 
soil tem¬ 
peratures. 
Num¬ 
ber of 
plants. 
u nfec- 
tion 
rating. 
°C 
a 8 
b 12 
c 16 
c 20 
c 24 
c 28 
c 32 
c 35 
90 
89 
94 
93 
92 
83 
5 i 
6 
24.4 
38. 2 
36. I 
44. 2 
46.4 
55-6 
34-8 
41. 6 
°C. 
16 
20 
24 
28 
32 
34 - $ 
no 
77 
102 
9 i 
88 
55 
20. 6 
34-3 
44.6 
72.3 
53 ' 0 
30. 0 
•c. 
12 
l6 
20 
24 
28 
32 
34-5 
47 
a jj 
37 
28 
13 
14 
6 
33 *o 
49. 0 
69. 0 
63. 0 
82. 0 
83-3 
16. 6 
°C. 
12 
16 
20 
24 
28 
32 
34 - 5-35 
47 
74 
69 
74 
62 
5 i 
22 
33 ' 0 
35 ' 2 
49 ' 1 
5 i -3 
69.9 
63.6 
29. 4 
a Ended Mar. 18. 
* Ended Mar. 12. 
c Ended Feb. 23. 
d Number of seedlings reduced due to ravages of mice. 
« This summary does not include the 8° or the 12 0 temperature data from experiment 1, since these 
are for older plants. 
While the results of these experiments show that the Helminthosporium 
disease can develop at all of the soil temperatures employed, they also 
indicate that the disease is not favored by either relatively high or rela¬ 
tively low temperatures. From the curves shown in figure 1 it is strik¬ 
ingly evident that rather high soil temperatures (28° to 32 0 C.) favor the 
development of the disease on the underground parts of the plants during 
the early period of their development. Although the exact explanation 
of this result can not be given at this time, it should be noted that the 
disease temperature optimum is above that for the best development of 
the host plants and also above that for the best vegetative growth of the 
parasite in pure culture, as is shown in figure 1. This relation suggests 
that the relatively high temperature requirements for the best develop¬ 
ment of the parasite (24 0 to 28°) together with the probable weakening of 
the hosts (host optimum 20° to 24 0 ) at such temperatures partially ex¬ 
plain the high optima (28° to 32 0 ) for the development of the disease. 
It should also be noted that the optimum temperature is apparently 4 0 
higher in the case of Harvest Queen wheat than in the case of Marquis 
wheat or the barleys. The same tendency is suggested in the data 
published by Dickson (4) on the Fusarium seedling blight of wheat, 
except that he reports lower optima. The explanation of these relations 
may be tied up with differences in varietal susceptibility or with a num¬ 
ber of other unanalyzed factors. 
