26 ‘BULLETIN 1347, U. S. DEPARTMENT OF AGRICULTURE 
TaBLE 4.—Influence of temperature on the growth of Helminthosporium 
sativum isolated from barley and from wheat 
[Growth determined by diameter of colonies] 
| Temperature (° C.) Diameter of colonies (mm.) 
| | 
Series ; Fungus from barley} Fungus from wheat 
| 
Range Mean 
A B A B 
Bi LE) OnE. © 
| 6-8 7.4 0 Oyo 2 Re ee eee 
| 10-13 a es, 5 315 bie Cae cad Coe) ho ae RT 
15-17 15. 9 15 1S R52 he ts ee es 
No. 1, 6 days’ duration_-0 023 20-23 Pi a OAS| 2th SENS Sree eee SES Sy 
24-26 25. 1 7 (7 ee cree Se 3) SS 
30-33 31.7 26 D0 (ie A ig (cee ee 
[ 34-36 35. 0 7 HET. Sey ee SE Se 
37-40 38. 7 0 Oyl2Si 2 et See elo ee 
7-9 8.0 8 8 ry) AE RE Ee 
8-13 10. 5 35 34 40 35 
16-19 IVES 70 75 75 75 
INo22s.9 daysduration= =<) =e 18-22 20. 0 87 90 O04 a= at ee 
é 24-25 24.5 90 90 iB] ee eee se 
28-33 S{Veiotgl |e ene Sees 60 28 22 
35-36. 5 35. 7 0 0 0 0 
38. 5-39 38. 7 0 ) 0 0 
7. 5-10 9.2 10 11 12 15 
12-13. 5 12.7 29 38 30 37 
15-17. 5 16. 2 49 dl 41 35 
ING, 3:16 Gays’ Curation =. = 2_— 42252-2332 20-21 20. 5 68 56 AOA ota E Dy 
25-26. 5 Pasay 67 59 85 79 
29-31 30. 0 54 53 SO ithe 
34-37 35. 5 Dilwale 23 A 0 2 
Experiments (45) dealing with the influence of different dates of 
sowing in the field show that early fall seeding favors infection. 
Although field experimental evidence is lacking in regard to the in- 
fluence of seeding on infection in spring wheats, from the evidence 
on fall seeding it would seem that late spring sowing would tend to 
increase infection. However, further study is required before this 
conclusion can be drawn definitely. On a basis of temperature 
studies with the parasite, Christensen (73) concluded that early 
spring sowing would be unfavorable for seedling infection. How- 
ever, it should be pointed out that the optimum temperature for the 
growth of a parasite is not necessarily an index to the favorable 
temperature for disease development, as shown in previous work 
with several parasites and diseases. 
As pointed out earlier (43, 45), the optimum temperature for 
growth of the organisms used in the writer’s infection studies is 
near 24° ©. Although the fungus sporulates more abundantly 
at the optimum temperature for growth, sporulation is not seriously 
hindered even at the very high temperatures or at the very low tem- 
peratures. In all cases the organism was grown in the dark in Petri 
dishes of uniform size containing 20 cubic centimeters of potato-glu- 
cose agar made up to a reaction of +10 Fuller’s scale. The mycelium 
from young single-spore cultures was transferred with blocks of 
agar about 3 millimeters square to the center of each of the Petri 
dishes, and the dishes were placed in chambers which, in turn, were 
placed in water-bath incubators held as near the desired temperature 
as possible. The data obtained from these experiments are given 
in Table 4. 
