PATHOGENICITY OF H. SATIVUM 25 



While the germination of //. sativum spores in these solutions is 

 not necessarily the same as in a soil solution, certain general relation- 

 ships may be pointed out. The spores will germinate through a wide 

 range of hydrogen-ion concentration. Optimum germination occurs 

 near the neutral point or on the alkaline side. The spores will tolerate 

 high degrees of alkalinity. Germination studies in solutions more 

 nearly approximating soil solutions are still desirable from the stand- 

 point of a closer analysis of the development of the disease. 



INFECTION 



Marquis wheat and Lion barley were grown under sterile conditions 

 in test tubes containing white sand. When the seedlings were about 

 an inch high, the coleoptile was inoculated with a suspension of spores 

 and incubated at various temperatures. At 22, 25, and 30 C. char- 

 acteristic minute brown lesions were visible after 18 hours. At the 

 end of five days no infection had occurred at 6 on the barley ; very 

 light infection was evident on the wheat. Light infection also occurred 

 on both wheat and barley at 14 and 34, and on wheat at 30. Mod- 

 erate to heavy infection occurred on both hosts at 22 and 25, and 

 also on the barley at 30. In these cases, the typical basal browning 

 characteristic of the seedling blight occurred. This was as far as it 

 was possible to follow the disease under these conditions. The results 

 indicate that infection will take place to some extent through a rather 

 wide range of temperature from 6 to 34 C. but that for the severe 

 development of the disease the range is narrower, probably 22 to 

 30. To some extent moisture, as well as temperature, was the limit- 

 ing factor at the extremes. 



F. L. Stevens (13) reports that, "In an adaptation of the rag-doll 

 seed tester, which allows the use of seedlings under aseptic conditions 

 and variations of moisture and temperature as desired, inoculation by 

 spores of Helminthosporium upon the uninjured sheath was followed 

 within 24 hours by entrance of the mycelium into the host cells, and 

 within 48 hours by a browned, diseased spot visible to the naked eye. 

 Subsequently, when conditions favored, the mycelium invaded the inner- 

 most leaves and caused general rotting and death. When inoculated 

 upon the roots, there was general invasion of the cortex with very slight 

 discoloration." Stevens does not report under what conditions of tem- 

 perature and moisture the disease developed best. 



An attempt was made to arrive at the temperature relations gov- 

 erning leaf infection by inoculating fresh excised leaves with spores 

 of H. sativum, placing them in moist chambers and incubating them at 

 various temperatures. After incubating for 72 hours at 6 C., both 



