PATHOGENICITY OF H. SATIVUM 5 



2. Relation of hydrogen-ion concentration and temperature to Fpore 

 germination. 



3. Development of the disease in various types of soil. 



4. Influence of soil moisture on the development of the disease. 



5. Influence of soil fertilization on the development of the disease. 



6. Comparison of several root-rotting organisms. 



7. Morphological variation in the fungus with regard to its specific 

 identity. 



METHODS 

 SOURCE OF PATHOGENE 



During the spring and summer of 1920, tissue cultures were made 

 from lesions caused by Helminthosporium on cereals and grasses. 

 Twenty-two strains (isolations from various parts of different hosts 

 or from different localities) of the sativum type were obtained from 

 the roots, stems, nodes, leaves, and kernels of barley; from the roots, 

 stems, leaves, and kernels of wheat ; and from leaf spots of various 

 grasses. Material was obtained from Anoka, Clay, Mahnomen, Nicol- 

 let, Ramsey, and St. Louis counties in Minnesota; from Tennessee, 

 and from Spruce Grove and Edmonton, Alberta. 



Seven of these strains were selected for preliminary inoculation 

 experiments. As a virulent root-rotting organism was desired, only 

 soil inoculations were made. Four-inch pots filled with soil were treated 

 with live steam for two hours on each of three successive days. Six 

 pots of such soil were inoculated with each of the various strains of 

 Helminthosporum. For this purpose, spores were scraped from the 

 surface of potato dextrose agar cultures and mixed with water. The 

 suspension of spores was poured over the soil, and the pots were in- 

 cubated for several days. Three pots which had been inoculated with 

 each strain were then sowed with Marquis wheat and three with 

 Manchuria barley (Minn. 105). Some infection was obtained in each 

 case, on both the leaves and the roots. (The check plants were slightly 

 infected, as the seed had not been treated.) The plants inoculated 

 with strain 82a, however, were decidedly more heavily attacked than 

 the others. This was especially true of the barley plants. A Helmin- 

 thosporium of the sativum type was re-isolated from lesions on both 

 the barley and the wheat. A single spore culture was then made from 

 the original 82a culture, and all subsequent work was done with this 

 single spore strain. 



Culture 82a was originally isolated from the darkened base of 

 badly stunted barley plants sent to the laboratory from the peat plots 

 on the Fens experimental field, St. Louis County, Minn., in the summer 



