FACTORS INFLUENCING THE PATHOGENICITY OF 

 HELMINTHOSPORIUM SATIVUM 



By LOUISE DOSDALI^ 



INTRODUCTION AND HISTORICAL REVIEW 



In 1910 Pammel, King and Bakke (9) described a new Helmin- 

 thosporium disease of barley which they called "late blight." The 

 causal organism was named Helminthosporium sativum n. sp. Pammel, 

 et al., had observed the disease in Iowa in 1907 and 1908. In. 1909 it 

 was very serious. In the same year, they report that it was also found 

 in South Dakota, Minnesota, and Saskatchewan. These authors de- 

 scribe the disease as follows : "Brown spots of irregular outline occur 

 upon the leaves causing them to turn brown. The leaves are easily 

 broken up, and in some cases completely destroyed. The disease also 

 occurs upon the glumes, spikelets and seed. The straw at harvest 

 is dull brown, and instead of standing erect becomes a tangled mass. 

 The date of ripening of the grain corresponds with the time of full 

 development of the late blight." They observed that there was con- 

 siderable difference in varietal susceptibility, the degree of .infection 

 ranging from o to 100 per cent. Late blight was considered the most 

 serious disease of barley in Iowa. 



In 1913 A. G. Johnson (7) differentiated clearly the three Helmin- 

 thosporium diseases of barley in Wisconsin, and he designated the one 

 caused by H. sativum P.K.B., the "American blotch disease." 



Louise Stakman (n), in 1920, showed that a Helminthosporium 

 similar to the organism described as H. sativum by Pammel, King 

 and Bakke, but isolated from various parts of diseased wheat and rye 

 plants, was capable of causing a serious seedling blight of these hosts, 

 and could also attack the older parts of the plants, namely, the leaves, 

 nodes, culms, roots, glumes, and grains. In addition to wheat and 

 rye, successful infections were obtained on barley and a number of 

 grasses. In the spring and early summer of 1919, serious attacks of 

 seedling blight caused by Helminthosporium occurred in practically all 

 the wheat-growing regions of Minnesota. 



F. L. Stevens (12), also in 1920, reported that a species of 

 Helminthosporium was constantly associated with foot rot disease of 

 wheat in Madison County, 111. Inoculations with the organism gave 

 positive results. He concluded that Helminthosporium was the cause 

 of the disease. 



1 The writer wishes to express her appreciation to Dr. E. C. Stakman, under whom the 

 work was done, for advice and criticism, and to Mr. M. N. Levine for his helpful criticism in 

 the presentation of the biometrical studies. 



43978 



