'* 4 TECHNICAL BULLETIN 17 



'''In Jaw4*: 1922, Hamblin (5) reported a Helminthosporium foot- 

 rot disease of wheat in New South Wales, Australia. The disease 

 symptoms are very similar to those of the true take-all caused by 

 Ophiobolus graminis Saccardo, but there are distinguishing characters. 

 Hamblin's description of the foot-rot in Australia corresponds very 

 closely with that of Mrs. Stakman and of F. L. Stevens. His descrip- 

 tion of the poorly developed root system with an abnormal develop- 

 ment of root hairs close to the culm, giving the dead or dying root a 

 "fuzzy" appearance, and the frequent growth of secondary roots above 

 the first node of the affected straws, applies equally well to conditions 

 observed in Minnesota during 1921. In Hamblin's opinion, the Hel- 

 minthosporium disease was responsible for far more damage in 1921 in 

 Australia than was the better known take-all. 



In recent years, a foot-rot disease of cereals, particularly wheat, 

 rye, and barley, has been destructive in certain localities in Minnesota. 

 This was especially true on certain peat lands in Anoka and St. Louis 

 counties and on some of the sandy soils in Anoka, Nicollet, and 

 Mahnomen counties. A Helminthosporium of the sativum type has 

 been consistently isolated from the diseased plants. This organism 

 is very widely distributed throughout the cereal growing region. The 

 severity of its attack apparently must be greatly influenced by eco- 

 logical conditions. In order to obtain more detailed and accurate in- 

 formation concerning these conditions, a study of the physiology of 

 the fungus, to the extent of its possible correlation with the pathogenicity 

 under given conditions, was undertaken. 



PROBLEM 



In this study attention was directed primarily to the root- and foot- 

 rots caused by H sativum. Little attention was given to secondary in- 

 fections on leaves and heads. The soil environment was, therefore, 

 of chief concern. In analyzing the factors which might influence the 

 development of a disease of this type, temperature, moisture, and 

 acidity would affect the growth of both the pathogene and the host, 

 and possibly also the reaction between the two. The' vigor of the host 

 conceivably might greatly influence the development of a disease caused 

 by a facultative parasite, such as H. sativum. The type of soil in 

 which they grew and the available nutriment might, therefore, change 

 the balance between host and pathogene. It is difficult to separate 

 and analyze the individual factors, because certain combinations intro- 

 duce various complexities which are difficult to interpret. 



The following phases of the problem were investigated especially: 



i. Relation of temperature to the growth of the fungus, to spore 



germination, to infection, and to the development of the disease. 



