1020 Walter H. Burkholder 



Except under very prolonged drought there is sufficient moisture in the 

 soil for spores to germinate and infect the host. Temperature appears 

 to be the chief limiting factor, and from recent articles on the subject this 

 varies greatly with the pathogene and the host. Gilman (1914 and 1916) 

 considers high temperature favorable to infection of cabbage by Fusarium 

 conglutinans Wr. Tisdale (1917 a) came to similar conclusions in his 

 observations on the infection of flax by Fusarium lini Bolley, and states 

 that from 15° to 16° C. is the minimum temperature at which infection 

 will occur. Ramsey (1918), on the other hand, is of the opinion that a 

 cool, moist soil is essential for infection by Spongospora subterranea 

 (Wallr.) Johnson to occur on potato tubers. 



In working with Fusarium martii phaseoli, the organism under con- 

 sideration, Roddick (1917) foimd that infection occurred between tem- 

 peratures of 15° and 34° C. His results have been substantiated by the 

 writer. These temperatures include, with the exception of a few cases, 

 the limits of the soil temperature found to exist at Perry, New York, 

 during the growing seasons of 1916 and 1917. Records were taken at 

 that place with a continuous self-recording soil thermograph. In no case 

 was the temperature recorded higher than 30° C, and only a few times 

 did it drop below 15° C; in the latter instances it always rose imme- 

 diately. From these data it is apparent that the soil temperature about 

 Perry, which is near the center of the bean district, is always sufficient 

 for the bean plant to become infected with F. martii phaseoli. 



Besides the effect that soil temperature has on infection, there is also 

 its effect on the progress of the disease after infection has once taken 

 place. The latter is possibly of the greater importance. The problem 

 here is more complex and very few definite conclusions have been drawn 

 pertaining to it. Reddick, in the article cited above, has shown that soil 

 temperature influences very greatly the growth of the bean plant. High 

 temperatures allow much more rapid yet healthy growth than do low 

 temperatures. Thus it is difficult to analyze data concerning the effect 

 of the disease at different temperatures of the soil, since the rate of growth 

 of the host plant varies so much. There were, however, in experiments 

 conducted under these conditions, indications that the disease is more 

 severe at a soil temperature of 22° C. than at 34° C. The former tem- 

 perature is nearer the average of the soil temperature found in the bean 

 district during the growing seasons of 1916 and 1917. 



