1923] 



LEHMAN — POD AND STEM BLIGHT OF SOYBEAN 141 



produced vigorous germ tubes when placed in tap water. It is 

 not known how long an individual pycnidium may continue to 

 produce spores under favorable conditions. In cultures on stems 

 spore production is usually terminated by loss of moisture from 

 the substratum. Cultures on stems of Melilotus abla, made 

 August 10 and kept in a covered glass dish to retard drying, were 

 still sporulating on December 22. It is very probable that the 

 same pycnidium may sporulate abundantly in the fall, remain 

 dormant during the unfavorable temperatures of winter, sporu- 

 late again when favorable conditions return, and thus constitute 

 a source from which the new crop may become infected. 



The fact that the causal organism may be isolated from seeds 

 suggests that this is a means of overwintering. Badly infested 

 seeds fail to germinate; others less severely injured germinate 

 but soon after are killed by the parasite. Pycnidia formed on 

 the dead seedlings sporulate during moist weather and thus 

 constitute a source of inoculum from which healthy plants may 



become infected. 



Dissemination of this disease comes about for the most part 

 through infected seed. Much of the infected seed is badly 

 shrunken, light, and non-viable. Most of this will be removed 

 in the cleaning process. Other seeds which become infected at a 

 later stage of development differ very little in weight and appear- 

 ance from healthy seed and are still viable. This class of seed is 

 the chief means of dissemination of this disease over long distances. 

 Wind, rain, and insects all probably serve to spread the disease 

 from Dlant to plant. 



Varietal Susceptibility 



Of the 3 seasons during which pod and stem blight of soy- 

 bean have been under observation, in those of 1920 and 1922 

 only did the disease appear in the field with sufficient prevalence 

 to constitute a basis of observation of varietal susceptibility. 

 In these years, the variety known as Black Eyebrow was attacked 

 first and suffered more severely than others. Austin and Haber- 

 landt were next in point of damage done, although these two 

 varieties were much more lightly attacked than Black Eyebrow. 

 It seems probable, however, that the greater damage done to 



