TOXIN PRODUCTION BY HELMINTHOSPORIUM SATIVUM P.K. & B. AND ITS SIGNIFICANCE IN DISEASE DEVELOPMENT

Abstract

The production of toxic substances by Helminthosporium sativum P.K. & B. on a variety of artificial media was evaluated by means of a barley seed germination test. The results suggest that these substances also limit the growth of the organism itself giving a fixed maximum level of toxin production. Destruction of toxin and renewed production continue until some other factor of the medium limits further growth, and culture filtrates then rapidly become inactive. The toxins are relatively nonspecific and appear to affect susceptible hosts by conditioning them to invasion by the organism. A loose correlation was found to exist between toxin production and pathogenicity in a limited number of Helminthosporium strains. Even in the presence of abundant toxin, however, these strains differed in their ability to invade barley seedlings indicating that factors other than toxin production were also involved in pathogenicity.