TRICHOTHECENES AND THEIR POSSIBLE INVOLVEMENT IN PATHOGENICITY OF MYROTHECIUM RORIDUM.

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Macrocyclic trichothecene roridin E, produced in culture or in plant host tissue by a strain of Myrothecium roridum pathogenic to muskmelon (Cucumis melo L), and roridin A and myrotoxin A+B, trichothecenes from M. roridum strains nonpathogenic to muskmelon were investigated for their role in pathogenicity of M. roridum. Roridin E did not affect the growth of the pathogen in vitro but significantly increased sporulation and lesion diameter on inoculated muskmelon leaves whereas roridin A and myrotoxin A+B did not affect sporulation and lesion size. All trichothecenes induced phytotoxic reactions in muskmelon and increased electrolyte leakage from muskmelon leaf tissue. Muskmelon cultivar rankings with respect to the phytotoxic responses and level of electrolyte leakage induced by roridin E were similar to cultivar rankings after inoculation with M. roridum. Roridin A and myrotoxin A+B did not elecit cultivar-specific responses.
Characteristic lesions caused by the pathogen were similar to lesions caused by roridin E. These results suggest that roridin E is involved in the establishment of pathogenicity by M. roridum in muskmelon tissue.