A Volatile Self-Inhibitor from Colletotrichum Graminicola

ABSTRACT

Germination of conidia of Colletotrichum graminicola was inhibited by volatile metabolites produced by C. graminicola cultures grown on oatmeal agar. The volatile material suppressed conidium germination but did not kill conidia. Sorghum mesocotyls inoculated with conidia and exposed to volatiles from cultures failed to develop symptoms because conidia were prevented from germinating, forming appressoria, and penetrating into the tissue. In contrast, conidia on inoculated, nonexposed mesocotyls that were incubated in identical chambers produced appressoria and penetrated the tissue with the result that seedlings responded by the production of deoxyanthocyanidin phytoalexins. Attempts to identify the volatile inhibitor by gas chromatography and mass spectrometry showed that acetic acid was the primary component of the volatile preparation. It is believed that the acetic acid was formed as a result of degradation of a parent compound during gas chromatography suggesting that the native volatile self-inhibitor is a substituted acetate.

Key Words:

• conidium germination
• deoxyanthocyanidin
• phytoalexin