A VOLATILE SELF-INHIBITOR FROM COLLETOTRICHUM-GRAMINICOLA

Germination of conidia of Colletotrichum graminicola was inhibited by volatile metabolites produced by C. graminicola cultures grown on oatm eal agar. The volatile material suppressed conidium germination but di d not kill conidia. Sorghum mesocotyls inoculated with conidia and exp osed to volatiles from cultures failed to develop symptoms because con idia were prevented from germinating, forming appressoria, and penetra ting into the tissue. In contrast, conidia on inoculated, nonexposed m esocotyls that were incubated in identical chambers produced appressor ia and penetrated the tissue with the result that seedlings responded by the production of deoxyanthocyanidin phytoalexins. Attempts to iden tify the volatile inhibitor by gas chromatography and mass spectrometr y showed that acetic acid was the primary component of the volatile pr eparation. It is believed that the acetic acid was formed as a result of degradation of a parent compound during gas chromatography suggesti ng that the native volatile self-inhibitor is a substituted acetate.