CUTIN, CUTINASE AND ESTERASE AS RELATED TO THE INDUCED SYSTEMIC RESISTANCE OF CUCUMBER AGAINST COLLETOTRICHUM LAGENARIUM

Cucumber leaf cutin was isolated from leaves 2 and 3 of unimmunized (control) plants and plants systemically immunized by infiltrating leaf 1 with conidia of Colletotrichum lagenarium. The cutins were used as sole carbon sources in a liquid medium, and their effects on the growth and production of cutinase and esterase by C. lagenarium were compared. C. lagenarium grew better on the medium containing cutin isolated from leaves of control plants than on the medium containing cutin from leaves of immunized plants. The differences in fungal growth were statistically significant 9, 12 and 15 days after inoculation of the media. Statistically, significant differences were not apparent in fungal esterase and cutinase activities in media containing the cutins. The activity of esterase produced by C. lagenarium on control and systemically-immunized cucumber leaves was also studied. Esterase activity increased sooner in water droplets containing conidia of C. lagenarium retrieved from leaves of control plants as compared with those from leaves of immunized plants. Our data suggest that cutin from immunized leaves may be hydrolysed with greater difficulty by the fungus and cutin and/or other leaf surface components in immunized leaves may inhibit activity or reduce production of fungal esterase.