Sarig, P., Dept. Postharvest Sci. Fresh Prod., Agricultural Research Organization, Ber-Dagan 50250, Israel
Zutkhi, Y., Dept. Postharvest Sci. Fresh Prod., Agricultural Research Organization, Ber-Dagan 50250, Israel
Monjauze, A., Dept. Postharvest Sci. Fresh Prod., Agricultural Research Organization, Ber-Dagan 50250, Israel
Lisker, N., Department of Agronomy, Agricultural Research Organization, Ber-Dagan 50250, Israel
Ben-Arie, R., Dept. Postharvest Sci. Fresh Prod., Agricultural Research Organization, Ber-Dagan 50250, Israel

The phytoalexins resveratrol and pterostilbene were produced in berries of Vitis vinifera following inoculation with Rhizopus stolonifer. The amounts produced in cv. Perlette were similar to those elicited by exposure to u.v.-C irradiation (254 nm) for 10 min. The time course for the accumulation of both stilbenes differed for each method of elicitation. Maximum resveratrol accumulation in grape berries was 4.0-8.5 times higher than that of pterostilbene depending on cultivar. Both stilbenes reached highest concentrations 24 h after inoculation and thereafter these declined gradually. Following u.v.-C irradiation, resveratrol reached its highest concentration 18 h after exposure and this declined rapidly thereafter; whilst pterostilbene reached its peak after approximately 40 h. This pattern was observed in all cultivars at all stages of development. The phytoalexins were fungitoxic in vitro, inhibiting spore germination and hyphal growth of R. stolonifer and Botrytis cinerea. The dosage required to inhibit each pathogen was higher than that which accumulated in treated berries. A negative correlation was found between the potential for resveratrol accumulation in different cultivars and their susceptibility to decay caused by R. stolonifer. Phytoalexin accumulation declined with advancing maturity of the berries, coinciding with their increased susceptibility.