Resistance factors to grey mould in grape berries:: identification of some phenolics inhibitors of Botrytis cinerea stilbene oxidase

Grey mould caused by Botrytis cinerea is one of the most important diseases of grapes. Between bloom and veraison, grape berries are resistant to B. cinerea, although they can harbour the pathogen without any visible signs of disease development. After veraison, B. cinerea can produce disease in susceptible grape varieties (e.g. Gamay), but remains quiescent in resistant varieties (e.g. Gamaret). Pathogen resistance in the quiescent stage is not yet fully understood, but is thought to involve multiple parameters including chemical and mechanical factors. The pathogenesis of B. cinerea is essentially linked to excretion of lytic enzymes such as polyphenoloxidases or laccases. One lytic enzyme, stilbene oxidase, can detoxify grape stilbenic phytoalexins, destroying the grapes' defence mechanisms and allowing the fungus to grow. Some constitutive grape berry phenolic compounds, however, strongly inhibit stilbene oxidase activity. Constitutive berry phenolic compounds were isolated from Gamay and Gamaret varieties and their biological activities, concentrations and chemical structures were comparatively analysed. Catechin, epicatechin-3-O-gallate, trans-caftaric, trans- and cis-coutaric and trans-coumaric acids, taxifoline-3-O-rhamnoside and quercetine-3-O-glucuronide were identified as potent stilbene oxidase inhibitors. High concentrations of some of those compounds could be closely involved in the persistence of the quiescent stage of B. cinerea, between bloom and veraison in all grape varieties and after veraison in resistant varieties. (C) 1999 Elsevier Science Ltd. All rights reserved.