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. c inerea, although they can harbour the pathogen without any visible signs of disease development. After veraison, B. cinerea can produce disease in sus ceptible grape varieties (e.g. Gamay), but remains quiescent in resistant v arieties (e.g. Gamaret). Pathogen resistance in the quiescent stage is not yet fully understood, but is thought to involve multiple parameters includi ng chemical and mechanical factors. The pathogenesis of B. cinerea is essen tially linked to excretion of lytic enzymes such as polyphenoloxidases or l accases. One lytic enzyme, stilbene oxidase, can detoxify grape stilbenic p hytoalexins, destroying the grapes' defence mechanisms and allowing the fun gus to grow. Some constitutive grape berry phenolic compounds, however, str ongly inhibit stilbene oxidase activity. Constitutive berry phenolic compou nds were isolated from Gamay and Gamaret varieties and their biological act ivities, concentrations and chemical structures were comparatively analysed . Catechin, epicatechin-3-O-gallate, trans-caftaric, trans- and cis-coutari c and trans-coumaric acids, taxifoline-3-O-rhamnoside and quercetine-3-O-gl ucuronide were identified as potent stilbene oxidase inhibitors. High conce ntrations of some of those compounds could be closely involved in the persi stence of the quiescent stage of B. cinerea, between bloom and veraison in all grape varieties and after veraison in resistant varieties. (C) 1999 Els evier Science Ltd. All rights reserved.