Production of the Phytoalexin Resveratrol by Grapes as a Response to <i>Botrytis</i> Attack Under Natural Conditions

Abstract Resveratrol (3,5,4′‐trihydroxystilbene) is one of the stress metabolites produced by grapevines in response to fungal infection or injury. The distribution of this compound in limited lesions caused by Botrytiscinerea on ripe grape clusters in the vineyard has been examined. Resveratrol was present predominantly in the non‐infected fruits close to the necrotic area. This localized response can help to arrest the spread of established B. cinerea lesions as long as climatic conditions are unfavourable to the pathogen. When conditions become favorable, i.e. after a mild and humid period rapidly spreading lesions are observed on fruits despite the continued increasing production of resveratrol in the grapes which can reach three‐ to five‐fold the value found before rot intensification. Significant amounts of resveratrol can be found prior to any detectable lesions in fruits collected from apparently healthy clusters thus suggesting that phytoalexin response in initiated soon after the recognition of the pathogen by the plant. The involvement of one or more endogenous signals coming from either the fungus or the plant in the induction of host defence responses has also been discussed.