The Significance of Stilbene-Type Phytoalexin Degradation by Culture Filtrates of Botrytis Cinerea in the Vine-Botrytis Interaction

Abstract

Phytoalexins, antimicrobial compounds, synthesized by a plant in response to infection or a variety of stresses are known to be the most efficient way by which grapevines withstand an attack by Botrytis cinerea Pers., the causal organism for grey mould. In that plant, such responses include the production of a simple stilbene, resveratrol, and the biosynthetically related compounds, viniferins and pterostilbene. If stilbene-type phytoalexins represent a contributory factor in the resistance of grapevines to B.cinerea, the capacity of the pathogen to metabolize antifungal compounds released by the host could also play a significant role in the outcome of the interaction between grapevines and B.cinerea.Indeed, the net accumulation of phytoalexins within plant tissues infected by various pathogens is probably controlled by a balance which may result, on the one hand, from the ability of the host cells to resist colonization by creating an inhibitory barrier for the parasite, and, on the other hand, from tolerance of the pathogen to antifungal compounds produced by the plant and from its ability to detoxify the phytoalexins to which it is exposed. Thus, the resistance of plants to infection depends on the phytoalexin production/degradation balance following attack by the pathogen. A variety of factors can alter this balance in favour of either the parasite or the host, resulting in non-compatible or compatible interactions. Among these, the capacity of B.cinerea to detoxify the phytoalexins produced by grapevines was investigated. We present here good evidence that this fungus produces a stilbene oxidase which can degrade resveratrol and pterostilbene. No detoxication of stilbenes is detected during the germination process in vitro, suggesting that stilbene-degrading activity does not seem to be constitutive in dormant conidia of Botrytis.