Bioassays on the activity of resveratrol, pterostilbene and phosphorous acid towards fungi associated with esca of grapevine

An examination was carried out under laboratory conditions to determine whether resveratrol, pterostilbene and mixtures of each stilbene with phosphorous acid had an inhibitory activity against some fungi involved in esca: Phaeoacremonium aleophilum, Phaeomoniella chlamydospora, Libertella blepharis (anamorph of Eutypa lata), Fomitiporia punctata and Stereum hirsutum. An inhibition of mycelial growth by resveratrol was not found but there was a clear correlation between pterostilbene concentration and reduction of radial growth confirming the antifungal activity of this phytoalexin. Although phosphorous acid proved to be generally ineffective, an increase of antifungal activity of stilbenes in the mixtures was observed with all fungi except F. punctata. The possible relation between fungal phenol oxidase activity and inhibition by mixtures of stilbenes and phosphorous acid was discussed.