Resveratrol is a major phytoalexin in grapevine but its synthesis in response to phytopathogen attack decreases with grape berry ripening. A chimeric gene combining an alfalfa PR 10 promoter and Vst1 (Vitis stilbene synthase 1) gene was introduced into the genome of 41B rootstock. Transgenic plants were analysed for resveratrol production in leaves infected with Botrytis using an in vitro test. Among the 50 transgenic lines analysed, some exhibited a production lower than the non-transgenic control, but others accumulated resveratrol from 5-100-fold. Moreover, in the latter clones, symptoms were highly reduced in response to infection. These results were a good indication that the combination of a pathogen-inducible promoter and a defence gene may increase tolerance against fungi in grapevine. The efficacy of this approach should be further tested by experiments conducted in the vineyard.

In order to evaluate the impact of ethylene in maize tissue culture, silver nitrate has been used as an inhibitor of ethylene action. Type II callus initiation rate was improved when immature embryos were cultured on a modified Murashige & Skoog medium containing various concentrations of silver nitrate (5, 10, 20 mg 1-J ). Regeneration ability of calli initiated and maintained in presence of silver nitrate was enhanced. No modification of callus growth rate neither of ethylene production has been detected.

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