France is a worldwide leader in grape production and has to face global changes including climate evolution and transitions towards sustainable systems of production. One major problem in viticulture is indeed the high susceptibility of most of the grown cultivars to cryptogamic diseases, such as downy mildew (Plasmopara viticola). Maintaining a satisfactory health status of grapevine currently requires numerous fungicide treatments. However, in an objective of sustainable viticulture, there is increasing societal request, winegrower awareness, and political incitation to reduce this use of pesticides. For these reasons, alternative strategies of protection are currently investigated at the lab and field levels. Three of the most promising strategies are the use of: 1) resistant hybrids, 2) elicitors of grapevine defense reactions, 3) beneficial microorganisms. It is essential to study the physiological impact of stresses emerging from the climate changes on grapevine natural resistance to pathogens and on resistance induced by elicitors or rhizobacteria in order to assess the relevance of these alternative strategies in the vineyard for the future. Abiotic stresses associated to climate changes and biotic stresses will be applied alone or in combination to grapevine plants to assess their effects on natural or induced defense responses and resistance to Plasmopara viticola. Defense responses and the level of resistance to P. viticola will be followed using molecular, biochemical, and microscopic methods. The impact of defense activation on grapevine physiology will be assessed by following the plant development, photosynthesis and primary / secondary metabolism. Functional analysis experiments will be conducted on the plant model Arabidopsis to allow rapid assessment of the effects of abiotic and biotic stresses on the ability of the plants to activate defense responses after elicitation and to determine the fitness cost.