WATER STRESS IN TANNAT AND DURAS GRAPEVINE CULTIVARS (VITIS VINIFERA L.): LEAF PHOTOSYNTHESIS AND GRAPE PHENOLIC MATURITY

Our study focuses on the physiological responses and berries phenolic maturity of Tannat and Duras red wine grape cultivars, which are autochthonous from the southern France, under water stress condition from pre-véraison to harvest by limiting water availability to 30% of the control well-watered. Methode and result : Predawn and midday leaf water potentials served as an indicator to maintain water stress level compared to the control. The seasonal reduction of leaf net assimilation rate under saturating irradiance (An) under water stress over six weeks stress period versus well-watered was 60% for Tannat and Duras as compared to 64 and 46% for leaf stomatal conductance (gs) for Tannat and Duras cultivars respectively. These responses qualify Tannat as a good candidate for adapting to limited water availability. For both Tannat and Duras cultivars, relationships between the fresh mass, skin and flesh in six different berry size categories, ranged from about 0.5 to 2.0 g, were assessed on ripe fruit from grapevines subjected to well-watered and water stressed treatments. Fresh mass components for both treatments varied significantly depending on the grape cultivar and water availability. Tannat showed that seed represented around 6%, skin around 12%, and flesh about 82% of the berry total fresh weight. The Duras cultivar showed that seed represented around 3%, skin around 12% and flesh around 85%. Exact proportion of seed, skin and flesh varied according to berry size category. There was an increase in total seed mass per berry to water stress treatment. Anthocyanin content and the seed tannin concentration varied depending on the grape variety and water stress treatment. In comparison with skin tannin or anthocyanin content, seed tannin varied more with berry size and less with vine water status. Tannat variety showed a positive effect of water stress on anthocyanin content but not Duras. At last, seed and skin tannin concentrations decreased with berry fresh weight.