Short and long-term acclimation to water status at leaf and plant level of fungus-tolerant genotypes

Today's viticulture faces the double challenge of reducing chemical input while adapting plant material to future climate conditions. Adopting fungus disease-tolerant varieties appears to be a long-term solution as long as they are performant under abiotic constraints, such as drought. This study aimed to study the effects of water deficit (WD) and characterise the different strategies adopted to cope with drought in six new fungus disease-tolerant varieties selected by INRAE compared to Syrah. During five consecutive seasons (2018 to 2022), a gradient of WD was applied in field conditions and monitored through vine predawn water potential measurements. Grape development was non-destructively tracked by imaging to determine the arrest of berry phloem unloading. All variables were collected at the single plant level. The impacts of WD on leaf gas exchange and intrinsic water use efficiency (WUEi), vegetative development and yield components were assessed, as well as the genotypic sensitivity to WD at the leaf, vegetative and reproductive levels. All variables were negatively impacted by WD, except for intrinsic water use efficiency and total non-structural carbohydrate concentrations. Genotypes were differently impacted by WD at the physiological and vegetative levels, while no genotype-dependent response was observed for most reproductive variables. Generally, genotypes with the highest potential (highest intercept) in a certain variable were also the most sensitive to water deficit (higher slope). The most sensitive genotype regarding physiological and reproductive variables was G5, which showed higher reductions in berry weight, photosynthesis and WUEi, contrasting with Syrah, 3159B and Floreal. In this study, we observed a diversity of strategies to cope with WD in the long term, where some genotypes opted to reduce most variables (G5 and Artaban) or to maintain functioning at higher levels (Syrah and 3176N). Others displayed mixed responses: either reducing vegetative growth more than yield (3159B) or vice-versa (G14).