Phenological Sensitivity of Cabernet Sauvignon to Water Stress: Vine Physiology and Berry Composition

There is little information on the sensitivity of berry composition to early-season water stress and how it compares to the effects of late-season stress. This study aimed to quantify the effects of water stress on berry growth and composition of Cabernet Sauvignon grapevine at three phenological stages: anthesis to fruit set, fruit set to veraison, and veraison to harvest. Potted vines were used to facilitate imposing water stress early in the season. Four irrigation levels (0%, 25%, 50%, and 100% of calculated crop evapotranspiration, ETc) were applied and midday leaf water potential and leaf gas exchange were measured. Berry composition was evaluated by measuring titratable acidity and concentrations of soluble solids, anthocyanins, and polyphenols. Water stress decreased net CO2 exchange rate and vine green leaf area. Berry composition significantly correlated with the vine water status, but the nature of the relationship depended on the phenological stage and on the parameter measured. Berry composition (in terms of concentration of anthocyanins and polyphenols) was improved when no water stress occurred from anthesis to fruit set (irrigation replacing 100% of ETc), with mild water stress between fruit set and veraison (irrigation replacing 25% and 50% of ETc), and with moderate to severe water stress in postveraison (irrigation replacing 0% of ETc).