Canopy shading as an adaptation strategy to maintain grapevine berry composition under water deficit

Drought, increasingly driven by climate change, is a major challenge in viticulture along with reduced availability of irrigation water. Therefore, strategies to mitigate negative influences of drought on berry quality while reducing irrigation water amount are needed. Developing these strategies requires a precise understanding of direct and indirect effects of water deficit on berry composition. To investigate these effects, a field experiment was carried out using Vitis vinifera cv. Cabernet Sauvignon grapevines. Water deficit was applied before or during berry ripening, or both, and compared with regulated deficit irrigation and full irrigation to assess its impact on sun exposed and shaded berries. Yield components and berry composition were analysed. Water deficit before fruit ripening directly reduced berry size independently of sun exposure and reduced leaf area, leading to a more open canopy with a higher proportion of sun-exposed berries. These direct effects subsequently led to the indirect effects of an increased surface to mass ratio and thus a higher concentration of phenolic compounds in berries and a higher proportion of sun exposed berries, which influenced berry composition. The interaction of direct and indirect effects amplified the overall impact of water deficit. Negative impacts of water deficit on berry composition may be mitigated by managing indirect effects. The comparison of naturally shaded and sun-exposed berries suggests that applying shading to the fruit zone may allow reduced irrigation during fruit ripening without compromising yield or quality.