Long‐Term Industrial‐Scale Study on Regulated Deficit Irrigation′s Effect on Flavonoid and Volatile Composition in Cabernet Sauvignon (Vitis Vinifera L.) Grapes

Background and Aims Climate change and reduced precipitation pose significant challenges for the wine industry, particularly in vulnerable regions, where it is essential to incorporate irrigation management tools. Regulated deficit irrigation (RDI) is a step forward in that direction. Still, its adoption in Chile has been slow, partly due to inconsistent results regarding its impact on grape composition, a product of low experimental scalability, and, in general, highly variable applied water and vine stress due to the lack of actual evapotranspiration (ETa) assessment on study sites. This study aimed to understand the impact of RDI on yield, vine balance, and grape volatile and nonvolatile composition in an industrial‐scale 5‐year trial using precise ETa‐based irrigation. Methods and Results A five‐year experiment with three RDI regimes and a control was conducted in Maule Valley, Chile. Different portions of ETa from pea size to harvest were replenished as follows: 100% ETa (control), 70% ETa, 50%–100% ETa, and 35%–100% ETa (50 or 35% ETa before veraison and 100% ETa after). The experiment covered 4.54 ha, including a 1.2 ha control treatment in which a flux tower was installed to assess ETa. Midday stem water potential, yield components, and grape volatile and phenolic composition were measured. RDI reduced yield, mainly due to lower cluster weight as a result of smaller and fewer berries. Concentration on a fresh‐weight basis of total anthocyanin, tri‐hydroxylated anthocyanins, tannins, and specific flavonols, including quercetin, myricetin, and syringetin glycosides, was higher in the two most water‐restrictive RDI treatments, while total soluble solids and acidity were lower. Also, the same treatments showed increases in positive aromas, including α‐terpineol, β‐damascenone, linalool, and nerol, as well as possibly undesired aromas such as IBMP and hexenal. While some metabolites indeed increased their per‐berry content, suggesting an upregulation of metabolism, most of the observed increments were simply driven by berry size reduction. Conclusions Overall, most of the changes caused by RDI are positive in terms of grape quality, with higher color and aroma concentrations. To achieve most of the positive effects, RDI needs to reach at least 50% of the ETa, particularly from pea size to veraison .