Regulated Deficit Irrigation based upon optimum water status improves phenolic composition in Monastrell grapes and wines

The effects of three deficit irrigation strategies pre and post-véraison, on soil–plant water status and their influence on leaf area, cluster microclimate, fruit growth, yield and berry and wine quality were evaluated for three years (2009–2011) in field-grown Monastrell grapevines under semiarid conditions in South-Eastern (SE) Spain. Three treatments were applied: a Sustained Deficit Irrigated treatment (SDI) was irrigated at 40% of the Crop Evapotranspiration (ETc) throughout the orchard cycle, 211 mm year−1; a Regulated Deficit Irrigation treatment 1 (RDI-1threholds) received 30% ETc (2009 and 2010) or 20% ETc (2011) from budburst to fruit set. From fruit set to harvest the irrigation was established by maintaining an average mid-day stem water potential (Ψs) within the range −1.2 > Ψs ≥ −1.3 MPa and from véraison to harvest within the range −1.3 > Ψs > −1.4 MPa, 106 mm year−1); And a Regulated Deficit Irrigation treatment 2 (RDI-2cutoff-thresholds) received 20% ETc (2009 and 2010) or 10% ETc (2011) from budburst to fruit set and from fruit set to véraison an irrigation cut-off was applied. Then, from véraison to harvest, an irrigation recovery was applied based on maintaining mid-day Ψs within the range of Ψs proposed: −1.3 > Ψs > −1.4 MPa (similar to RDI-1), 76 mm year−1). A recovery of irrigation at 40% ETc was used in all treatments from harvest to leaf fall. The RDI-1thresholds strategy, which applied moderate water stress during pre and post-véraison, saved water, reduced vine vigor and vegetative development, controlled yield, improved cluster microclimate, maintained similar or even higher sugar content in the berries and improved the phenolic composition of Monastrell grapes and wines compared to the SDI and RDI-2 strategies. RDI-1thresholds vines increased color intensity, sugar and total anthocyanins in the berries, and color intensity, alcohol content, concentration of polyphenols and total anthocyanins and flavonols in the wines. In contrast, in the RDI-2cutoff-thresholds strategy, which had complete irrigation cut-off during the pre-véraison period (from fruit set to véraison) substantially decreased lateral shoot and berry growth at véraison, and also excessively reduced photosynthetic activity, water status pre-véraison and the resilience of photosynthesis during véraison- early ripening period, which was not beneficial from a physiological and agronomical point of view for Monastrell grapevines in SE Spain.