Grapevine water stress management in Douro region: long-term physiology, yield and quality studies in cv. Touriga Nacional

Abstract

In Douro Region (Northeast Portugal) grapevines are often exposed to severe water stress in the summer. During 11 years (2002 – 2012) a study was conducted in a commercial vineyard with cv. Touriga Nacional x 196-17 growing under three water regimes, non-irrigated (NI) and two irrigation strategies (WR1-30% ETc and WR2-60% ETc). The site has a Mediterranean-type climate with average annual rainfall of 560 mm. The water application starts when the predawn leaf water potential (Ψ_pd) reach the value of -0.3MPa (late June / mid-July according the years), and stop near 2 weeks before the harvest. Leaf gas exchange and chlorophyll fluorescence measurements were performed only in2009 and 2011. Berry ripening was followed weekly, and at harvest, yield, vigour, pruning weight per vine was determined in 20 samples, and fruit composition using a 200 berry samples, for analysis of soluble solids, pH, titratable acidity, phenols and total anthocyanin’s.Results showsthat predawn leaf water potential reached several times values below -1.2 MPa, with negative consequences in the photosynthetic productivity. Both irrigation levels had a positive significant effect on leaf gas exchange, yield, shoot weight and berry weight, with an increase in sugar content and a reduction in acidity, while no significant effects were registered on pH, phenols or anthocyanin’s. Thresholds in predawn water potential for monitoring deficit irrigation strategies can be oriented between the values -0.4 MPa ≥ Ψ_pd ≥ -0.6 MPa between veraison and harvest.