Response of two grapevine (Vitis vinifera L.) Portuguese varieties Tinta Roriz and Touriga Nacional to different irrigation regimes in the Douro Region, Portugal

The effect of several deficit irrigation regimes on vine water status, grape yield and quality parameters were studied in two Portuguese cultivars, Tinta Roriz (2007 and 2008 growing seasons) and Touriga Nacional (2014 and 2015 growing seasons) (Vitis vinifera L.) grown in a commercial vineyards located in the Douro region, Portugal. Treatments consisted of non-irrigated vines and three deficit irrigation regimes with a constant fraction of reference evapotranspiration (ETo): 0.2, 0.4 and 0.6. The reference evapotranspiration was calculated using modified FAO Penman-Monteith equation and water was applied three times a week, from pre-veraison until one week before harvest, through a drip irrigation system. The results showed that moderate water supplies during ripening period, for the region where the study was conducted (severe water deficits), improved significantly the grapevine water status, leaf photosynthesis and transpiration in both cultivars. Yield components and pruning weights showed a significant increase in irrigated treatments with more water supplied. There were no significant differences in the majority of fruit quality parameters. However, the total phenols and the colour intensity showed a tendency to decrease in irrigated treatments with more water supplied.

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