The thermal increase, due to the changed climatic context, is leading to marked variations in the yield and quality of the grapes and causing an increase in the use of water resources in several viticultural areas. Nevertheless, in some environments, rainfalls are scarce and there is no water availability. In this study, we compared the impact of low water irrigation volumes (DI, replacement of 70% of crop evapotranspiration) with respect to non-irrigated vines (NI), on the physiological, yield and qualitative performances of near-isohydric variety 'Montepulciano', trained to overhead trellis system, which requires a high-water supply. The stomatal conductance and photosynthesis values, in basal and median leaves, were higher in DI vines. All NI leaves suffered water stress, showing in the youngest leaves (position 20 and 25 along the main shoot) higher carbon isotope discrimination (delta C-13) (- 25.38 parts per thousand and 25-25.77 parts per thousand, respectively). At harvest, DI vines showed yield higher of 30% and 33% than NI vines in 2005 and 2006, respectively, and 18% in 2007. In environments with prolonged water shortage and low water resource, near-isohydric 'Montepulciano' vines, trained to overhead trellis system and irrigated with limited volumes, determined a significant improvement of 'vineyard efficiency' with a yield of 19.2 t/ha with respect to 13.4 t/ha of NI vines, ensuring also more sugar content (+ 31%), anthocyanin concentration (+ 13%) and polyphenolic substances (+ 8%) than NI vines.
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