Morpho-structural and physiological response of container-grown Sangiovese and Montepulciano cvv. (Vitis vinifera) to re-watering after a pre-veraison limiting water deficit

A better physiological and productive performance of cv. Montepulciano versus cv. Sangiovese under well-watered conditions has been recently assessed. The objective of this study was to verify that this behaviour is maintained when a pre-veraison deficit irrigation (vines held at 40% pot capacity from fruit-set to veraison) followed by re-watering (pot capacity reported at 90%). Single leaf assimilation rate and stomatal conductance, diurnal and seasonal whole-canopy net CO2 exchange (NCER) and water use efficiency were always higher in Sangiovese under deficit irrigation. Due to water shortage Montepulciano displayed a more compact growing habit due to decreased shoot and internode length. Sangiovese showed excellent recovery upon re-watering as NCER resulted to be higher than the pre-stress period; however, this might also relate to early and severe basal leaf yellowing and shedding. Early deficit irrigation affected xylem characteristics of Montepulciano more than in Sangiovese; vessel density increased (37 vs 29%, respectively, compared with well-watered vines) and the hydraulic conductance decreased more (-13 vs -3% respectively) compared with well-watered vines. Yield components and technological maturity were similar in the two cultivars, whereas Montepulciano grapes had lower anthocyanins and phenolics. Higher physiological and productive efficiency under non-limiting water conditions showed by Montepulciano compared with Sangiovese was basically reversed when both cultivars were subjected to an early deficit irrigation.