Sustainable irrigation strategy in organic 'Victoria' table grape in Apulia region

Table grape vines (Vitis vinifera L.) are usually grown under irrigation in arid climate regions, characterized by low rainfall and high environmental evaporative demand, such as southern Italy. However, in recent years the need to reduce water consumption in irrigated vineyards has risen considerably because of increased water costs and restrictions on allocated amounts of irrigation water. Only limited guidelines are available for managing irrigation to obtain an optimal balance between vegetative growth, yield, berry quality and water use efficiency in organic seeded table grapes in southern Italy. The research was carried out during the 2015 season in an experimental vineyard located in a grape growing area in southern Italy (Valenzano, Bari, Italy), where the climate is sub-arid Mediterranean. Vitis vinifera ‘Victoria’ vines were grafted onto 140 Ruggeri rootstock and trained to a “tendone overhead trellis”. Two watering regimes, corresponding respectively to 100% (V1) and 80% (V2) of daily crop evapotranspiration (ETc) were compared. Irrigation started after berry set to one week before harvesting. Midday stem water potential was measured from berry set to harvest and parameters of physiological leaf functioning were measured on a typical summer day. At harvest the following parameters were assessed: bunch and berry weight, berries per cluster, berry diameters, total soluble solids, pH and titratable acidity; the TSS/TA ratio was calculated. The effect of water stress, although moderate, was evident after fruit set. At all phenological stages considered, midday stem water potential values were statistically different and the lowest vine water stress occurred in the V1 treatment. Leaf gas exchange measured in vines subjected to V1 and V2 treatments differed significantly only with regards to leaf transpiration and no difference was noted for water use efficiency. Water availability significantly affected berry growth, inducing the lowest berry weight in V2 treatment that received the lowest watering volumes. As a consequence of the mild water stress during the vine crop cycle, fruit yield was not significantly affected by the different water regimes. Finally, preliminary results in this trial show that a mild water stress did not affect total soluble solid concentration, titratable acidity and pH of ‘Victoria’ table grapes, with a positive reduction of amount and cost of irrigation water applied.