The effect of rootstock on water relations and gas exchange of Vitis vinifera cv. Xinomavro

The effect of two rootstocks of different drought tolerance (1103 Paulsen and 3309 Couderc) on sap flow, water relations and gas exchange of cv. Xinomavro (Vitis vinifera L.) was investigated during the 2005 season in Naoussa, Greece. Soil was maintained at field capacity for both rootstock treatments until mid July when a restricted water regime was applied by irrigation cutoff. Sap flow diurnals for the Xinomavro-1103P combination showed a rapid decrease of flow after midday, under water stress conditions. On the contrary, vines grafted on 3309C maintained the transpiratory flux during the day, despite conditions of limited water availability. Vines grafted onto 1103P had significantly higher (less negative) values of late afternoon (16h00) stem water potential, compared to those grafted on 3309C. Simultaneous assimilation and stomatal conductance values were significantly lower for the Xinomavro-1103P combination compared to Xinomavro on 3309C. These results support the possibility of a more sensitive drought avoidance mechanism for vines grafted on 1103P based on stomatal control. On the contrary, 3309C allowed this cultivar to maintain higher stomatal conductance and water uptake under water deficit. Grapes from the Xinomavro-3309C combination exhibited significantly superior sugar content at harvest, expressed on a per g of fresh berry weight basis. Since growth and yield parameters were similar among treatments, this finding is likely to be related to the higher afternoon photosynthetic rate of 3309C-grafted vines, prior to harvest.