Can early defoliation improve fruit composition of Tempranillo grapevines in the semi-arid terroir of Utiel-Requena, Spain?

Early defoliation has been found a useful tool to reduce cluster compactness and to improve fruit composition in vigorous sites of different viticultural areas. Our objective was to test the usefulness of this technique under the semi-arid climatic conditions of the Utiel- Requena D. O. (Valencia, south-east Spain) with the cv. Tempranillo. In deficit drip irrigated vines, planted in north- south oriented rows with vertical shoot positioning, four treatments were applied during 2008 and 2009. Control (C), non-defoliated vines, were compared with defoliation performed either just before anthesis (phenological stage H, treatment ED), or at fruit set (phenological stage J, treatment LD). In both defoliation treatments leaves from the first 6 nodes, including laterals, were removed. In a fourth treatment, only the leaves facing east from the first 8 nodes were removed at phenological stage H (EED). Sixteen vines per treatment were randomly selected within the vineyard. In the first season, as an average for all defoliation treatments yield was reduced 21 % by leaf pulling. In the second season, there was a heavier reduction in yield (41 %). Flower and berry number per cluster were similar in 2008, but in 2009 flower number decreased for ED, and berry number for ED and LD. In both years, lower berry weights at harvest were obtained in all defoliation treatments. Fruit composition was also modified by early-defoliation. For grapes harvested at the same date, treatment LD increased sugar content in 2009.The malic acid concentration decreased for all defoliation treatments in 2008, and the tartaric acid levels increased for all defoliation treatments in both years. Total acidity decreased for ED and LD in both years, though significantly only in 2008, when it decreased in proportion to the intensity of defoliation. Both ED, and particularly LD, improved berry composition, increasing the concentration of total phenolics, anthocyanins and tannins. The synthesis of phenolic substances was instead not increased by leaf pulling. Overall results indicate that defoliation carried out at fruit set is the most effective treatment to improve berry phenolic concentration and soluble solids. However, growers should take into account the important yield penalty due to defoliation, particularly in the mid-term. In addition, a decrease in malic acid concentration could be also detrimental during wine-making. This indicates that the early defoliation technique needs to be used with caution in the semi-arid and warm terroirs.