Effect of moderate irrigation on aroma potential and other markers of grape quality

The variation of different parameters of grape quality during veraison and over the maturation period was studied in Tempranillo, a common Spanish cul tivar and Manto Negro, a local cultivar of Mallorca. Both cultivars were su bjected to two different soil water regimes, drought (without irrigation, t raditional for this area) and moderate irrigation (0.3 of ETP measured on a weekly basis). Analyses of fresh and dry berry weight, pH, total acidity, soluble solids, total polyphenols and anthocyanins were made in Tempranillo and Manto Negro grapes and must for both treatments. Glucose and fructose as well as organic acids were determined by HPLC. In addition, aroma potent ial was determined for the last three sampling times (maturation period) us ing the Glycosyl-glucose (g-g) assay (Williams et al., 1995). Irrigation increased berry fresh weight in Manto Negro but not in Tempranil lo. However, sugar content (degrees Brix) was clearly higher in irrigated T empranillo. The pH increased from 2.5 to 3.3-3.5, without differences betwe en treatments and cultivars. The major changes in these parameters were dur ing veraison. Under irrigation, Anthocyans content decreased in Manto Negro berries but increased in Tempranillo ones. Total poliphenols showed to be unaffected by irrigation but were dearly higher in Tempranillo. Clear differences between cultivars and treatments were observed in the aro ma potential during ripening. Both cultivars showed higher values for the i rrigated than for the drought treatment (around 20-30% in Manto Negro and 4 0-60LTo in Tempranillo). A contrasting pattern of aroma potential developme nt was observed for both cultivars. Manto Negro showed a maximum at mid mat uration, while for Tempranillo this maximum was achieved at the end of ripe ning (last sampling).