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Effect of Late Season Deficit Irrigation on Fruit Composition in Grape (Vitis vinifera L.) cv. Merlot

A study was performed in 2002 on the experimental field of Udine University (Northeastern, Italy), to study the effect of late season deficit irrigation on qualitative and quantitative characters in red grapes (Vitis vinifera L.) cv. Merlot. In this research 8 year old grapevines grafted on "S04" rootstock were selected. The control vines received a considerable amount of rain, about 70 mm during verasion (60 days after full bloom) to harvest, while the stressed vines were irrigated only two times (60 and 103 days after full bloom respectively) with scant water, about 2 mm each time. Some characters (berry size, total soluble solids, pH, total polyphenols and anthocyanin) were recorded once a week. The results of variance analysis indicated, that, there were significant differences (P0.01) at the time of recording, between water stress and control treatments for total polyphenols, anthocyanin, pH, titrable acidity and berry size (weight and volume). Titrable acidity was significantly higher in control vines, but pH in grape juice was higher in stressed vines. In the stressed vines total polyphenols as well as anthocyanin concentration were significantly higher than in control vines. Water stress decreased berry size (weight and volume). The correlation coefficients of anthocyanin concentration with total soluble solids (r4l.85), pH (r4.76) and berry size (r= 0.51) were positive and significant. The correlation coefficients of anthocyanin with titrable acidity (r=-0.78) and stem water potential (r=-0.48) were negative and significant.