EFFECTS OF POSTVERAISON WATER REGIME ON THE PHENOLIC COMPOSITION OF GRAPES AND WINES OF CV. AGIORGITIKO (VITIS VINIFERA L.)

Aims: Vine water deficit is widely accepted as a powerful means to control grape and wine attributes. However, quality improvement is often achieved at the expense of a reduction in yield, especially when water deficit conditions are applied during the preveraison period. The aim of the present work was to test an irrigation regime based on manipulating water availability from veraison to harvest, as a means to control berry and wine composition with minimum effect on reproductive growth parameters. Methods and results: A field trial was conducted during two consecutive years (2007-2008) in Nemea, Southern Greece. Three irrigation treatments were applied on seven-year-old, vertical shoot positioned and spur pruned Agiorgitiko vines (Vitis vinifera L.), from veraison through harvest: irrigation at 70 % of crop evapotranspiration (ETc) (170), irrigation at 30 % of ETc (130) and non irrigated (NI). Irrigation amount produced significant differences in postveraison midday stem water potential pattern, especially during the drier year 2008. Yield was increased by irrigation in 2008, whereas berry growth was unaffected in both seasons. Berries of NI vines achieved higher total skin anthocyanin content in 2007, although individual anthocyanin levels were not affected by water regime. Irrigation effect on skin tannins was inconsistent but seed tannins were higher in 170 vines, with increased levels of catechin and epicatechin monomers. Among wine attributes, tannin concentration, but not anthocyanin, was mostly responsive to water deficit-induced changes in berry phenolic composition. The wines made from 170 grapes had a higher tannin content than those made from NI grapes. Conclusions: The results presented show that postveraison water regime had a significant effect on skin anthocyanins and, more markedly, on seed tannins, without altering berry growth parameters. Especially for seed tannins, this effect appears to predominate over variations in climatic conditions between years. Significance and impact of the study: This trial suggests that Agiorgitiko vines grown on the loamy soils of Nemea perform better under non irrigated conditions during the postveraison period since rainfed vines had improved phenolic composition (higher colour with lower contribution of seed tannins) without significant loss in productivity.