Crop yield response to water - Cra

Figure 9Wine quality score as a function of total irrigation for Cabernet Sauvignon in Adulam, Israel.Source: Bravdo et al. (1985).20 bunches per vine 40 bunches per vine 60 bunches per vine1413Wine quality score1211109200 250 300 350 400 450Irrigation (mm)pruning, thinning, and canopy management maybe important to achieve both high yield andhigh quality.Water deficit generally increases the concentration of phenolic compounds, but has a differentialeffect on individual groups of phenols depending on timing and severity of the stress. Tanninbiosynthesis can be negatively affected by severe stress after anthesis (Ojeda, 2002), but laterdeficits often increase tannin concentration (Roby et al., 2004). In most cases, anthocyaninconcentration responds positively to water shortage after veraison but less frequently topre-veraison deficits (Matthews and Anderson, 1988); although the expression of genes involvedin anthocyanin biosynthesis can be increased by water stress pre-veraison (Castellarin et al.,2007). Aside from phenolic compounds, aroma attributes may also be affected (Chapman et al.,2005). Differences in the response of varieties are likely but not well documented (see: SuggestedRDI regimes below for examples). In addition to the effects on amount and proportion of keycompounds, water deficit can cause more subtle but relevant effects. For example, water deficitafter veraison has been shown to increase the structural complexity (degree of polymerisation)and to reduce the extractability of phenolic compounds in berries of several red varieties (Ojedaet al., 2002; Sivilotti et al., 2005). The effects of water deficit on berry attributes are partiallyrelated to reductions in berry size, although size-independent effects have also been reported.Allometric analysis is required (i) to separate size-dependent effects of water deficit on aparticular component, e.g. sugar, and (ii) to compare the relative responsiveness of differentberry components to water deficit (Sadras et al., 2007 and Sadras and McCarthy, 2007). Forexample, allometric analysis revealed that water deficit accelerated the rate of accumulation ofanthocyanins with respect to sugar of Cabernet Sauvignon in a warm environment (Figure 12).Water management is therefore important to ensure a certain coupling of key berry componentsduring ripening; this will eventually affect wine balance.472crop yield response to water