Crop yield response to water - Cra

Table 1Key vegetative and reproductive components in low and high-yielding vineyards (Pearce andCoombe, 2005).Component Low HighYield (kg m -2 ) 0.20 5.0Equivalent volume of table wine (litre m -2 ) 0.12 3.0Pruning weight (kg m -2 ) 0.03 1.0Leaf area index (m 2 m -2 ) 0.50 5.0Number of nodes (m -2 ) 3 30Number of shoots (m -2 ) 2.5 25Number of bunches (m -2 ) 5 50Berry growth has a characteristic double-sigmoidal pattern; it is dominated by cell division in thefirst two weeks after flowering and by cell expansion afterwards. The first sigmoidal trajectoryreaches a plateau in synchrony with full seed size in seeded varieties. After an interveninglag-phase, the onset of the second sigmoidal phase is characterized by berry softening,accumulation of sugars, decline in acid concentration and accumulation of pigments in the skinof coloured varieties. This stage is called veraison (Stage 35 in Figure 2) and is very responsive toenvironmental factors. For example in physically constrained berries, the threshold cell turgorpressure ≈ 0.1 MPa associated with veraison under the experimental conditions of Matthewset al. (2009) was delayed by two weeks in relation to controls, and a similar delay was recordedfor the onset of sugar accumulation. The second sigmoidal stage ends in a plateau correspondingto variety- and environment-specific maximum berry size. Varieties like Shiraz, which oftenexhibit substantial berry dehydration late in the season are characterized by a decline in freshweight rather than a plateau at the end of the second phase (Sadras and McCarthy, 2007). Thisdecline is also observed when harvest is delayed to enhance berry traits associated with winequality at the expense of fruit weight and yield. Harvest maturity (Stage 38 in Figure 2) is definedby winemaking criteria for fruit composition; it is often specified in terms of sugar concentrationor sugar: acid ratio in cooler climates, but colour and flavour criteria complement these simpledefinitions. Environmental variables including temperature, radiation and water availabilityduring berry growth and ripening can have substantial impact on berry composition and henceon wine attributes. This viticulturally important aspect of berry biology is beyond the scope ofthis section, but readers are referred to reviews by Coombe and Iland (2005), Conde et al. (2007),and Dai et al. (2010). We focus on the effects of water deficits on berry and wine attributes in afurther on in this section.Varietal differences in developmentThe developmental plan outlined in the previous section applies to all grape varieties. However,grapevine 463