Handbook for Irrigation of Wine Grapes in South Africa

Chapter 1

to revert to strip wetting or drip irrigation. Drought tolerant scion cultivars that are more adapted to drier and warmer atmospheric conditions should be selected and planted. However, it is important that wines for export markets should be made from such cultivars. Another aspect that could play a role is the ability of grapevines to adapt if climate change occurs. In this regard, it appears that stomatal density of Shiraz grapevines responds to the mean daily maximum air temperature during the three months following budbreak (unpublished data). Stomatal density decreases substantially if the climate is warmer in the period following budbreak (Fig. 1.10). This indicates that the grapevine is capable of reducing its number of stomata per unit leaf area as a primary water saving mechanism in warmer climates. The adaptation of grapevine stomatal density to air temperature seems to occur irrespective of the cultivar. Stomatal densities of Shiraz, Merlot and Sauvignon blanc were lower near Lutzville in the Lower Olifants River region compared to cooler conditions following budbreak near Wagga Wagga in Australia (Fig. 1.11). The foregoing suggests that it is possible for grapevines to undergo changes in order to adapt to environmental conditions. The adaptation of stomatal density will be important if climate change results in warmer atmospheric conditions. Any similar physiological adaptations will reduce the negative effect of climate change.

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Wagga Wagga, Australia (Rogiers et al. , 2009) Estremoz, Portugal ( Costa et al. , 2012) Nuriootpa, Australia (Sadras et al. , 2012)

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T orres Vedras, Portugal ( Monteiro et al. , 2013) T hessaloniki, Greece (T heodorou et al. , 2013) Glasshouse, Nevada, U SA ( Hopper et al. , 2014) Glasshouse, Bet-Dagan, Israel (Gerzon et al. , 2015) Stellenbosch, South Africa ( Venter, 2015) Glasshouse, Mendoza, Argentina ( Gonzá lez t al. , 2016) Lutzville, South Africa ( unpublished data)

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y = -19 837x + 613 31 R² = 0 9186

0

16 18 20 22 24 26 28 30 32 34

Temperature (°C)

FIGURE 1.10. The relationship between stomatal density of Shiraz at different localities and the mean maximum daily air temperature during the three months following budbreak at each locality.

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a

Lutzville

IRRIGATION OF WINE GRAPES 27 Wagga Wagga

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