Handbook for Irrigation of Wine Grapes in South Africa

Chapter 6

6.3

FACTORS AFFECTING GRAPEVINE WATER STATUS

6.3.1 CULTIVARS The fact that water potential in different grapevine cultivars may respond differently to water constraints is well documented. Under comparable soil and atmospheric conditions, grapevine water status can also differ inherently between cultivars (Winkel & Rambal, 1993; Medrano et al. , 2003; Schultz, 2003). In certain cultivars, leaf water potential remains more or less constant during the day, i.e. it does not respond to changes in soil and/or atmospheric water status (Fig. 6.12). Such cultivars are referred to as being “isohydric”. Leaf water potential rarely falls below -1.5 MPa in isohydric grapevines (Lovisolo et al. , 2010 and references therein). In contrast, when leaf water potential in grapevines follows a distinct diurnal pattern, and decreases in response to soil water deficits it is referred to as being “anisohydric” (Schultz, 2003 and references therein). Isohydric wine grape cultivars include V. vinifera cultivars such as Grenache, Trincadeira Preta and Tempranillo (Lovisolo et al. , 2010 and references therein). Anisohydric grapevine cultivars include the species V. labrusca and V. californica Benth., as well as many V. vinifera cultivars, including Chardonnay, Cabernet franc, Cabernet Sauvignon, Syrah, Riesling, Carignan, Muscat, Thompson Seedless and Touriga Naçional. However, it appears that the same cultivar can show iso- or anisohydric behaviour, depending on the prevailing conditions, e.g. V. labruscana (Lovisolo et al. , 2010 and references therein). The same study showed that Pinot noir was anisohydric in response to pre-véraison water constraints, but responded isohydrically to post-véraison water constraints. On the other hand, Tempranillo and Manto Negro seem to be isohydric during most of the growing season, but depending on the year, they exhibited iso- or anisohydric behaviour later in the season (Lovisolo et al. , 2010 and references therein).

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