Some Critical Issues in Environmental Physiology of Grapevines: Future Challenges and Current Limitations
Grapevines are cultivated in six out of seven continents, between latitudes 4° and 51° in the Northern Hemisphere (NH) and between 6° and 45° in the Southern Hemisphere (SH) across a large diversity of climates (oceanic, warm oceanic, transition temperate, continental, cold continental, Mediterranean, subtropical, attenuated tropical, arid and hyperarid climates) (Peguy 1970, Tonietto and Carbonneau 2004). Accordingly, the range and magnitude of environmental factors differ considerably from region to region and so do the principal environmental constraints for grape production. Problems of low winter temperatures have limited grape cultivation in the past in areas with continental climates in Eastern Europe, Asia and North America. Low temperatures during the growing season have prevented the extension of grape-growing in regions approximately be-
yond the 12°C temperature isotherm (April-October (NH), October-April (SH)) (Jones et al. 2005a). The effects of hot temperatures, on the contrary, are less clear with respect to the distribution of grapevine cultivation areas. In general, the 22°C temperature isotherm is considered limiting for wine grape production (Jones 2007a, Schultz and Jones 2008), but many areas in the tropics are much warmer than this (Tonietto and Carbonneau 2004) and detrimental effects of high temperatures may be largely mitigated if water supply is sufficient and/or if humidity is high. Within the existing production areas, water shortage is probably the most dominant environmental constraint (Williams and Matthews 1990), and even in moderate temperate climates, grapevines often face some degree of drought stress during the growing season (Morlat et al. 1992, van Leeuwen and Seguin 1994, Gaudillère et al. 2002, Gruber and Schultz 2009).