Physiological mechanisms used by grapevine varieties to cope with water deficit

Historically grapevines have originated from different environments and have evolved a range of physiological strategies to deal with abiotic stress. However, current irrigation practices do not always take into account the different responses that grapevine varieties display towards water deficit. In the semi-arid Murray-Darling region of Australia, irrigation is vital for grapevine growth, but experience with irrigating in this environment has shown that there may be an advantage in tailoring irrigation management strategies to take into account differences between cultivars in their responses to water deficits. Recent research has indicated the potential for categorising varieties based on their anisohydric or isohydric responses to water stress and we have been investigating how these responses may influence vine performance under a range of irrigation levels. In 2004, field trials were established in north-west Victoria, Australia to explore the mechanistic responses of 'Shiraz' and 'Cabernet Sauvignon' to sustained water deficit. The vines were drip irrigated with a full (control) irrigation (100% field capacity) or sustained deficit irrigation (approximately 44% volume of the control). Diurnal measures of stomatal conductance (g(s)) and Psi(I) leaf water potential (Psi(I)) were made from veraison to harvest. Initial observations indicate differences in g(s) and between both irrigation treatment and cultivar. Preliminary studies in 2003/04 showed no significant differences in yield, and compositional parameters, despite approximately only half the amount of water being applied for some of the sustained deficit treatments. Overall, this project seeks to understand why some cultivars are better able than others to deal with water deficit and how this may affect subsequent fruit composition.