No abstract

Water is critical for viticulture sustainability since grape production, quality and economic viability are largely dependent on water availability. The total water consumption of vineyards, 300 to 700 mm, is generally higher than the annual average precipitation in many viticultural areas, which induces a risk for sustainability of vineyards. Improving vineyard water use efficiency (WUE) is therefore crucial for a sustainable viticulture industry in semi-arid regions. Increased sustainability of water resources for vineyards can be achieved using both agronomical technology and cultivar selection. Here, we review advances in grapevine water use efficiency related to changes in agronomical practices and genetic improvements. Agronomical practices focus on increasing green water use by increasing soil water storage capacity, reducing direct soil water loss, or limiting early transpiration losses. Cover crops for semi-arid areas show a favorable effect, but careful management is needed to avoid excessive water consumption by the cover crop. Canopy management practices to reduce excessive water use are also analyzed. This is a genetic based review focused on identifying cultivars with higher WUE.

Long-term induced water stress in field-grown grapevine leads to a progressive decline of stomatal conductance, accompanied by a decrease in CO 2 assimilation (40%). The apparent quantum yield also decreases (59%), which may reflect a relative increase in alternative processes for electron consumption. There is also a shift to non-stomatal regulation, as judged from significant depletions (37%) in maximum photosynthesis rate at saturating CO 2 related to limited ribulose biphosphate (RuBP) regeneration, whereas small, non-significant effects are observed on carboxylation efficiency. A high correlation (87%) between photosynthesis and stomatal conductance is observed for all experimental data and declines in intercellular CO 2 concentration parallel reductions in stomatal conductance. The data show that field response of grapevines to increasing soil water deficit involves stomatal and non-stomatal effects but, due to gradually induced drought, regulation mechanisms able to adjust mesophyll capacity to the average CO 2 supply. The non-stomatal adjustment seems to be exerted mainly in metabolic pathways related with the RuBP regeneration. Contrasting characteristics were observed for both cultivars. Tempranillo exploited the non-stressful conditions successfully, whereas Manto Negro, responding to its reputation as more drought resistant, showed a higher intrinsic water use efficiency, particularly for low water availability. This advantage seems to be due to lower non-stomatal limitations.

Background and Aims: Improving water-use efficiency (WUE) is desirable for future grapevine growth and grape production, especially in Mediterranean areas where water is predicted to be limiting. Understanding the genetic variability in WUE is important to identify the most appropriate cultivars to be used in semi-arid areas. Most previous studies have focused at leaf-level WUE, while information on whole-plant level is scarce. This study explored the genetic variability of grapevine in whole-plant WUE (WUEWP) to determine whether several leaf WUE (WUEl) indicators are suitable as proxies of WUEWP. Methods and Results: Three similar experiments were performed to compare WUE in up to eight different grapevine cultivars under irrigation and water-stress treatments. Although WUEl and WUEWP varied with cultivar and treatment, WUEl was not a reliable parameter to predict WUEWP. Conclusions: Large variability in WUEWP between grapevine cultivars was observed, although this variability was not described by leaf-level indicators of WUE. Significance of the Study:This study showed that the large variability existing for WUEWP in different cultivars offers an potential method for selecting the more suitable cultivars to grow in water-scarce viticulture areas, although WUEl is not reliable for estimating WUEWP.Abbreviations d 13 C carbon isotope ratio; YMD midday leaf water potential; AN net CO2 assimilation rate; AN/E instantaneous water-use efficiency; AN/gs intrinsic water-use efficiency; E leaf transpiration rate; gs stomatal conductance; LA leaf area; SWC soil water content; WUEl leaf water-use efficiency; WUEWP whole-plant water-use efficiency Keywords: drought, grapevine, genetic variability, leaf water-use efficiency, whole-plant water-use efficiency 164Genotypic variability of water-use efficiency