Author : Alexander David Levin
Publisher :
Page : pages
File Size : 16,89 MB
Release : 2016
Category :
ISBN : 9781369615692
In recent years, deliveries of water for agricultural use in the San Joaquin Valley (SJV) of California have been reduced, or in some instances cut all together. Since 1980, the acreage of annual crops has decreased by 40%, while the acreage of perennial crops has increased by 77%. Recent research has shown that perennial crops have a higher potential for water conservation. Also, it has been shown that yields do not decrease significantly under some moderate levels of water stress. As trends in California agriculture shift away from traditional field crops, more detailed information is needed on the amount of water required to grow tree and vine crops. Vineyards now account for nearly half of the total acreage of woody perennial crops in California. Worldwide, approximately 10,000 grapevine cultivars are grown on over 8 million hectares of land covering a wide range of climates, from hot and dry to cold and wet. This apparent genetic diversity has led researchers to group different cultivars according to the drought responses of numerous vegetative and reproductive parameters. However, no studies have utilized an established cultivar trial to directly compare multiple cultivars grown at the same site and subjected to the same water stress. Growers in the SJV would have the most potential to conserve water if the more was known about how individual cultivars response to drought at different times of the growing season. Seventeen different red wine grape V. vinifera L. cultivars grafted on to the same rootstock (1103P) were grown in a replicated cultivar trial, and subjected to three different deficit irrigation regimes over four years in order to manipulate [psi][subscript l] at various times throughout the growing season. An early deficit treatment (ED) received no applied water from berry set until veraison, and then was irrigated at 50% of ET[subscript c] from veraison until harvest. A late deficit treatment (LD) was irrigated at 100% ET[subscript c] from berry set until veraison, and then received no applied water until harvest. The sustained deficit treatment (SD) was irrigated at 50% of ET[subscript c] from berry set until harvest. Previous work has categorized wine grape cultivars into ‘isohydric’ or ‘anisohydric’ groups based on the response of stomatal conductance (g[subscript s]) to plant water status (leaf water potential ([psi][subscript l])). Significant differences in l among cultivars were observed during both time periods, but the effects of the water deficits were consistent across growing seasons. There were no significant differences in maximum stomatal conductance (g[subscript max]) among cultivars. Cultivar-specific responses of g[subscript s] to [psi][subscript l] did not separate into two distinct groups, but were broadly distributed based on a negative relationship between the [psi][subscript l] threshold for the beginning of stomatal closure at 95% of g[subscript max] and the rate of stomatal closure. Cultivar mean [psi][subscript l] values were positively related to the [psi][subscript l] threshold for the end of stomatal closure at 25% of g[subscript max]. Potential mechanisms of stomatal closure related to vascular anatomy are discussed. The quantitative models of g[subscript s] response to [psi][subscript l] presented in this study provide baseline threshold [psi][subscript l] values from which to compare cultivars in future research. With increasing competition for water resources, accurate information regarding crop water requirements is needed for informed irrigation management decisions. Early (preveraison) water deficits (ED-treatment) consistently and significantly reduced yields compared to the control across all years and cultivars, but the late (post-veraison) deficit (LD) treatment vines were not different from the control. The reduction in yield with ED was primarily due to a significant reduction in berry fresh weight (FW), and clusters per vine, with little change in berries per cluster. The LD treatment had a limited effect on berry FW and did not affect other yield components. Variation in yield was mostly due to berries per vine rather than berry FW, although this depended on cultivar. There were also cultivar differences in the proportion of variation in berries per vine explained by either clusters per vine or berries per cluster. Irrigation treatment or applied water amounts did not have a consistent effect on the water footprint but it was strongly dependent on yield. Implications of the timing of water deficits on the productivity of wine grapes in the SJV are discussed with respect to cultivar differences in yield formation. Previous research has shown that berry size is the most important component in grapevine yield, and that the sensitivity of grape berry growth to water deficits depends on the timing of those deficits. Berry growth was significantly reduced in ED for every cultivar, and berry absolute and relative growth rates (AGR and RGR, respectively) were significantly lower at the first measurement date after imposition of irrigation treatments. RGR was consistently higher in ED compared to SD and LD postveraison, but lost growth was not made up for in ED berries at harvest. AGR and RGR were significantly more sensitive to vine water status preveraison compared to postveraison for all cultivars. Ripening rate was highly conserved across cultivars and years, and was only slightly (but significantly) reduced in ED compared to SD and LD. In comparison, sugar translocation rate varied widely among cultivars and years, and was significantly different among all irrigation treatments. Sugar translocation rate depended strongly on berry size at veraison, but ripening rate did not. Irrigation treatments and cultivars affected the timing of ripening events independently with no interaction, and the timing of events was more dependent on berry sugar concentration (TSS) than days after anthesis (DAA). The results of this study may provide growers with cultivar-specific pre- and postveraison vine water status targets for irrigation scheduling, as well as assist with the timing of vineyard operations through better understanding of the timing of ripening events near the end of the season.