UC Davis

Chloride-induced grapevine toxicity is a leading contributor to abiotic stress in viticultural regions characterized by aridity and limited water availability. Although an essential element for plants, in large enough quantity chloride can reduce net photosynthesis, leaf area, and water uptake in grapevines. Furthermore, the scarcity of water for irrigation has promoted the use of water use efficient irrigation methods such as dripline application, which can limit leaching of nutrients and toxins, and a build-up of salts on the periphery of the wetting-zone. Deficit irrigation practices can also be utilized to improve fruit quality. This dissertation explores the range of tolerance to toxic soil-chloride concentrations in genus Vitis, limitations and thresholds for chloride tolerance in grapevines, and the potential for breeding chloride tolerant grapevine rootstocks. Each topic is expanded in chapters 1, 2, and 3 of this dissertation, respectively. The historic threat of Grapevine Phylloxera in vineyards has resulted in the proliferation of grapevine rootstock cultivars to address this pest and other stressors. Relative to many other perennial crops, grapes have a wide selection of stock to choose from. However, there are innumerable, untested, and often undiscovered species and landraces undisturbed in their native habitats of the Americas that may hold further benefits to vineyards worldwide. To better define the range of chloride tolerance in Vitis germplasm, we examined the resistance to chloride toxicity in six species of wild grapevine collected from the south and southwestern United States alongside several cultivated and widely utilized rootstock cultivars. Presented in chapter 1, results from this survey suggest untapped potential for quasi-halophytic properties in some wild grapevine species such as V. acerifolia and V. doaniana. In chapter 2 common varieties were tested against a gradient of applied sodium chloride ranging from 0 – 100 mM NaCl to better define the chloride concentration threshold at which photosynthetic function begins to decline in commercial rootstock cultivars and chloride becomes toxic. Chapter 2 establishes a range of NaCl exposure between 25-75 mM NaCl in which photosynthetic function begins to break down in many rootstock varieties. Finally, chapter 3 crosses a highly tolerant and highly susceptible parent to explore the breeding potential of chloride tolerance phenotypes in grapevine offspring. Throughout the 77 tested offspring we observed a wide range of continuous increments of foliar chloride accumulation, suggesting possible heritability of chloride-excluding phenotypes. These experiments suggest an untapped source of chloride tolerance in grapevines exists, the range at which these semi-tolerant varieties have the highest efficacy and support the heritability of chloride-excluding phenotypes in subsequent generations. Taken together, this project increases the likelihood a breeding program can introduce chloride-tolerant grapevine rootstock phenotypes that could be successful.