Chloride Exclusion Capability of Wild Vitis Accessions from the Southwest United States

The salinization of vineyards in California and worldwide is a growing problem due to the decreasing availability of quality irrigation water as well as cultural practices such as deficit irrigation. Grapevines are especially sensitive to chloride, which accumulates in roots, leaves and fruits in saline areas. Excess chloride in the leaves and fruit reduces growth rate, yield, and fruit quality. Some rootstocks can "exclude" chloride from the scion -- most likely by sequestration in the roots -- however this trait has not yet been fully characterized either physiologically or genetically. Nearly all studies have focused on commercial rootstocks rather than a characterization of the trait by species, and more understanding of the distribution and genetic origin of the trait in wild accessions is necessary before active breeding for salt tolerance can begin.;The European grapevine (Vitis vinifera) is grown almost exclusively on rootstocks derived from native North American wild species (Vitis sp.) due to their tolerance of many soil-borne pests and diseases. The North American Vitis species are taxonomically complex because of their dioecious, outcrossing nature and the lack of any reproductive barriers between the species. Those in the Southwest U.S. (southern California, Nevada, Utah, and Colorado; Arizona, New Mexico and West Texas) are particularly poorly characterized, despite their potential for breeding for marginal environments.;This paper describes the first wide-scale germplasm screen for chloride exclusion among V. arizonica and associated species from the southwestern United States. We applied a previously developed greenhouse chloride exclusion screen (Fort 2012) to a total of one hundred and five unique grape accessions, and a subset was repeated the following year to test the reliability of both the trait and the greenhouse screen. We identified many accessions with leaf chloride concentrations below that found in all other commercial rootstocks tested, indicating that this material should be an excellent resource for breeding. We also found the greenhouse screen provided consistent results across separate trials and over multiple years. While this screen did not point to a definite geographic or taxonomic origin of the chloride exclusion trait, we did find a majority of chloride excluding genotypes in V. girdiana from western Nevada and V. doaniana from the Texas/Oklahoma border region, indicating the potential for more than one mechanism of chloride exclusion in North American Vitis..;This work is the first step in identifying the origin(s) of chloride exclusion in wild grapevines and evaluating a large germplasm collection for use in rootstock breeding. Our results indicate that while chloride exclusion is widespread among Vitis species in the southwest U.S., more work is necessary on the physiological mechanisms behind the trait as well as the genetic basis before an efficient breeding program can begin. Future work should include more intensive screening of the accessions labeled "excluders" in this study, studies on the patterns of inheritance, and further elucidation of the genetic relationships among the species.