Kevin Fort, Claire Heinitz, and M. Andrew Walker*
*Department of Viticulture and Enology, University of California, Davis, CA 95616 (walker@ucdavis.edu)

Soil salinity can reduce yields in grape at levels as low as 2.5 dS/m ECe, a level commonly exceeded in salt-affected viticultural regions of California. Viticultural soils in these areas can have double this salt concentration and some promising but undeveloped sites have triple. Using a rapid screen for chloride exclusion, 326 accessions of wild American Vitis species were tested for chloride exclusion. The best-performing genotypes were subsequently assayed for rooting ability. Six genotypes were selected that exhibited both strong chloride exclusion and high rootability from dormant cuttings: three accessions of Vitis acerifolia and one accession each of V. treleasei, V. rupestris, and V. girdiana. These accessions and ten commercial rootstocks were grafted with a Cabernet Sauvignon scion and grown in large containers in a shadehouse in 2014 without salinization. In 2015, NaCl was increased gradually over one month to a final concentration of 75 mM and maintained for an additional two months. All ten commercial rootstocks and two of the six wild accessions showed some combination of high chloride concentration in the leaves, characteristic chloride-induced leaf necrosis, nutrient deficiency symptom in the leaves, or leaf loss. Four of the six wild accessions were asymptomatic, had shoot biomass comparable to the commercial rootstocks, and had relatively low chloride uptake into the leaves, even compared with the strongest chloride-excluding commercial rootstock, Ruggeri 140. The two strongest excluders, accessions of V. acerifolia and V. treleasei, had 29 and 32% of the chloride accumulation measured in Ruggeri 140, respectiverly. A nutrient analysis of the leaves is currently being conducted. These results support the utility of the rapid chloride screen, the existence of superior germplasm for salt tolerance, and the possibility of improved nutrient acquisition under high salinity conditions.

Funding Support: E&J Gallo Winery, the California Grape Rootstock Improvement Commission, the California Grape Rootstock Research Foundation, the American Vineyard Foundation, the CDFA Improvement Advisory Board, the California Table Grape Commission, and the Louise Rossi Endowed Chair in Viticulture.