Deconstructing cold hardiness: variation in supercooling ability and chilling requirements in the wild grapevine Vitis riparia

Background and Aims Grapevine production in cool climates is limited by aspects of winter survival and frost risk. Cold hardiness‐related traits are key to future viticultural sustainability as climate variations, including acute cold events and frost, are predicted to increase even in traditional cultivation regions. This study examines the variation in dormant bud cold hardiness (supercooling) and dormancy (chilling requirement) in 43 different genotypes of the wild grapevine species Vitis riparia, the dominant wild species used to incorporate cold hardiness traits into new hybrid grapevine cultivars. Methods and Results Cold hardiness was evaluated bi‐weekly in 2 years using measures of low temperature exotherms. Whole winter responses were modelled to determine significant factors affecting cold hardiness and determine genotypic differences. Results demonstrate significant differences in supercooling ability and deacclimation rate (loss of cold hardiness) between genotypes. Conclusions This study determined that genotypic differences contribute to initial differences in cold hardiness. However, data modelling suggests that midwinter cold hardiness changes are driven by environment as all Vitis riparia tested in this study respond to temperature in the same manner during the endodormant period of winter. In contrast, responses to warming temperature during ecodormancy are significantly different by genotype. Significance of the Study This study has demonstrated that these two traits interact to determine differences in early versus late winter cold hardiness and help identify breeding germplasm with delayed loss of cold hardiness.