%0 Journal Article %A Jacob Cragin %A Marcelo Serpe %A Markus Keller %A Krista Shellie %T Dormancy and Cold Hardiness Transitions in Wine Grape Cultivars Chardonnay and Cabernet Sauvignon %D 2017 %R 10.5344/ajev.2016.16078 %J American Journal of Enology and Viticulture %P ajev.2016.16078 %X Cold injury is a major cause of economic loss in wine grapes (Vitis vinifera L.) grown at high-latitudes. The objectives of this study were to investigate the relationship between dormancy and cold hardiness transitions in two cultivars with differing freeze-tolerance (Chardonnay and Cabernet Sauvignon). Cold hardiness was measured by differential thermal analysis, and a bud forcing bioassay was used to measure stage and depth of dormancy. Canes were sampled from field-grown grapevines in Parma, ID, at periodic intervals during two consecutive winters. Both cultivars transitioned into endodormancy each year in Sept when day length was ~12.5 hr. Cold acclimation in both cultivars occurred each year in Oct during endodormancy and steadily increased during ecodormancy to a maximum hardiness in Dec. Temperatures effective for release from endodormancy were lower for Chardonnay (−3 °C) than for Cabernet Sauvignon (3 °C) and, each year, Chardonnay transitioned to ecodormancy earlier than Cabernet Sauvignon. From Oct to Dec each year, the buds of Chardonnay were more cold hardy than the buds of Cabernet Sauvignon. The number of days to break bud under forcing conditions steadily increased during endodormancy and decreased during ecodormancy. Resistance to deacclimation during ecodormancy was inversely related to the level of bud cold hardiness and the duration of time in ecodormancy, suggesting that the mechanisms that impart hardiness may interact with those involved in resumption of growth. Results from this study show that influences of autumn weather events on dormancy and cold hardiness transitions can alter vulnerability to subsequent cold injury and have important implications for changing global climates. Differences between cultivars in dormancy and cold hardiness transitions can be used to enhance cultivar and site selection. %U https://www.ajevonline.org/content/ajev/early/2017/01/05/ajev.2016.16078.full.pdf