Kinetics of winter deacclimation in response to temperature determines dormancy status and explains budbreak in differentVitisspecies

2. Bud dormancy and cold hardiness are critical adaptations for surviving winter cold stress for temperate perennial plant species, with shifting temperature-based responses during the winter. The objective of this study was to uncover the relationship between dormancy transition (chilling requirement) and temperature on the loss of cold hardiness and budbreak. Dormant cuttings of Vitis vinifera , V. aestivalis , V. amurensis , and V. riparia were examined to determine the relationship between chilling requirement and temperature on rate of deacclimation ( k deacc ). Differential thermal analysis was used to determine k deacc using mean low temperature exotherms. Effect of chill was evaluated as the deacclimation potential (ψ deacc ), which was the change in k deacc due to chill accumulation. Budbreak was also evaluated in fully chilled buds at different temperatures. Results indicate that ψ deacc varies dependent on dormancy state, following a logarithmic response to chill accumulation. The effect of temperature on k deacc was exponential at low and logarithmic at high temperatures. The combination of ψ deacc and k deacc resulted in good prediction of deacclimation. Budbreak phenology was also explained by differences in k deacc . Deacclimation rates can be used as a quantitative determinant of dormancy transition and budbreak, and to refine models predicting effects of climate change.