Cold hardiness-informed budbreak reveals role of freezing temperatures and daily fluctuation in a chill accumulation model.

This article focuses on evaluating bud dormancy and chill accumulation in grapevines (Vitis interspecific hybrids) by incorporating bud cold hardiness into dormancy assessments. The study compares three chilling treatments—constant (5 °C), fluctuating (−3.5 to 6.5 °C daily), and natural field conditions—and finds that freezing temperatures promote greater cold hardiness gains, which in turn affect time to budbreak, a common dormancy phenotype. Existing chill models (North Carolina, Utah, and Dynamic) inadequately describe chill accumulation when adjusted for cold hardiness effects, leading to the proposal of a new chill model that includes freezing temperatures and accounts for daily temperature fluctuations as enhancers of chill accumulation. The findings emphasize the importance of measuring cold hardiness alongside chill accumulation to improve dormancy modeling and suggest that future research should incorporate fluctuating temperatures and cold hardiness evaluations for more accurate characterization of dormancy in perennial plants.