Cultivar-specific responses of sweet cherry flowering to rising temperatures during dormancy

• Agroclimatic requirements of 20 sweet cherry cvs. estimated with PLS regression analysis. • Temperature during chilling, or both chilling and forcing, drive cultivar-specific flowering dates. • Declining chill accumulation caused by global warming generally resulted in flowering delays . Temperate fruit trees can enter dormancy during autumn-winter and resume active phenological development in spring in response to warm conditions. In a global warming context, recent temperature dynamics are causing changes in phenology and flowering that directly affect fruit production and yield. However, understanding how temperature regulates phenology remains a challenge. In this work, we analyzed the temperature response periods, agroclimatic requirements and sensitivity to temperature changes of 20 sweet cherry ( Prunus avium L.) cultivars. We used Partial Least Squares (PLS) regression to correlate bloom dates with daily chill accumulation according to the Dynamic Model (in Chill Portions; CP) and heat accumulation according to the Growing Degree Hours model (in Growing Degree Hours; GDH) for a 20-year record from Zaragoza, Spain. The chilling periods contained several phases that clearly contributed to chill accumulation, which were disrupted by periods with no significant model coefficients. The forcing periods were reflected by consistently negative model coefficients. Chill requirements ranged from 51.6 CP to 65.2 CP, from 779 CH to 1,008 CH, and from 728 CU to 1,150 CU. The heat requirements ranged from 4,994 GDH to 7,315 GDH. Depending on the cultivar, flowering dates were determined by temperatures during both chilling and forcing phases or almost exclusively by conditions during the chilling phase. Delays of sweet cherry flowering dates appeared to arise as a response to a decrease in chill and heat accumulation by about 7 CP and about 390 GDH over the past 30 years.