Chilling requirements of sweet cherry genotypes for endodormancy release

Sweet cherry trees as temperate fruit species need to accumulate a cultivar-specific amount of a cold period (chill) to complete their life cycle during endodormancy and of a heat during ecodormancy to flower properly in spring. Without these periods they would not complete their development, trees would produce less pollen, which would affect the fruit set and the overall harvest. Thus information of cultivar chilling requirement is valuable information for growers. In period from 2017 till 2021 dormancy chilling requirement of 40 genotypes (cultivars and hybrids) of sweet cherries was evaluated. Three main models (Dynamic model, Chilling hours model and Utah model) were compared. Results confirmed different chill requirements of evaluated cultivars. The lowest chilling requirement was assessed for cultivar ‘Adélka’ that is the only cultivar evaluated in the low chilling requirement category with chill hours (CH) below 500 calculated according the Chilling Hours Model. Cultivar ‘Kasandra’ with chilling hour requirement in the range of 500-750 CH is also the only one in the low–moderate chilling requirement category. In the category moderate-high requirement (750-1000 CH) were evaluated 19 genotypes. In the high requirement category with chill hours 1000-1500 were classified 19 cultivars. For the category very high requirement (over 1500 CH) was not recorded any tested genotype.