Comparison of chilling and heat requirement in some peach and apricot cultivars

Bud Dormancy in deciduous fruit trees of the temperate zones is a phase ofdevelopment that occurs annually and enables trees to survive cold winters. Chilling andheat requirements for breaking dormancy and flowering were studied in five peach (Kosary,Haj Kazemi, Anjiry Asali, Anjiry Zafarany, and Zoud Ras) and four apricot (asgarabad,shamlo, shakarpare, tabarze ghermez) cultivars. Various models (two chilling hour models,the <7C and 0-7C models, and two chilling unit models, the Utah and Low Chill) were usedto measure the accumulation of chilling requirement. The heat requirements were calculatedas the growing degree hours (GDH) accumulated from breaking of dormancy to the F50 (50%of opened flowers). The cultivars studied showed a range of chilling requirements (chillunits, CU), between 746 to 868 CU for peach and 652-826 CU for apricot. The heatrequirements for peaches and apricots were between (4099 to 4543GDH) and (2987 to3465GDH) respectively. Apricot cultivars with lower chilling and heat requirements showedearlier flowering dates. Thus apricot cultivars bloomed between 15 and 16 day before peachcultivars and Heat requirements were found to be more important for regulation offlowering time than were chilling requirement in our climatic condition.