evaluation of temperature requirements of six apricot cultivars under lab and field conditions in shahrood

in this research, chilling and heating requirements of six local cultivars of apricot (jafari, ghavami, jahangiri, khiari, khiveaee and rajabali) were evaluated under field and lab conditions. under lab condition, ‘rajabali’ and in some extent ‘johangiri’ began flowering after 500 hours in 4°c. other cultivars except ‘khiari’ flowered at 750 h. ‘khiari’ flowered at 1000 h. in field, due to little difference of flowering time among cultivars, there was a low difference in chilling requirement among cultivars in all models. calculation of chilling requirements based on chilling hours was around 1400 h while based on utah, north carolina and low chilling models was 1000, 740 and 770 unit, respectively. chilling requirement in all cultivars was 71 portions based on dynamic model calculation. amount of heating requirement ranged from 1829 growth degree hours (gdh) in ‘khivea’ to 3387 gdh in ‘jafari’. although little differences exist in flowering onset of cultivars, the differentiation of flowering period among cultivars was around one week. cultivars showed little differences in flowering onset in locations they meet their chilling requirement.