evaluation of chilling requirement in local cultivars of grapevine growing in fars province

it is necessary to determine the amount of chilling requirement of present cultivars and also to produce new low chill cultivars through breeding programs because of the global warming phenomenon and tendency to grow temperate fruit in warm climate. in this study, the amount of chilling requirement in ‘askari’, ‘rotaby’, ‘yaghuty’, ‘rish baba’ and ‘monaga΄ were evaluated. uniform cuttings of mentioned cultivars were harvested when leaves were abscised in autumn, and then transferred to refrigerator (2˚c). cuttings were subject to 0 (unchilled control), 100, 200, 300, 400, 500 chilling hours, then cutting were brought from chilling condition and put them in distilled water at room temperature (20º c) and continues light conditions. number of sprouting bud and data of first and last bud break were recorded. the lowest bud break percent in ‘askari’ and ‘rotaby’ were in unchilled control (25%). the highest bud break percent in ‘askari’, ‘rotaby’ and ‘yaghuty’ were at 500 h chilling (100%), 400 and 500 h, (100%), and 400 and 500 h, respectively. there were no significant differences between 200, 300 and 500 h chilling in ‘monaga’ and bud break was 100% in these treatments. the highest bud break in ‘rish baba’ was at 400 and 500 h. the shortest required period time to 50% bud break was in ‘askari’ at 400 h (23d), ‘rotaby’ at 500 h (23 d), ‘yaghuty’ at 400 h (13 d), ‘rish baba’ at 400 h (18 d) and in ‘monaga’ at 200 h (16 d). in conclusion the chilling requirements of studied cultivars were as following: ‘monaga’ (200 h), ‘rotaby’ (300 h), ‘askari’ (300h) ‘rish baba’ and ‘yaghuty’ (400 h).