Abstract: Utah model was used for estimating bud chilling requirements of 65 fruit tree cultivars from 5 species in greenhouse during 1995 - 1999. Bud (both leaf and flower bud) chilling requirements were significant differences among different kinds of species and cultivars : grape and sweat cherry possessed the highest chilling requirements (respectively 1 010 - 1 840 c. u , 910 - 1 240 c. u) , chiuing reqairement of plum and apricot were lower (800 - 880 c. u , 790 - 910 c. u) , then those of peach cultivars were the lowest (500 - 910 c. u) . Moreover , the same cultivars had significantly different chilling requirements between different years , it indicated that chilling requirements
not only were affected by genetic factors but also regulated by enviromental variations. No regular relationship was found between chilling requirements and fruit development period , It also noted that flower bud had higher chilling units than leaf bud in almost all the experimental cultivars. In procssing of endodormancy , root might have some effects and in the experiment it affected the chilling requirements : high root temperature (in fact the temperature was the most suitable for root growth and development) reduced the flower bud chilling requirements , but lower and natural root temperature had no effects. Spraying growth regulators of different concentration also affected the chilling requirements : 10 - 50 mg·L^-1 6-BA reduced the chilling requirements and sprouting or blooming , 10 -
50 mg·L - 1 GA₃ increased the chilling requirements , but ABA had no ffects , compared with the control of spraying of H₂O.

Key words: Fruit tree, Chilling requirement, Greenhouse