Objective   Functions of endogenous hormones in Pyrus pyrifolia on regulating the flower bud dormancy were studied.

  Method  Flower buds of P. pyrifolia Huanghua and P. pyrifolia Mixue in various stages of dormancy were collected to determine the contents of GA₃, ABA, IAA, and ZT as well as the ratios of GA₃/ABA, IAA/ABA, ZT/ABA, and (IAA+GA₃)/ABA by HPLC.

  Result  GA₃ and ABA exerted significant effects on the bud dormancy mostly during the endodormancy-releasing/bud-germinating stage as GA₃ initiated but ABA inhibited the release. IAA showed no significant effect in that regard, and ZT in Huanghua promoted the release, while ZT in Mixue initiated the dormancy. The ratios of GA₃/ABA and (IAA+GA₃)/ABA of both pear varieties were similarly low during dormancy. They rose significantly when the dormancy-release started and slightly declined afterward. The IAA/ABA ratio changed little, whereas the ZT/ABA decreased slightly in Huanghua, but the opposite in Mixue, at the initiation of dormancy-release.

  Conclusion  GA₃ and ABA played a major role in the dormancy of the pear flower buds, but ZT did not directly affect the dormancy-release. The process appeared to be regulated by an integrated effect of balance among these endogenous hormones, rather than individually. Although the changes on the endogenous hormones during flower bud dormancy differed between the two pear varieties, a similar general trend seemed existed.