Relationship between endogenous hormone content and physiological fruit drop of Fengtang plum

【Objective】To clarify the pattern of young fruit drop and physiological characteristics of fruit drop of Fengtang plum,and to provide a basis for fruit preservation and control in production.【Method】The contents of growth hormone(IAA),gibberellin(GA₃),zeatin(ZT) and abscisic acid(ABA) in normal and abscised fruits during physiological fruit drop were measured by enzyme-linked immunoassay,and the dynamics of young fruit drop and the growth of young fruits and shoots were also recorded.【Result】The fruit weight and fruit diameter of normal fruit were significantly higher than those of dropped fruit in all periods after flowering(P<0.05),and the growth of normal fruit was fast while that of dropped fruit was slow; the accumulation of fruit weight of dropped fruit was slow,and the growth of fruit diameter of normal fruit was faster than that of dropped fruit. The whole fruit drop period of Fengtang plum lasted from 14 to 70 d after flowering and was divided into rapid fruit drop period(14-28 d after flowering) and slow fruit drop period(28-70 d after flowering),with rapid fruit drop period being the main fruit drop period and the peak of fruit drop at 28 d after flowering,when about 82.73% of young fruits fell off. Young fruits grew slowly in the early stage and started to enter the rapid growth period at 42 d after flowering; new tip growth showed a fast-slow-fast trend,and new tip growth was positively correlated with fruit dropping rate from 21 to 28 d after flowering. Throughout the physiological fruit drop period,the contents of GA₃,IAA and ZT accumulated in the normally developing young fruits were higher than those in the dropped fruits,and ABA content lower than that in the dropped fruits. The ratios of growth-promoting and growth-inhibiting hormonesIAA/ABA,GA₃/ABA,ZT/ABA and(IAA + GA₃+ ZT) /ABAin normally developing fruits were greater than those in dropped fruits,indicating that medium and high levels of growth-promoting hormones and low concentrations of growth-inhibiting hormones in fruits were beneficial to fruit setting.【Conclusion】The high content of ABA and low content of GA₃ and IAA in young Fengtang plum fruits may be the root cause of large number of young fruit drop,in addition,shoot elongation is also an important factor causing fruit abscission.