（1College of Horticulture，Hunan Agricultural University，Changsha 410128，Hunan，China；2Hunan Xuefeng Seed
Industry Co.，Ltd，Shaoyang 422001，Hunan，China；3Management Committee of Huaihua National Agricultural Science and
Technology Park-district，Huaihua 418005，Hunan，China）
Abstract：In order to explore the out-break regularity of watermelon female and male flowers，and
regulate their flowering sequence，so as to simplify the process of watermelon hybrid seed production，this
study took watermelon variety ‘Xuelong No.1’ as material；conducted treatments with different temperatures
and concentrations of ethephon and mepiquat chloride; and statistically calculated the expression of sex
differentiation in watermelon．This study also measured the endogenous hormone content in the shoot tip of
watermelon seedling by efficient liquid chromatography-tandem mass spectrometry．Results showed that the
effect of mepiquat chloride on the expression of sex differentiation in watermelon was related to temperature．
Under a suitable higher temperature spraying mepiquat chloride could achieve better effect．Under different
temperatures，the effects of mepiquat chloride were different with the changing of its concentration．The
effect of promoting the first male flower and the first female flower node position and increasing the number
of female flowers were the best when spraying mepiquat chloride at a concentration of 400 mg · L-1 under 25
℃ /20 ℃．The effects of ethephon on watermelon sex differentiation were significant．All 3 concentrations of
ethephon could vastly delay the formation of watermelon female flowers．In the former 30 knots，there was
no expression of female flower development，but only male flower formation．In addition，when spraying
ethephon and mepiquat chloride simultaneously，the effect of ethephon is dominant．After spraying ethephon，
the content of various endogenous hormones in watermelon decreased by different degrees．Regardless whether
it was the endogenous IAA，conducive to the differentiation expression of watermelon female flowers under
a high level，or the endogenous ABA，JA，GA3 and GA1，conducive to the expression of watermelon male
flowers under a high level，their contents were lower than that of the CK．
