Abstract: ObjectiveThe present study explored the key period for flower bud differentiation of Summer Black Grape in different regulation measures,in order to provide reference and guidance for regulation of flower bud differentiation of Summer Black Grape in two-crop-a-year cultivation in southern Guangxi.MethodEight-year-old Summer Black Grape seedlings were used as materials.When the shoots grew five-seven leaves,buds at the sixth node were sampled weekly and made into paraffin sections.Effects of different summer pruning intensities(pinching at the second node above anthotaxy,pinching at the forth node above anthotaxy and pinching at the sixth node above anthotaxy) and different concentrations of ethephon spraying treatments (200,400 and 800 mg/L) on flower bud differentiation process and flower formation rate in two-crop-a-year cultivation in southern Guangxi.ResultIn different summer pruning intensity treatments,the time span between beginning of flower bud differentiation (March 29) of wiuter buds on shoots and formation of flower cluster(April 27-May 4) was 29-37 days,which was 14-22 days shorten than that in control group(no pinching and no ethephon spraying).The key period for flower bud differentiation was around April 13 (full flowering stage).After different summer pruning intensity treatments,flower bud differentiation of the sixth node on shoots was concentrated with short duration and high flower formation rate(53.3%-73.3%).On the contrary,different concentrations of ethephon spraying resulted in dispersed stages of flower bud differentiation,longer duration (52 days) and lower flower formation rate (33.3%-