Effect of grafting methods on physiological change of graft union formation in cucumber grafted onto bottle gourd rootstock

•TAG had obviously higher daily growth rate than HIG, SG during grafted 7 days.•Isolation layer, callus formation and vascular connection were all happened at graft junction using HIG, TAG, SG.•Vascular bridging first occurred between scion and rootstock using HIG or TAG at 5 DAG; this process was delayed with SG.•Higher level of POD, CAT activities and total phenolic compounds, and lower level of PPO activity and lignin content were maintained at graft union using TAG at 7DAG.