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

To determine the effect of grafting method (hole insertion grafting, HIG; tongue approach grafting, TAG; and spliced grafting, SG) on graft union formation in cucumber grafted onto bottle gourd rootstock, an anatomical and physiological study was carried out during the healing stage. The results showed that the TAG method resulted in an obviously higher daily growth rate than the other grafting methods 7 days after grafting (DAG), with significantly higher values in the scion than in the rootstock. The isolation layer, callus formation, and vascular connection all occurred at the graft junction when using HIG, TAG, and SG. Vascular bridging first occurred between scion and rootstock using HIG or TAG at 5 DAG; this process was delayed with SG. The activities of superoxide dismutase (SOD), POD (peroxidase), CAT (catalase), PAL (Phenylalanine ammonia-lyase), and PPO (polyphenol oxidase) were significantly enhanced in the graft union during the healing process when different grafting methods were used. Compared with HIG and SG, the POD and CAT activities and total phenolic compounds were higher with TAG at 7 DAG; a reduction in PPO activity and lignin content were also overserved at the graft with TAG at 7 DAG. These results suggest that the association of TAG with a higher growth rate during the healing period is linked with the earlier improvement in vascular bundle connection that may be caused by increased antioxidant activities and lower lignin content at the graft junction. These morphological and physiological differences may provide valuable information for revealing the graft union healing process.