Effects of CEPA and 1-MCP on flower bud differentiation of apple cv. ‘Nagafu No.2’ grafted on different rootstocks

The apple ( Malus domestica Borkh.) has a relatively long juvenile period which prevent the fruit breeding. The understanding of the flowering system is important to improve breeding efficiency in the apple. In this context, 2-year-old “Fuji” apple cv. “Nagafu No.2” trees that were grafted on dwarf self-rooted rootstock M.26, vigorous rootstock M. sieversii and interstock M.26/ M. sieversii , respectively. Spraying with clean water (as controls), 800 mg·L −1 2-Chloroethylphosphonic acid (CEPA) and 2 μL·L −1 1-methylcyclopropene (1-MCP). The results showed that CEPA significantly repressed the vegetative growth attributed to the increase of the ABA and ZT synthesis, and the decrease of IAA synthesis in leaves and buds. However, there was no significant difference or significant inverse effect between 1-MCP and control. Furthermore, CEPA promoted flower formation, increased the flowering rate and advanced the blossom period for 2 days compared with the control, which accompanied by the accumulation of soluble sugar, glucose and sucrose, and the increase of α-amylase (α-AMY) and sucrose phosphate synthase (SPS) activities, and the decrease of the starch contents and sucrose synthase (SS) activities in leaves and buds. However, the blossom period was delayed for 2 days after spraying with 1-MCP. Finally, the expression of TFL1 was significantly repressed while the AP1 was significantly promoted in buds from M.26 and M.26/ M. sieversii after spraying with CEPA, while the effect was not significant from M. sieversii. However, the expression levels of TFL1 and AP1 were not significantly different from the control after the application of 1-MCP. In spite of this, CEPA was more susceptible to easy-flowering M26, followed by M26/ M. sieversii , and still less susceptible to difficult-flowering rootstock M. sieversii . Abbreviations 1-MCP 1-methylcyclopropene α-amylase (α-AMY) ABA abscisic acid CEPA 2-Chloroethylphosphonic acid CTK cytokinins ETH ethylene GA gibberellin SPS sucrose phosphate synthase SS sucrose synthase ZT zeatin.