Exogenous Applications of Plant Growth Regulators Improve Quality of ‘Fuji’ Apple
Apple production and consumption in Asian regions are increasing with economic development and the demand for highquality fruit. In this study, we conducted three experiments: i) GA3 and GA4+7 paste treatment, ii) forchlorfenuron (CPPU) treatment with and without GA4+7 spraying and iii) CPPU spray treatment at different concentrations under different conditions. The GA3 and GA4+7 paste treatments conducted 30 days after full bloom (DAFB) enhanced fruit growth without malformation; however, the application of this treatment was difficult. In contrast, CPPU spraying with or without GA4+7 enhanced fruit growth easily, but the 4 DAFB treatments induced severe fruit malformation. Among the application stages and CPPU concentrations tested, the 1 mg L-1 CPPU treatment on 10‒20 DAFB and the 5‒10 mg L-1 CPPU treatment on 30 DAFB produced 9‒18% larger fruits without malformation than the control. The 1 mg L-1 CPPU treatment applied 10‒20 DAFB induced a 1% decrease in the soluble solid content; whereas, 5‒10 mg L-1 CPPU treatment application on 30 DAFB did not decrease soluble solid content. In conclusion, 1 mg L-1 CPPU treatment application on 10‒20 DAFB or 5‒10 mg L-1 CPPU treatment on 30 DAFB are recommended to improve the fruit size of ‘Fuji’ apples.