Effect of Foliar Application of Gibberellic Acid and Machine Oil Emulsion Mixture on Flowering and Fruit Quality of Satsuma Mandarin (C. unshiu Marc. cv. Miyagawa) Cultivated on Open Fields

Abstract

In satsuma mandarin (C. unshiu Marc. cv. Miyagawa), alternate bearing is frequently occurred. It is very difficult to control and maintain the optimum production because satsuma mandarin is a very sensitive citrus cultivar. We carried out the experiment to find out the effects of foliar application of gibberellic acid (GA₃) and machine oil emulsion mixture on flowering and fruit quality of satsuma mandarin grown on open field. The treatments were composed of control (no application), GA₃ (25, 50 and 100 mg?L -1 ), machine oil emulsion 100 times and mixture of GA₃ (25 and 50 mg?L -1 ) with machine oil emulsion 100 times on 16 year-old ‘Miyagawa’ satsuma mandarin on December 30, 2012. Foliar application of GA₃ during winter season led to a reduction of the flowering in the following year. GA₃ decreased flowering in dose dependant manner. However, application of GA₃ and machine oil emulsion (100 times-diluted mixture) inhibited effectively the flowering compared to GA₃ only. Also, flower-leaf ratio was significantly decreased by the application of GA₃3 25 (0.54) and 50 (0.41) mg?L -1 with machine oil emulsion mixture in comparison to GA₃ 25 (0.86) and 50 (0.60) mg?L -1 only. The number of leaves per fruit increased in application of GA₃ and machine oil emulsion mixture as concentration of GA₃ increased. Fruit weight and sugar-acid ratio also increased in comparison to the control whereas fruit size, soluble solid content and acidity remained unchanged. From the results, it was suggested that GA₃ application can reduce the number of flowers on the alternate bearing of satsuma mandarin. Moreover, application of GA₃ (25 and 50 mg?L -1 ) with machine oil emulsion 100 times mixture can reduce the flowering effectively without altering fruit maturity and soluble solid contents. Therefore, it can be concluded that the application of GA₃ 25 and 50 mg?L -1 with machine oil emulsion 100 times might be useful in controlling alternate bearing in satsuma mandarin.