Improvement in Handpicking Efficiency of Satsuma Mandarin Fruit with Combination Treatments of Gibberellin, Prohydrojasmon and Ethephon

To improve labor-saving during harvests, the efficiency of handpicking fruit was examined for the satsuma mandarin with the plant growth regulators gibberellin (GA), prohydrojasmon (PDJ), and ethephon (ET). In this study, concentrations of plant growth regulators were set 5 mg.L-1 for GA and 50 mg.L-1 for PDJ, respectively. Spraying of a GA plus PDJ solution on Aug. 27, Sep. 21, and Oct. 27 (triplicate spraying) improved the success rate of handpicking (SRH), as compared with a control. Furthermore, ET treatment in addition to triplicate spraying of GA plus PDJ increased SRH. A one-time treatment of GA plus PDJ also showed a significant effect on handpicking efficiency when applied in mid to late September. It was clear that the effect of GA plus PDJ on SRH was improved when 400 mg.L-1 ET was used instead of 200 mg.L-1, but this ET concentration (400 mg.L-1) caused massive leaf abscission (data not available). Spraying with 300 mg.L-1 ET alone showed 37.1% leaf abscission: therefore, we assumed that a GA plus PDJ treatment with a combination of less than 300 mg.L-1 ET would increase peel firmness without serious leaf abscission and a negative effect on SRH. In addition, the soluble solids and the acidity in the combination spraying of GA plus PDJ in late September with 300 mg.L-1 ET and less were almost the same as the control. Thus, our results indicated that the treatment of 5 mg.L-1 GA plus 50 PDJ in late September combined with ET (200 mg.L-1 < ET < 300 mg.L-1) from late October to early November was suitable for increasing SRH without impairing fruit quality and causing serious leaf abscission.