Article ID: MI-107
In order to promote increases in the size of ‘Kosui’ Japanese pear [Pyrus pyrifolia (Burm.) Nakai] fruit by plant growth regulators, we applied gibberellin (GA)3+4 paste [2.7% (w/w), A3:A4 = 90:10] in combination with prohexadione-calcium [1%, PCa; BAS-125 (3-oxido-4-propionyl-5-oxo-3-cyclohexene-carboxylate)], an inhibitor of GA 2β-hydroxylation that catabolizes active GA into an inactive form, to fruit pedicels at approximately 30 days after full bloom. GA3+4+PCa treatment advanced fruit growth only in the early stages, but fruit weight did not show any significant differences between the untreated control and GA3+4+PCa-treated fruits at harvest. In contrast, when GA4+7 [2.7% (w/w), A4:A7 = 66:34] was applied, the fruit weight at harvest was greater than that of untreated fruit. Moreover, GA4+7 treatment in combination with PCa resulted in an even higher fruit weight at harvest. The GA4 concentration in fruit flesh was not affected by GA3+4 application at 1 week after the treatment (WAT) either with or without PCa, but GA4 levels increased with GA4+7+PCa treatment, resulting in a significant increase in fruit weight at harvest. A single GA4+7 application almost doubled the GA4 concentration compared with the untreated control, but the difference was not significant. These results indicate that fruit weight at harvest was greater when the GA4 concentration was higher in the fruit flesh at 1 WAT. The higher concentration of GA4 in the GA4+7+PCa-treated fruit compared with the GA4+7 treatment alone may be attributed to the function of PCa that acts to prevent the inactivation of GA4 to GA34 by inhibiting 2β-hydroxylation.