Induction of parthenocarpic fruit growth with endogenous Gibberellins of loquat

Developing fruits from mature trees (10 years old) of loquat (Eriobotrya japonica L. cv. Fusahikari) grown at the Chiba Prefectural Agricultural Experiment Station were collected in 1999. GA-like substances were extracted from I kg of seeds with 100% MeOH. After purifying the acid EtOAc-soluble fraction as usual, the extract was fractionated by ODS-HPLC, and GA activity was monitored by the microdrop rice seedling bioassay using dwarf rice 'Tan-ginbozu'. Each GA-fraction was resolved with 50% MeOH, and the 100 muL solutions equivalent to 10 g fresh weight of immature seeds were applied to the emasculated flowers of loquat at the balloon stage in 2000. Treatments were repeated after 4 weeks. To compare with parthenocarpic fruit induced by endogenous GAs, treatment of GA(3) at 500 and 1000 ppm were prepared. The fractions, that showed strong GA-like activity, were fractions No. 13, 16, 17, 19, 20 and 22. Five GA-fractions (No. 16, 17, 19, 21 and 22) induced parthenocarpic fruit set. The percentages of parthenocarpic fruit sets were about 4, 7, 39, 28 and 11, respectively. The most active fractions in inducing parthenocarpic fruit growth were 19 and 21, but fruit size was smaller than that of seeded fruit. No fruits developed to maturity when treated with GA(3). The results indicated that endogenous GAs were more effective than exogenous GA(3) in inducing parthenocarpic fruit growth of loquat.