Effects of Gibberellin Synthesis Inhibitors on Flower Setting of Satsuma Mandarin.

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Foliar applications of gibberellin inhibitors and GA3 on satsuma mandarin (Citrus unshin Marc.) were investigated with respect to flower induction.1. Paclobutrazol, uniconazole-P, prohexadione-Ca, and CCC were applied 3 times during autumn. The number of flowers on vegetative shoots were increased in the following spring by paclobutrazol and uniconazole-P treatments.2. Foliar sprays of paclobutrazol, uniconazole-P, prohexadione-Ca and GA3 were made in winter. There was a significant increase in the number of flowers by paclobutrazol treatments made on 10 and 30 Jan., uniconazole-P at 30 Jan., and prohexadione-Ca at 20 Dec., 10 and 30 Jan. GA3 application reduced the number of flowers and inhibited bud sprout break in the spring.3. Foliar applications of the above three GA inhibitors at 100, 300, 1, 000 and 3, 000 ppm were made on 30 Jan. Paclobutrazol at 100 to 1, 000 ppm, uniconazole-P at 100 ppm and prohexadione-Ca at 300 and 1, 000 ppm were effective for the flower induction. Treatments with 100 ppm paclobutrazol and 3, 000 ppm prohexadione-Ca induced the dropping of flowers and fruitlets.4. To determine the optimum time (s) of application, trees were sprayed with paclobutrazol, uniconazole-P, and prohexadione-Ca on 10 Jan., 30 Jan. and 20 Feb., repeatedly. With any agent, thrice treatments were most effective in promoting flowering, but once and twice applications were sufficient for a significant increase in flower bud formation with any chemicals. Chemical names used (2 RS, 3 RS) -1- (4-chlorophenyl) -4, 4-dimethy1-2- (1 H-1, 2, 4-triazol-1-yl) pentan-3-ol, (paclobutrazol) ; (E) -1- (4-chlorophenyl) -4, 4-dimethy1-2- (1, 2, 4-triazol-1-yl) -1-penten-3-ol, (uniconazole-P) ; Calcium-3, 5-dioxo-4-propionyl cyclohexanecarboxylate, (prohexadione-Ca).