Effects of plant growth regulators and their time of application on flowerbud formation of Japanese pear 'Kosui'

Effects of several plant growth regulators on flower bud initiation on curr ent shoots in Japanese pear (Pyrus pyrifolia Nakai) cv. Kosui were investig ated. The applications of maleic hydrazide (C -MH, 1,2-dihydro-3,6-pyridazi nedione choline); uniconazole-P (UCZ, (E)-(S)-1-(4-chlorophenyl)-4,4-dimeth yl-2-(1H-1, 2, 4-triazol-1-yl)pent-1-en-3-ol); benzylaminopurine (BA, N-(ph enylmethyl)-1H-purin-6-amine); and abscisic acid (ABA) from early June to e arly August promoted flower bud formation or were ineffective depending on the time of application. C-MH increased flower bud number when applied in J uly, whereas UCZ was effective only when applied before or in early July. B A and ABA applications increased flower bud number when applied between ear ly June and late July. The effect of gibberellin (GA(4)) application differ ed depending on the application date. Compared to the control, fewer flower buds were initiated by early June application; whereas more were formed by an early August spray. The possible mechanism(s) on how these regulators a ffect newer bud initiation on shoots of Japanese pear 'Kosui' are discussed .