Effects of Plant Growth Regulators and their Time of Application on Flower Bud Formation of Japanese Pear 'Kosui'.

Abstract

Effects of several plant growth regulators on flower bud initiation on current shoots in Japanese pear (Pyrus pyrifolia Nakai) cv. Kosui were investigated. The applications of maleic hydrazide (C-MH, 1, 2-dihydro-3, 6-pyridazinedione choline) ; uniconazole-P (UCZ, (E)-(S)-1-(4-chlorophenyl)-4, 4-dimethyl-2-(1H-1, 2, 4-triazol-1-yl) pent-1-en-3-ol) ; benzylaminopurine (BA, N-(phenylmethyl)-1H-purin-6-amine) ; and abscisic acid (ABA) from early June to early August promoted flower bud formation or were ineffective depending on the time of application. C-MH increased flower bud number when applied in July, whereas UCZ was effective only when applied before or in early July. BA and ABA applications increased flower bud number when applied between early June and late July. The effect of gibberellin (GA4) application differed 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 affect flower bud initiation on shoots of Japanese pear 'Kosui' are discussed.