The mechanism of the effect of (2RS, 3RS)-paclobutrazol on flower initiation of pear cvs Doyenne du Comice and Conference

Abstract

SummaryThe mechanism of action of paclobutrazol in promoting flower initiation in two cultivars of pear was studied by comparing responses to overall sprays, localized treatment of shoot tips and shoot tipping by hand, and by monitoring bud development in ‘Doyenne du Comice’. Flower initiation was promoted as effectively by localized shoot tip applications as by overall sprays. Shoot tipping did not promote flower initiation, and did not affect the stimulation of flower bud production by overall sprays. Shoot extension in both varieties was inhibited equally by shoot-tip applications, but not by overall sprays, the effects of which on ‘Comice’ were followed by a compensatory promotion of growth. In the season after overall spraying, ‘Comice’ produced many more new, mostly “bourse” shoots. This effect was not produced by shoot tipping or by paclobutrazol treatment of shoot tips or fruitlets. Repeated sprays of paclobutrazol at 250 mg l−1, but not a single spray at 1 g l−1 in July, delayed flower initiation...