Site of (2RS, 3RS)-pacIobutrazol promotion of axillary flower initiation in pear cv. Doyenne du Comice

Abstract

The aim of this work was to examine how localized treatment of pear shoot tips with (2RS, 3RS) paclobutrazol is able to stimulate flower initiation throughout the tree. The chemical was applied locally on three occasions during June and July, before floral induction, to the tips or the bases of vigorous vertical new shoots of cv. Doyenne du Comice. Basal treatment stimulated flower initiation without inhibiting shoot extension. Small amounts of the chemical, as measured by combined gas chromatography mass-spectrometry, were found to have moved rapidly between the shoot tip and basal nodes in both the acropetal and basipetal directions, and to persist for several months. Paclobutrazol was also found in axillary vegetative and floral buds sampled in October from the tip- or basally-treated shoots; the floral buds in both containing twice as much. Much less chemical appeared to be required to promote flowering than to inhibit shoot growth, the amounts freely mobile within the shoot apparently being sufficien...