FORCING SPRING BUD BREAK IN 'HASS' AVOCADO

Strategies to increase spring floral bud break of ‘Hass’ avocado (Persea Americana) to increase floral intensity hold promise for increasing fruit set, yield and grower income. Such strategies would be especially important during the spring following the heavy on-crop when trees flower poorly. Both apical and lateral buds on 1-year-old bearing spring shoots (shoots that set fruit the previous year with fruit present through bloom in California) excised from on-crop trees in spring (March) underwent minimal bud break and plant bioregulators (PBRs) had no effect on lateral bud break even when the apical bud was removed. In contrast, apical buds on 1-year-old nonbearing spring shoots (shoots that did not set fruit the previous spring) excised from off-crop trees had a greater percent bud break than lateral buds and produced predominantly floral shoots. When the apical bud was removed, 6-benzyladenine (BA) increased lateral bud break of both floral and vegetative buds. In a commercial orchard, removal of the apical bud before the end of March increased bud break of lateral vegetative buds on 1-year-old bearing and nonbearing shoots of on- and off-crop ‘Hass’ avocado trees, respectively. Early spring (Feb) foliar applications of BA significantly increased bud break of apical buds, which were floral, but not lateral buds, of nonbearing shoots on off-crop trees; PBRs had no effect on apical or lateral bud break on bearing shoots of on-crop trees. A January trunk injection of a proprietary product to increase bud cytokinin concentration combined with the auxin-transport inhibitor 2,3,5-tri-iodobenzoic acid significantly increased bud break of apical and lateral floral buds on both nonbearing and bearing shoots of on-crop trees. In spring, ‘Hass’ avocado floral buds are dormant due to correlative inhibition of apical and lateral buds caused by mature fruit on bearing shoots of on-crop trees and also due to apical dominance of lateral buds.