Vol. 74 No: 1

Title:
Winter trunk injections of gibberellic acid altered the fate of 'Hass' avocado buds: Effects on inflorescence type, number and rate of development

Authors:
S. SALAZAR-GARCIA and C.J. LOVATT

pp: 69-73

Abstract:
The objective of this study was to quantify the effects of high GA₃ concentrations applied through trunk injection on the developmental fate of buds of young (glasshouse study) and mature (field study) 'Hass' avocado (Persea Americana Mill.) trees. The goal of this research was to determine whether a high dose of GA₃ could be used to promote vegetative growth, reduce flowering intensity and fruit set and to even out alternate bearing. In both studies, GA₃ injections were made at bud swell, prior to bud break. For young trees, injections of 25 or 50 mg GA₃ per tree caused precocious inflorescence development and anthesis three weeks earlier than in control trees. GA₃ injections did not affect the number of vegetative shoots produced but increased the number of indeterminate inflorescences, at the expense of determinate ones. Increased bud abscission resulting from the GA₃ treatments reduced total inflorescence number. Mature trees in a commercial orchard injected with GA₃ at 1.0 or 2.5 g per tree on 5 January (before bud break) started anthesis 3 and 23 d later than control trees, respectively. No determinate inflorescences were produced in any treatment. GA₃ injections increased the proportion of inactive (quiescent) buds, resulting in fewer indeterminate inflorescences, but did not affect vegetative shoot number. The results of this research are the first to demonstrate that a high concentration of GA₃ trunk-injected in the winter prior to bud break can, through increased bud abscission or inactivity, reduce inflorescence number, with no effect on vegetative shoot number. Yield reduction would be anticipated in response to trunk injection of 1.0 g GA₃ per tree, because this treatment reduced both inflorescence number and fruit set/inflorescence. This, or a lower concentration, may prove useful in evening-out alternate bearing.

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