Abstract

Gibberellins play a key role in flower and fruit development, and fruits often contain high gibberellin concentrations. This study quantified endogenous gibberellins in flowers and immature fruits of the macadamia cultivars, H2 and 246, to assist in developing growth-regulator treatments for improving fruit set. GA₁, GA₃, GA₈, GA₉ and GA₂₀ was detected in flowers or fruits of both cultivars, and GA₄were detected in flowers of cultivar 246. The timing of gibberellin accumulation was consistent between cultivars but total concentrations were very low (< 7 pmol g^-1 fresh weight). Low gibberellin levels are consistent with the inability of the gibberellin-synthesis inhibitor, paclobutrazol, to influence fruit retention in macadamia.

Key words: Abscission, fruit drop, kernel, nut, paclobutrazol, plant growth regulators, Proteaceae.