Effect of spraying gibberellin on the flower bud formation of Macadamia(Macadamia integrifolia)

Effect of gibberellin(GA3) on floral morphogenesis was examined with 5-year-old trees of O.C macadamia cultivar(Macadamia integrifolia Maiden Betche cv.O.C).Phenology of flower bud differentiation was compared between plants spared by GA3 and the control.Concentrations of endogenous hormones in fine roots,shoots and leaves during floral differentiation were determined.The results showed that the vegetative growth was promoted and floral initiation was suppressed by GA3 spray.Raceme elongation was delayed,and the number of raceme per node was remarkably reduced from 2.55 to 2.6 of the control plants to 1.45 to 1.52.The concentrations of GA3 and indole acetic acid(IAA) in shoots and leaves declined during floral differentiation,while abscisic acid(ABA) concentration rose.The higher ratio of(ABA+ZT)/(GA3 +IAA) seemed to promote the floral differentiation in macadamia.GA3 treatment enhanced endogenous GA3 and IAA accumulation but reduced ABA levels and hence resulting in low(ABA+ZT)/(GA3+IAA)ratios in the shoots and leaves.However,the treatment had little effect on hormones in the roots.