Response of Eucalyptus nitens seedlings to gibberellin biosynthesis inhibitors

The plant growth regulators (PGRs) paclobutrazol, chlormequat chloride and prohexadione where applied to 11 month old seedling of Eucalyptus nitens to examine their relative effects on precocious flowering, growth and levels of GA(20) and GA(1) in the shoot apex. Paclobutrazol was most effective in reducing growth and levels of GA(20) and GA(1) in the seedlings followed by chlormequat chloride with prohexadione being least effective. Paclobutrazo l and chlormequat chloride reduced both GA(20) and GA(1) levels by similar degrees, but prohexadione reduced GA(1) levels considerably more than GA(20 ) levels. None of these PGRs was effective in promoting precocious flowerin g. This suggests that there is an extra level of reproductive control opera ting in juveniles of this species compared to those of the closely related species E. globulus previously found to flower precociously in response to similar paclobutrazol treatments.