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 GA20 and GA1 in the shoot apex. Paclobutrazol was most effective in reducing growth and levels of GA20 and GA1 in the seedlings followed by chlormequat chloride with prohexadione being least effective. Paclobutrazol and chlormequat chloride reduced both GA20 and GA1 levels by similar degrees, but prohexadione reduced GA1 levels considerably more than GA20 levels. None of these PGRs was effective in promoting precocious flowering. This suggests that there is an extra level of reproductive control operating 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.