Effects of three plant growth regulators on growth, morphology, water relations, and frost resistance in lemonwood (pittosporum eugenioides A.Cunn)

Abstract

Pittosporum eugenioides is a native ornamental species with a wide distribution throughout New Zealand. The effects of the application of two plant hormones (gibberellic acid and abscisic acid) and a gibberellin biosynthesis inhibitor (paclobutrazol) on the growth and development, frost resistance, and water loss on two-year old seedlings of P. eugenioides were studied. Gibberellic acid increased plant growth, stem diameter, and shoot succulence, while also inducing leaf hyponasty and vegetative bud break of apices. Abscisic acid induced growth suppression while being effective in promoting leaf epinasty and inhibiting bud break. Paclobutrazol induced growth suppression, promoted epinasty, decreased shoot succulence, inhibited bud break in apices, and increased foliar frost resistance. The effects of paclobutrazol were also overcome by the addition of gibberellic acid. The results are compared with those gained from species not native to New Zealand, and indicate the potential for the application of plant growth regulators to a New Zealand species of ornamental value. © 1995 Taylor & Francis Group, LLC.