Effects of paclobutrazol on leaf anatomy and gas exchange of Toona ciliata clones

Abstract

Interest in Australian cedar (Toona ciliata M. Roemer var. australis) has increased due to its economic potential as an alternative to the use of native hardwood, and because of its resistance to the Hypsipyla grandella moth, which affects native cedars. The use of growth regulators such as paclobutrazol (PBZ) in the planting of T. ciliata is aimed mostly at obtaining seedlings with greater resistance to H. grandella and a desirable height for handling. However, this growth regulator tends to induce modifications to both leaf anatomy and photosynthetic potential. The present study aimed to evaluate the effect of increasing concentrations of PBZ on the leaf anatomy and gas exchange pattern in different T. ciliata clones. Seedlings from four T. ciliata clones (BV1110, BV1321, BV1120 and BV1151) were propagated by rooting cuttings and exposed to four concentrations of PBZ (0 μM, 0.5 μM, 1.0 μM and 2.0 μM), then the anatomy of the leaf blade and midrib vascular bundles and parameters related to gas exchange were analysed. Clones were significantly different for most of the characteristics studied. PBZ showed an effect only on the thickness of the palisade and spongy parenchyma. There was no effect of PBZ on gas exchange, but higher concentrations of PBZ induced thicker leaflets with scleromorphic characteristics.