Modulation of the initial growth of Eucalyptus clones using paclobutrazol: When smaller is better

Abstract

Modulating the growth rates of Eucalyptus during the initial vegetative phase via plant growth regulators can improve field establishment. The objective of this study was to verify the impacts of different concentrations of paclobutrazol (PBZ) on two Eucalyptus hybrids during the initial phase of growth. Experiments were conducted in a greenhouse using an E. urophylla × E. grandis hybrid (AEC 1528) and a spontaneous hybrid of E. urophylla (144 AEC). Both clones were subjected to PBZ concentrations of 0, 50, 100, 150 and 200 ppm active ingredient (a.i.) applied to the soil. The treatments were part of a 2 × 5 factorial design, and they were arranged into randomized blocks and consisted of five replicates. Cuttings were transplanted into 20-L pots; each pot contained one cutting and was considered an experimental unit. At90 days after the application of PBZ, the growth and development of both Eucalyptus clones subjected to all concentrations were inhibited. The inhibition effects intensified as the concentration of PBZ increased until approximately 90 to146 ppm and increased the plant sturdiness ratio (H/D; S//diameter) due to the inhibition of height caused by PBZ. Clone AEC 144 performed better than clone AEC 1528with respect to dry mass accumulation, LN and leaf area. However, clone AEC 1528 was superior with respect to resource partitioning due to a lower S/R ratio, aiding survival underwater deficit conditions.