EFFECTS OF A GROWTH RETARDANT AND SHOOT PRUNING ON THE GROWTH OF <em>ACACIA</em> <em>MANGIUM</em> SEEDLINGS

Abstract

Two experiments of chemical manipulation using a growth retardant, paclobutrazol, and a physical manipulation by shoot pruning were conducted in an attempt to develop an effective nursery technique to control excessive growth of Acacia mangium seedlings prior to transplanting. The first experiment involved foliar spraying of 10-week-old seedlings with paclobutrazol at concentrations of 0, 0.25, 0.5, 1, 2, 4, 8 and 12gl-1 in the presence of a Du Pont agricultural surfactant. The effects of two frequencies of application were also tested. Twelve weeks after treatment, factorial analyses revealed the main effects of concentration and frequency of application to be significant in reducing the plant height, leaf area, shoot and root dry weights and increasing the root length to leaf area ratio. Only the main effects of concentration were statistically significant in reducing the diameter increment and total root length. No interactions were recorded between the two factors for most of the parameters measured and effects on growth appeared additive. Growth retardation increased with increasing chemical concentration to a maximum at 12gl^-1. The second experiment tested the effects of pruning the main shoot of 10-week-old seedlings at 0, 30 and 60% of their total length before planting out. Similar growth parameters as for the first experiment were monitored for 12 weeks and the results showed maximum reduction in plants with 60% shoot removed. The effect of shoot pruning was statistically significant for all the parameters measured except for height increment and root to shoot ratios. Chemical control of growth was more promising than shoot pruning.