EFFECTS OF TWO DIFFERENT GROWTH REGULATORS ON THE GROWTH AND WATER RELATIONS OF <em>ACACIA</em> <em>MANGIUM</em> SEEDLINGS

Abstract

Acacia mangium seedlings overgrow in size when the timing between plant production and field planting cannot be synchronized. Survival and growth of these overgrown seedlings are reported to be poor because of unfavourable root to shoot ratio resulting in desiccation during post-transplanting. This study compares the effectiveness of two different growth regulators, namely, paclobutrazol and daminozide, for controlling the growth and water relations of A. mangium seedlings with the objective of improving their post transplanting establishment. Fourteen-week-old potted A. mangium seedlings were foliar sprayed with paclobutrazol or daminozide at concentrations of 0,25,50,75,100, 150 and 200 mg l^-1. Plants were measured for height and leaf area increments, transpiration and stomatal conductance at weekly intervals. They were harvested after 12 weeks for measurements of height, leaf area, number of branches, total root length, root and shoot dry weights and the ratios of total root length to leaf area and root to shoot dry weight. Both paclobutrazol and daminozide reduced root and shoot growth, root to shoot ratio, transpiration and stomatal conductance of A. mangium seedlings. The effects of the chemicals increased with increasing concentration from 25 to 200 mg l^-1. Weekly measurements of height and leaf area increments, transpiration and stomatal conductance revealed that the differences in values of treated plants
compared to the control generally increased with time. Paclobutrazol was more potent than daminozide in affecting seedling growth and water relations, and the two chemicals differed in their effects. The results are discvissed with implications for practical application.