EFFECTS OF PACLOBUTRAZOL ON THE GROWTH OF SEEDLINGS OF TWO DIPTEROCARP SPECIES

Abstract

Shorea leprosula and S. parvifolia seedlings of two different heights, 20 cm (small) and 45 cm (big), were foliar sprayed to runoff with a growth retardant, paclobutrazol (PP₃₃₃), at concentrations of 0, 0.1, 0.25, 0.5, 1.0, 2.0, 4.0, 8.0 and 12.0 g l^-1. Plants were harvested after 12 weeks for measurements of height, diameter, leaf area, number of branches, root and shoot dry weights and their ratio. Height increment was monitored at weekly intervals. Paclobutrazol was found to be effective in controlling the growth of the two species at both sizes tested. The effects of the chemical increased with increasing concentration. Weekly measurements of height increment revealed the onset of growth retardation to occur about 2 weeks after treatment. There was no complete recovery for any of the growth parameters even at the lowest concentration tested 12 weeks after treatment. The results are discussed with implications for practical application.