GENETIC VARIATION IN WOOD MECHANICAL PROPERTIES IN TEN-YEAR-OLD <em>ACACIA</em> <em>CRASSICARPA</em> GROWN IN VIETNAM

Abstract

Wood mechanical properties of Acacia crassicarpa were assessed at the age of ten years old in a progeny test at Cam Lo, Quang Tri Province, central Vietnam. A total of 208 trees from 52 open-pollinated families were selected for study. Height and diameter at breast height were measured for all selected trees and spiral grain was also measured at breast height on the standing trees using a Chalmers device, which measures the grain angle of the surface wood. Basic density and shrinkage were measured on one 12-mm bark-tobark increment cores taken at breast height from each sampled tree. Microfibril angle was measured on fiber prepared from the core samples using polarized light microscopy. Genetic parameters of the wood and growth traits were estimated using individual-tree linear mixed models. High coefficients of additive genetic variation (CV_a, 17-34%) and high heritabilities (h² = 0.61-0.82) for all wood traits indicated that there is potential to improve basic density, wood shrinkage, grain angle and microfibril angle in the species in central Vietnam. The genetic correlation between DBH and shrinkage was positive and thus unfavourable, whereas correlations between DBH and both spiral grain and microfibril angle were negative and favourable. The Chalmers device appeared to be a reliable indirect method for investigating genetic variation in spiral grain in A. crassicarpa. Index selection, based on genetic parameters and economic weighting dependent on breeding objectives is suggested for development of seed orchards to deliver genetic gain for A. crassicarpa in central Vietnam.