GENETIC IMPROVEMENT FOR WOOD PRODUCTION IN MELALEUCA CAJUPUTI

Genetic parameters was estimated for growth (tree height, diameter at breast height (DBH) and volume), stem form, MOE (wood stiffness), bark thickness and bark ratio in a half-sib family progeny trial of Melaleuca cajuputi comprising 80 families in South Vietnam. MOE of standing trees was measured indirectly by acoustic velocity using microsecond timer. Narrow-sense heritability ranged from 0.13 to 0.27 at age 7 years. MOE and stem form had positive genetic correlations with growth while negative correlation between bark ratio and growth was also favourable. Breeding for simultaneous improvement of multiple traits, faster growth with higher MOE and reduction of bark ratio should be possible in M. cajuputi. Index selection based on volume and MOE showed genetic gains of 31% in volume, 6% in MOE and 13% in stem form. In addition, heritability and age–age genetic correlations for growth traits increased with time and optimal early selection age for growth of M. cajuputi based on DBH alone was 4 years. Selected thinning resulted in an increase in heritability due to considerable reduction of phenotypic variation but had little effect on genetic variation.