Breeding of Acacia auriculiformis A.Cunn. ex Benth in Vietnam, which commenced in 1996, has focused to date on improving tree growth and stem straightness. Little attention has been paid to important properties of wood such as basic density, shrinkage, bending stiffness and strength, which determine suitability for specific end-use applications. The aim of the studies reported here was to obtain knowledge of genetic factors associated with wood traits and their relationships with growth and tree form, in order to facilitate improvement of A. auriculiformis for sawn timber production. Empirical data were gathered in a progeny test, three clonal tests and three genetic gain tests in four provinces of Vietnam. Genetic parameters for the studied traits were estimated at ages ranging from 3 to 9 years. The results showed that individual within-provenance heritabilities (h2) and clonal repeatabilities (H2) for growth, stem straightness, basic density and shrinkage increased with age, but those for mechanical properties were stable with age. In the progeny test, h2 ranged from 0.36 to 0.39 for growth traits, 0.40-0.61 for density and 0.12–0.31 for stem straightness. In clonal tests, H2 ranged from 0.21 to 0.56 for growth traits, 0.16-0.38 for shrinkage traits, and 0.21-0.57 for mechanical properties. Growth and wood properties had coefficients of additive genetic variation (CVA) and genotypic variation (CVG) ranging from 5-12%. High age-age correlations for most studied traits were found, suggesting that there would be more gain per unit time by selecting trees at 3 to 4 years old than at greater ages. Growth traits showed consistent positive genetic correlations with stem straightness, but non-significant correlations with wood properties, except for a significant negative correlation between diameter and stiffness. Genotype by environment interaction was important for growth and stem straightness in clone trials across southern, central-north and northern Vietnam, but not important for a number of improved and unimproved seedlots compared in genetic gain trials across northern, central-north and central Vietnam. Predicted and realised gains for growth were substantial for seed orchard seedlots produced by the current breeding program, compared with natural-provenance and local commercial control seedlots. Good gains in growth and form traits and wood properties could be obtained from clonal selection, although the absence of strong, favourable correlations between growth and wood properties indicates that gains for individual traits would be reduced if a multi-trait improvement approach was adopted. The findings clearly demonstrate that there is potential to improve tree growth, stem straightness, wood density, shrinkage and mechanical properties of A. auriculiformis in Vietnam.
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