Genetic control of growth and form in Eucalyptus urophylla in Northern Vietnam

Genetic parameters for growth, stem straightness and branch size were estimated in two open-pollinated progeny trials of Eucalyptus urophylla at two sites in northern Vietnam. Each trial tested 144 open-pollinated families from nine natural provenances, with 134 of these families being common to both trials. Height (HT) and diameter at breast height (DBH) were measured at ages 1, 2, 3 and 5 years in both trials, also at age 8 years in one trial, and at ages 7 and 9 years in the other trial. Stem straightness (STR) and branch size (BRA) were assessed at age 5 years and at the final measurement. At age 5 years, the Lewotobi provenance displayed the fastest growth, with only minor differences among other provenances. Growth traits had within-provenance, narrow-sense heritabilities ranging from 0.10 to 0.31. Heritability for DBH increased with age, but for HT it became stable after age two years. Coefficients of additive genetic variation for growth traits ranged from 7.3 to 12.4%. Heritabilities for STR and BRA were from 0.09 to 0.22. Age−age genetic correlations for growth traits between earlier and later measurements increased with age from 0.27 to 0.97. The genetic correlations between growth (DBH, HT) and form ( STR, BRA) were weak to moderate. Genetic correlations between sites for DBH and HT increased with age and became stable after age 3 years. Optimum selection efficiency for growth traits was reached at age 2 or 3 years, depending on the anticipated plantation rotation age.