Evaluating approaches for developing elite Acacia hybrid clones in Vietnam: Towards an updated strategy

Acacia hybrid (A. mangium A-A. auriculiformis) clones are planted on a large scale in Vietnam and it is desirable to expand the genetic base beyond the 10 commercial clones that comprise most of the plantation estate. Two approaches for developing elite clones from new Acacia hybrid genotypes derived from open-pollinated pure-species seedlots were compared. Method 1 involved identifying candidates in the nursery on the basis of seedling morphology followed by field trials of about 5000 putative hybrid seedlings. At 2 years, the best 3% of seedling candidates were reselected, captured and propagated for clonal screening trials. Method 2 captured and then clonally tested all putative hybrid genotypes identified on their morphology in pure-species field progeny trials at age 2 years. Method 1 was found to be much more effective at identifying promising new clones. Eighty-one of 196 candidate clones from this method had stem diameters at 2-3 years greater than or equal to the mean of commercial clone controls included in the clone trials. Method 2 yielded only 13 similarly promising new clones from 262 candidates. Maternal parents of both species yielded promising new clones. Overall timelines and a strategy are proposed and discussed for developing new elite Acacia hybrid clones, superior not only in growth but also in disease tolerance, wind-firmness and other important traits

Growth of triploid and diploid acacia clones in three contrasting environments in Viet Nam

We assessed the growth and adaptability of triploid acacia clones in comparison with commercially planted diploid clones of the same taxa to age three years at three contrasting sites in north, central and south Viet Nam. Application of phosphorus fertiliser at planting gave a growth response only in the trial in central Viet Nam. One triploidAcaciahybrid (Acacia auriculiformisxmangium) clone was constantly the best performer in all sites, achieving mean annual increments at three years of 30.1, 26.6 and 32.1 m(3)ha(-1)in northern, central and southern Viet Nam, respectively. Two other triploid hybrid clones outperformed the diploid controls in southern Viet Nam. A single triploidA. auriculiformisclone and two diploid clones of this species grew much more slowly. TriploidAcaciahybrid clones had a lower incidence ofCorticium salmonicolor(pink disease) andCeratocystisdisease symptoms than did diploid hybrid clones. The wind-firmness of triploidAcaciahybrid clones was comparable with or better than the diploid hybrid clones. Triploid breeding offers a promising new pathway in the development of improvedAcaciaplanting material