GENETIC VARIATION IN A SECOND GENERATION PROGENY TRIAL OF <em>ACACIA</em> <em>AURICULIFORMIS</em> IN THAILAND
Keywords:Acacia auriculiformis, progeny trial, genetic variation, height, diameter, stem form, branching habit, heritability, Thailand
Open-pollinated seed from selected families from a first-generation progeny trial/seedling seed orchard of Acacia auriculiformis was used to establish second-generation progeny trials. There were 106 families, of which 13 were descended maternally from three Thai land races (candidate plus trees), 47 from four Papua New Guinea provenances, 25 from six Queensland provenances and 21 from seven Northern Territory provenances. In addition, two unimproved families from a local Thai land race were included for comparison. Assessment was made at age 36 months for height, diameter at breast height and individual tree volume, and at age 40 months for stem form (axis persistence and stem straightness) and branching habit (presence of upright branches on the lower part of the stem, repeated forking on the multiple stems and branch thickness). All families from the first-generation seedling seed orchard grew significandy faster than local unimproved seed trees. Families maternally descended
from the Queensland region were most productive, followed by those from Papua New Guinea, Northern Territory and Thailand. Despite a considerable increase in growth rate over unimproved seed trees, families descended from the Thai land races were clearly out-performed by those originating from Australia and Papua New Guinea. Most families produced single-stemmed trees with good stem axis persistence and a low frequency of upright branches on the lower part of the stem, indicating a considerable improvement in the stem form over the first generation. Estimates of individual-tree, narrow-sense heritabilities for most growth and form parameters were low, but statistically significant, ranging from 0.06 for repeated forking to 0.20 for stem straightness. Heri lability was not significant for presence of upright branches.