Abstract

The tropical acacias from Australia and Papua New Guinea are introduced to other tropical countries since early 1900s to afforest highly degraded, lateritic and infertile soils. Early introductions with very low genetic base led to severe inbreeding depression. Proper attention was also not given to introduce the appropriate seed sources. Such lapses led to stunted growth, poor tree form and susceptibility to diseases. In this context, a research project was initiated to select the best species/provenance trial was conducted in three species of Acacia namely, A. aulacocarpa, A. crassicarpa and A. mangium with 8, 5 and 9 provenances was monitored up to 12 months. The study showed that there were significant differences between provenances for grwothin A.aulacocarpa and A. mangium but not in A.crassicarpa. The genetic variations and heritability status for height and girth are found to be moderate to high in A. aulacocarpa and, a high genetic gain is expected by selecting the best provenannce. In A.mangium genetic variations were moderate with low heritability and by selecting the best provenance, moderate genetic gain in expected. In A. aulacocarpa the best performers were Bensbach and Arufi whereas in A.mangium the best provenances were Bensbach,Wipim and Guram. A species-cum-seed source trail also was conducted to select the best species/seed source for growth and other characters. Four species namely, A.aulacocarpa, A.auriculiformis and A.crassicarpa and A.mangium, each with one provennance and a seed orchard source (improved seeds), were tested. The seedlings were monitored up to 20 months. The study showed that there were highly significant differences bewteen species with respect to height, girth and number of branches. But within species there were no significant difference between seed sources with respect to these three characters. With regard to growth A. auriculiformis excelled others, especially the provenance Oriomo from Papua New Guinea. A.mangium had the least number of branches which is a desirable character and for this character provenance Oriomo was the best performer. The natural or artificial hybrids between these two species are reported to be highly promising and expressing hybrid vigour. Hence, hybride production followed by selection for the best characters can be opted for genetically improving the growth and other characters. The best seed sources should be used for hybridization to exploit the maximum gain