Estimation of genetic variation in Thailand rosewood (Dalbergia cochinchinensis Pierre)
Creators: name: Soonhuae, Prachote
Publisher: name: University of British Columbia
Year: 2009

description: Genetic diversity conservation of tropical forest trees, particularly economically valuable and endangered species, is urgently needed for maintaining ecological balances and sources of materials for direct, indirect and optional uses and their existing values. Thailand rosewood (Dalbergia cochinchinensis Pierre) is an economically important tree species of Southeast Asia. Undisturbed populations in natural forest reserves were suspected to have different genetic variability from that of disturbed populations in farm and public areas. The objectives of this study were to evaluate genetic variation and the mating system of Thailand rosewood in order to consider conservation strategies for the species. The variation was studied using quantitative and isozyme characteristics. Using open-pollinated families, quantitative variation was assessed in seed and 9 months old seedlings from eight populations, and in four years old seedlings grown in a progeny trial from seven populations. The differences among families were significant for most traits in all of the material tested. However, significant differences among populations were relatively high for most traits. The variation between undisturbed and disturbed populations for all traits was not significant. Root tips of three day old germinants from eight populations provided the material for isozyme studies. Twelve enzyme systems coding eighteen loci were analyzed. The overall mean of expected heterozygosity was relatively high (0.229) and the mean number of alleles per locus was moderate (2.2). F-statistics and Nei’s genetic distances indicated moderate differentiation among the populations (F(ST) = 0.127). There was no significant difference between the undisturbed and disturbed populations. The outerossing rates (t) estimated for the species were close to 1.0 for all populations. The results indicated high genetic variability within populations for both quantitative traits and isozymes, but the among population variability was relatively high for quantitative traits and moderate for isozymes. The species was highly outcrossed, with low inbreeding. Due to the fact that remnant populations or subpopulations of the species are naturally small and there is difference between populations from central and northeastern regions, about one thousand individuals collected from several populations would assure sufficient genetic viability for the conservation in each region. The conserved populations should also be distributed throughout the natural range of the species to maintain adaptability of desired quantitative traits. Both in situ and ex situ conservation are needed for this endangered species. Disturbed populations should also be maintained as seed sources. Ex situ conservation of about 1,000 individuals collected from subpopulations within each region and planted within the regional area would preserve the broad genetic base and prevent the random drift of the species. In addition, successful conservation requires strong support from government, involvement from local people, and international cooperation for technical and financial support.