ISOZYME ANALYSIS OF A TROPICAL FOREST TREE, PTEROCARPUS-MACROCARPUS KURZ IN THAILAND

Genetic variation within and among 11 natural populations of Pterocarp us macrocarpus Kurz. from different forest habitats in Thailand was ex amined by starch gel electrophoresis of 18 loci coding for 11 enzymes. The species possesses a high level of isozyme variation. The percenta ge of polymorphic loci per population ranged from 66.67 to 100% with a mean of 82.32% and the number of alleles per locus per population ran ged from 2.44 to 2.94, averaging 2.67. Observed average population het erozygosity at 0.222, was lower than the expected average population h eterozygosity (0.246) and the estimate of F-IS, at 0.099, suggests som e degree of inbreeding within populations. There was a high degree of among-population differentiation. All 18 loci exhibited allelic hetero geneity and the estimate of F-ST was 0.12. Cluster analysis revealed a n east-west pattern of population grouping, in accordance with signifi cant correlations between allelic frequencies and longitudes at eight loci. The correlation coefficient between genetic and geographic dista nce at 0.515 (P < 0.0001) suggests that isolation by distance might in part have been a contributing factor to population differentiation in this tropical forest tree.