Patterns of genetic variation and characterization of the mating system of Pinus merkusii in Thailand.

Abstract

A genetic inventory in 11 natural populations of Pinus rnerkusii in Thailand revealed only little genetic diversity at 14 isozyme gene loci (average 6, = H, = 0.058). Allelic differentiation among populations is also small (6 = 0.034), but higher than the differentiation reported from many other conifers, if measured as a proportion of the total variation (F,, = 0.104). Genotypic structures of seed samples are characterized by a deficiency of heterozygotes relative to Hardy-Weinberg expectations in most populations, while the genotypic structures of the seed trees, which represent the adult forest stand, do not differ significantly from Hardy-Weinberg proportions. Estimation of outcrossing rates revealed extraordinary high proportion of selfing (0.017 c t, < 0.65 for 9 out of 10 analyzed populations), which account for the high inbreeding coefficients. The low genetic diversity is explained by bottlenecks and consequently genetic drift in the evolutionary history of the populations. Scarcity of foreign pollen available for fertilization of ovules due to low population density, poor synchronization of flowering periods, and over-mature of most stands resulting in limited flower production are mentioned as probable reasons for the high inbreeding.