Gene flow and mating system in a seedling seed orchard and a natural stand of Pinus merkusii Jungh. et de Vriese in Indonesia

Abstract

Isozyme gene markers were used to study gene flow and the mating system in a seedling seed orchard and a natural stand of P. merkusii in Indonesia. Embryos and megagametophytes of at least twenty seeds per family were analysed electrophoretically in order to determine allele frequencies at eight polymorphic isozyme gene loci (GOT-B, GOT-C, GOT-D, PGM-A, PGM-B, SKDH-A, NDH-A and FDH-A). Outcrossing rates were estimated based on a mixed mating model. In the seedling seed orchard the average single-locus estimate of outcrossing (t _s )was 0.83±0.04, while the multilocus estimate (t _m )was 0.87±0.03. Both estimates were slightly higher (t _s = 0.90±0.05 and t _m = 0.98±0.03) in the natural stand. Estimates of outcrossing rates of single trees were more heterogeneous in the seed orchard than in the natural stand. Individual outcrossing rates in the seed orchard seemed to be related to their ancestral background. Trees belonging to one particular open-pollinated family tended to have homogenous outcrossing rates. Two open-pollinated families consisting of three trees showed lower outcrossing rates than the remaining three. Pronounced variation of outcrossing rates was not detected between individual trees in the natural stand, although comparisons were made between trees growing in contrasting density, i.e. closely together and spatially isolated. The pattern of allelic differentiation among effective pollen clouds was slightly different between the seed orchard and the natural stand. In general, pollen allele frequencies of single seed trees were moderately homogeneous in both populations.