Analysis of mating system in two Pinus cembra L. populations of the Ukrainian Carpathians

Abstract

In natural pine populations, a mixed mating system is typical, characterized by the proportions of selfed and outcrossed seeds. Swiss stone pine (Pinus cembra L.) is one of the least studied European conifers in this respect. The mating system of six polymorphic allozyme loci were studied in haploid megagametophytes and diploid open-pollinated embryos in two stands located in the East Carpathians. In the 'Gorgany' population (24 trees, 198 seeds) the mean single- locus estimated outcrossing rate (ts) was 0.731, and the multilocus estimate (tm) was 0.773. In the 'Yayko' population the outcrossing rate was lower (27 trees, 213 seeds, ts=0.645, tm=0.700), suggesting 23-30% of seeds are self-pollinated. Correlation of outcrossing rate estimates among loci was less than 1, (0.300 in 'Gorgany' and 0.469 in 'Yayko') indicating biparental inbreeding occurred. Differences between tm and ts (0.042 in 'Gorgany' and 0.056 in 'Yayko') can also be influenced by consanguineous mating, indicated by the presence of spatial and genetic family structure. In small iso- lated populations of Pinus cembra, which are typical for the Carpathian part of the species' range, inbreeding depression may negatively affect seed quality. The high proportion of selfed seeds observed here can be expected in any seedlot of this species and should be taken into account while planning gene conservation or reforestation measures. Maternal trees in these populations showed no heterozygote deficiency at these allozyme loci, and instead showed increased proportions of heterozygotes (inbreeding coefficient FIS = -0.200 in 'Gorgany' and -0.142 in 'Yayko'). Balancing selection may explain heterozygosity levels up to and above equilibrium proportions.