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Genetic status of Polish larch (Larix decidua subsp. polonica (Racib. Domin)) from Chełmowa Mountain: implications for gene conservation

The Polish larch (Larix decidua subsp. polonica (Racib. Domin), a subspecies of European larch, is one of the most valuable forest-forming trees in Poland. It was first discovered on the Chełmowa Mountain where Natural Reserve has been established to protect this subspecies. Currently, this unique population is at risk of extinction. Nonetheless, the knowledge on the genetic diversity of this population and surrounding larch forests is insufficient to undertake actions aimed at conservation of genetic resources. In this study, we examined the level of genetic diversity and differentiation of four subpopulations of Polish larch from Nature Reserve on the Chełmowa Mountain and surrounding areas. We used eleven nuclear microsatellite markers (SSRs) combined in two multiplex PCR reactions. In total, 344 individuals of Polish larch were genotyped and subjected to further population genetic analyses. We found the high level of genetic diversity (average: He = 0.752, Ho = 0.720) and low levels of genetic differentiation (average: Fst = 0.022). The effective population size was large and homogeneous across subpopulations (mean Ne=90.7), and we found no sign of inbreeding. The spatial genetic structure was detected in two older subpopulations but not in the younger one, suggesting its artificial origin. The old larch subpopulations were genetically homogeneous and they were related to the ancestral group of Polish lowland populations. The old larch core populations growing on Chełmowa Mountain are relatively homogeneous and they well represent the ancestral genetic group of Polish lowland larch populations. However, they still exhibit relatively high genetic diversity and sufficiently large effective population sizes assuring their adaptive potential for a long-term existence. Surrounding larch populations are even more genetically diverse but this might be the effect of an admixture of seed sources from various populations from a wider area of Central Europe. We recommend that specific conservation efforts should be undertaken to promote natural regeneration of the core larch populations, even supplemented by the planting of seedlings derived from the oldest larch trees. Other management actions should focus on limiting external gene flow to this unique population of Polish larch.