Mating system patterns of natural populations of Pinus koraiensis along its post-glacial colonization route in northeastern China.

To understand the genetic mechanisms underlying the endangerment of Pinus koraiensis, we studied the mating system of 49 families of this species in 3 natural populations along its post-glacial colonization route across ~1500 km in northeastern China using the chloroplast simple sequence repeat technique. We analyzed 11 polymorphic loci with clear and repeating bands, and we calculated the multi-locus outcrossing rate (tm), single-locus outcrossing rate, inbreeding index, and fixation index (F). Intra-population variation was not observed, but a large inter-population variation was observed in the outcrossing rate, and the tm increased from 0.767 (the south population) to 0.962 (the north population) along the post-glacial colonization route. The tm values within a population did not change with time over 2 consecutive years. The F values for the 3 populations were <0, which indicates an excess of heterozygotes. The mean effective number of alleles, Shannon diversity index, and Nei's genetic diversity index did not show a south-north pattern. The north population had the highest outcrossing rate but the lowest genetic diversity. The average genetic differentiation of P. koraiensis populations was 0.1251, which was within the average range of woody plants with outcrossing and wind pollination. This study suggests that the current endangerment of P. koraiensis is not related to its genetic structure; perhaps it is mainly caused by man-made and natural disturbances such as deforestation and fire. Therefore, reducing disturbances and enhancing habitats, rather than the genetic aspects, play more important roles in the long-term protection of P. koraiensis.