Outcrossing and paternity analysis of Pinus densiflora (Japanese red pine) by microsatellite polymorphism

This study employed microsatellite loci to analyse outcrossing rate and pollen dispersal in Japanese red pine (Pinus densiflora) in an isolated stand. The average offspring outcrossing rate for 29 cones was 0.955. Significant differences in outcrossing rates between offspring groups on individual branches that extended in different directions at different heights were not detected. Male parents of 874 offspring collected from the maternal tree were assessed by exclusion using polymorphisms at three microsatellite loci. Paternity analysis indicated that at least 31% of the offspring were fertilized by pollen from trees outside the stand. The average distance of pollen migration within the study stand was 68 m, with a maximum value of 325 m. There was excess mating with nearby P. densiflora trees, of which only a few were predominant pollen donors. In addition, a weakly directional bias in P. densiflora pollination was also detected in the study stand, suggesting that female strobili on a branch of the maternal tree were more easily fertilized by pollen from trees in that direction.