Variation of paternal contribution in a seed orchard of Cryptomeria japonica determined using microsatellite markers

We investigated gene flow and pollen contamination in a seed orchard of Cryptomeria japonica D. Don using six microsatellite markers. The quality of a seed crop is determined by many factors, including the rate of pollen contamination from outside sources, degree of self-fertilization, and equality of the clones as pollen donors. The surveyed seed orchard consisted of 62 clones and a total of 360 ramets. The seeds from 12 mother trees in the seed orchard were investigated using six highly polymorphic loci with high multipaternity exclusion probability (0.999). The estimated average pollen contamination rate was high at 47.78% (+-4.12%), and the clonal self-fertilization rate was 2.22% (+-0.94%) when we assumed that null alleles were present. The high pollen contamination rate could dramatically reduce the quality of the seed crop. The contamination rate differed from tree to tree, but the differences were not related to the location of each individual. The levels of contribution as pollen donors differed significantly amongst clones in the seed orchard. Differences in flowering phenology and relative pollen fecundity may be responsible for the differences in paternal contributions. The effective distance of pollen dispersal in this C. japonica seed orchard seemed to be greater than previously estimated.