Microsatellite analysis of maternal half-sib families of Quercus robur, pedunculate oak: II. inferring the number of pollen donors from the offspring

We present an approach to infer the number of pollen donors directly from g enotype data of open-pollinated progeny of Quercus robur (pedunculate oak), a highly outcrossing tree species. The approach is based on closely linked , highly polymorphic codominant microsatellite markers. initially the close linkages between three previously mapped microsatellite loci were confirme d by studies of linkage disequilibrium (LD). Then an approach to track the pollen donors contributing to maternal half-sib families (open-pollinated f amilies) was developed by analysing haplotype arrays of closely linked micr osatellite markers transmitted from the fathers to the progeny. Simulated d ata of five linked microsatellite loci segregating in eight open-pollinated families were used to study the relationship between the number of paterna l chromosomes detected by this "haplotype approach" and the number of diplo id fathers contributing to the families. The results showed that the number of diploid pollen donors can be expressed as an exponential function of th e number of paternal chromosomes inferred from the progeny. The 95% confide nce interval of this regression function is used to determine the minimum n umber of fathers contributing to a genotyped open-pollinated family of Quer cus robur. Finally this open-pollinated family is used to demonstrate the r esolution obtained with the "haplotype approach" Six independent microsatel lite loci were used to study relatedness among all pairs of pollen gametes that share a haplotype of three linked markers. The results suggest that th e majority of such gametes are identical by descent from the same father. T he "haplotype approach" presented here can be used to monitor the number of contributing pollen donors in commercial seedlot samples from oak or any o ther outcrossing tree species for which closely linked, highly polymorphic, codominant genetic markers are available.