Analysis of transmission of heterozygosity by 2n gametes in Populus (Salicaceae)

It is well known that polyploidy is a major force in plant evolution and diversification. Evaluating the transmission of heterozygosity by 2n gametes with different formation mechanisms is of crucial importance. In the present study, 120 triploid hybrids [originating from first-division restitution (FDR), second-division restitution (SDR), and postmeiotic restitution (PMR) 2n eggs of the same female parent] and 30 pairs of polymorphic simple sequence repeat (SSR) markers (distributed across all 19 chromosomes of Populus) were used to evaluate the maternal heterozygosity transmitted by each type of 2n eggs. FDR, SDR, and PMR 2n eggs transmitted different parental heterozygosities (0.7480, 0.3958, and 0.3590, respectively) in Populus. In addition, compared with the small coefficient of variation (CV=13.50 %) of heterozygosity transmitted by the 19 chromosomes of FDR 2n eggs, there was greater variation in heterozygosity transmitted by SDR and PMR 2n eggs (CV=51.92 % and CV=63.14 %, respectively). This may have resulted from the locations of the applied SSR markers, in addition to the different formation mechanisms of 2n gametes. Variations in locus-centromere distance resulted in variations in recombination rates, which influence the degree of heterozygosis at the detected locus. In conclusion, our data provides a useful reference point for the suitable applications of 2n gametes in future studies, promoting the further research of polyploidy in plants.