FDR and SDR processes in meiosis and diploid gamete formation in poplars (Populus L.) detected by centromere-associated microsatellite markers

Abstract

Sexual polyploidisation is one of the appropriate approaches in poplar breeding. Controlled pollinations were carried out with spontaneously formed, as well as induced, 2n gametes. Among the offspring individuals, 36 triploid plants and 1 tetraploid individual were detected by flow cytometry. The parental clones and all polyploid offspring individuals were genotyped by 18 nuclear microsatellite markers. The allelic configurations, especially tri-allelic patterns, and dosage effects were used to recognise diploid contributions of the male or female gamete. Three out of 18 markers localised near the centromeres of linkage groups I, X and XV. They are assumed to be unaffected by crossing over events and, therefore, able to ascertain the mechanism of first division restitution (FDR) or second division restitution (SDR) to generate diploid gametes. The applied three unlinked centromere-associated microsatellite markers allow a very effective determination of FDR resp. SDR processes. Altogether, 21 diploid pollen (10 FDR and 11 SDR) and 13 diploid ovules (1 FDR and 12 SDR) as well as 2 cases of postmeiotic reconstitution were determined with no inconsistency for the three markers. A female hybrid aspen clone (Populus tremula × Populus tremuloides) was assured to be able to frequently spontaneously form diploid ovules by the SDR mechanism. The transferred average heterozygosity in FDR gametes was assessed to be remarkably higher than that in SDR gametes. However, a selective inducement to favour FDR gametes seems not to be feasible with the current thermo-treatment techniques.