Assessment of the genetic composition of triploid hybrid Populus using SSR markers with low recombination frequencies

The induction of nonreduced gametes, whether from first-division restitution (FDR), second-division restitution (SDR), or both, is an important approach for polyploidization. However, an accurate method for determining the genetic constitution of polyploid hybrids is not available. In this study, based on both flow cytometric analysis and somatic chromosome counting, 164 triploid hybrids of the female parent Populus pseudo-simonii × P. nigra ‘Zheyin3#’ (2n = 2x = 38, abbreviated ZY3) and male parent P. × beijingensis (2n = 2x = 38, abbreviated BJY) were produced by high-temperature treatment during ZY3 megasporogenesis. Using six simple sequence repeat (SSR) markers with low recombination frequencies to reduce the impact of recombination, we analyzed the allelic configurations of the obtained triploid hybrids. Although the allelic configurations were not always consistent at all six loci, by combining the allelic configurations at the six loci, we inferred that 40 triploids originated from FDR 2n eggs of ZY3, whereas the others originated from SDR 2n eggs. In conclusion, our study provides a novel and effective tool for analyzing 2n gametes and performing early selection to improve triploid poplar breeding programs.