Polyploid formation pathways have an impact on genetic rearrangements in resynthesized Brassica napus

Polyploids can be produced by the union of unreduced gametes or through somatic doubling of F-1 interspecific hybrids. The first route is suspected to produce allopolyploid species under natural conditions, whereas experimental data have only been thoroughly gathered for the latter. We analyzed the meiotic behavior of an F-1 interspecific hybrid (by crossing Brassica oleracea and B. rapa, progenitors of B. napus) and the extent to which recombined homoeologous chromosomes were transmitted to its progeny. These results were then compared with results obtained for a plant generated by somatic doubling of this F-1 hybrid (CD.S-0) and an amphidiploid (UG.S-0) formed via a pathway involving unreduced gametes; we studied the impact of this method of polyploid formation on subsequent generations. This study revealed that meiosis of the F-1 interspecific hybrid generated more gametes with recombined chromosomes than did meiosis of the plant produced by somatic doubling, although the size of these translocations was smaller. In the progeny of the UG.S-0 plant, there was an unexpected increase in the frequency at which the C1 chromosome was replaced by the A1 chromosome. We conclude that polyploid formation pathways differ in their genetic outcome. Our study opens up perspectives for the understanding of polyploid origins.