Development and characterization of an allooctaploid (AABBCCRR) incorporating Brassica and radish genomes via two rounds of interspecific hybridizations

Abstract

Interspecific hybridization, which leads to the combination of the genomes from different species, not only contributes to speciation but also enriches the genetic stock of crops. Production of interspecific/intergenetic hybrids between Brassica species or Brassica and relative species has been a desirable goal for plant breeders and genetic researchers. In this study, we initially generated the allotetraploid Raphanobrassica (CCRR, 2n = 36) through a cross between maternal Raphanus sativus (RR, 2n = 18) and paternal Brassica oleracea (CC, 2n = 36). We then developed an allooctaploid (AABBCCRR, 2n = 72) that incorporated three Brassica subgenomes and radish genomes through crosses between the newly formed Raphanobrassica and B. juncea (AABB, 2n=36), followed by the chromosome doubling. PCR amplification of genome-specific primers and fluorescence in situ hybridization (FISH) analysis were employed to identify the true hybrids and their chromosome complements. The new allooctaploid showed a mosaic morphology of three parents and produced some seeds, despite the very low pollen stainability. The chromosome pairing and segregation of the allooctaploid were largely normal during the meiosis of pollen mother cells. So the first allooctaploid can be used as an intermediate germplasm to transfer desirable traits into Brassica crops, or as the founder for the experimental synthesis of new species.