Brassica napus (oilseed rape, rapeseed, canola) is an agriculturally important allotetraploid (2n = AACC) species in the Brassica genus. However, due to its recent origin from only a few hybridization events between progenitor diploid species B. rapa (2n = AA) and B. oleracea (2n = CC), and due to stringent breeding selection pressure for oil-quality traits, B. napus has very narrow genetic diversity. This creates a problem for breeders, who need genetic diversity for continual improvement of agronomic traits. Innovative strategies can be proposed using homologous recombination to generate more stable material from crosses with progenitor species B. rapa and B. oleracea as well as related allopolyploids B. juncea (2n = AABB) and B. carinata (2n = BBCC), as all share a genome or subgenome (set of chromosomes) in common with B. napus. These methods are useful for trait introgression into B. napus, whatever their genetic control, as higher recombination frequencies allow a smaller genomic region to be introgressed with less chance of linkage drag. However, useful traits can be also transferred via homeologous pairing (between chromosomes from different genomes) in interspecific hybrids between B. napus and close relatives. This method is difficult and generally results in large genomic introgression regions, with an increased chance of linkage drag (co-introgression of genes with a negative effect on yield traits), but is relevant for traits under monogenic control. The advantages and limitations of each strategy according to the ploidy level of the hybrids are presented.

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