Genome-Based Gene Pool Expansion and Heterotic Haplotype Capture in Rapeseed

Brassica napus is a very recent allopolyploid species, which in just the last few decades has become an important global crop (rapeseed, canola) through intensive human selection. As for many facultative outcrossing species, breeding efforts focussed on inbred line varieties until effective male-sterility systems became available. With an almost exclusive focus today on hybrid cultivars, breeders face major challenges to separate strongly intermixed breeding pools into effective heterotic pools to maximise hybrid performance. Simultaneously they must reverse extreme genetic bottlenecks, caused by isolated polyploidisaiton events and subsequent selection for ecogeographical adaptation and seed quality in all major germplasm groups. Fortunately it is possible to introduce de novo variation from the secondary gene pool by resynthesis using the diploid progenitor species. Here we describe large-scale efforts to rejuvenate rapeseed diversity using genome-based approaches in highly novel populations. Genome sequence reconstruction from extensive nested diversity populations allows us to associate novel haplotypes with hybrid performance, and to capture useful diversity for implementation into genome-based breeding programs.