Ancient and Recent Polyploid Evolution in Brassica

The Brassica genus contains phenotypically diverse species and many important vegetable, oilseed and condiment crop types. Much of this phenotypic diversity and breeding utility may be traced back to the highly complex genome structures of this group. Several Brassica species are recent allopolyploids, including the most agronomically important crop species (canola, rapeseed), which is thought to have formed through human agricultural practices in the last few hundred to few thousand years. Prior to this event, though, the entire Brassica genus had undergone several rounds of polyploidization and hybridization, followed by genome-downsizing and loss of redundant gene copies. These processes might have played a role in diversification and speciation in this genus, as extra genomic content provides an adaptive substrate by which novel genetic diversity and functionality can arise. Understanding the history of ancient and recent polyploidy in Brassica is important for modern-day breeding approaches, particularly in identifying the genetic underpinnings of complex phenotypic traits.