The Genetics of Brassica napus

Brassica napus L. belongs to the Brassicaceae family of the Kingdom Plantae and is considered to be a newly formed species (5,000–10,000 mya) probably originating from independent and spontaneous inter-specific hybridizations between genotypes of turnip rape (Brassica rapa; AA, 2n = 20) and cabbage/Kale (Brassica oleracea; CC, 2n = 18). Genetically, B. napus is an allopolyploid (AACC, 2n = 38) exhibiting disomic inheritance. Within the species, two botanical varieties have been defined: B. napus L. var rapifera (DC) Metzger (2n = 4×= 38) and B. napus L. var oleifera Delile (2n = 4×= 38). The latter has taken much of the attention and has become the second most cultivated oilseed crop (rapeseed) worldwide, after soybean. The appearance of annual and biannual rapeseed lines with low erucic acid (<2% in the oil) and low glucosinolates (<30 mg/g in the meals) has granted rapeseed CanOLA (Canadian Oil Low Acid) status as an excellent source for edible vegetable oil. The lipid profile of CanOLA oil is extremely well balanced (low in saturated fats, high in monosaturated fats, and rich in omega-3 fatty acids) making it the oil of preference by nutritionists worldwide. In this context, the commercial interest for rapeseed CanOLA has launched an impressive amount of genetics and genomics research which has made possible to make genetic gains in agronomical and quality traits through modern plant breeding. In fact, rapeseed ranks among the top crops for which molecular tools have been developed. To date, over 30 molecular linkage maps have been published using a range of different molecular marker types, population structures, and parental lines exhibiting different flowering time behaviors. These maps have proved extremely useful in order to dissect the genetic nature of the traits underlying the genetic variation found in rapeseed. This chapter will focus on the genetics and genomics aspects of rapeseed breeding describing the current knowledge on the origin of B. napus, genetics/genomic tools for the species, and specific target traits affecting B. napus oil production and quality.