Canola is rapeseed bred to lose a mildly toxic acid
Those vivid yellow fields in spring are rapeseed, a hybrid of cabbage and turnip ancestors grown for oil-rich seeds. The wild seed carries erucic acid, which is mildly toxic, so breeders developed low-erucic types known as canola. Today the plant ranks third among the world's sources of vegetable oil.
Brassica napus arose when two other brassicas, B. oleracea and B. rapa, crossed and doubled their chromosomes, giving it two complete genomes. Its close kin include the swede or rutabaga, a separate subspecies of the same plant, and Siberian kale, a leafy form once common as a winter vegetable. The name rape has nothing to do with its modern English meaning; it comes from the Latin rapa, turnip.
People have grown brassicas for as long as 10,000 years. Rapeseed was farmed in India by 4000 BCE and reached China and Japan about two millennia ago. Besides oil, the pressed seed makes it the second-largest source of protein meal on Earth, much of it for animal feed.
The flowers are about 17 millimetres across, four petals in a cross, opening from the bottom of the stalk upward over several days. Pods ripen from green to brown and hold rows of tiny round black seeds. The crop is mainly wind-pollinated, yet bees can nearly double yields in some cultivars. In most of Europe and Asia farmers sow a winter form in autumn, because it needs cold to trigger flowering; it waits out the winter as a flat rosette and blooms in late spring. Canada, northern Europe and Australia favour spring types that skip that chilling.
European growers slot winter rape into rotations of three or four years with wheat, barley, peas and beans, breaking cycles of pests and disease. The plant is hungry. It needs more sulphur than any other arable crop, a demand that became obvious once air pollution delivered less sulphur after the 1980s. Heavy nitrogen fertiliser adds a climate cost, since an estimated 3 to 5 percent of that nitrogen ends up as nitrous oxide.
Source: Rapeseed
