Rapeseed (Brassica napus subsp. napus), also known as rape and oilseed rape and canola, is a yellow-flowered member of the Brassicaceae family. The plant is cultivated primarily for its oil-rich seed, which naturally contains mildly toxic erucic acid. The term canola refers to a group of rapeseed cultivars with very low levels of erucic acid that are prized as food for humans and animals. The plant is the third-largest source of vegetable oil and the second-largest source of protein meal in the world.
Description
Brassica napus grows to 100 centimetres (39 inches) in height with hairless, fleshy, pinnatifid and glaucous lower leaves which are stalked whereas the upper leaves have no petioles. Rapeseed flowers are bright yellow and about 17 millimetres (3⁄4 in) across. They are radial and consist of four petals in a typical cross-form, alternating with four sepals. They have indeterminate racemose flowering starting at the lowest bud and growing upward in the following days. The flowers have two lateral stamens with short filaments, and four median stamens with longer filaments whose anthers split away from the flower's center upon flowering. The rapeseed pods are green and elongated siliquae during development that eventually ripen to brown. They grow on pedicels 1 to 3 cm (3⁄8 to 1+3⁄16 in) long, and can range from 5 to 10 cm (2 to 4 in) in length. Each pod has two compartments separated by an inner central wall within which a row of seeds develops. The seeds are round and have a diameter of 1.5 to 3 mm (1⁄16 to 1⁄8 in). They have a reticulate surface texture, and are black and hard at maturity.
Similar species B. napus can be distinguished from B. nigra by the upper leaves which do not clasp the stem, and from B. rapa by its smaller petals which are less than 13 mm (1⁄2 in) across.
Taxonomy The species Brassica napus belongs to the flowering plant family Brassicaceae. Rapeseed is a subspecies with the autonym B. napus subsp. napus. It encompasses winter and spring oilseed, vegetable and fodder rape. Siberian kale is a distinct leaf rape form variety (B. napus var. pabularia) which used to be common as a winter-annual vegetable. The second subspecies of B. napus is B. napus subsp. rapifera (also subsp. napobrassica; the rutabaga, swede, or yellow turnip). B. napus is a digenomic amphidiploid that occurred due to the interspecific hybridization between B. oleracea and B. rapa. It is a self-compatible pollinating species like the other amphidiploid Brassica species.
Etymology The term "rape" derives from the Latin word for turnip, rāpa or rāpum, cognate with the Greek word ῥάφη, rhaphe.
Ecology In Northern Ireland, B. napus and B. rapa are recorded as escapes in roadside verges and waste ground.
Cultivation
Crops from the genus Brassica, including rapeseed, were among the earliest plants to be widely cultivated by humankind as early as 10,000 years ago. Rapeseed was being cultivated in India as early as 4000 B.C.E. and it spread to China and Japan 2000 years ago. Rapeseed is predominantly cultivated in its winter form in most of Europe and Asia due to the requirement of vernalization to start the process of flowering. It is sown in autumn and remains in a leaf rosette on the soil surface during the winter. The plant grows a long vertical stem in the next spring followed by lateral branch development. It generally flowers in late spring with the process of pod development and ripening occurring over a period of 6–8 weeks until midsummer. In Europe, winter rapeseed is grown as an annual break crop in three to four-year rotations with cereals such as wheat and barley, and break crops such as peas and beans. This is done to reduce the possibility of pests and diseases being carried over from one crop to another. Winter rape is less susceptible to crop failure as it is more vigorous than the summer variety and can compensate for damage done by pests. Spring rapeseed is cultivated in Canada, northern Europe and Australia as it is not winter-hardy and does not require vernalization. The crop is sown in spring with stem development happening immediately after germination. Rapeseed can be cultivated on a wide variety of well-drained soils, prefers a pH between 5.5 and 8.3 and has a moderate tolerance of soil salinity. It is predominantly a wind-pollinated plant but shows significantly increased grain yields when bee-pollinated, almost double the final yield but the effect is cultivar dependent. It is currently grown with high levels of nitrogen-containing fertilisers, and the manufacture of these generates N2O. An estimated 3–5% of nitrogen provided as fertilizer for rapeseed is converted to N2O. Rapeseed has a high demand for nutrients - in particular, its sulphur demand is the highest among all arable crops. Since the decrease of atmospheric sulphur inputs during the 1980s sulphur fertilization has become a standard measure in oilseed rape production. Among the micronutrients, special attention in rapeseed cultivation has to be given to boron, manganese and molybdenum.
Climate change
The cultivatable range for rapeseed is expected to decrease due to climate change. The quality of the crop, in both yield and volume of oil, is also expected to decrease substantially. Some researchers recommend finding alternative varieties of Brassica for cultivation.
… excerpt ends here. Continue reading the full article.
