Brassica (PROSEA Vegetables)
- Protologue: Sp. pl.: 666 (1753); Gen. pl. ed. 5: 299 (1754).
- Family: Cruciferae
- Chromosome number: x= 8 (genome B), 9 (genome C), 10 (genome A); 2n= 16 (BB,B. nigra), 18 (CC,B. oleracea), 20 (AA,B. rapa), 34 (BBCC,B. carinata), 36 (AABB,B. juncea), 38 (AACC,B. napus).
Major species and synonyms
- Brassica carinata A. Braun, Flora 24: 267 (1841), synonym: B. integrifolia (West) Thellung var. carinata (A. Braun) O.E. Schulz (1919).
- Brassica napus L., Sp. pl.: 666 (1753), synonyms: B. campestris DC. (1821) non L. (1753), B. campestris L. ssp. napus (L.) Hooker (1872) - see chapter on Minor Vegetables.
- Brassica nigra (L.) Koch, Deutschld. Fl. ed. 3, 4: 713 (1833), synonyms: Sinapis nigra L. (1753), B. sinapoides Roth (1830), Sisymbrium nigrum (L.) Prantl (1884).
- B. carinata: Ethiopian mustard (En). Moutarde éthiopienne (Fr).
- B. juncea: Indian mustard, Chinese mustard, vegetable mustard (En).
- B. napus: Colza, rape, rutabaga (En). Colza, rutabaga (Fr).
- B. nigra: Black mustard (En). Moutarde noire (Fr).
- B. oleracea: Cole crops (En).
- B. rapa: Neep crops (En).
Origin and geographic distribution
The six cultivated Brassica species are all native to the Eurasian continent. Many of their crops are now cultivated worldwide. It is generally agreed that the three diploid species, i.e. B. nigra, B. oleracea and B. rapa, are the parents of the amphidiploid species, i.e. B. carinata, B. juncea and B. napus, which must have originated through interspecific hybridization between the primary species under domestication.
The three primary species occur wild and in cultivation.
- B. nigra occurs wild in the Mediterranean, on the Ethiopian plateau, in the Middle East and throughout central Europe. It is cultivated in various parts of the world.
- B. oleracea occurs in the wild, together with related wild species, along the coasts of the Mediterranean and as far north as the coasts of England. The amazing range of cole crops was domesticated in Europe, and many of them are now grown all over the world.
- B. rapa occurs in wild forms in central Asia. The turnip appears to be the most ancient crop, domesticated in a rich variety both in Europe and Japan. An impressive range of leafy vegetable crops developed in Asia (China and Japan). Oilseed forms have been cultivated since ancient times in the south of the Indian subcontinent, where they are still important.
The three amphidiploid species are only known from cultivation.
- B. carinata (B. nigra × B. oleracea) is mainly grown at present in a part of the East African Plateau, especially Ethiopia, but is also encountered occasionally on the east and west coasts of Africa.
- B. juncea (B. nigra × B. rapa) probably originated in Central Asia where both parental species occur, and where oilseed types are predominant. In China a great variety of vegetable types evolved.
- The biennial forms of B. napus (B. oleracea × B. rapa) originated in western Europe, the annual type probably being a derived form. It is now mainly grown in Europe and Canada.
In South-East Asia B. juncea, B. oleracea and B. rapa are cultivated in great quantity. B. carinata, B. napus and B. nigra occur only occasionally if at all.
Brassica shows an unparalleled diversity of crop forms and utilization. Brassicas are raised for vegetable (swollen root and stem, leaves, flower buds, curd), fodder, as dried, salted and pickled foods such as sauerkraut, as accessories to meat dishes, for oil and table mustard from the seed, and for medicinal and ornamental uses.
- B. nigra: the seeds are used for table mustard.
- B. oleracea : all parts are used as vegetable and as fodder; the cole crops comprise cabbages, cauliflower, broccoli, Chinese kale, Brussels sprouts, kohlrabi, borecole and kales.
- B. rapa: the seed is used for oil production (turnip rapes); all other parts are used as vegetable and as fodder (worldwide); the vegetable crops comprise Chinese cabbage, pak choi, caisin, vegetable turnip, turnip greens, mizuna, taatsai.
- B. carinata: oil from the seeds is its major use, but the leaves are also used as a vegetable (Ethiopia).
- B. juncea: the seeds are used for oil extraction (India) and for table mustard (worldwide); the leaves, stems, shoots and roots are used as vegetable (China, South-East Asia).
- B. napus: the seeds are used for oil production (Europe, Canada); the green parts and the swollen roots (rutabaga) are used as forage and as vegetable (Europe, North America, Russia).
Production and international trade
Most Brassica vegetables and fodder crops are destined for fresh consumption and have to be marketed and consumed within a few days after being harvested. Local production, marketing and consumption are therefore the main features, often escaping official statistics, but the importance of this group of vegetables can hardly be overestimated. In large parts of Asia, Brassica crops should be considered as staple food.
All Brassica crops contain glucosinolates which in crushed leaves are broken down by the enzyme myrosinase yielding bitter-tasting goitrogenic substances: isothiocyanates, thiocyanates, nitriles and goitrin. At an early stage in domestication, selection for less bitter-tasting individuals must have taken place, because in wild cabbage bitter-tasting principles can be present in up to four times the amount found in cabbage eaten by man.
- Annual or biennial, rarely perennial herbs, with taproot that may be fleshy.
- Stem erect or ascending, glabrous or with simple hairs, sometimes very glaucous.
- Lower basal leaves often pinnatifid with large terminal lobe.
- Inflorescences ebracteate racemes; sepals 4; petals 4, long-clawed, usually yellow; stamens 6, 2 short, 4 long.
- Fruit a silique with convex valves, tipped by an indehiscent seedless beak.
- Seeds in a single row in each loculus, spherical, brown-black or yellowish.
- Germination is epigeal.
Some general characteristics of the three major species cultivated in South-East Asia:
- B. juncea. Annual or biennial herb, usually with firm taproot and erect, much branched stem. Leaves thin, green or thinly glaucous, more or less pilose; lower leaves lobed, usually with a large apical lobe; leaves gradually becoming smaller towards the apex of the stem, often narrowly oblanceolate finally. Flowers small, usually less than 1 cm wide and long, buds positioned just below the expanded flowers. Fruit 2-8 cm long, beak short and stout.
- B. rapa. Annual or biennial herb with firm or tuberous taproot and erect, branched stem. Leaves often slightly glaucous and clasping the stem, more or less pilose; lower leaves lobed, usually with a large apical lobe and with a petiole; upper leaves sessile, undivided. Flowers small, up to 1 cm long with sepals spreading, buds positioned just below the expanded flowers. Fruit 4-10 cm long, beak up to 3 cm long.
- B. oleracea. Annual or biennial herb with very strong taproot, but never with swollen roots. Stem erect and strong, sometimes fleshy and swollen. Leaves rather thick, glaucous, glabrous, very variable in shape, colour, size and thickness. Flowers rather large, up to 2 cm long, buds raised far above the expanded flowers. Fruit 5-10 cm long, beak tapering.
Growth and development
The vegetative growth phase of B. juncea (AABB) and B. rapa (AA) is a rosette, while B. oleracea (CC) grows an elongated stem. In the annual forms these phenomena are often masked because of very early bolting. The B. oleracea winter vegetables of temperate climates (cabbages and kales) can only be vernalized when they have at least 6 well-developed leaves, at temperatures below 8°C during up to 3 months. Biennial forms of B. juncea and B. rapa may be induced to flower by exposing pre-germinated seed or seedlings to low temperatures for up to 2 months. Annual forms will flower rapidly when exposed to long daylengths and/or high temperatures. Early flowering induction will make plants skip the commercial sink (cabbage head, turnip), resulting in a short generation cycle, a phenomenon most important for breeding. Brassica species are entomophilous, the diploid species are cross-fertilizing and B. napus (AACC) is self-pollinating. However, detailed studies are lacking.
Other botanical information
The taxonomy of the Brassica crops is confused and overloaded with names and botanical classification systems, no single one being clear and distinctive for all existing taxa. Infraspecific classification may be done more conveniently by grouping cultivars into cultivar groups. First attempts towards such classifications, however, are far from being complete and generally accepted.
Several parallel variations are manifest in the Brassica species. The most obvious character is the swollen hypocotyl and root, producing a wide range of turnip morphotypes in B. rapa (AA). In both amphidiploid species carrying the A genome, B. napus (AACC) and B. juncea (AABB), similar crops exist. The range of rutabaga (B. napus) morphotypes is practically the same as in B. rapa and difficult to distinguish. Less obvious, but most important for crop production, is the phenomenon of the vegetative stem in B. oleracea (CC), which is on the one hand the basis of the kale crops and Brussels sprouts, whereas the short stem inside the cabbage gives it the high degree of compactness. Vegetative stems are also apparent in B. carinata (BBCC) and B. napus (AACC), making them suitable leafy fodder crops, but no vegetable types like the cole crops were domesticated.
Most Brassica crops originated in temperate regions and grow best in cool moist climates and at higher altitudes in the tropics. They are not really suited to the lowland humid tropics. The ideal soil is a rich sandy loam.
All Brassica crops are grown from seed. When moistened, seeds germinate immediately and seedling growth is rapid and uniform. Sowing is done in nurseries or boxes or directly in the field. Land should be well prepared before planting. The crops respond well to organic manure and mineral fertilizer, particularly to nitrogen. Weeding is very important. Notorious diseases and pests are: black leg (Phoma lingam), black rot (Xanthomonas campestris ), downy mildew (Peronospora parasitica), clubroot (Plasmodiophora brassicae), cabbage mosaic virus, root-knot nematode (Meloidogyne spp.), cabbage white butterfly (Ascia monuste), cabbage budworm (Hellula phidilealis), diamond-back moth (Plutella xylostella). Snails and slugs can cause much damage. Brassica field crops are known in Europe to be good "break" crops with an improving effect on other crops in the rotation. Some care has to be taken to prevent Brassica crops from escaping from cultivation and becoming weeds. This danger is due to the shattering nature of the siliques and the small oilseed that survives in the soil for many years and readily germinates under suitable conditions.
Genetic resources and breeding
The demand of vegetable growers throughout the world for F1hybrids is resulting in the replacement (loss) of most landraces and open-pollinated cultivars. This replacement is virtually complete in Europe, North America, Japan and Korea. Most genetic variation has been collected. World collections are kept in gene banks in Tsukuba (Japan), in Wellesbourne (United Kingdom), Wageningen (the Netherlands), Braunschweig (Germany) and in Beltsville (United States). A network is operational and coordinated by the International Board for Plant Genetic Resources (IBPGR).
Mastery of flowering is the key to success in Brassica breeding. With adequate facilities for flowering induction three generations may be grown in a year. Disease-resistant cultivars and cultivars which will thrive in the low hot humid tropics are urgently required.
The Brassica crops with their perplexing variability will remain important all over the world. In general they are easy to grow, for home consumption as well as for commercial purposes, and their nutritional value is good. In South-East Asia, research should focus on the forms available in endless variation in China and Japan.
- Bailey, L.H., 1922, 1930. The cultivated Brassicas, Part 1 and 2. Gentes Herbarium 1: 53-108 (Part 1, 1922), 2: 210-267 (Part 2, 1930).
- Herklots, G.A.C., 1972. Vegetables in South-East Asia. George Allen & Unwin, London, United Kingdom. pp. 182-224.
- IBPGR, 1981. Genetic resources of cruciferous crops. International Board for Plant Genetic Resources (IBPGR), Rome, Italy. 48 pp.
- Nieuwhof, M., 1969. Cole crops. Leonard Hill, London, United Kingdom. 353 pp.
- Sinskaia, E.N., 1928. The oleiferous plants and root crops of the family Cruciferae. Bulletin of Applied Botany, Genetics and Plant Breeding 19: 555-626.
- Toxopeus, H., 1974. Outline of the evolution of turnips and coles in Europe and the origin of winterrape, swede-turnips and rape kales. Proceedings of the Eucarpia Meeting on Cruciferae, Dundee, 25-27 September, 1974. pp. 1-7.
- Toxopeus, H., Oost, E.H. & Reuling, G., 1984. Current aspects of the taxonomy of cultivated Brassica species. Cruciferae Newsletter No 9: 55-58.
- Tsunoda, S., Hinata, K. & Gomez-Campo, C. (Editors), 1980. Brassica crops and wild allies: biology and breeding. Japan Scientific Societies Press, Tokyo, Japan. 354 pp.
- H. Toxopeus & P.C.M. Jansen