Brassica oleracea (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Brassica oleracea L.

Protologue: Sp. pl.: 667 (1753).

Family: Cruciferae

Chromosome number: 2n= 18

Major taxa and synonyms

Cv. group names are proposed here.

• Cv. group Brussels Sprouts. Synonym: B. oleracea L. var. gemmifera DC. (1821).
• Cv. groups Cauliflower & Broccoli. Synonyms: B. oleracea L. var. botrytis L. (cauliflower), B. oleracea L. var. italica Plenck (broccoli) - see separate article.
• Cv. group Chinese Kale. Synonym: B. oleracea L. var. alboglabra (L.H. Bailey) Musil - see separate article.
• Cv. groups of other Kales. Synonym: B. oleracea L. var. acephala DC. (1821). Many groups are distinguished, e.g. cv. group Borecole or Curly Kale (syn.: var. sabellica L. (1753), var. laciniata L. (1753); cv. group Collard (syn.: var. viridis L. (1753), var. plana Peterm. (1838); cv. group Marrowstem Kale (syn.: var. medullosa Thellung (1918); cv. group Palmtree Kale (syn.: var. palmifolia DC. (1821); cv. group Portuguese Kale (syn.: var. costata DC. (1821); cv. group Thousand-headed Kale (syn.: var. ramosa DC. (1821), var. millecapitata (Lév.) Helm (1959).
• Cv. group Kohlrabi. Synonym: B. oleracea L. var. gongylodes L. (1753).
• Cv. groups White Headed Cabbage, Red Headed Cabbage and Savoy Headed Cabbage. Synonyms: B. oleracea L. var. capitata L. (white and red cabbage), B. oleracea L. var. sabauda L. (savoy cabbage) - see separate article.

Vernacular names

General:

• Cole crops (En).

Cv. group Brussels Sprouts:

• Brussels sprouts (En)
• Chou de Bruxelles (Fr)
• Cambodia: spéi tôôch tôôch
• Thailand: kalam-dao.

Cv. groups of Kales:

• Kale (En)
• Chou vert (Fr)
• Philippines: kales, kolis (Tagalog)
• Cambodia: spéi barang
• Thailand: khana-farang.

Cv. group Kohlrabi:

• Kohlrabi, turnip kale (En).
• Chou-rave (Fr)
• Thailand: kalam-pom
• Vietnam: su hào, thò lò.

Origin and geographic distribution

Wild cabbage (B. oleracea L. var. oleracea) is indigenous to the Mediterranean region, south-western Europe, and southern England where it grows on sea cliffs. It was brought into cultivation about 5000 years ago and gave rise to numerous cultivated forms, varying widely in vegetative morphology. Probably other wild species (e.g. B. cretica Lamk, B. insularis Moris and B. rupestris Raf.) were also involved in the origin of the present-day richness of forms and cultivars of B. oleracea. Cole crops are cultivated all over the world, but are most important in temperate climates.

Brussels sprouts originated in the 18th Century in Belgium and became established as an important vegetable crop in north-western Europe. Early-maturing Asian types have been developed in Japan.

Kales are ancient cole crops, closely related to the wild forms of B. oleracea. Many distinctive types were developed in Europe such as thousand-headed kale, marrowstem kale, collards and curly kale, the latter two being the most important as vegetables.

Kohlrabi first appeared in the Middle Ages in central and southern Europe. The crop has become established in parts of Asia over the course of the last two centuries and is important in China and Vietnam.

These cole crops are grown in many temperate countries and on a small scale at higher elevations in tropical areas such as South-East Asia.

Uses

The main use of B. oleracea is as a vegetable, although some forage cultivars exist as well. Depending on cultivar, the stem, the leaves or the inflorescence, or a combination of these, form the edible parts.

In Brussels sprouts it is the miniature axillary heads (leaves) which are consumed as a cooked vegetable. The kales are a polymorphic group comprising vegetable types (curly kale, collard) and types mainly used as fodder crops (thousand-headed kale, marrowstem kale, collard). The vegetable types are grown for their smooth or curly foliage, usually consumed cooked. Kohlrabi is principally grown for its swollen stem, which is used cooked. The foliage can be consumed as well. Kohlrabi is also an important fodder.

Production and international trade

Brussels sprouts, curly kale and kohlrabi are popular vegetables in temperate regions, the first two especially during the winter months. Only kohlrabi has developed a strong foothold in mainland Asia (China, Vietnam). In Malesia they are minor crops cultivated at higher elevations. No production statistics are available.

Properties

Per 100 g edible portion, kale comprises: water 82-88 g, protein 3.9 g, fat 0.7 g, carbohydrates 6.6 g, fibre 1.2 g, carotene 3.2-4.5 mg, vitamin C 35-115 mg, Ca 200-329 mg, P 58-87 mg, Fe 1.0-1.9 mg. The energy value is 185 kJ/100 g. Brussels sprouts have a similar composition apart from lower contents of carotene (0.24-0.60 mg) and calcium (29-46 mg). The same applies to kohlrabi tubers, which in addition have lower protein (1.8 g) and fat (0.1 g) contents, and a lower energy value (125 kJ/100 g).

Description

• Very polymorphous, annual or biennial, erect herb, up to 1.5 m tall, glabrous, often much branched in upper part. Stem usually subterete, sometimes much thickened, pruinose.
• Leaves variable, lower ones usually petioled; leaf-blade lyrate or obovate, subentire or undulate, more or less deeply and irregularly lobed, very variable in shape, colour, size and thickness.
• Inflorescence racemiform or paniculiform, up to 1(-2) m long, racemes 20-40-flowered, lax, terminal; flowers rather large, pedicel up to 2 cm long, buds raised far above the expanded flowers; sepals 4, erect; petals 4, about twice as long as the sepals, oblong-spathulate, 1.5-2 cm long; stamens 6, erect.
• Fruit a stalked silique, cylindrical, 5-10 cm × 0.2-0.5 cm, with a tapering beak.
• Seed globose, 2-4 mm in diameter, grey-black to red-brown.

• Cv. group Brussels Sprouts: Biennial with simple erect stem up to 1 m tall. Axillary buds develop into compact miniature cabbage heads or sprouts, about 3 cm in diameter. On top of the stem is a rosette of leaves. Leaves generally petiolate; leaf-blade rather small, subcircular.

• Cv. groups of Kales: A very variable group of forms, morphologically most closely related to wild cabbage. Stem coarse, neither branched nor markedly thickened, 30-100 cm long. At the apex of the stem a rosette of generally oblong, sometimes red-coloured leaves occurs; sometimes the leaves are curled (caused by disproportionate rapid growth of leaf tissue along the margins). In borecole or curly kale the leaves are crinkled and more or less finely divided, often green or brownish-purple, and they are used as vegetable. Collards have smooth leaves, usually green; they are most important as forage in western Europe. Marrowstem kale has a succulent stem, up to 2 m tall, which is mainly used as forage in western Europe. Palmtree kale is up to 2 m tall, with a rosette of leaves at the apex; it is mainly used as an ornamental. Portuguese kale has leaves with succulent midribs which are used as a vegetable. Thousand-headed kale bears a whorl of young shoots at some distance above the soil, together more or less globular in outline; it is mainly used as forage.

• Cv. group Kohlrabi: Biennial in which secondary thickening of the short stem produces the spherical edible portion, 5-10 cm in diameter, green or purple. Leaves glaucous with slender petioles, arranged in a compressed spiral on the swollen stem.

Growth and development

The seedling forms an often red-coloured hypocotyl, several centimetres long, two notched cotyledons and a taproot with lateral roots. The first true leaves are usually petiolate, but sessile in headed cabbage and cauliflower. Leaves are glabrous, coated with a layer of wax. After some time, typical deviations in growth occur depending on cultivar, e.g. extreme secondary growth in thickness of the stem in kohlrabi, head formation of the leaves in headed cabbages, miniature head formation of axillary buds in Brussels sprouts, metamorphosed inflorescences in cauliflower and broccoli. In temperate regions B. oleracea is usually biennial: vegetative growth during the first season, vernalization during winter, and flowering and fruiting during the second season. The flowers are insect-pollinated, especially by bees. The fruit (silique) reaches its maximum length 3-4 weeks after anthesis. When it is ripe, dehiscence takes place through the two valves breaking away from below upwards, leaving the seeds attached to the placentas.

The time taken for the swollen stem to develop in kohlrabi depends on the cultivar: from 4-6 weeks after planting for early cultivars, from 10-12 weeks for late cultivars.

Other botanical information

The enormous variability of cultivated Brassicas and the uncertainty about their exact origin led to numerous classifications and a confusing botanical nomenclature. At present, the cultivated 2n = 18 Brassica group is generally considered to belong to one species: B. oleracea, including e.g. white, red and savoy cabbage, cauliflower, broccoli, Brussels sprouts, kohlrabi and different kinds of kale. Usually those subunits are classified as botanical varieties and forms (e.g. white and red cabbage as var. capitata L., savoy cabbage as var. sabauda L.), but there is no general agreement. Below species level it seems better to classify directly into cultivar groups and cultivars.

Ecology

Brussels sprouts and kales are the hardiest of the cole crops, withstanding temperatures of -10 °C, but also high summer temperatures. The vernalization requirements for flower induction (varying periods at low temperatures, depending on the cultivar) are usually not met in tropical areas. Seed vernalization, however, is possible in certain kohlrabi cultivars. It involves storing germinated seed for 35-50 days at -1 °C. Other kohlrabi cultivars lack a juvenile phase and premature bolting is a problem; it is probably caused by exposure of plants to temperatures below 10 °C. High temperatures tend to affect the compactness of the axillary buds of Brussels sprouts, resulting in loose-leafed buds. In kohlrabi, high temperatures, as well as shade and ample nitrogen, favour the formation of elongated swollen stems.

These crops do not demand much from the soil. They are usually grown on light to medium-heavy soils. Optimum pH is 6.0-7.5.

Agronomy

All cole crops are grown from seed. Propagation by cuttings is sometimes practised in tropical areas, as flowering does not occur. Brussels sprouts, kales and kohlrabi are usually sown on a seed-bed and transplanted when the seedlings are 3-5 cm tall. Steady growth is essential for Brussels sprouts and kohlrabi. A check in growth causes the swollen stems of kohlrabi to become fibrous, whereas too rapid growth causes them to crack and Brussels sprouts to become loose-leafed.

Diseases and pests are the same as those of other cole crops.

Brussels sprouts are normally harvested repeatedly, as the lower sprouts grow more rapidly. The growth of upper sprouts can be hastened by removing the main growing point. In kales, usually the complete rosette of leaves at the top of the stem is harvested, but sometimes individual leaves are picked. Kohlrabi should be harvested before the stems are full grown to avoid toughness. Usually the foliage is left on the swollen stem.

In temperate regions, yields vary between 5-10 t/ha for Brussels sprouts, 10-25 t/ha for kales, and 15-40 t/ha for kohlrabi. Seed yields of Brussels sprouts and kales are 300-1300 kg/ha.

Apart from being consumed fresh, these crops are also processed by canning and freezing in temperate regions.

Genetic resources and breeding

Main germplasm collections of Brussels sprouts, kales and kohlrabi are maintained in European countries and the United States. Attempts are being made to breed annual cultivars to make seed production possible in tropical areas. Kales are the main source of genes conferring resistance to environmental stress.

Prospects

With increasing standards of living, the importance of Brussels sprouts, kales and kohlrabi has been declining steadily in western countries. It is not expected that they will become important crops in South-East Asia, maybe with the exception of kohlrabi.

Literature

• Brown, H.D. & Hutchinson, C.S., 1949. Vegetable science. Lippincott, Chicago, United States. pp. 287-413.
• Dickson, M.H. & Wallace, D.H., 1986. Cabbage breeding. In: Bassett, M.J. (Editor): Breeding vegetable crops. Avi Publishing Company, Westport, Connecticut, United States. pp. 395-432.
• George, R.A.T., 1985. Vegetable seed production. Longman, New York, United States. 318 pp.
• 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.
• Snogerup, S., 1980. The wild forms of the Brassica oleracea group (2n = 18) and their possible relations to the cultivated ones. In: Tsunoda, S., Hinata, K. & Gomez-Campo, C. (Editors): Brassica crops and wild allies: biology and breeding. Japan Scientific Societies Press, Tokyo, Japan. pp. 121-132.

See also the genus page

Authors

• P.C.M. Jansen, J.S. Siemonsma & J.O. Narciso