Brassica napus (PROTA)

Plant Resources of Tropical Africa Introduction

List of species

General importance
Geographic coverage Africa
Geographic coverage World
Vegetable
Vegetable oil
Medicinal
Forage / feed
Auxiliary plant
Food security

distribution in Africa (planted)

1, basal stem leaf; 2, upper part of flowering and fruiting stem; 3, tuber of swede. Redrawn and adapted by Iskak Syamsudin

harvest of leaves

young plants

tuber of swede

field of oilseed rape

inflorescence

Brassica napus L.

Protologue: Sp. pl. 2: 666 (1753).

Family: Brassicaceae (Cruciferae)

Chromosome number: 2n = 38

Vernacular names

• Rape kale (En).
• Colza potager, colza fourrager (Fr).

• Swede, rutabaga (En).
• Rutabaga, chou-navet (Fr).
• Nabo amarelo, nabo de Suécia (Po).

• Oilseed rape, colza, canola (En).
• Colza (Fr).
• Colza (Po).

Origin and geographic distribution

Brassica napus is an amphidiploid with one genome originating from Brassica oleracea L. (2n = 18) and the other from Brassica rapa L. (2n = 20). It is not known in the wild and probably originated in the eastern Mediterranean and West Asian region. It was introduced to western Europe where several types were developed.

Rape kale is a minor leafy vegetable in western Europe and a rather important fodder during winter. It is of some importance in southern Africa, where it was introduced during colonial times. Swede (the thickened upper taproot and lower stem) is a minor vegetable in western Europe and in North America, on rare occasions found in southern Africa. In northern Mali and in oases in the Sahara an ancient introduction of swede is still grown. Fodder swede is occasionally grown in western Europe, but not recorded in tropical Africa. Oilseed rape was originally grown in India for its edible oil; later it became important as an industrial and lamp oil in Europe. Cultivars with a much improved quality edible oil have been developed from Brassica napus, Brassica juncea (L.) Czern. and Brassica rapa L. (collectively known as ‘canola’), and these have become important oil crops in Europe, North America, China, Japan and India. Oilseed rape is also grown in the cooler highlands of Kenya and Tanzania, and reported as a minor oil crop from Ethiopia. Here and there, Brassica napus is found as an escape from cultivation, but less common than Brassica rapa.

Uses

The use of rape kale is similar to leaf cabbage cultivars (Brassica oleracea L.) such as ‘sukuma wiki’ in East Africa and Portuguese kale in southern Africa; its taste is somewhat more pungent. It is used as a vegetable dish or prepared into sauces accompanying the starchy staple food. In rural areas in Zimbabwe, rape kale leaves are dried for long-term preservation to provide vegetables during the dry season. In Europe young seedlings of Brassica napus are occasionally eaten in salads and used as garnish, replacing white mustard (Sinapis alba L.) and garden cress (Lepidium sativum L.). In Africa swede is rarely used as a root vegetable and only occasionally as a fodder crop. Oilseed rape is occasionally planted in East Africa for its edible oil, which is also used for soap making. The seeds are used to feed birds.

Production and international trade

Rape kale and swede are only produced for the domestic market. No data on production or trade are available. Brassica oilseeds are the third most important source of vegetable oil after only soya bean and oil palm; specific information on production and trade of Brassica napus oil is not available.

Properties

The nutritional composition of rape kale per 100 g edible portion (midribs removed, 87% of the product as purchased) is: water 88.2 g, energy 155 kJ (37 kcal), protein 3.8 g, fat 0.3 g, carbohydrate 4.8 g, Ca 250 mg, Mg 85 mg, P 81 mg, Fe 1.7 mg, carotene 1990 μg, thiamin 0.07 mg, riboflavin 0.06 mg, niacin 0.8 mg, ascorbic acid 55 mg. Compared to most other leafy vegetables, the content of micronutrients is high and the iron is in an easily digestible form. As all other members of Brassica, rape kale contains high levels of glucosinolates, which during the preparation form compounds with antioxidant and anticancer activities. The nutritional composition of swede per 100 g edible portion (thinly peeled, 73% of product as purchased) is: water 91 g, energy 100 kJ (24 kcal), protein 0.7 g, fat 0.3 g, carbohydrate 5.0 g, dietary fibre 2.4 g, Ca 26 mg, Mg 4 mg, P 11 mg, Fe 0.1 mg, Zn 0.1 g, carotene 350 μg, thiamin 0.15 mg, riboflavin trace, niacin 1.2 mg, folate 31 μg, ascorbic acid 31 mg (Holland, B., Unwin, I.D. & Buss, D.H., 1991).

The oil of Brassica napus is similar to that of other Brassica species and is made up of erucic acid 25–55%, oleic acid 8–33%, linoleic acid 12–21%, linolenic acid 8–14%, eicosenoic acid 6–12%, palmitic acid 2–4%, stearic acid 0.8–1.5%, arachidic acid 0.5–1.2%, palmitoleic acid 0.2–0.5%, nervonic acid 0–2%, behenic acid 0–1% and lignoceric acid 0–1%. Eicosenoic acid and erucic acid are long-chain fatty acids that have antinutritional and toxic properties. Cultivars yielding oil low in eicosenoic acid and erucic acid have been developed. They are generally recognized as safe for human consumption. Together with cultivars of Brassica juncea and Brassica rapa, yielding similar oil, they are known as ‘canola’ in English and ‘zéro-érucique’ in French.

Adulterations and substitutes

In dishes rape kale can be replaced by leaf cabbage (Brassica oleracea), brown mustard (Brassica juncea) or Ethiopian kale (Brassica carinata A.Braun). Swede is very similar to turnip (from Brassica rapa).

Description

• Erect, annual to biennial herb up to 1.5 m tall, with stout taproot, sometimes partly swollen (swede); stem branched.
• Leaves arranged spirally but in a rosette during the vegetative stage; stipules absent; lower leaves more or less petiolate, pinnately parted with 1–5 pairs of small lateral lobes and large terminal lobe up to 90 cm × 35 cm, crenate, toothed, sinuate or entire, glabrous or sparsely hairy, glaucous; stem leaves pinnately parted to simple, clasping at base, glabrous, glaucous.
• Inflorescence a terminal raceme up to 60 cm long, with buds overtopping the open flowers.
• Flowers bisexual, regular, 4-merous; pedicel up to 3 cm long, ascending; sepals 6–8 mm long, erect to slightly spreading, yellow-green; petals obovate, 1–1.5 cm long, clawed, bright to dark yellow; stamens 6; ovary superior, cylindrical, 2-celled, stigma globose.
• Fruit a linear silique 4.5–11 cm × 3–4 mm, with a tapering beak 1–3 cm long, dehiscent, up to 30-seeded.
• Seeds globose, 1.5–2.5 mm in diameter, finely reticulate, bluish black to dark brown.
• Seedling with epigeal germination, with a taproot and lateral roots; hypocotyl c. 5 cm long, epicotyl 2–4 mm long; cotyledons with petiole c. 2 cm long, blade cordate, 1–1.5 cm long, cuneate at base, notched at apex.

Other botanical information

Brassica napus is often difficult to distinguish from Brassica rapa. It differs in its basal leaves, which are usually less hairy and bluish green (bright green in Brassica rapa) and in its open flowers not over-topping the buds at the top of the inflorescence. The swede tuber can be distinguished from that of turnip (Brassica rapa) by its apex bearing a number of ridges, which are scars of leaf-bases. It is composed of the swollen upper part of the taproot (hypocotyl) and lower part of the stem, whereas the tuber of turnip is composed of the swollen upper part of the taproot (hypocotyl) only.

Brassica napus has been divided into 3 varieties: var. napus comprising the oil-seed crops, var. pabularia (DC.) Rchb. comprising rape kale and var. napobrassica (L.) Rchb. comprising swede. The plants cultivated in the Sahara, which have been distinguished as var. sahariensis Chev., belong to the latter variety, although it has also been suggested that they belong to Brassica rapa. A classification into cultivar-groups would be more appropriate.

Growth and development

The seeds take 3–5 days to emerge at 20–25°C. First a rosette of leaves develops, in swede cultivars followed by thickening of the lower part of the stem and upper part of the root. Brassica napus is generally self-fertile, although insects improve seed setting.

Ecology

Rape kale is a temperate climate vegetable and grows best under cool conditions. In southern Africa it grows best in the highlands and during the cool season with night temperatures of about 10°C and day temperatures of 15–20°C. It needs well-drained, fertile, neutral to slightly alkaline soils (pH 6.2–7.7) with a high organic matter content. Most swede cultivars are also adapted to temperate climates. The ecological requirements of the cultivars grown in the Sahara are not known. Those of oil-seed crops are similar to rape kale.

Propagation and planting

Rape kale is grown exclusively by seed. The seedlings are raised in seedling trays or in a seedbed. The 1000-seed weight is about 5 g. If raised in a seedbed, about 500 g of seed is enough for 1 ha. The seedbed should be well drained and have a fine tilth, and should not have been planted with a Brassica crop for at least three years. The seed should be buried no more than 5 mm below the ground and is drilled in rows 10–15 cm apart. A basal dressing, e.g. with NPK fertilizer 5–18–20 at a rate of 100 g/m², helps to hasten seedling development. Under optimum conditions seedlings are ready for transplanting in 4 weeks. When seedling trays are used, care should be taken to ensure that the seedlings receive adequate nutrition, especially phosphorus, to avoid retarded growth. In the field, plants are spaced at 75–100 cm between rows and 45–60 cm within the row.

For oil production rape is always direct seeded at a seed rate of 5–9 kg/ha, aiming at a density of 160,000 plants/ha.

Management

Weed control is very important during early establishment. Two rounds of weeding are usually required. If rainfall is insufficient, the crop should be irrigated regularly. Since the leaves are continuously harvested, the uptake of minerals is high, and inorganic fertilizers should be applied, e.g. 700–800 kg/ha NPK 5–18–10 before planting. Side dressing of N helps to keep the crop in the vegetative state allowing more leaves to develop. A gift of 100 kg/ha urea, applied after a harvest, assures high yields.

For an oilseed rape crop yielding 2 t seed, application of N 40–50 kg/ha, P 50–60 kg/ha and K 25–30 kg/ha before planting and a topdressing of N 40–50 kg/ha is generally recommended. Seed set and consequently yields are often improved by placing beehives near flowering rape seed fields.

Diseases and pests

Seedlings are very susceptible to damping off caused by Rhizoctonia and Fusarium. A protectant fungicide may be applied as a seed-dressing or as a drench. Black rot (Xanthomonas campestris) and soft rot (Erwinia carotovora) are important diseases, Fusarium yellows sometimes cause problems. At the seedling stage, cut worms (Agrotis spp.) are a major pest. As the crop develops further, aphids may become a major problem and so is diamondback moth (Plutella xylostella), web worm (Hellula undalis) and bagrada bug (Bagrada hilaris).

Harvesting

Harvesting starts 4 weeks after planting under favourable conditions and can last for 3 months. Leaves are harvested when they have attained a size that is acceptable at the market. Swede can be harvested usually 90 days after sowing; oilseed rape after 75–100 days.

Yield

Yields of rape kale of 25–50 t/ha (fresh weight) can be expected. In Zimbabwe yields of up to 75 t/ha have been achieved. Yields of swede in Europe may attain 50–80 t/ha. World average seed yield of oilseed rape is 1400 kg/ha. Smallholders in India or China harvest only 500–800 kg/ha, large farms in Canada or Australia 900–1600 kg/ha, whereas yields in Europe are 2000–4000 kg/ha.

Handling after harvest

Leaves are harvested individually and then tied together into bundles that vary in size depending on whether they are coming from the farm or from the wholesale market. Harvesting usually takes place just before dusk or at dawn and the harvested leaves are taken to the market straight away. As the leaves are very perishable, traders regularly sprinkle them with cold water to keep them fresh. Most oilseed rape is processed in large factories, where the oil is extracted by screw press or by solvent and then refined. Colza oil is light-coloured and bland-tasting.

Genetic resources

Germplasm collections of Brassica napus are maintained in several European genebanks.

Breeding

Western seed companies have made little effort to genetically improve rape kale or swede. Japanese seed companies have created new amphidiploid Brassica napus types by crossing Brassica oleracea and Brassica rapa. By crossings of heat tolerant cultivars of white headed cabbage and Chinese cabbage, new types of heading Brassica napus for the tropics might be developed, combining the strength of white headed cabbage with the finer taste of Chinese cabbage, and disease resistances of both parental species. In southern Africa farmers use farm-saved seed of rape kale from introductions that were made a long time ago. Selections from these local cultivars are now being made by East-West Seed Company in Zimbabwe. In oilseed rape open-pollinated cultivars are now being replaced by higher yielding F₁ hybrids.

Prospects

Rape kale has an excellent nutritional composition and taste, but due to the high perishability in comparison with leaf cabbage, and also to its low adaptability to tropical conditions, it will remain of minor importance as a leafy vegetable in tropical Africa, unless systematic efforts are made to breed cultivars more adapted to tropical conditions. Swede is also likely to remain of local importance only. If adapted cultivars are developed oilseed rape may become a more important oil-seed crop for the African highlands.

Major references

• Burkill, H.M., 1985. The useful plants of West Tropical Africa. 2nd Edition. Volume 1, Families A–D. Royal Botanic Gardens, Kew, Richmond, United Kingdom. 960 pp.

• Hegi, G., 1986. Illustrierte Flora von Mittel-europa. 3rd Edition. Pteridophyta, Spermatophyta. Band 4, Angiospermae, Dicotyledones 2. Verlag Paul Parey, Berlin, Germany. 598 pp.

• Holland, B., Unwin, I.D. & Buss, D.H., 1991. Vegetables, herbs and spices. The fifth supplement to McCance & Widdowson’s The Composition of Foods. 4th Edition. Royal Society of Chemistry, Cambridge, United Kingdom. 163 pp.

• Jonsell, B., 2000. Brassicaceae (Cruciferae). In: Edwards, S., Mesfin Tadesse, Demissew Sebsebe & Hedberg, I. (Editors). Flora of Ethiopia and Eritrea. Volume 2, part 1. Magnoliaceae to Flacourtiaceae. The National Herbarium, Addis Ababa University, Addis Ababa, Ethiopia and Department of Systematic Botany, Uppsala University, Uppsala, Sweden. pp. 121–154.

• Jonsell, B., 1980. Cruciferae (Brassicaceae). Flore du Cameroun. Volume 21. Muséum National d’Histoire Naturelle, Paris, France. pp. 3–24.

• Mansfeld, R., 1986. Verzeichnis landwirtschaftlicher und gärtnerischer Kulturpflanzen (ohne Zierpflanzen). 2nd edition, revised by J. Schultze-Motel. 4 volumes. Springer Verlag, Berlin, Germany. 1998 pp.

• Rubatzky, V.E. & Yamaguchi, M., 1997. World vegetables: principles, production and nutritive values. 2nd Edition. Chapman & Hall, New York, United States. 843 pp.

• Sherf, A.F. & MacNab, A.A., 1986. Vegetable diseases and their control. 2nd Edition. John Wiley & Sons, New York, United States. 728 pp.

• USDA, 2002. USDA nutrient database for standard reference, release 15. [Internet] U.S. Department of Agriculture, Beltsville Human Nutrition Research Center, Beltsville Md, United States. http://www.nal.usda.gov/fnic/foodcomp. June 2003.

• van den Bergh, M.H., 1993. Minor vegetables. In: Siemonsma, J.S. & Kasem Piluek (Editors). Plant Resources of South-East Asia No 8. Vegetables. Pudoc Scientific Publishers, Wageningen, Netherlands. pp. 280–310.

Other references

• Godfrey Sam Aggrey, W. & Tekkie, Y., 1989. Horticultural crop production: Vegetable Crops. UNDP/FAO, ZIM/86/021, Agritex, Ministry of Lands and Rural Resettlement, Harare, Zimbabwe.

• Jonsell, B., 1982. Cruciferae. In: Polhill, R.M. (Editor). Flora of Tropical East Africa. A.A. Balkema, Rotterdam, Netherlands. pp. 15–17.

Sources of illustration

• Mansfeld, R., 1986. Verzeichnis landwirtschaftlicher und gärtnerischer Kulturpflanzen (ohne Zierpflanzen). 2nd edition, revised by J. Schultze-Motel. 4 volumes. Springer Verlag, Berlin, Germany. 1998 pp.

• Vaughan, J.G. & Geissler, C.A., 1997. The new Oxford book of food plants. Oxford University Press, Oxford, United Kingdom. 239 pp.

Author(s)

• H. Toxopeus, Wageningen, Netherlands

• B. Mvere, East West Seed International Ltd., P.O. Box BW 141, Borrowdale, Harare, Zimbabwe

Correct citation of this article

Toxopeus, H. & Mvere, B., 2004. Brassica napus L. [Internet] Record from PROTA4U. Grubben, G.J.H. & Denton, O.A. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands.

Accessed 12 December 2024.