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Brassica oleracea L. (Brussels sprouts)

Family
Brassicaceae (Cruciferae)
Chromosome number
2n = 18
Vernacular names
Brussels sprouts (En). Chou de Bruxelles (Fr). Couve de Bruxelas (Po).
Origin and geographic distribution
The origin of Brussels sprouts lies in Belgium, where it was first mentioned at the end of the 18th Century. It spread from there to the rest of north-western Europe, where it is an important autumn and winter crop. In tropical Africa it is very rare, only occasionally grown in the highlands above 2000 m for people of European origin.
Uses
Brussels sprouts is grown for the enlarged buds (sprouts) formed in the leaf axils of the erect long-stemmed plant. The sprouts, resembling very small cabbages, are consumed as a cooked vegetable and mostly purchased as a fresh product, although in recent years the frozen product has gained in popularity.
Properties
The nutritional composition of Brussels sprouts per 100 g edible portion (69% of the product as purchased, base trimmed, outer leaves removed) is: water 84.3 g, energy 177 kJ (42 kcal), protein 3.5 g, fat 1.4 g, carbohydrate 4.1 g, dietary fibre 4.1 g, Ca 26 mg, Mg 8 mg, P 77 mg, Fe 0.7 mg, Zn 0.5 mg, carotene 215 μg, thiamin 0.15 mg, riboflavin 0.11 mg, niacin 0.2 mg, folate 135 μg, ascorbic acid 115 mg (Holland, B., Unwin, I.D. & Buss, D.H., 1991). Glucosinolates determine the characteristic flavour and taste.
Botany
Erect, glabrous, biennial herb up to 120 cm tall, with unbranched stem, developing lateral buds (sprouts) in leaf axils; root system strong and branched. Leaves alternate, simple or lower ones with some small side lobes at base; stipules absent; all leaves with distinct petiole, but upper ones with short petiole giving the top of the plant a rosette-like appearance; blade more or less circular, undulate or irregularly incised, blue-green. Inflorescence a terminal paniculate raceme. Flowers bisexual, regular, 4-merous; pedicel up to 2 cm long, ascending; sepals oblong, c. 1 cm long, erect; petals obovate, 1.5–2 cm long, clawed, pale to bright yellow or whitish; stamens 6; ovary superior, cylindrical, 2-celled, stigma globose. Fruit a linear silique 5–10 cm Χ c. 5 mm, with a tapering beak 5–15 mm long, dehiscent, up to 30-seeded. Seeds globose, 1.5–2 mm in diameter, finely reticulate, dark brown. Seedling with epigeal germination, with a taproot and lateral roots; hypocotyl 3–5 cm long, epicotyl absent; cotyledons with petiole 1–2 cm long, blade cordate, 1–1.5 cm long, cuneate at base, notched at apex.
Brussels sprouts has been classified as var. gemmifera DC. or convar. gemmifera (DC.) Gladis. It can best be considered as a cultivar-group and as such has been called Brussels Sprout Group.
Breeders have developed early (summer), mid-early and late (winter) types, and together with variation in planting time, growers in Europe can plan the production of Brussels sprouts from the end of August till March.
Ecology
Brussels sprouts is adapted to a cool and rather humid climate. Most production takes place in coastal areas of north-western Europe. Only the early types can be cultivated in high -altitude regions of the tropics or during the winter season in the subtropics.
Management
Seeds are sown on seedbeds or modules. Young seedlings need shading to prevent sun scorch. The 1000-seed weight is 3–5 g; seed requirement 160–200 g/ha. Transplanting to the field should be done when seedlings have 7–9 true leaves, 30–40 days after sowing. Plant density is 30,000–40,000 plants/ha.
Soil preparation includes deep digging, followed by fine tillage. NPK fertilizers – type and rates depending on soil type, mineral reserves in the soil and expected yields – are applied before planting; another one or two N fertilizer dressings are applied for continued growth. A high-yielding crop needs 180–200 kg N, 140 kg P and 500 kg K per ha.
A pH of 7 is recommended to prevent clubroot damage. Sowing, planting and harvesting of Brussels sprouts is highly mechanized in Europe, where the crop is harvested with a single cutting. Home gardeners, and small-scale African producers, can better harvest the sprouts in several rounds of hand picking. The yield of early types is about 14 t/ha. Sprouts can be stored under controlled conditions for 6–10 weeks. Diseases and pests are the same as for headed cabbage. Considerable progress is being made with effective methods of integrated pest management.
Genetic resources and breeding
Germplasm collections of Brussels sprouts are available in several European genebanks, e.g. at the Centre for Genetic Resources (CGN), Wageningen, Netherlands. The possibility of interspecific hybridization within the Brassicaceae family makes the genepool very wide.
The main breeding objectives include quality, yield, earliness, stress tolerance and resistance to diseases (e.g. clubroot). Seed companies focus exclusively on the production of single-cross F1 hybrids. During the last forty years breeders have changed the shape of the plants from a pyramidal sprout setting, with big sprouts at the bottom and small ones at the top, to a plant type with a cylindrical sprout setting with all sprouts of the same size, suitable for once-over mechanical harvesting. As in the other Brassica vegetables, hybrids based on self incompatibility are now being replaced by hybrids based on cytoplasmic male sterility. Increasingly, inbred lines are being developed from anther and microspore cultures. DNA-markers are used for precise screening for resistance to diseases and other important traits.
Prospects
Brussels sprouts will remain a rather insignificant vegetable for tropical Africa, unless heat-tolerant cultivars become available, in which case Brussels sprouts might become interesting for African highlands as a high-yielding and nutritious vegetable.
Major references
• 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.
• Jansen, P.C.M., Siemonsma, J.S. & Narciso, J.O., 1993. Brassica oleracea L. In: Siemonsma, J.S. & Kasem Piluek (Editors). Plant Resources of South-East Asia No 8. Vegetables. Pudoc Scientific Publishers, Wageningen, Netherlands. pp. 108–111.
• Nieuwhof, M., 1969. Cole crops: botany, cultivation, and utilization. Leonard Hill, London, United Kingdom. 353 pp.
• Salunkhe, D.K. & Kadam, S.S. (Editors), 1998. Handbook of vegetable science and technology: Production, composition, storage, and processing. Marcel Dekker, New York, United States. 721 pp.
• Shinohara, S. (Editor), 1984. Vegetable seed production technology of Japan. Vol. 1. Shinohara's Authorized Agricultural Consulting Engineer Office, Tokyo, Japan. 432 pp.
Other references
• Buishand, T., Houwing, H.P. & Jansen, K., 1986. The complete book of vegetables. Gallery Books, New York, United States. 180 pp.
• Crisp, P., Crute, I.R., Sutherland, R.A., Angell, S.M., Bloor, K., Burgess, H. & Gordon, P.L., 1989. The exploitation of genetic resources of Brassica oleracea in breeding for resistance to clubroot (Plasmodiophora brassicae). Euphytica 42: 215–226.
• Pelletier, G.R., 1986. Plant organelle genetics through somatic hybridization. Oxford Surveys of Plant Molecular and Cell Biology 3: 96–121.
• Pelletier, G.R., 1989. Organelle manipulation by hybridization: methods, results and applications. Proceedings of the Fifth Crucifer Genetics Workshop. pp. 15–16.
• Rubatzky, V.E. & Yamaguchi, M., 1997. World vegetables: principles, production and nutritive values. 2nd Edition. Chapman & Hall, New York, United States. 843 pp.
• Taylor, J.P., 1982. Carbon dioxide treatment as an effective aid to the production of selfed seed in kale and brussels sprouts. Euphytica 31: 957–964.
• Verkerk, R., 2002. Evaluation of glucosinolate levels throughout the production chain of Brassica vegetables, toward a novel predictive modelling approach. Thesis Wageningen University, Wageningen, Netherlands. 136 pp.
Author(s)
• P. Tjeertes
Kweekwal 21, 1602 ED Enkhuizen, Netherlands


Editors
• G.J.H. Grubben
Prins Hendriklaan 24, 1401 AT Bussum, Netherlands
• O.A. Denton
National Horticultural Research Institute, P.M.B. 5432, Idi-Ishin, Ibadan, Nigeria
Associate Editors
• C.-M. Messiaen
Bat. B 3, Rιsidence La Guirlande, 75, rue de Fontcarrade, 34070 Montpellier, France
• R.R. Schippers
De Boeier 7, 3742 GD Baarn, Netherlands
General editors
• R.H.M.J. Lemmens
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
• L.P.A. Oyen
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
Photo Editor
• E. Boer
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Correct citation of this article:
Tjeertes, P., 2004. Brassica oleracea L. (Brussels sprouts) In: Grubben, G.J.H. & Denton, O.A. (Editors). PROTA 2: Vegetables/Lιgumes. [CD-Rom]. PROTA, Wageningen, Netherlands.
plant habit