Brassica oleracea Cauliflower (PROSEA)

Plant Resources of South-East Asia
Introduction

List of species

Brassica oleracea L. cv. groups Cauliflower & Broccoli

Protologue: Cv. group names are proposed here.

Family: Cruciferae

Chromosome number: 2n= 18

Synonyms

Cv. group Cauliflower. Synonyms: B. oleracea L. var. botrytis L. (1753), B. cauliflora Gars. (1764), B. botrytis (L.) Miller (1768).

Cv. group Broccoli. Synonym: B. oleracea L. var. italica Plenck (1794).

Vernacular names

Cv. group Cauliflower:

Cauliflower (En)
Chou-fleur (Fr)
Indonesia: kubis bunga, kol bunga, blumkol
Malaysia: kubis bunga
Papua New Guinea: koli flawa
Cambodia: phkaa sp√©i
Laos: kalampii dook
Thailand: kalam-dok
Vietnam: súp lơ, cải hoa

Cv. group Broccoli:

Broccoli, sprouting broccoli, calabrese (En)
Chou brocoli (Fr)
Indonesia: brokoli
Papua New Guinea: brokoli
Thailand: brokkholi

Origin and geographic distribution

A remarkable diversity of cauliflower and broccoli-like vegetables exists in Italy; they probably evolved from germplasm introduced in Roman times from the eastern Mediterranean. During the last 400 years, white-headed cauliflowers spread from Italy to central and northern Europe, which became important secondary centres of diversity for the annual and biennial cauliflowers presently cultivated worldwide in temperate climates. Cauliflowers adapted to hot and humid tropical climates evolved in India during the last 200 years from biennial cauliflowers mainly of British origin. Broccolis with multiple green, purple or even white flowerheads (sprouting broccoli) became popular in northern Europe in the 18th Century. Broccoli with one main green head (calabrese) was introduced into the United States by Italian immigrants during the early 20th Century. From the United States it has spread to northern Europe, Japan and other regions in the last 50 years.

Uses

Cauliflower and broccoli are grown for their large, edible, very young inflorescences. Cauliflower heads (curds) are mostly consumed as a cooked vegetable, sometimes cut into small pieces (florets) and used in salad mixes or in pickles. The flowerheads of broccoli and the fleshy upper portion of the stem are also consumed as a cooked vegetable. Broccoli, and to a lesser extent cauliflower, have become popular as a quick-frozen vegetable, particularly in the United States and Europe. Both are also processed in dried mixtures of soup vegetables.

Production and international trade

Total world production of cauliflower is estimated at 5.5 million t per year from 410 000 ha. Major cauliflower producing countries are: India 95 000 ha, China 90 000 ha, France 45 000 ha, United States and Mexico 40 000 ha, Italy 23 000 ha, United Kingdom 21 000 ha, Spain 13 000 ha, Japan 11 000 ha, Taiwan 6100 ha. In South-East Asia cauliflower is still generally a minor crop and mostly restricted to the cool dry season or to the highlands: Thailand 4000 ha, Indonesia 2000-3000 ha, Vietnam 1500 ha. World statistics on broccoli production are incomplete and often mixed with cauliflower data. The most important broccoli producing countries are: United States 26 000 ha, Taiwan 7200 ha, United Kingdom 5000 ha, Italy 4000 ha, Spain 1500 ha. In Asia all cauliflower and broccoli are produced for local and urban markets.

Properties

The nutritional value of cauliflower is good, but that of broccoli is better due to higher carotene, vitamin C and calcium contents. Per 100 g fresh edible portion, cauliflower curd contains on average: water 88 g, protein 4 g, fat 0.3 g, carbohydrates 6 g, fibre 1.5 g, Ca 25 mg, K 325 mg, carotene 200 mg, vitamin C 40 mg. Values are similar for broccoli except for Ca 150 mg, carotene 800 mg and vitamin C 100 mg. The energy value is 245 kJ/100 g.

The 1000-seed weight for cauliflower and broccoli is 2.5-4 g.

Description

Cauliflower is a biennial or annual herb, 50-80 cm tall at the mature vegetative stage, 90-150 cm when flowering.
Root system strongly ramified, concentrated in the top 30 cm of the soil, some thicker lateral roots penetrating into deeper layers.
Stem unbranched, 20-30 cm long, thickening upwards.
Leaves in a rosette (frame) of 15-25 large, oblong, more or less erect leaves surrounding the compact terminal flowerhead (curd); usually no lateral buds develop in the leaf axils; leaves almost sessile, glabrous, coated with a layer of wax; leaf-blade grey- to blue-green with whitish main and lateral veins, in shape varying from short and wide (40-50 cm × 30-40 cm) with curly edges to long and narrow (70-80 cm × 20-30 cm) with smooth edges.
The curd consists of a dome of proliferated floral meristems, white to cream or yellow, on numerous short and fleshy peduncles. The curd varies from a rather loose to a very solid structure, a flattish to a deep globular shape, 10-40 cm in diameter.
Young leaves may envelop the curd until a far advanced stage of development. Bolting cauliflower plants often have several flower stalks.
Inflorescence a raceme, 40-70 cm long, extending from the terminal point of the main stem; pedicel 1.5-2 cm long; flowers tetramerous, bisexual; sepals erect, green; petals spathulate, 25 mm × 10 mm, yellow, sometimes white; stamens 6, 2 short and 4 long; ovary superior with false septum and 2 rows of campylotropous ovules; nectaries 2, situated between the base of the ovary and the short stamens.
Fruit a silique, 0.5 cm × 5-10 cm, containing 10-30 seeds.
Seed globose, 2-4 mm in diameter, brown.
Germination is epigeal. Seedlings have a thin taproot and cordate cotyledons; the first true leaves are ovate with a lobed petiole.

Broccoli (the single-headed type or calabrese) differs from cauliflower in the following aspects: leaves are more divided and petiolate; the main head consists of clusters of fully differentiated flower buds, green to purple, less densely arranged and with longer peduncles; axillary shoots with smaller flower heads usually develop after removal of the dominant terminal shoot. The flower head is fully exposed from an early stage of development. Broccoli plants carry inflorescences from lateral branches too.

Sprouting broccoli bears many, more or less uniform, relatively small flowerheads instead of one large head as in the calabrese type.

Growth and development

Cauliflower and broccoli seed (6% moisture content) will remain viable for at least 4-6 years when stored dry at temperatures below 18 °C. Seeds germinate within 3-6 days and seedlings have 7-9 true leaves within 30-40 days at > 20 °C average daily temperatures.

Differentiation of floral primordia in cauliflower can only start at the end of the juvenile phase, when plants have 12-15 leaves for early types to more than 25-30 leaves for late biennial types. Good curd formation requires a subsequent period of 20-30 days at slightly lower temperatures (18-20 °C) for very early types to < 15 °C for late types. Higher than optimum temperatures during this period will cause delayed and abnormal curd formation, except for the heat-tolerant early cauliflowers developed in India.

Vernalization requirements of most broccoli types are similar to those of cauliflower, except that broccolis are probably also devernalized by short photoperiods.

Heads of annual cauliflower and broccoli types are ready for harvesting 75-150 days after sowing, depending on cultivar and climate.

Very soon after the optimum harvesting date, curds of cauliflower plants start to enlarge, become loose, the peduncles lengthen and turn green and the floral meristems develop into inflorescences. Particularly in the modern cultivars with very firm and dense curds, only part of the floral meristems will develop into flowers, with the rest aborting and becoming a substrate for pathogenic fungi under humid conditions. In broccoli the head is already a mass of fully developed flower buds and normally very little abortion takes place.

Flowering starts at the base of the racemes and continues for about one month in cauliflower and for 20-25 days in broccoli plants. Sporophytic self-incompatibility (1-locus system with multiple alleles) precludes self-fertilization in most cauliflower and broccoli, except the annual cauliflower types developed in northern Europe which are selected for self-fertility (absence of S-alleles). Insects, especially bees, effect pollination. Seeds are mature 45-50 days after anthesis.

Other botanical information

Although much confusion exists regarding classification and nomenclature of cauliflowers and broccolis, the two cv. groups can easily be distinguished on the basis of the marketable product. In cv. group Cauliflower the head is a mass of proliferated floral meristems in which no individual flower buds can be distinguished. In cv. group Broccoli the head or heads (sprouts) are a mass of fully differentiated, clearly visible flower buds.

Cultivars with intermediate characteristics are hybrids between the two cv. groups and can best be classified in separate cv. groups, e.g. cv. group Hybrid Cauliflower or cv. group Hybrid Broccoli, depending on its most prominent characteristic. The vernacular nomenclature of cauliflowers and broccolis cannot always be trusted.

Present-day cauliflower cultivars have evolved, often by re-combination, from a number of types which can be grouped according to their phylogeny:

Italian: very diverse annuals and biennials, some with peculiar curd formations and colours; e.g. "Jezi", "Naples", "Autumn Giant", "Fano", "Romanesco", "Flora Blanca".

Northern European annuals: early summer to autumn types developed over the past 400 years from material of Italian or eastern Mediterranean origin ; e.g. "Erfurter", "Snowball", "Mechelse", "Alpha", "Danish Perfection", "Giant", "Le Cerf".

North-western European biennials: overwintering and winter-hardy types developed in maritime climates over the past 300 years from Italian material; e.g. "Roscoff", "St. Malo", "Old English", "Cornish", "Angers", "Walcheren".

Australian: late-maturing annuals developed from European annual and biennial types introduced some 200 years ago; e.g. "Barrier Reef", "Snowy River", "Kangaroo".

Asian: early maturing annuals adapted to hot and humid climates, developed in India since the early 19th Century from English winter types; e.g. "Patna", "Benaras", "Early Market". This material was later also used in Brazil, Hawaii, Japan and Taiwan to develop cultivars adapted to hot climates. The main drawback, however, is the formation of rather loose, uneven and yellowish-coloured curds.

In broccoli the main distinction is between:

Sprouting types: multi-branched with relatively small heads with green, purple or even white flower buds; e.g. "Purple Sprouting".

Heading types or Calabrese: a mass of flower buds in one large main head on a short central stalk; smaller heads may develop on lateral branches after removal of the main head; the colour of the head can be dark purple (e.g. "Purple Cape", "Sicilian Purple"), brownish (e.g. "Brown Headed"), yellowish-green (e.g. "Sulphur Coloured"), dark green (e.g. "Chartreuse"), or white.

In Indonesia and other South-East Asian countries, seed of broccoli is mostly bought from international seed companies. However, cauliflower is mostly grown from seed produced by the farmers. There are many farmers' selections, probably originating from early cauliflower introductions from Europe. The local cauliflower type grown in Indonesia in the highlands above 1000 m is early-maturing with loose curd, tasty but with an inferior external quality. Farmers select the best curds from their fields, replant them under a plastic cover, and remove with a knife part of the curd in order to stimulate flowering.

The open-pollinated cauliflower cultivars are increasingly being replaced by F₁ hybrids. All present-day broccoli cultivars are F₁ hybrids. Japanese breeders were the first to start developing F₁ hybrids in annual cauliflower and broccoli some 30 years ago.

Ecology

Most cauliflower and broccoli cultivars only produce heads of good quality when grown at average daily temperatures of 15-20 °C and a diurnal variation of at least 5 °C. In tropical regions such conditions are only found at elevations above 800 m. The heat-tolerant Asian cauliflowers are more adapted to tropical lowland conditions, but curd quality is generally inferior.

A regular supply of water is required throughout the growing season, but the heads of cauliflower and broccoli are easily affected by fungal rots when continuously exposed to wet conditions. The mature plant stage and harvesting should, therefore, be planned as much as possible outside the rainy season and overhead irrigation should be avoided. For successful seed production a fairly cool and dry climate is also a prerequisite. Soils should be well-drained and fertile, have good moisture retaining capacity, and high organic matter content; optimum pH is 6.5-7.5.

Propagation and planting

Dormancy of freshly harvested seed can be reduced by overnight soaking and rinsing in water; it also disappears after 3-4 months of storage. Seeds are sown on seed-beds, peat blocks or trays; young seedlings may have to be shaded to prevent sun scorching. Seed requirements are 300-350 g/ha. Transplanting to the field should be done when seedlings have 7-9 true leaves, 30-50 days after sowing. Plant densities for cauliflower are 20 000-35 000 plants/ha; for broccoli similar or somewhat higher densities are applied.

Vegetative propagation of broccoli plants is possible by rooting and transplanting of lateral shoots. In cauliflower lateral shoots are not available, but propagation through tissue culture from young floral meristems is easy to realize. This is often practised in breeding programmes to maintain selected plants.

Husbandry

Soil preparation includes deep digging, mixing with compost or stable manure (20 t/ha), 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 two or three N fertilizer dressings are applied later to stimulate good head formation.

Nitrogen deficiency at the early growth stage will cause "buttoning": stunted plants with reduced leaf and head development. Cauliflower and broccoli have a high demand for Mg, Bo and Mo and applications of dolomitic limestone, borax and ammonium molybdate may be necessary to prevent physiological disorders such as plants without a heart and browning of the head. Deficiencies occur earlier on acid soils.

The young crop should be kept free of weeds. Mulching, e.g. with rice straw, is beneficial to growth as it retains moisture, keeps soil temperatures down and suppresses weeds.

Growth of the plants should be regular and undisturbed. Sudden increases in temperature or water stress may cause bracting (green leaves) and riciness (extended young flower stalks) of cauliflower curds, irregular head formation and premature flowering in broccoli. Maturing cauliflower curds must be protected from direct sunlight by covering with broken off leaves to prevent them from turning yellow and/or pink. Many modern cultivars are self-protecting, i.e. inner leaves wrap tightly around the curd.

Diseases and pests

Diseases and pests are similar to those of cabbage in tropical regions. For important diseases such as fusarium yellows (Fusarium oxysporum f.sp. conglutinans), downy mildew on leaves and heads (Peronospora parasitica), black rot (Xanthomonas campestris pv campestris) and clubroot (Plasmodiophora brassicae), resistance or field tolerance have been found in cauliflower and broccoli accessions, but the majority of present-day cultivars are still susceptible. Other diseases causing problems are the two seedborne diseases black leg (Phoma lingam = Leptosphaeria maculans) and Alternaria blight (A. brassicae), and powdery mildew (Erysiphe polygoni), damping-off (Pythium ultimum), stem rot (Rhizoctonia solani), bacterial soft rot (Erwinia carotovora) as storage disease, and cauliflower mosaic virus (CauMV). Root knot nematodes (Meloidogyne spp.) can be a serious problem and should be avoided by proper crop rotation.

Important pests are diamond-back moth (Plutella xylostella), cutworm (Agrotis spp. and Spodoptora littoralis), cabbage moth (Crocidolomia binotalis), cabbage butterfly (Pieris canidia) and aphids (Aphis spp. and Brevicoryne brassicae), the vectors of CauMV. Diamond-back moth is extremely noxious because the pupae hide in the heads or curds and removal is virtually impossible. Methods of integrated pest management as applied to cabbage (with parasitoids, sex pheromones, trap plants and very restricted chemical control) can also be effective in cauliflower and broccoli.

Harvesting

Annual cauliflower and broccoli are ready for harvesting 60-120 days after transplanting; some early heat-tolerant cultivars, mainly F₁ hybrids, even within 45-55 days in tropical regions. Harvesting takes place over a period of 1-2 weeks.

Cauliflower heads are cut with sufficient trimmed leaves still attached to protect the curds during packing and transport. Broccoli heads are harvested with 10-15 cm of stem, without leaves.

Yield

Cauliflower yields can attain 12-30 t/ha and broccoli yields 4-10 t/ha; in the tropics highest yields are obtained above 1000 m. Seed yields are 200-600 kg/ha in temperate climates.

Handling after harvest

Cauliflower and broccoli heads will deteriorate quickly unless cooled soon after harvesting. Cauliflower curds can be stored for about 3 weeks at 1 °C and 95% relative humidity, but storage life for broccoli is much shorter and heads are usually wrapped in polythene film to prevent rapid desiccation and yellowing.

Genetic resources

Germplasm collections of cauliflower and broccoli are available in several research centres, particularly in Europe, the United States, India and Japan. However, within the main Italian and secondary central and northern European gene centre, every effort should be made to preserve the genetic variability for future breeding purposes. Genetic erosion also is a real danger in all South-East Asian countries, because local selections are being replaced by commercial cultivars from seed companies. Many old cultivars have already disappeared, representing considerable genetic erosion and probable loss of unique genes. The single-headed broccoli (calabrese) is particularly very narrow-based genetically .

Breeding

F₁hybrids, based on single crosses between inbred lines, are now the main goal of most breeding programmes in cauliflower and broccoli. Seed production depends on the system of sporophytic self-incompatibility present in most types. S-alleles have been re-introduced in the self-compatible annual cauliflowers of northern Europe. Self-fertilization, necessary to develop homozygous inbred lines, is effected by bud pollination or treatment with CO₂(2-6%) before bee pollination, to temporarily break the self-incompatibility. Inbred lines have also been developed from di-haploid plants regenerated from anther or microspore cultures.

The main breeding objectives include: head shape, size, firmness, weight, colour (pure white in cauliflower, dark green in broccoli), no physiological disorders, yield, earliness, standing ability, heat tolerance, resistance to diseases and pests.

Prospects

The importance of cauliflower and broccoli is likely to increase further in South-East Asia. Heat-tolerant cultivars enable cultivation at low altitudes, but market gardening will continue to prevail in the highlands because of higher yields, better head quality and fewer disease and pest problems. Considerable progress is being made with effective methods of integrated pest management, as in cabbage, and this will reduce pesticide use. Cultivars resistant to fusarium, black rot and downy mildew will gradually become available, but durable resistance to clubroot is very hard to realize.

The development of DNA markers for more precise indirect screening for resistance to diseases, pests and other important traits can increase breeding efficiency. Cytoplasmic male sterility might, in the long run, replace self-incompatibility as a more reliable technique for hybrid seed production.

Literature

Crisp, P., 1982. The use of an evolutionary scheme for cauliflower in the screening of genetic resources. Euphytica 31: 725-734.
Crisp, P., Crute, I.R. et al., 1989. The exploitation of genetic resources of Brassica oleracea in breeding for resistance to clubroot (Plasmodiophora brassicae). Euphytica 42: 215-226.
Gray, A.R., 1982. Taxonomy and evolution of broccoli (Brassica oleracea var. italica). Economic Botany 36: 397-410.
Gray, A.R. & Crisp, P., 1977. Breeding systems, taxonomy and breeding strategy in cauliflower (Brassica oleracea var. botrytis). Euphytica 26: 369-375.
Nieuwhof, M., 1969. Cole Crops. Leonard Hill, London, United Kingdom. 353 pp.
Shinohara, S. (Editor), 1984. Vegetable seed production technology of Japan. Shinohara's Authorized Agricultural Consulting Engineer Office, Tokyo, Japan. Vol. 1. pp. 55-81.
Swarup, V. & Chatterjee, S.S., 1972. Origin and genetic improvement of Indian cauliflower. Economic Botany 26: 381-392.
Whitwell, J.D., Jones, G.L. & Williams, J.B., 1982. Cauliflowers. ADAS/MAFF Reference Book 131, Growers Books, London, United Kingdom. 87 pp.

Authors

H.A.M. van der Vossen