Brassica oleracea Chinese Kale (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Brassica oleracea L. cv. group Chinese Kale

Protologue: Cv. group name is proposed here.

Family: Cruciferae

Chromosome number: 2n= 18

Synonyms

• B. alboglabra L.H. Bailey (1922),
• B. oleracea L. var. alboglabra (L.H. Bailey) Musil (1948).

Vernacular names

• Chinese kale (En)
• Broccoli de Chine (Fr)
• Indonesia: kailan
• Malaysia: kailan
• Cambodia: spéi sââ
• Thailand: phakkhana.

Origin and geographic distribution

Whereas most forms of B. oleracea evolved in Europe, Chinese kale is a cultigen native to southern and central China. It is now widely cultivated and popular in South-East Asia.

Uses

Chinese kale is commonly grown for its stem, young leaves and young inflorescences which are consumed cooked or fried, sometimes raw. It can be used from the young vegetative stage up to the early flowering stage. In the latter case, thick stems have developed which must be peeled before cooking. The older leaves are rather tough in texture and strong in taste.

Production and international trade

Few statistics are available, but Chinese kale ranks among the ten most important market garden vegetables in some South-East Asian countries such as Thailand (6700 ha in 1988). It is also widely grown in home gardens and market gardens around cities. Its short growing period hampers correct registration of acreages and production. In Indonesia, Chinese kale is still of minor but increasing importance.

Properties

The edible parts of Chinese kale have a high content of essential micronutrients. Per 100 g edible portion it contains: vitamin A 7540 IU, vitamin C 115 mg, Ca 62 mg, Fe 2.2 mg. The dry matter content varies between 10-14%, depending on the harvesting stage. The 1000-seed weight is about 3 g.

Description

• Annual herb, up to 40 cm tall during the vegetative stage, up to 1(-2) m tall at the end of flowering, all vegetative parts glabrous and glaucous.
• Taproot strongly branched.
• Stem single, narrow-branching or forking in upper part.
• Leaves alternate, thick, firm, petiolate; leaf-blades ovate to orbicular-ovate, margin irregularly dentate and often undulate, characteristically auriculate at base or on the petiole; basal leaves smaller; upper leaves narrowly oblong, subsessile, without auricles.
• Inflorescence a terminal or axillary raceme, 30-40 cm long; pedicel 1-2 cm long; flowers usually white, sometimes yellow, rarely red, 2-3 cm in diameter, 4-merous but with 6 (tetradynamous) stamens.
• Fruit a silique, 3-9 cm long, with a conical beak.
• Seed subglobose, 2-3 mm in diameter, brown to black, minutely foveolate (pitted).

Growth and development

Seeds germinate 3-5 days after sowing. Vegetative development is slow during the first two weeks, but then accelerates. Flowering usually starts 55-80 days after sowing depending on cultivar and cultural practices. Chinese kale is cross-pollinated by insects. Seeds mature in 50-60 days from pollination.

Other botanical information

Chinese kale is only known in a cultivated state and no wild relatives are known. Sometimes it is considered as a distinct species (B. alboglabra), more often as a variety (var. alboglabra) of B. oleracea. As it is only known cultivated, it seems more appropriate to classify it as a cultivar group within B. oleracea. It is not clear to which other forms within B. oleracea it has most affinity: to the European kales or to the cauliflower/broccoli group which shows a tendency towards annuality.

There are numerous landraces in China and South-East Asia. Some cultivars are available from Chinese, Taiwanese and Thai seed companies. Cultivars are distinguished on the basis of flower colour, leaf shape, leaf texture and colour, internode length, and usage.

Ecology

Optimum temperatures range from 25-30 °C for germination, and from 18-28 °C for vigorous growth. Low temperatures promote early flowering and are also necessary for complete floral development. Chinese kale is frost-tolerant. It does well under sunny conditions in moist, well-drained soils. Chinese kale can be grown year-round in the tropics.

Propagation and planting

Chinese kale is propagated by seed. The most common practice is sowing by broadcasting at a rate of 3-6 g/m² (30-60 kg/ha) for the harvest of very young plants. When only plants in the early blooming stage are preferred, it is more economical to sow on nursery beds and to transplant 3-week-old seedlings to the field, in order to avoid long field occupancy. The seed requirement is then only 3 kg/ha.

Husbandry

In Thailand, where consumers prefer Chinese kale in a young growth stage, farmers generally broadcast the seed on well-prepared land. On poor soils, the application of 10-20 t/ha of organic manure and 250 kg/ha of NPK (15-15-15) is recommended. The seedlings are thinned 14 days after sowing. The second thinning, performed 3-4 weeks after sowing when the plants have formed about 5 true leaves and the stem is 0.5 cm in diameter is also the first harvest. Thinning is repeated regularly until the plant spacing becomes approximately 30 cm × 30 cm. Plants are then left to grow until the final mature harvest. Top dressings of 20 kg/ha of a nitrogen fertilizer are recommended every 10 days after the first thinning.

Diseases and pests

A serious disease is damping-off (Pythium sp.), which can be controlled to some extent by good drainage, by avoiding overdense sowing, and with fungicides such as dithiocarbamates. Downy mildew (Peronospora parasitica) is another serious disease during the damp and cool season.

Insects are the most serious problem for the Chinese kale grower. Flea beetles, diamond-back moth, borers and cabbage looper are the most harmful, besides aphids, grass hoppers and crickets. Spraying insecticides up to twice a week is generally practised, causing problems with harmful residues due to the high harvest frequency. In Thailand whole fields of Chinese kale are sometimes netted against diamond-back moth. The same IPM technology as developed for cabbage may be applied.

Harvesting

Harvesting can be done at any growth stage, from 3 weeks after sowing up to the early flowering stage. During the early stages, the crop is usually harvested by thinning, whereas at the mature stage, the plants are cut at ground level. Another method is harvesting by repeated cuttings every 3 weeks (ratooning). In this case, wide spacing is needed (at least 30 cm × 30 cm) and cutting must be practised in such a way that at least 2 leaves and buds are left for regrowth.

Yield

Yield varies from 0.8-4 kg/m² depending on the harvesting method.

Handling after harvest

Chinese kale can be kept fresh for some days under moist, cool storage. In markets and shops it is regularly sprinkled with water to maintain a fresh appearance. It is tied in bunches and sold by unit of money or by weight.

Genetic resources

Small germplasm collections of Chinese kale are kept at various institutions in South-East Asia such as national gene banks, universities and seed companies. Despite its wide distribution, there appears to be relatively little diversity of type, probably because of the absence of gene flow from other cole crops. Supplementation of existing collections is recommended, particularly with Chinese germplasm.

Breeding

The main breeding objective is earliness. Chinese kale is more heat tolerant than its B. oleracea relatives, and is used to improve this character in broccoli.

Prospects

Chinese kale is recognized as a very productive crop for the tropics, very suitable as a cheap green for large city markets. Research should focus on optimizing cultural practices, in particular pest control with less harmful residues. Resistance to diamond-back moth and the development of integrated pest management (IPM) must be further pursued.

Literature

• Bailey, L.H., 1922, 1930. The cultivated Brassicas. Brassica alboglabra. Gentes Herbarum 1(2): 79-81, 2(5): 233-234.
• Herklots, G.A.C., 1972. Vegetables in South-East Asia. George Allen & Unwin, London, United Kingdom. pp. 193-195.
• IBPGR, 1981. Genetic resources of cruciferous crops. International Board for Plant Genetic Resources (IBPGR), Rome, Italy. 48 pp.
• Phillipps, K. & Dahlen, M., 1985. A popular guide to Chinese vegetables. MPH Bookstores, Singapore. p. 21.
• Thuanthavee, M. & Panyatona, S., 1982. Vegetable garden. Agri Book Group, Bangkok, Thailand. pp. 118-121.

See also the species page

Authors

• C. Sagwansupyakorn