Brassica rapa Chinese Cabbage (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Brassica rapa L. cv. group Chinese Cabbage

Protologue: Toxopeus, Yamagishi & Oost in Cruc. Newsl. 12: 5 (1987).

Family: Cruciferae

Chromosome number: 2n= 20

Synonyms

• Brassica pekinensis (Lour.) Rupr. (1860),
• B. campestris L. ssp. pekinensis (Lour.) Olsson (1954),
• B. rapa L. ssp. pekinensis (Lour.) Hanelt (1986).

Vernacular names

(some in common with cv. group Pak Choi).

• Chinese cabbage, celery cabbage, Peking cabbage, petsai (En)
• Chou de Chine, chou de Shangton (Fr)
• Indonesia: petsai, sawi putih
• Malaysia: petsai, sawi putih, kobis cina
• Papua New Guinea: kapis
• Philippines: pechay Baguio, wong bok
• Cambodia: pe-chhaay, spéi khiew
• Laos: kaad chiin
• Thailand: phakkat-khaopli, phakkat-khaoyai
• Vietnam: cải bắc kinh.

Origin and geographic distribution

Chinese cabbage is a native of China. It probably evolved from the natural crossing of Pak choi (non-headed Chinese cabbage), which was cultivated in southern China for more than 1600 years, and turnip, which was mainly grown in northern China. Much of its varietal differentiation took place in China during the past 600 years. Its derivatives were introduced into Korea in the 13th Century, the countries of South-East Asia in the 15th Century, and Japan in the 19th Century. An illustration of the headed shape of Chinese cabbage with wrapping leaves was first recorded in China in 1753. At present, Chinese cabbage is grown all over the world.

Uses

Chinese cabbage is used from crisp-raw, to tender-crunchy, to silky-soft over-cooked. Fresh leaves are stir-fried, added to delicate broths during the last few minutes of cooking, or simmered for a long period of time in thick, stewy soup. In East Asia, it is a standard part of meals in the form of simple salted and spiced pickles, whether sweet-sour and fresh, or hot-peppery and long-fermented. Leaves treated this way can be kept for several weeks. Raw, succulent white midribs of the leaves are also sliced or coarsely shredded for salads, or cut in strips for platters. Leaves are also dried and kept for weeks before being used as vegetables.

Production and international trade

Chinese cabbage is one of the most important vegetables in East Asia. It is favoured by small farmers because of its short cropping duration and wide adaptation to different growing conditions. The cultivated area in China was about 260 000 ha in 1982, or 27% of the total vegetable production area. In Japan, about 32 000 ha were planted with this crop in 1988, or 5% of the total vegetable production area. In Korea, the production area was about 48 000 ha in 1986, or 13% of the total vegetable production area. In Taiwan, the production area of 8000 ha in 1988, or 4% of the total vegetable production area, was second only to white cabbage. In Thailand, some 8000 ha were planted with this crop and Pak choi in 1986. In South-East Asia, there has been a considerable increase in production in recent years because of the availability of cultivars adapted to tropical conditions. International trade of this crop in the region is negligible. The bulk of the seeds are imported from temperate or subtropical countries, mostly Japan and Taiwan.

Properties

Per 100 g edible portion, leaves contain approximately: water 95 g, protein 1.2 g, fat 0.2 g, carbohydrates 2.2 g, fibre 0.5 g, Ca 49 mg, Fe 0.7 mg, vitamin A 0.9 mg, and vitamin C 38 mg. It is low in energy value, about 65 kJ/100 g. The 1000-seed weight is about 3 g. Seeds contain 35-40% oil, and keep their viability well in air of low relative humidity.

Description

• Biennial herb, cultivated as an annual, 20-50 cm tall during the vegetative stage, reaching up to 1.5 m in the generative stage.
• Taproot and lateral roots prominent in older plants, forming an extensive, fibrous, finely branched root system.
• During the vegetative stage leaves are arranged in an enlarged rosette, forming a short conical more or less compact head, with ill-defined nodes and internodes and alternate heading and non-heading leaves; leaves 20-90 cm × 15-35 cm, shape varying with growth stage; outer heading leaves narrowly ovate with long, winged petioles, dark green; inner heading leaves broad, subcircular, whitish-green; flowering stem leaves lanceolate, much smaller than heading leaves, with broad compressed petioles and blades, clasping the stem.
• Inflorescence an indeterminate, terminal, much-branched raceme, 20-60 cm long; pedicel 1-1.5 cm long; flowers bisexual, perfect; sepals 4, 0.5 cm long, yellow-green; petals 4, 1 cm × 0.5 cm, bright yellow; stamens 6, tetradynamous.
• Fruit a silique, 7 cm × 3-5 mm, glabrous, with short and stout beak, 10-25-seeded.
• Seed globose to ovoid, 1-2 mm in diameter, greyish-black to red-brown.

Growth and development

Chinese cabbage seeds take 3-5 days to emerge at 20-25 °C. There are normally five leaves in two whorls or eight leaves in three whorls. These first whorls of leaves are fully expanded into more or less horizontal position. Seedlings are usually set out to the field at this stage. Subsequent leaves are continually formed, and the inner leaves start to grow more upright. Heading begins at about the 12th to 13th leaf stage for the early-maturing cultivars or the 24th to 25th leaf stage for the late-maturing, when the innermost leaves start to curve inwards and touch at their tips. As new leaves form and expand around the crown, their margins become temporarily trapped against the upright leaves. In the early stages of head formation, these temporarily trapped leaves finally unfold, become upright, and roll outward to develop into the outer head leaves. As more leaves are produced, they become increasingly entrapped and remain folded to form the head. There is a limited increase in height at this stage, but the plant assumes its characteristic headed shape. Some 50-100 days after sowing, the heads can be harvested as vegetable. The stem normally elongates (bolts) as the flower buds initiate and develop. Flowers are insect-pollinated, and have an outcrossing type of mating. After fertilization, the siliques develop rapidly and reach their full size within 3-4 weeks. The fully developed siliques require another 2 weeks to mature.

Other botanical information

Cv. group Chinese Cabbage comprises headed and semi-headed cultivars of leaf neeps with characteristically winged petioles. In the taxonomic literature it has often been classified as belonging to B. chinensis L., together with cv. group Pak Choi. Cv. group Pak Choi comprises non-headed leaf neep cultivars, with fleshy, conspicuous, but not winged petioles.

According to shape, size and organization of the head, three basic types of Chinese cabbage can be distinguished from which numerous cultivars have developed:

• cephalata type: head large, compact, ovoid to obovoid; the heading leaves curve inward and overlap at the top;

• cylindrica type: head compact, erect and elongated, more or less pointed and spirally wrapped at the top; with or without heading leaves over the top;

• laxa type: head loose, open; the top and the upper margins of the heading leaves may be erect or curled outward, and are yellow or yellow-white.

Ecology

Chinese cabbage grows best and forms heads in climates with temperatures in the range of 12-22 °C; therefore they are usually grown at high altitudes (500-1500 m) in the tropics. Temperatures above 25 °C prevent most temperate cultivars from forming marketable heads. High temperatures also enhance tip burn (physiological disorder) and the development of diseases. The heat-tolerant cultivars developed by seed companies nowadays make it possible to produce good Chinese cabbage crops in the lowlands. Daylength does not affect head formation but short days with reduced amounts of incoming radiation will reduce the growth rate and weight of leaves. The water requirement greatly increases with advancing growth stages, particularly during the heading stage. Drought stress in the heading stage prevents head formation. Flooding during the rainy season makes normal plant growth impossible, especially the formation of heads. Crops usually die within 3-5 days of flooding in the lowland tropics because of the synergistic effect of high temperatures.

A period of 1-4 weeks at 5-13 °C, either before or after heading, is required for flower initiation to take place. The sensitivity to low temperature increases with increasing plant age. A combination of low temperature and long day is required for maximum flowering. Devernalization may occur at temperatures above 16 °C. Heat-tolerant genotypes tend to bolt early if grown in the cool tropical highlands. Chinese cabbage thrives well in a fertile, clayey loam soil with a pH of 6.0-7.5 and a large amount of organic matter.

Propagation and planting

Chinese cabbage is propagated by seed. The seeds of either open-pollinated cultivars or hybrids are supplied by seed firms or national programmes. To minimize seedborne diseases, the seeds are sometimes soaked in 50¬∞C water for 25 minutes and then in 1% sodium hypochlorite for 10 minutes, if the seeds are not treated in advance by the seed supplier. Both direct seeding and transplanting methods are employed. For direct seeding, seeds are dibbled in drills and then covered with a thin layer of soil and rice straw. At the 2-3 true leaves stage, stands are thinned by cutting to keep vigorous normal seedlings at 1 plant/hole and 30-50 cm between plants. Transplanting with the use of a nursery to raise seedlings is preferred to direct seeding to shorten the crop duration in the field and to secure a better and more uniform stand. In this case, seeds are sown in pots at 2-3 seeds per pot, or per hole in seedling beds at a spacing of 6 cm × 6 cm, and then covered with a thin layer of soil, compost or rice hulls. Seedlings at the 2-3 true leaves stage are thinned to one seedling per pot or hole. The growth medium for seedling preparation is sometimes disinfected by steam sterilization. About 3-4 weeks after sowing, seedlings with 5-8 leaves are transplanted to the field, usually in the late afternoon, at 50 cm between rows and 30-50 cm within rows on a 1.5 m wide raised bed. The quantity of seeds required for a stand of 30 000 plants/ha for both methods is 0.5-0.8 kg (175 000-275 000 seeds). Land preparation is usually carried out by plowing with a water buffalo, roto-tilling and then harrowing, or hoeing.

Husbandry

As most of the feeder roots of this vegetable grow to a depth of 30 cm, irrigation to maintain the top 30 cm at a soil moisture level between 65-85% of field capacity is of great importance. For both transplanting and direct seeding methods, water is provided right after sowing by fine spraying, or by using a small watering can after transplanting. When the seedlings have established in the field, furrow irrigation is practised once every 7-10 days, depending on ambient conditions. As a rule, the plants are irrigated if wilting occurs in midday or early afternoon. In the rainy season, good soil drainage is essential for plant survival. Mulching with rice straw is useful in reducing weeds, soil erosion, soft rot, and downy mildew. Raised beds at 30 cm or earthing-up in combination with weeding can minimize flooding damage during the rainy season. Leaf-tying at the early stage provides a good initial posture for heading.

Both fast-acting chemical fertilizers and slow-acting organic fertilizers are normally used. In the case of direct seeding, part of the chemical fertilizer is given at sowing and the rest at intervals of 14-20 days after thinning. In the case of transplanting, part of the chemical fertilizer is incorporated into the bed, the rest being split-applied after transplanting, at intervals of 10-14 days. The recommended rates are 120-200 kg/ha of N, 40-60 kg/ha of P₂O₅ and 70-150 kg/ha of K₂O. Depending on the cropping conditions, more chemical fertilizer may be added during the rest of the growing cycle. Organic fertilizers such as compost, green manure, chicken or pig manures, oil cakes, or night soil are essential to improve the efficiency of chemical fertilizers and to retain optimum physical and chemical soil conditions. Chinese cabbage is grown in rotation with field crops or in multiple cropping systems with other vegetables, preferably with unrelated crops to prevent a build-up of insects and diseases.

Diseases and pests

Chinese cabbage often suffers from various diseases and pests. Soft rot (Erwinia carotovora) is the most damaging disease in the humid tropics. The incidence of soft rot can be dramatically reduced by shortening the growth period. Downy mildew (Peronospora parasitica) and turnip mosaic virus (TuMV) are important in dry environments. Some new cultivars possess a considerable level of resistance to both pathogens. Clubroot (Plasmodiophora brassicae) and Alternaria leaf-spot are also serious, although confined to certain tropical highland areas. Tip burn, a Ca-related disorder of the marginal tissue of either outer wrapper leaves or inside the head, also often occurs in tropical lowlands. Split applications of nitrogen fertilizer and a decreased total rate of fertilizer are recommended as means of avoiding too vigorous an initial growth, a predisposition for tip burn.

Diamond-back moth (Plutella xylostella) is a most destructive pest, particularly during the dry season. The combination of two larval parasites (Diadegma eucerophaga and Apanteles plutellae) and a bacterial insecticide, Bacillus thuringiensis, can provide satisfactory biological control of diamond-back moth. Brief sprinkler irrigation repeated daily at dusk is also effective to decrease mating, oviposition and, consequently, infestation. Aphids are also serious during the dry season. Damage by adult striped flea beetles (Phyllotreta striolata) is common on leaves in the dry season. Cabbage webworm (Hellula undalis) is serious during the wet season.

Harvesting

Heads are harvested when compact, i.e. they do not collapse easily when pressed firmly with both hands. Prematurely harvested heads lack development of young, tender leaves and are relatively light; over-matured heads may burst, thus reducing marketability. The head is cut at the base, keeping the entire head intact. Outer leaves are trimmed to 2-3 non-heading leaves for protection during transport.

Yield

Average crop yields range from 10-60 t/ha, depending upon season, cultivar, duration, and location. Average head weight ranges from 0.5-4.5 kg.

Handling after harvest

Most tropical countries face difficulties of transportation and storage. Bamboo baskets, the most frequently used packing material in South-East Asia, are often overloaded. This causes injuries and leads to infections by pathogens. Under humid, tropical conditions, Chinese cabbage can be stored for only a few days. Lack of storage facilities, adequate packing materials and sufficient transport hampers the marketing of the crop.

Genetic resources

China has the richest source of Chinese cabbage germplasm; by the end of 1985 about 1000 landraces were collected and about 150 of them have been placed in long-term storage in the Chinese Academy of Agricultural Sciences (CAAS), Beijing. Over the years, AVRDC has also built up a sizeable collection of about 860 accessions. AVRDC's collection is also preserved at the Institute of Horticultural Research, Wellesbourne, United Kingdom.

Breeding

Objectives of varietal improvement in South-East Asian national programmes, private seed firms, and AVRDC, are heat tolerance (defined as the ability to form heads in hot weather), non-bitter flavour, high yield, early maturity and resistance to major diseases. Improved open-pollinated cultivars, synthesized from intercrosses of the new breeds, and hybrids, showing pronounced hybrid vigour and uniformity, obtained upon crossing two homozygous inbred lines, have been released in the region. Desirable characteristics may be obtained from any other form of B. rapa by hybridization and applying standard breeding procedures.

Prospects

The advent of the heat-tolerant, tropically adapted cultivars open up possibilities for production in the humid lowland tropics. However, an increase in the cultivation area in South-East Asia is only to be expected with the introduction of improved production technology as well as improved storage, transport and marketing facilities. The use of hybrid seed is of growing importance and its share in the international seed trade is increasing. Countries that depend entirely on this trade are looking for means to produce their own seed. The countries of South-East Asia could develop seed production of tropical cultivars in the relatively cool, dry highland climate. A skilled cadre of seed production specialists and appropriate technology for seed production are required.

Literature

• Chen, C., 1984. Morphology of Chinese cabbage. Science Publishing Company, Beijing, China. 116 pp.
• Jiang, M.C., 1981. Cultivation of Chinese cabbage. Agriculture Publishing Company, Beijing, China. 260 pp.
• Li, Chia-wen, 1984. Chinese cabbages of China. Agricultural Publishing Company, Beijing, China. 234 pp.
• Ope√±a, R.T., Kuo, C.G. & Yoon, J.Y., 1988. Breeding and seed production of Chinese cabbage in the tropics and subtropics. Technical Bulletin No 17. Asian Vegetable Research and Development Center (AVRDC), Shanhua, Tainan, Taiwan. 92 pp.
• Talekar, N.S. & Griggs, T.D. (Editors), 1981. Chinese cabbage. Proceedings of the First International Symposium of Chinese Cabbage. Asian Vegetable Research and Development Center (AVRDC), Shanhua, Tainan, Taiwan. 489 pp.
• Toxopeus, H., Oost, E.H., Yamagishi, H. & Prescott-Allen, R., 1988. Cultivar group classification of Brassica rapa L.: update 1988. Cruciferae Newsletter No 13: 9-11.

• See also the species page

Authors

• C.G. Kuo & H. Toxopeus