Brassica rapa Caisin (PROSEA)

Plant Resources of South-East Asia
Introduction

List of species

Brassica rapa L. cv. group Caisin

Protologue: Cv. group name is proposed here.

Family: Cruciferae

Chromosome number: 2n= 20

Synonyms

Brassica parachinensis Bailey (1922),
B. chinensis L. var. parachinensis (Bailey) Tsen & Lee (1942).

Vernacular names

Caisin, flowering white cabbage (En)
Mock pak choi (Am)
Indonesia: caisin, sawi hijau, sawi kembang
Malaysia: sawi bunga
Thailand: phakkwangtung, phakkat-kheokwangtung.

Origin and geographic distribution

Caisin is generally believed to have differentiated along with the leaf neeps (Chinese cabbage, pak choi) from the oil-yielding turnip rape, which was introduced into China from the Mediterranean area through western Asia or Mongolia. Caisin originated in middle China where it was selected and popularized for the use of its inflorescences. It may be seen as parallel variation in B. rapa comparable with Chinese kale (B. oleracea L. cv. group Chinese Kale) in B. oleracea. Where headed Chinese cabbage is hardly grown, caisin and the non-headed leaf neeps (e.g. pak choi) are indispensable vegetables. Caisin is cultivated in southern and central China, in South-East Asian countries such as Indonesia, Malaysia, Thailand, Vietnam, in other parts of Indo-China, and in some parts of West India.

Uses

Caisin has been developed for use in the early flowering stage, although harvest before flowering is preferred in certain regions. The inflorescences are more tender and smoother (glabrous) than those of other leafy Brassica crops and plants are cut for fresh consumption when the flowers begin to open. It is delicious when stir-fried, retaining much of its crispness and its salts and vitamins in the process. Because of its general tenderness, it is not suited to pickling and other post-harvest processing.

Production and international trade

Very limited data are available on production and externally traded volume of caisin. In each country, most caisin is consumed locally because it is very perishable. The production figures for caisin are usually lumped together with other leafy Brassica crops. In Indonesia it is one of the three most popular vegetables, together with kangkong and amaranth. In Thailand where caisin may be considered as the main leafy Brassica vegetable, reported area and production in 1988/89 were 2783 ha and 46 437 t respectively.

Properties

Per 100 g fresh edible portion, caisin contains: water 95 g, protein 1.2 g, fat 0.2 g, carbohydrates 1.2 g, vitamin A 5800 IU, vitamin B₁ 0.04 mg, vitamin B₂ 0.07 mg, niacin 0.5 mg, vitamin C 53 mg, Ca 102 mg, Fe 2.0 mg, Mg 27 mg, P 37 mg, K 180 mg, and Na 100 mg. The energy value is 54 kJ/100 g. The 1000-seed weight is approximately 3 g.

Description

Annual taprooted herb, 20-60 cm tall, with usually open to erect but sometimes prostrate growth habit.
Stem usually less than 1 cm in diameter, small in comparison to other leafy cabbages, usually profusely branched.
Rosette leaves few, usually with only 1-2 leaf layers and with a 2/5 phyllotaxy, long-petioled, spathulate or oblong, bright green; stem leaves not clasping, petiolate, glabrescent to glabrous, green to purple-red, finely toothed when young; lower stem-leaves ovate to nearly orbicular; central stem-leaves ovate to lanceolate to oblong with long and narrow, grooved petioles that are sometimes obscurely winged; upper stem-leaves gradually passing into narrow bracts.
Inflorescence a terminal raceme, elongating when in fruit; flowers bisexual, perfect, ca. 9 mm in diameter, cream-coloured to very light yellow, 4-merous; petals pandurate; stamens 6, tetradynamous.
Fruit a silique, slender, up to 5 cm long with slender brief beak, containing 10-20 seeds.
Seed globose, about 1 mm in diameter, smooth with faint raphal line.

Growth and development

Caisin seed has no dormancy, but it is advisable to wait for at least a week after seed drying before sowing them. Caisin seeds require 3-5 days to germinate under optimum soil moisture and temperature (20-25 °C). The time to harvesting differs according to the cultivar; it varies from 40-80 days after sowing. Bolting and flowering generally are not depending on low temperatures; caisin tends to bolt early under long days. Bolting is generally indicated by the elongation of the main stem when the flower buds initiate and develop. After fertilization by insect pollinators like honeybees, the thin slender siliques develop rapidly and reach full length some three weeks later and are ready for harvest in another two-week period.

Other botanical information

The cv. group Caisin can be considered a leaf neep or more specifically an inflorescence neep. Characteristic features of cv. group Caisin are its orbicular basal leaves, its hardly winged petioles and its non-clasping stem-leaves. It is rather similar to a European crop known as "broccoletto" or "cima di rapa" in Italy. The Asian and European crops are organoleptically distinguishable (the latter usually have a stronger flavour), but morphologically they are quite similar.

Ecology

Caisin can be grown all-year round for its leaves and tender flower stalks in the subtropical and tropical zones, indicating that flower induction is not influenced by temperature. Generally, there is a tendency towards faster bolting during the long days of the summer at higher latitudes. A light, well-drained fertile sandy loam or clay-loam soil is best for caisin production. A soil pH of 5.5-6.5 is preferred.

Propagation and planting

Caisin can be direct-seeded or transplanted. In subtropical areas, direct seeding is preferred. Normally this is done by broadcasting or by drilling the seeds. In the humid tropics, transplanting is preferable because of the relatively poorer conditions for growth and development. Moreover, direct seeding is normally expensive and time-consuming as close attention to thinning and weeding is necessary.

Seedlings for transplanting are often raised in special nurseries, such as well-prepared raised beds or specially prepared seed boxes. Seeds are broadcast or sown in shallow furrows, covered lightly with soil, and then adequately watered. Seeds may be previously dusted with fungicides (e.g. thiram) to fend off attack by harmful diseases such as damping-off. In the tropics, the nursery is often covered with straw. Watering two to three times daily is necessary to encourage vigorous growth of the young plants. Watering the seedlings once a week with a 0.1% urea or ammonium sulphate solution is sometimes practised to further enhance plant vigour. Seedlings are hardened by lightly withholding water about one week before transplanting. Two to three weeks after sowing the seedlings are ready for transplanting.

Field beds should be well-prepared, raised, about 1 metre wide with between-bed furrow space of 20-25 cm. With direct seeding, spacing is about 10-15 cm × 10-15 cm between hills and rows. In transplanting, the young seedlings are set in such a manner that the first true leaves are approximately at ground level when the hole is filled with soil. Between-plant spacing varies depending upon cultivar types. Early cultivars are normally spaced about 30 cm; late-maturing cultivars require wider spacing. Spacing between the rows could be 30-40 cm. Seedlings should be watered quickly after they have been transplanted in the field.

Husbandry

Caisin grows moderately fast and therefore requires adequate moisture for optimum growth and development. In the tropics, watering with 5-7 mm per day or 2-3 cm every four days appears to be sufficient to sustain growth. The weeds must be hoed until the plants are able to outgrow them. Like the other leafy cabbages, caisin responds well to compost and fertilizer application. Often, 10-15 t/ha of compost combined with 60-110 kg/ha of N, 40-60 kg/ha of P₂O₅ and 80-100 kg/ha of K₂O are adequate to sustain a good crop. Nitrogen is often split-applied, half of the total as basal fertilizer and the residual side-dressed two weeks or so later. With late-maturing cultivars, more nitrogen is often applied, split into at least three applications. The last is normally applied a week before the onset of flower stalk formation. Caisin is easy to grow and as many as 10 crops can be grown successively without rotation except changing the cultivar type.

Diseases and pests

Soft rot (Erwinia carotovora), downy mildew (Peronospora parasitica), turnip mosaic virus (TuMV), clubroot (Plasmodiophora brassicae), Alternaria leaf-spot (A. brassicae or A. brassicicola) and Sclerotinia rot are the major diseases affecting cruciferous vegetables including caisin. Soft rot is very serious during the hot wet season. No effective control measures have been developed; however, early maturity or rapid growth usually enable crops to escape this disease. Fungicides such as dithane, maneb, and zineb can effectively control downy mildew and the Alternaria leaf-spots. Turnip mosaic virus (TuMV) is serious during the dry season. It can be reduced by controlling aphids which serve as the vector. Liming is known to reduce the incidence of clubroot. Field sanitation should be rigorously observed to reduce the spread of this disease to clean fields.

Diamond-back moth (Plutella xylostella) is the most destructive insect and is most common during cool dry periods. It usually is controlled by chemical sprays but the insect quickly develops pesticide resistance. Integrated pest management (IPM) using biological parasites such as Diadegma eucerophaga and Apanteles plutellae, combined with selective microbial insecticides like Bacillus thuringiensis provide a satisfactory control, besides being safe and sustainable. Other pests such as the webworm (Hellula undalis) and leaf webber (Crocidolomia binotalis), aphids (especially during the dry period) and striped flea beetle (Phyllotreta striolata) can sometimes be major limiting production factors.

Harvesting

Caisin is ready for harvest about 40 days after sowing in the earliest maturing cultivar. This is normally a once-over harvest by pulling the whole plant. In contrast, the more vigorous, late-maturing cultivars could be in the field for as long as 80 days and one or two well-grown side shoots could be harvested later after harvesting the main stalk.

Yield

The estimated yield range of caisin in the subtropics such as Taiwan is 10-20 t/ha. In 1989, the average productivity in Taiwan was 15 t/ha. The average yield reported in Thailand in 1988/'89 was 17 t/ha.

Handling after harvest

The harvested plants should be moved immediately to a shady place. Keeping the plants covered with wet materials or sprinkling occasionally with water could reduce water loss and apparent wilting. They are then washed well and cleaned of old, decaying, injured or unsightly leaves to prepare them for the market. The harvested plants or leaves could be packed in suitable containers such as bamboo baskets (as normally practised in the Asian tropics) but other materials such as plastic boxes or paper cartons with holes to allow air circulation may be used, if locally available and inexpensive. Packages for supermarkets are often of 300 g capacity; caisin normally lasts two days in these containers. For the traditional markets, caisin is usually prepared in 300 g bunches and normally lasts only one day.

Genetic resources

China is considered as the centre of diversity of caisin. The best known form of differentiation is in crop duration. Reported maturity of available cultivars ranges from 40 to 80 days. Usually caisin has green foliage, but a purple-leafed cultivar is available in Taiwan. Caisin collections are available in China, Japan, and Taiwan although collections in the latter two countries are relatively modest.

Breeding

There is no major breeding effort to improve caisin. Farmers in South-East Asia use local cultivars from own seed or from local seed dealers. Some cultivars are imported, usually from China or Taiwan. The variability between cultivars available in the region appears to be small. Some superior selections from local cultivars are available from seed companies in Indonesia, Thailand and the Philippines. Any attempt to improve caisin through breeding begins with simple breeding techniques, such as mass selection, applied to genetically variable cultivars. No data on disease resistance of commonly grown cultivars are available, to derive any hypotheses on the potential of breeding for disease resistance.

Prospects

The potential to genetically improve caisin using the variation in presently available cultivars seems to be limited. However, enforced introgression from the leaf neeps is easy and therefore the available genetic diversity of the latter could be readily exploited in any serious breeding effort on this vegetable. The prospect of successful technology for integrated pest management to control insect pests in the hot and humid lowland areas appears to be good.

Literature

Bantoc Jr, G.B., 1970. Chinese cabbage and the mustards. In: Knott, J.E. & Deanon Jr, J.R. (Editors): Vegetable production in South-East Asia. University of the Philippines Press, Los Baños, the Philippines. pp. 276-284.
Bettencourt, E. & Konopka, J., 1990. Directory of germplasm collections. 4. Vegetables. International Board for Plant Genetic Resources (IBPGR), Rome, Italy. pp. 55-95.
Herklots, G.A.C., 1972. Vegetables in South-East Asia. George Allen & Unwin, London, United Kingdom. pp. 208-211.
Li, Chia-wen, 1984. Chinese cabbages of China. Agricultural Publishing Company, Beijing, China. 234 pp.
Opeña, 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.
Teo, K.H. Christopher, 1970. Identification of some common Brassica species by their vegetative characters. The Malayan Agriculturist 9: 53-70.
Yamaguchi, M., 1983. World vegetables: principles, production and nutritive values. Avi Publishing Company, Westport, Connecticut, United States. pp. 218-231.

See also the species page

Authors

R.T. Opeña & D.C.S. Tay