Raphanus sativus (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Raphanus sativus L.

Protologue: Sp. pl.: 669 (1753).

Family: Cruciferae

Chromosome number: 2n= 18

Major taxa and synonyms

Cultivar group names are proposed here.

• Cv. group Chinese Radish. Synonyms: Raphanus sativus L. var. niger (Miller) Persoon (1807), var. hortensis Backer (1907), var. longipinnatus Bailey (1923).

• Cv. group Leaf Radish. Synonyms: R. sativus L. var. oleiformis Persoon (1807).

• Cv. group Rat-tailed Radish. Synonyms: R. caudatus L. (1767), R. sativus L. var. caudatus (L.) Vilmorin (1925), var. mougri Helm (1957).

• Cv. group Small Radish. Synonyms: R. sativus L. var. sativus , var. radicula Persoon (1807).

Vernacular names

General:

• Radish (En)
• Radis (Fr)
• Indonesia, Malaysia: lobak
• Philippines: labanos (Tagalog), rabanos (Ilocano), alibanos (Pangasinan)
• Burma: monla
• Cambodia: chhaay thaaw
• Laos: kaad khaaw
• Thailand: phakkat-hua (central), phakkhithut (northern)
• Vietnam: cải củi.

Cv. group Chinese Radish:

• Chinese radish, oriental radish, daikon (En)
• Indonesia, Malaysia: lobak, lobak putih.

Cv. group Leaf Radish:

• Indonesia: lobak daun.

Cv. group Rat-tailed Radish:

• Rat-tailed radish (En)
• Radis serpent (Fr)
• Thailand: phakkhithut (northern).

Cv. group Small Radish:

• Small radish, western radish (En)
• Petit radis (Fr)
• Indonesia: rades (Javanese), lobak berem (Sundanese).

Origin and geographic distribution

The origin of R. sativus is not known but the area of maximum diversity runs from the eastern Mediterranean to the Caspian Sea; the variability diminishes gradually from the Caspian Sea to China, and still more to Japan. Radish is a crop of ancient cultivation in the Mediterranean (before 2000 BC), from where it spread to China in about 500 BC and to Japan in about 700 AD. It has now spread throughout the world.

Cv. group Chinese Radish is most important in Japan, Korea, China and South-East Asia. Cv. group Leaf Radish is gaining importance in Europe as forage and green manure. Cv. group Rat-tailed Radish is most important in India and eastern Asia. In South-East Asia it is important in northern Thailand and Burma. Cv. group Small Radish is most important in temperate climates.

Uses

Radish is grown mainly for its thickened fleshy root. The western radish (cv. group Small Radish) is pungent and is prized as a relish or appetizer and for adding colour to dishes. The oriental radish (cv. group Chinese Radish), being crisp with mild flavour, plays a much wider role in South-East Asia. The roots are thinly peeled, sliced or diced and put into soups and sauces or cooked with meat. They can be preserved in salt. Sometimes, as in the Philippines, they are eaten fresh, mixed with other vegetables like tomato. Tops (leaves) are eaten as salad or spinach. Seedlings known as radish sprouts are used as greens for appetizers or cooked as spinach. The rat-tailed radish (cv. group Rat-tailed Radish) is grown for the immature seed pods, consumed raw, cooked or pickled. Leaf radish (cv. group Leaf Radish) is mainly grown as green manure and forage (central and western Europe). In South-East Asia (Indonesia) it is sometimes cultivated for the leaves that are used as vegetable.

Production and international trade

World production of radish roots is estimated at 7 million t per year, about 2% of the total world production of vegetables. Radish ranks very high in importance in Japan, Korea and Taiwan. Production data from South-East Asia are: Indonesia 27 800 t (1988), Malaysia 1250 t (1988), the Philippines 9000 t (1987), Thailand 32 000 t (1988).

Properties

Per 100 g edible portion, the root contains: water 93.5 g, protein 0.6 g, fat 0.1 g, carbohydrates 5.3 g, Ca 32 mg, P 21 mg, Fe 0.6 mg. It contains vitamin A in small quantity, vitamin B₁ 0.02 mg, vitamin B₂ 0.03 mg, and fair amounts of vitamin C (25 mg) and niacin (0.30 mg). The energy value is 90 kJ/100 g. The 1000-seed weight is about 10 g.

Description

• Erect, annual, more or less densely hairy herb, 20-100 cm tall; upper part of taproot and hypocotyl swollen, tuberous, globular, cylindrical or tapering, very variable in size, form and weight, red to white, sometimes grey to black, flesh white, sometimes red; stem at first short, growing out towards anthesis, hollow.
• Leaves alternate, glabrous to sparingly hispid; lower leaves in a radical rosette, petioles 3-5.5 cm long, leaf-blades oblong, oblong-ovate to lyrate-pinnatifid, 3-5-jugate with a round or ovate terminal lobe, 5-30 cm long; higher leaves much smaller, shortly petioled, lanceolate-spathulate, subdentate.
• Inflorescence a terminal, erect, long, many-flowered raceme; flowers 1.5 cm in diameter, fragrant, white to lilac; pedicel up to 2.5 cm long; sepals 4, oblong-linear, 6-10 mm long; petals 4, spathulate, clawed, 1-2 cm long; stamens 6, tetradynamous; style 3-4 mm long.
• Fruit cylindrical, up to 10(-30) cm × 1.5 cm, consisting of 2-several superposed joints, lower joint very short and seedless, upper one(s) much larger, terete, spongy and divided into 2-12 one-seeded compartments, indehiscent, with a long, seedless beak.
• Seed ovoid-globose, about 3 mm in diameter, yellowish.

• Cv. group Chinese Radish: very variable. The smaller forms (South-East Asia) with cylindrical root, 10-25 cm × 4-5 cm, white. Larger forms (China, Japan) can attain a weight of 20 kg, with leaves up to 60 cm long and with 8-12 pairs of pinnae.

• Cv. group Leaf Radish: no swollen roots.

• Cv. group Rat-tailed Radish: fruit can attain 30 cm or more in length.

• Cv. group Small Radish: root globose, ellipsoid or cylindrical, 0.5-4 cm × 0.5-4 cm, red, white, red and white or violet.

Growth and development

Radish seeds take about 4 days to emerge at 20-30°C. The taproot may grow to a depth of 1-1.5 m, the lateral roots are few and very slender. The edible part consists of the thickened hypocotyl (cv. group Small Radish) or of the thickened hypocotyl and upper part of the taproot (cv. group Chinese Radish). At first the leaves grow in a rosette, towards anthesis the stem elongates and branches. Flowers are cross-pollinated by insects. Growing time depends on cultivar and desired product. Small radishes can be harvested 3-5 weeks after sowing.

Other botanical information

The following wild species, closely related to the cultivated radish, possibly contributed to its origin: R. raphanistrum L., distributed in the Mediterranean, western Asia and in Europe; R. maritimus Sm., occurring along the coasts of the Atlantic Ocean in Europe, of the Mediterranean Sea and the Black Sea; R. landra Moretti ex DC. (considered as an inland form of R. maritimus ), especially in the western Mediterranean area; R. rostratus DC., distributed from Greece eastwards to the Caspian Sea. Sometimes these related species are considered as one species complex named R. raphanistrum, with the different taxa classified as subspecies.

R. sativus crosses freely with the related wild species. R. sativus is also closely related to several Brassica species and to Sinapis arvensis L. (charlock), with which it has also been successfully crossed. The taxonomy of R. sativus and its related species badly needs a thorough revision.

Radish cultivars are here classified into cultivar groups, but often a practical grouping of cultivars according to growing period, root shape and colour is followed:

• Summer radish (25 days to maturity):

a) round shape: red skin ("Scarlet Knight", "Cherry Beauty"), red/white ("Sparkler"), white or yellow ("Golden Globe", "Snowbelle");

b) half-long: red/white ("French Breakfast"), white ("Icicle").

• All-season radish (approximately 45 days to maturity): Chinese or daikon type, all elongate, white ("Wu Feng Early", "Oriental White", local South-East Asian cultivars).

• Winter radish (60 days to maturity):

a) round shape: white ("Ta May Hua"), black ("Round Black Spanish");

b) elongate: red ("Chinese Rose"), white ("Minowase", "Chinese White").

In China red-fleshed cultivars also occur.

Ecology

Cool conditions favour optimum growth. Although radish is known as a suitable crop for the highlands or for the cool season at higher latitudes, local cultivars in Indonesia are also quite common at medium elevation (200-700 m), but are rare in the lowlands (< 200 m) where yield is too low. Under short daylength, roots are well-shaped and tops small. Under long days (15 hours) roots are misshapen, tops elongate and early flowering occurs. Low temperatures followed by long photoperiods initiate bolting and development of the flowering stalk. Annual radishes flower after reaching edible size in warm temperatures. White-fleshed cultivars may flower under short days at low elevations, whereas red-fleshed cultivars require long days or elevations above 1000 m. Radish requires light, well-drained, deep soils with pH 6.0-6.5.

Propagation and planting

Propagation is by seed. Seed rates are 10-15 kg/ha for Chinese radish and 30-40 kg/ha for cv. group Small Radish. Seed is sown directly on prepared beds in drills. The oriental radish needs a rather wide spacing: 30 cm between rows and 15-25 cm between plants, depending on the cultivar. The western radish requires a narrow spacing of 10-25 cm between rows and is thinned to 2-4 cm between plants in the row. For small areas, seed is often broadcast.

Husbandry

In commercial cultivation, radish is normally grown as a sole crop. Intercropping with lettuce is also popular in many areas. An adequate supply of organic material, and a basal dressing of NPK followed by surface dressings of a nitrogenous fertilizer at regular intervals until the roots are mature, are recommended. To remain mild, tender and visually attractive, radish must grow rapidly with plenty of moisture. Water shortage induces root elongation. If growth is checked, the roots become hot-tasting, tough and pithy. Light shading improves root quality during hot, dry weather. Establishment in heavy soils promotes misshapen roots.

Diseases and pests

Common foliar diseases are Cercospora leaf-spot (C. brassicicola) and downy mildew (Peronospora parasitica). Serious root diseases in temperate areas are black rot (Aphanomyces aphani) and Fusarium yellows (F. oxysporum f. raphani). Club root (Plasmodiophora) is increasingly a problem in tropical highlands.

Important pests are flea beetles (Phyllotreta spp.) which attack young seedlings, aphids (Aphis gossypii, Lipaphis erysimi) which cause leaf-curls, and mustard sawfly (Athalia proxima) which feeds on the leaves. Root knot nematodes (Meloidogyne spp.) are important.

Harvesting

Radish must be harvested when fully developed but before the roots are overmature and become tough. It may be harvested with tops or without tops (i.e. leaves topped to 7-10 cm). Western radishes mature in 30-50 days from sowing and can be harvested mechanically, topped, trimmed, and bunched in one operation. Oriental radishes reach the harvestable stage in 50-90 days, and are normally harvested by hand.

Yield

Approximately 7-10 t/ha of fresh radish can be achieved for early-maturing cultivars of western radish. Yields of oriental radish vary between 15-20 t/ha; the weight of radishes may reach 2.5 kg/root in Chinese cultivars, and even 10-20 kg/root in Japanese cultivars. Some radishes may grow to a length of 75-100 cm.

Handling after harvest

Radishes are washed thoroughly to remove soil and to maintain a fresh appearance, followed by grading and packaging. When sold with tops, they are tied in bunches, and the leaves should be turgid, green, and free from blemishes. Rapid cooling, using crushed ice or cold water to remove heat, helps retain good quality. At high relative humidity and a temperature of 0 °C, radish can be stored for 28 days, but at 7 °C the storage life is less than 7 days. Roots with leaves attached have half the storage life of topped roots.

Genetic resources

Germplasm collections are maintained by NIAR (Tsukuba, Japan), IPB (Los Baños, the Philippines), Department of Agriculture (Bangkok, Thailand), USDA (Fort Collins, United States), and the Crucifer Genetics Cooperatives at the University of Wisconsin (Madison, United States).

Breeding

Most farmers in South-East Asia use their own local cultivars of cv. group Chinese Radish. Breeding work of seed companies aims primarily for attractive root shape, colour and mild flavour. Numerous cultivars have been bred by Japanese, Chinese and western seed companies. These modern cultivars have early maturity, resistance to bolting ("Minowase"), attractive root texture (crisp, firm, high solids content), tolerance to diseases such as black rot, Fusarium yellows ("Scarlet Knight") and club root ("Saxafire", "Novitas").

In seed production, open-pollinated cultivars may give a seed yield of 800 kg/ha; an isolation distance of 1000 m is required. Self-incompatibility and male sterility are available for the production of F₁ hybrid seed.

Prospects

Radish tolerates a wide range of climatic conditions and is consumed worldwide with a large array of uses. Cultivation in tropical lowlands will increase through the breeding of heat-tolerant cultivars. It will remain a popular vegetable with home gardeners and commercial growers. It is also very suitable as an emergency crop in the case of sudden loss of or damage to the normal food crops: as a consequence of its short crop duration, even the shortest season can accommodate radish production.

Literature

• Banga, O., 1976. Radish. In: Simmonds, N.W. (Editor): Evolution of crop plants. Longman, London, United Kingdom. pp. 60-62.
• Herklots, G.A.C., 1972. Vegetables in South-East Asia. George Allen & Unwin, London, United Kingdom. pp. 139-143.
• Larkcom, J., 1991. Oriental vegetables. The complete guide for garden and kitchen. John Murray, London, United Kingdom. pp. 111-120.
• Tindall, H.D., 1983. Vegetables in the tropics. MacMillan, London, United Kingdom. pp. 133-137.
• Tisbe, V.O., 1967. Carrot, garden beet, radish and turnip. 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. 305-317.

Authors

• Kasem Piluek & M.M. Beltran