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Latest revision as of 10:41, 23 March 2015

Plant Resources of Tropical Africa Introduction

List of species

Raphanus sativus L.

Protologue: Sp. pl. 2: 669 (1753).

Family: Brassicaceae (Cruciferae)

Chromosome number: 2n = 18

Synonyms

Vernacular names

Radish, Chinese radish, Japanese radish, mooli, daikon (En). Radis, daïkon, navet chinois (Fr). Rábano, rábão, rabanete chinês (Po). Mfijili (Sw).

Origin and geographic distribution

Raphanus raphanistrum L. is the most likely ancestor of the polymorphic Raphanus sativus. The area of maximum diversity of radish lies between the eastern Mediterranean and the Caspian Sea, which is probably the original gene centre for this species. Radish was cultivated already in ancient times in the Mediterranean, from where it spread to China in about 500 BC and to Japan in about 700 AD. The variability diminishes gradually from the Caspian Sea to China, and even more towards Japan. It is also a crop that has been cultivated since ancient times in the oases of the Sahara and in Mali. Radish can now be found as a cultigen throughout the world in many different forms, from small leafy annuals to biennials with large fleshy roots. The cultivars with relatively small roots (small radish) are most important in temperate climates of the world and only of limited importance in Africa, mostly in francophone countries amongst people originating from Europe. Larger-rooted cultivars (like Chinese radish) are most important in East and South-East Asia. In East Africa and elsewhere in the cooler parts of the African continent, large, white radishes are known under the Swahili/Arabic name ‘fijili’ and the Hindi name ‘mooli’ and these are becoming increasingly popular. In francophone West Africa Chinese radish is becoming popular, replacing the traditionally grown vegetable turnip (Brassica rapa L.), which is very susceptible to anthracnose. Large radishes with a dark grey-brown surface are occasionally seen in southern Africa and are sold under the name ‘black Spanish radishes’; they are more commonly grown in Europe under the name ‘black radish’.

The so-called ‘rat-tailed radish’, grown for its green or purple 20–60 cm long pods, is rather important in India and eastern Asia, but only of minor importance for Asian immigrants in East Africa, where it is called ‘mogri’. Finally, the so-called ‘leaf radish’ is gaining importance in Europe and South Africa as forage and green manure but is not known to be cultivated in tropical Africa.

In summary, radish occurs scattered throughout Africa; it has been recorded for over a dozen countries, from Mali to Eritrea, and southwards to South Africa and the Indian Ocean islands, but is probably cultivated in many more. It is commonly recorded as an escape from cultivation.

Uses

Radish is grown mainly for its thickened fleshy root. Small radishes are pungent and used as appetizer when eaten fresh and for adding colour to dishes. Oriental radish (to which Chinese radish, Japanese radish and mooli belong) is crisp with a mild flavour. The roots are thinly peeled, sliced or diced and put into soups and sauces or cooked with meat. They can be preserved in salt. Oriental radish can also be eaten fresh, mixed with other vegetables such as tomato. Also the leaves are eaten as salad or spinach. Seedlings known as radish sprouts are used as greens for appetizers in the same way as cress (Lepidium sativum L.) or cooked as spinach. Rat-tailed radish is grown for the immature crisp, fleshy fruits, consumed raw, cooked or pickled, but the roots are not edible. Leaf radish is mainly grown as green manure and forage in central and western Europe and is also grown as fodder for cattle in South Africa. There are forms of radish that are used as an oil-seed crop but these are not known to be grown in Africa. In traditional medicine, radish is used to treat hepatic disorders, bronchitis and coughs.

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. In Japan, Korea and Taiwan, but also in Yemen, radish ranks high in importance. No production data are known from tropical Africa but its significance is minor when compared with Asia or Europe.

Properties

The composition of the raw root of white radish (mooli) per 100 g edible portion (87% of the product as purchased) is: water 93.0 g, energy 64 kJ (15 kcal), protein 0.8 g, fat 0.1 g, carbohydrate 2.9 g, fibre 1.5 g, Ca 30 mg, P 25 mg, Fe 0.4 mg, carotene 0 μg, thiamin 0.03 mg, riboflavin 0.02 mg, niacin 0.5 mg, ascorbic acid 24 mg. The composition of the raw leaves per 100 g edible portion (90%) is: water 89.7 g, energy 137 kJ (33 kcal), protein 3.5 g, fat 0.5 g, carbohydrate 3.5 g, Ca 200 mg, P 44 mg, Fe 3.8 mg, carotene 3670 μg, thiamin 0.13 mg, riboflavin 0.35 mg, niacin 0.8 mg, ascorbic acid 63 mg (Holland, B., Unwin, I.D. & Buss, D.H., 1991).

The pungency of radishes depends on the content of isothiocyanates, which varies with cultivar and environmental conditions. The main compound is 4-methylthio-3-trans-butenyl isothiocyanate. Glucosinolates, which are the precursors of isothiocyanates, are also present. These compounds have long been known for their fungicidal, bactericidal, nematicidal and allelopathic properties, and have recently attracted attention because of their chemoprotective attributes against cancer.

Description

Erect, annual herb up to 100 cm tall; upper part of taproot and hypocotyl swollen, tuberous, globular, cylindrical or tapering, very variable in size (up to 100 cm long), form and weight (from a few g to 2.5(–20) kg), red to white, sometimes grey to black, flesh white, sometimes red. Leaves alternate, glabrous to sparingly hispid, lower leaves in a radical rosette; stipules absent; petiole 3–5.5 cm long; blade 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-spatulate, more or less dentate. Inflorescence a terminal, erect, long, many-flowered raceme. Flowers bisexual, 4-merous, c. 1.5 cm in diameter, fragrant, white to lilac; pedicel up to 2.5 cm long; sepals free, oblong-linear, 6–10 mm long; petals free, spatulate, clawed, 1–2 cm long; stamens 6, 4 long and 2 short; ovary superior, style 3–4 mm long. Fruit cylindrical, up to 10(–60) cm × 1.5 cm, consisting of 2(–several) superposed joints, lower joint very short and seedless, upper one much larger, terete, spongy and divided into 2–12 one-seeded compartments, indehiscent, with a long, seedless beak. Seeds ovoid-globose, c. 3 mm in diameter, yellowish.

Other botanical information

Radish is derived from the variable wild radish Raphanus raphanistrum L., which is frequently found as a weed in cooler parts of Africa and may act as a host for a range of pests and diseases affecting cruciferous crops. Raphanus is closely related to Brassica and it has been hypothesized that it was derived from hybridization between the Brassica rapa L. / Brassica oleracea L. complex and Brassica nigra (L.) Koch. This hypothesis is also supported by results of DNA sequencing. The taxonomy of Raphanus sativus is still confusing and further research is needed.

Some cultivars adapted to the tropics and used in Africa are the small radishes ‘Cherry Belle’ or ‘Radis Cerise’ (red and round), ‘Sparkler’ (round with a red top and white base), ‘French Breakfast’ or ‘Radis 18 Jours’ (similarly red/white but more cylindrical), ‘White Icicle’ (long and white, with a mild taste), and the mooli types ‘Red Bombay’, ‘White Bombay’, ‘Bombay Long White’, ‘Ural’ and ‘Himalaya’.

Growth and development

The edible part consists of the thickened hypocotyl (small radish) or of the thickened hypocotyl and upper part of the taproot (Chinese radish). Growing time depends on cultivar and desired product. Small radishes can be harvested 3–5 weeks after sowing whereas Chinese radishes usually take about 8–10 weeks from sowing till harvesting. At first the leaves grow in a rosette, but towards anthesis the stem elongates and branches. Flowers are cross-pollinated by insects.

Ecology

Radish is a vegetable of temperate regions, performing best in the tropics at higher latitudes (>10°) during the cool season and in highlands above 1000 m. Chinese radish or mooli tolerates higher temperatures than the Japanese or European types and produces well at lower elevations in East Africa. Under short daylength conditions, the roots are well shaped and tops small. Under long days (>15 hours) the roots can be misshapen, the tops elongate and pre-mature bolting may occur. Radish normally needs low temperature and a long daylength for bolting, but most radish types flower, although rather poorly, after reaching the edible size. Temperate types need at least 20 days below 15°C and a daylength of >16 hours for good seed setting, but for tropical cultivars of Chinese radish and mooli, bolting requirements are met at higher temperatures and short daylengths. White-fleshed cultivars flower more easily under short days at low elevations than red-fleshed cultivars, which require long days or elevations above 1000 m. Radish requires light, well-drained, deep soils with a pH of 6.0–6.5.

Propagation and planting

The 1000-seed weight is about 10 g. Seed rates are 10–15 kg/ha for large radishes and 30–40 kg/ha for small ones. Seed is sown directly on prepared beds in drills. Radish seeds take about 4 days to emerge at 20–30°C. Mooli types require a rather wide spacing of 30 cm between rows and 15–25 cm between plants, depending on the cultivar. Small 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.

Management

In commercial cultivation, radish is normally grown as a sole crop, but intercropping with lettuce is also practised in many areas. Adequate supplies of organic material, e.g. 20 t/ha, and a basal dressing of NPK followed by surface dressings of an N-fertilizer at regular intervals until the roots are mature, are recommended. A crop of 20 t/ha needs at least 250 kg N, 40 kg P and 350 kg K per ha. Too high levels of NPK increase the risk of pithiness unless moisture levels are kept high. To remain mild, tender and visually attractive, radish must grow rapidly with plenty of moisture. If growth is restrained, the roots become too pungent, tough and pithy. Light shading improves root quality during hot, dry weather. In heavy soils roots often become misshapen.

Diseases and pests

Common leaf diseases are Cercospora leaf spot (Cercospora brassicicola) and downy mildew (Peronospora parasitica). Downy mildew also attacks the tuberized part of the hypocotyl with black corky spots. It does not occur in the lowlands at day and night temperatures above 23°C and 12°C, respectively. Incorporating formulations of the systemic benzenoid fungicide metalaxyl with the seed at the rate of 4 g/kg seed just before sowing reduces field infestation of downy mildew. Serious root diseases in temperate areas are black rot (Aphanomyces raphani) and Fusarium yellows (Fusarium oxysporum f. raphani). Clubroot (Plasmodiophora) is increasingly a problem in tropical highlands in East and southern Africa on soils with a low pH. Important pests are flea beetles (Phyllotreta spp.), which attack young seedlings, aphids (Aphis gossypii, Lipaphis erysimi), which cause leaf curl and transmits cauliflower chlorotic ring virus, and mustard sawfly (Athalia proxima), which feeds on the leaves. Root-knot nematodes (Meloidogyne spp.) are sometimes a problem, but can be controlled by crop rotation and heavy organic manure application.

Harvesting

Radish must be harvested when fully developed but before the roots become over-mature and pithy or tough. It may be harvested with or without leaf tops. Small radishes can be harvested mechanically, uprooted, trimmed and bunched in one operation, but small scale gardeners harvest manually. Leaves are harvested when required.

Yield

Approximately 7–10 t/ha of fresh radish can be achieved for early-maturing cultivars of small radish. Yields of mooli types vary between 15–20 t/ha and more when roots are left in the field for a longer time.

Handling after harvest

Radishes are washed thoroughly to remove soil and to maintain a fresh appearance, followed by grading and packaging. Small radishes are usually sold with tops and these are tied in bunches. Their leaves should be turgid, green, and free from blemishes. The larger Chinese radish types and the Spanish black types are sold by weight or individually, especially for the larger roots. Fruits of rat-tailed radishes are offered loose but these are only occasionally found in markets, e.g. in Nairobi. 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, which is why some supermarkets now offer radishes without leaves.

Genetic resources

Germplasm collections are maintained by NIAR (Tsukuba, Japan), IPB (Los Baños, Philippines), Department of Agriculture (Bangkok, Thailand), USDA (Fort Collins, United States), and the Crucifer Genetics Cooperatives at the University of Wisconsin (Madison, United States). No local cultivars are known in tropical Africa.

Breeding

Although radish flowers and sets seed easily in most African countries where it is grown, virtually all seed is imported. No special breeding for adaptation to African conditions has been reported. For economic reasons radish seed is normally produced in more temperate climates and imported in tropical Africa. 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, especially the Chinese and mooli types, can successfully be cultivated in many places in tropical Africa. Although at the moment of relatively little importance, radish consumption will probably steadily increase. Breeding of heat-tolerant cultivars for cultivation in African lowland areas is recommended.

Major references

• Banga, O., 1976. Radish. In: Simmonds, N.W. (Editor): Evolution of crop plants. Longman, London, United Kingdom. pp. 60–62.

• Hadfield, J., 1960. Vegetable gardening in Central Africa. Purnell & Sons, Cape Town, South Africa. 178 pp.

• Herklots, G.A.C., 1972. Vegetables in South-East Asia. George Allen & Unwin, London, United Kingdom. 525 pp.

• Holland, B., Unwin, I.D. & Buss, D.H., 1991. Vegetables, herbs and spices. The fifth supplement to McCance & Widdowson’s The Composition of Foods. 4th Edition. Royal Society of Chemistry, Cambridge, United Kingdom. 163 pp.

• Kasem Piluek & Beltran, M.M., 1993. Raphanus sativus L. In: Siemonsma, J.S. & Kasem Piluek (Editors). Plant Resources of South-East Asia No 8. Vegetables. Pudoc Scientific Publishers, Wageningen, Netherlands. pp. 233–237.

• Larkcom, J., 1991. Oriental vegetables. The complete guide for garden and kitchen. John Murray, London, United Kingdom. 232 pp.

• Phillips, R. & Rix, M., 1993. Vegetables. Pan Books, London, United Kingdom. 270 pp.

• Tindall, H.D., 1983. Vegetables in the tropics. Macmillan Press, London, United Kingdom. 533 pp.

• Zeven, A.C. & Zhukovsky, P.M., 1975. Dictionary of cultivated plants and their centres of diversity. Pudoc, Wageningen, Netherlands. 219 pp.

Other references

• Burkill, H.M., 1985. The useful plants of West Tropical Africa. 2nd Edition. Volume 1, Families A–D. Royal Botanic Gardens, Kew, Richmond, United Kingdom. 960 pp.

• Fahey, J.W., Zalcmann, A.T. & Talalay, P., 2001. The chemical diversity and distribution of glucosinolates and isothiocyanates among plants. Phytochemistry 56(1): 5–51.

• FAO, 1988. Traditional food plants: a resource book for promoting the exploitation and consumption of food plants in arid, semi-arid and sub-humid lands of Eastern Africa. FAO food and nutrition paper 42. FAO, Rome, Italy. 593 pp.

• Pistrick, K., 1987. Study of the systematics of the genus Raphanus L. Untersuchungen zur Systematik der Gattung Raphanus L. Kulturpflanze 35: 225–321.

• Popovic, M., Lukic, V., Jakovljevic, V. & Mikov, M., 1993. The effect of the radish (Raphanus sativus ssp. niger) juice on liver function. Fitoterapia 64(3): 229–231.

• Yang, Y.W., Tai, P.Y., Chen, Y. & Li, W.H., 2002. A study of the phylogeny of Brassica rapa, B. nigra, Raphanus sativus, and their related genera using noncoding regions of chloroplast DNA. Molecular Phylogenetics and Evolution 23(2): 268–275.

Sources of illustration

• Vaughan, J.G. & Geissler, C.A., 1997. The new Oxford book of food plants. Oxford University Press, Oxford, United Kingdom. 239 pp.

Author(s)

• R.R. Schippers

De Boeier 7, 3742 GD Baarn, Netherlands

Correct citation of this article

Schippers, R.R., 2004. Raphanus sativus L. [Internet] Record from PROTA4U. Grubben, G.J.H. & Denton, O.A. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. <http://www.prota4u.org/search.asp>.

Accessed 23 December 2024.

• See the Prota4U database.