Dioscorea hispida (PROSEA)
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Introduction |
Dioscorea hispida Dennst.
- Protologue: Schlüss. Hort. Malab.: 15 (1818).
- Family: Dioscoreaceae
- Chromosome number: 2n= 40
Synonyms
Dioscorea triphylla L. (1754, not of Sp. pl., 1753), D. hirsuta Dennst. (1818), D. daemona Roxb. (1832).
Vernacular names
- Asiatic bitter yam, intoxicating yam (En)
- Indonesia: gadung (general), sikapa (Bali, Sulawesi), ondo (Ambon)
- Malaysia: ubi arak, gadongan, gadong mabok
- Philippines: nami (Tagalog), gayos (Bisaya), karot (Ilokano). Burma (Myanmar): kywe
- Cambodia: dâmlô:ng k'duöch (western)
- Laos: hwà ko:y (northern)
- Thailand: kloi (central), kloi-nok (northern), kloi-huanieo (Nakhon Ratchasima)
- Vietnam: củnê.
Origin and geographic distribution
D. hispida occurs naturally from India and southern China, through South-East Asia to New Guinea. There is no appreciable distribution or cultivation outside this area. Even in South-East Asia the plant is scarcely cultivated, so its spread is practically confined to its area of natural occurrence.
Uses
The tuber of D. hispida is the chief famine food of tropical Asia, as is D. dumetorum (Kunth) Pax for Africa. The tuber is poisonous because of a high content of the alkaloid dioscorine. Its preparation for food requires much time and skill and includes slicing, washing the fresh or boiled tuber in several changes of salt water, or in running water, and a final check on whether all poison has been removed. Starch extracted from the tubers can be used for culinary or industrial purposes, notably the manufacture of glucose.
The poison in the tubers is often extracted and used as bait for animals or other devious purposes. It is also used for eliminating fish from shrimp pond cultures. The pounded tubers are sometimes used externally as an antiseptic, and a decoction is drunk to alleviate chronic rheumatism.
Production and international trade
Most of the D. hispida used is gathered from the wild in times of food scarcity, and there are hardly any production statistics. Virtually all that is harvested is used and traded locally, with little or none entering into international trade.
Properties
The approximate composition of the tuber per 100 g edible portion is: water 78 g, protein 1.81 g, fat 1.6 g, carbohydrates 18 g, fibre 0.9 g, and ash 0.7 g. On a dry weight basis, the tuber also contains 0.2-0.7% diosgenin and 0.044% dioscorine; these poisons can cause paralysis of the central nervous system. Commercial starch extracted from the tubers contains 88.34% starch, 5.28% protein, 5.33% fibre, 0.23% fat, and 0.66% ash. Some tubers from India have been found to contain ovoid, non-stratified starch grains with a longitudinal diameter of 35-40μm, and a gelatinization temperature of 85°C. Unlike cassava or potato starches, its viscosity does not decline appreciably after prolonged heating. Its amylose content has been reported as 10.24%.
Description
Climbing herb with a fibrous root system. Tubers renewed annually from a superficial corm, from which they grow as lobes, in outline globose, sometimes slightly elongated, pale yellow to light grey; flesh white to lemon-yellow. Stem twining to the left, firm, 9 mm or more in diameter, usually prickly, drying bright yellowish, glabrescent. Bulbils absent. Leaves trifoliolate, herbaceous to chartaceous, pubescent; middle leaflet oblong-elliptical (rarely obovate or tripartite), up to 30 cm × 28 cm, acuminate; lateral leaflets inequilateral, the outer half 3-nerved; petiole usually longer than the middle leaflet, usually with small prickles on the back; petiolules up to 1 cm long. Male inflorescence spike-like, on leafless branches, 2-3-compounded, up to 50 cm long, with closely packed or spaced sessile flowers, fertile stamens 6. Female inflorescence solitary from upper leaf axils, pendulous, with flowers spaced. Fruit a large woody capsule, honey-coloured, 3-winged, facing upwards; wings 40-60 mm × 10-12 mm, margin sometimes freed in dehiscence. Seed winged.
Growth and development
Presumably, D. hispida follows a similar pattern of growth and development as other yams, i.e. emergence from the planted tuber and early root development are followed by extensive shoot growth, then tuber differentiation, bulking, and maturity. The crop is ready for harvest after 12 months.
Other botanical information
D. hispida is quite variable and 4 botanical varieties are distinguished:
- var. hispida : vigorous plants with long male inflorescences; flowers spaced; hairs honey-coloured; capsules truncate or retuse at apex; universal in South-East Asia.
- var. mollissima (Blume) Prain & Burkill: like var. hispida but hairs white and denser; from Burma (Myanmar) to Java, in similar localities to where var. hispida grows.
- var. scaphoides Prain & Burkill: less vigorous than var. hispida with much smaller, acute capsules; in Thailand.
- var. dalmona (Roxb.) Prain & Burkill: male spike dense, terminal flowering part less than twice as long as thick; foliage herbaceous; from India to Burma (Myanmar) and perhaps scattered elsewhere.
Ecology
D. hispida occurs mostly in rain-forest areas. It is found mainly at lower elevations in the Philippines, but has been found growing at altitudes of up to 1200 m in the Himalayas.
Agronomy
D. hispida perennates in the wild by means of the tuber. It is also propagated in cultivation by means of the tuber. As with other yams, best yields are obtained if planted on mounds or ridges. In cultivation, the crop is usually staked. Weeding is done at regular intervals, but the use of fertilizers is rare. No serious diseases and pests are known, only minor leaf spots have been reported. Harvesting occurs from wild stands, or from cultivated plants that are 12 months or older. Manual harvesting with the aid of a fork or digging stick is the usual practice. Individual tubers weigh 5-16 kg, but may be fused together into irregular clusters weighing up to 35 kg. Yields of up to 20 t/ha are obtainable. It has been suggested that the preparation of flour or starch from the tubers should proceed as follows: washing of the tubers, pulping, treating with lime water containing potassium permanganate, and final separation.
Genetic resources and breeding
Germplasm collections are available in Malaysia (Malaysian Agricultural Research and Development Institute (MARDI), Serdang) and in Puerto Rico (Mayaguez Institute of Tropical Agriculture (MITA), Mayaguez). For food, it would be desirable to breed for reduced alkaloid content so that the tubers can be consumed without elaborate detoxification procedures. Breeding for a higher starch content would also be useful both for food and industrial purposes.
Prospects
The present use for food of D. hispida continues to be hampered by the poisonous nature of the tubers, and the easier availability of other yams. Use for commercial starch extraction is limited because of the low starch content, the low intensity of cultivation/production, and the very wide area over which the production is scattered. Commercial extraction and use of dioscorine and diosgenin in the tuber is at present not economically feasible. D. hispida holds promise as a source of genetic material for various breeding programmes.
Literature
- Burkill, I.H., 1951. Dioscoreaceae. Dioscorea hispida. In: van Steenis, C.G.G.J. (Editor): Flora Malesiana. Series 1. Vol. 4. Noordhoff-Kolff, Djakarta, Indonesia. pp. 318-320.
- Kay, D.E., 1973. Crop and product digest 2: Root crops. Tropical Products Institute, London, United Kingdom. pp. 220-223.
- Onwueme, I.C., 1978. The tropical tuber crops. Wiley, Chichester, United Kingdom. pp. 3-106.
- Rao, P.S. & Beri, R.M., 1952. Tubers of Dioscorea hispida Dennst. The Indian Forester 78(3): 146-152.
Authors
I.C. Onwueme
