Eleocharis dulcis (PROSEA)
Eleocharis dulcis (Burm.f.) Trinius ex Henschel
- Protologue: Vita Rumphii: 186 (1833).
- Family: Cyperaceae
- Chromosome number: 2n= 64
- Eleocharis plantaginea Roemer & Schultes (1817),
- E. tuberosa Roemer & Schultes (1824),
- Heleocharis plantaginoidea W.F. Wight (1905).
- Chinese water chestnut (En)
- Indonesia: teki (Indonesian), peperetan (Javanese), babawangan (Sundanese)
- Malaysia: tike
- Philippines: apulid (Tagalog, Bikol), pagappo (Ibanag), buslig (Bisaya, Ilokano)
- Cambodia: mëm phlông
- Thailand: haeo (general), haeo-chin (central)
- Vietnam: mã thày, năn ngọt, năng.
Origin and geographic distribution
Chinese water chestnut is a widespread variable species of the Old World tropics, distributed from tropical West Africa and Madagascar through India eastwards to south-eastern China, Japan, South-East Asia, northern Australia, Micronesia and Melanesia.
Chinese water chestnut (tuber or corm) is used as a vegetable both raw or cooked in numerous local dishes such as omelets, soups, salads, meat and fish dishes, and even in sweet dishes in China, Indo-China, Thailand and other parts of South-East Asia. The larger corms are widely eaten raw as a substitute for fresh fruits. The smaller corms are used principally for making starch. In Indonesia and the Philippines, the corms are usually made into chips ("emping teki"). Stems are used for making sleeping mats (Sumatra, Sulawesi) and skirts (Papua New Guinea). They are also used as cattle feed or as mulch. The juice expressed from the corms contains antibiotic "puchiin", which is effective against Staphylococcus aureus, Escherichia coli, and Aerobacter aerogenes.
Production and international trade
Chinese water chestnut is a locally important crop in most countries in South-East Asia, India, China, Hong Kong, Taiwan, Hawaii and the southern United States. No statistics are available on production and trade.
Data on the nutritive value of corms from different regions show wide variation. Per 100 g edible portion the peeled corms contain: water 77.3-78.3 g, protein 1.4-1.5 g, fat 0.15-0.20 g, carbohydrates: starch 7-19 g, reducing sugar 1.94 g, sucrose 6.35 g, fibre 0.8-0.9 g, ash 1.1-1.2 g, Ca 4.0 mg, P 65 mg, Fe 0.6 mg and vitamin C 4.0 mg. The energy value is 328 kJ per 100 g. Starch grains are round, regular or irregular, up to 27μm long.
- A perennial, rhizomatous, semi-aquatic herb, often grown as an annual crop.
- Rhizome short with elongated stolons, each one often terminating in a zoned, depressed globose, brownish to blackish corm, 1-4 cm in diameter.
- Stem erect, terete, tufted, 40-200 cm tall, 3-10 mm in diameter, longitudinally striate, distinctly transversely septate, the intersepta 5-12 mm long, hollow, smooth, greyish to glossy dark green.
- Leaves reduced to some bladeless basal sheaths, 3-20 cm long, membranous, oblique or truncate at the apex, reddish brown to purple.
- Inflorescence a single, terminal, many-flowered spikelet, cylindrical, 1.5-6.0 cm × 3-6 mm, as thick as or somewhat thicker than the stem, apex obtuse to acute; glumes numerous, oblong, 4.0-6.5 mm × 1.7-3.2 mm, densely imbricate.
- Flowers bisexual, with perianth of 6-8, filiform, unequal, white to brown bristles; stamens 3, anthers linear, 2-3 mm long; style 7-8 mm long, 2-3-fid, the enlarged base persistent in fruit.
- Fruit an obovoid nut (achene), 1.5-2.2 mm × 1.2-1.8 mm, shiny yellow to brown.
Growth and development
About 6-8 weeks after corms have been planted they develop short subterranean rhizomes which start producing a number of daughter plants close to the mother stem, resulting in a clump. Because the plant does not develop normal leaves, the photosynthetic activity takes place in the numerous stems. When stems protrude about 15 cm above the surface of the water, they start forming inflorescences at their tips. Shortly after flowering, plants start producing corms at the end of about 12.5 cm long stolons which grow downwards into the mud at an angle of 45°to the surface of the mud. About 7-8 months after planting, the new corms are mature and the stems turn brown and eventually die.
Other botanical information
E. dulcis is extremely polymorphic, widely distributed and also extensively cultivated. The wild forms usually produce only very small, almost black corms up to 1 cm in diameter. The cultivated forms have more robust stems and larger, sweeter, purplish to brownish corms, up to 4 cm in diameter and about 2.5 cm long.
In Japan the cultivated form has been classified as var. tuberosa (Roxb.) T. Koyama but classification into cultivar groups and cultivars would be more appropriate.
In the literature Eleocharis can sometimes be found as Heleocharis.
Chinese water chestnut occurs in open places both in salt or brackish and in fresh water swamps, often forming pure stands surrounding the open water, from sea-level up to 1350 m altitude and as far as 40°N latitude in China. A long warm growing season with at least 220 frost-free days is needed for plant growth. Corms will only sprout at soil temperatures above 14°C. The field should be kept inundated for at least 6 months. Preferred soils are rich clay or muck soils with a pH of 6.9-7.3. Chinese water chestnut can be grown successfully in slightly more acid soils provided that these are limed.
Propagation and planting
Chinese water chestnut can be propagated by corms and by seed. For planting material, corms are dug out, dried in the shade for 2-3 days, then soaked in clean water for 2 days and planted in a nursery bed, 2-3 cm apart under light shade. When the young sprouts are 5-15 cm tall they are transplanted to a second nursery bed in rows 50 cm apart. The media used in the nursery beds could be rice husk charcoal, saw dust, or cocopeat and sand in a 1:1 ratio. Young plants can be transplanted to the permanent field when they are 3-5-stemmed or 15-20 cm tall. Spacing is rectangular at 50-100 cm × 50-100 cm or triangular at 45-60 cm × 45 cm. After planting, the field is flooded for 24 hours and then allowed to drain naturally.
As soon as the top growth reaches 20-30 cm height, the field must be kept permanently flooded and the water level at 10-12.5 cm until harvest. A pre-emergence herbicide is recommended at 7 days after transplanting to the field; regular hand weeding is also needed for about 1 month until the ground between plants is covered. Heavy applications of fertilizers are common in commercial production of Chinese water chestnut. In the United States, a high grade complete fertilizer at the total rate of 2.5 t/ha is recommended. In Thailand, the following practices are followed: 150-160 kg/ha of NPK 16-20-0 or 20-20-0 are applied 20 days after transplanting, 150-160 kg/ha of NPK 13-13-21 are applied when the plants begin to produce short lateral rhizomes with secondary plantlets, and 300-320 kg/ha of NPK 9-24-24 are applied when new corms are being formed.
Diseases and pests
Diseases and pests are common but rarely serious on Chinese water chestnut. Fusarium wilt and stem blight have been reported from China. In the United States, plants grown on acid soils (pH 5.5) are subject to attack by a stem fungus (Cylindrosporium sp.). In Thailand, diseases common in rice are also found on Chinese water chestnut, including foot rot, stem spot, downy mildew, yellow orange leaf virus and stem blight.
The billbug (Calendra cariosa), the stem nematode (Ditylenchus sp.), and the awl nematode (Dolichodorus heterocephalus) are reported to attack the crop. In the Philippines, it is sometimes attacked by a grasshopper (Ailopus tamalus). Common insect pests on Chinese water chestnut in Thailand are brown planthopper, whitebacked planthopper, green leafhopper and stem borers. Rodents, especially rats, can cause considerable losses at harvest.
Harvesting normally takes place at 7-9 months after transplanting to the field or after the stems have turned brown or been killed by frost. Usually, irrigation is stopped at least 3-4 weeks before harvest so that the field dries out. Harvesting may be delayed, since the corms do not deteriorate in the soil if they are not subjected to severe frost. In the United States, harvesting is carried out mechanically by a small plough and a rake. In China, two methods of harvesting are used for different cultivars. For the larger corm type, the water is drained off the field before harvest to permit the field to dry. At times it is flooded again and then allowed to dry a second time. This is believed to raise the sugar content of the corms. For the smaller corm type, harvesting is done without any prior draining of the water; the farmer wades in knee-deep mud and stoops over to claw out the corms by hand.
Average annual corm yield varies considerably from place to place: 20-40 t/ha in China, 28 t/ha in the United States, and 25-38 t/ha in Thailand.
Handling after harvest
Harvested corms are washed and dried in the shade before marketing. They can be kept satisfactorily up to 6 months at temperatures between -1°C and 4°C in moisture-proof, but not airtight containers. They will start sprouting if stored at 14°C or higher.
For commercial processing, dry corms are peeled and then processed similarly to potatoes. They can be canned or deepfrozen (at -18°C and kept for 12 months). In China, a simple method of starch extraction is practised. The corms are washed, crushed and the starchy mass transferred into a fine bamboo basket which is placed on a filter cloth and hung over a fire. Water is passed through the basket and the contents stirred for 15 minutes. The starchy water is collected and after standing for 5 hours, the starch has separated out and can be dried in the sun.
Genetic resources and breeding
At present, no germplasm collections or breeding programmes of Chinese water chestnut are known to exist. However, there is ample opportunity for breeders to improve both quantity and quality due to the enormous variation throughout the range of distribution.
Chinese water chestnut is one of the most popular vegetables among the Chinese around the globe and also among the people in South and South-East Asia and Oceania. In view of such a large number of consumers, there is quite a potential to develop the crop and to promote it for the international market. It is also one of the few crops that can be grown under aquatic condition like rice, but with better returns. It could be an interesting cash crop in places where the return from rice is low.
- Champangern, P., Sasiprapa, W., Sowan, S. & Duangpiboon, P., 1988. Plook haeo-cheen thee Supan Buri [Cultivating Chinese water chestnut in Supan Buri Province, Thailand]. Kasikorn 62(6): 515-519.
- Hodge, W.H., 1956. Chinese water chestnut or matai - a paddy crop of China. Economic Botany 10(1): 49-65.
- Kay, D.E., 1973. Crop and product digest No 2: Root crops. Tropical Products Institute, London, United Kingdom. pp. 43-49.
- Kern, J.H., 1975. Cyperaceae. In: van Steenis, C.G.G.J. (Editor): Flora Malesiana. Series I. Vol. 7. Noordhoff International Publishing, Leyden, the Netherlands. pp. 529-531.