Colocasia esculenta (PROSEA)

Plant Resources of South-East Asia
Introduction

List of species

Colocasia esculenta (L.) Schott

Protologue: Schott & Endl., Melet. bot.: 18 (1832).

Family: Araceae

Chromosome number: 2n= 28

Synonyms

Colocasia antiquorum Schott (1832),
Colocasia esculenta (L.) Schott var. antiquorum (Schott) Hubb. & Rehder (1939).

Vernacular names

Taro, old cocoyam, dasheen, eddoe (En)
Taro (Fr)
Indonesia: bentul, talas, keladi
Malaysia: keladi, keladi china, birah keladi
Papua New Guinea: anega, ba, biloun
Philippines: gabi (Tagalog), abalong (Bisaya), natong (Bikol)
Cambodia: tra:w
Laos: bo:n, phüak
Thailand: phuak (general), bon-nam (southern), tun (northern)
Vietnam: khoai nước, môn nước, khoai sọ.

Origin and geographic distribution

Taro originated in South-East or southern Central Asia, where it was probably cultivated before rice. Today taro is grown throughout the West Indies and in West and North Africa. In Asia, it is widely planted in south and central China and is grown to a lesser extent in India. It is now a staple food in many islands of the Pacific including Papua New Guinea, where it has prestigious as well as economic value, playing an important role in traditional gift-giving and ceremonies. In Indonesia, taro is a staple food on the Mentawai Islands and for Melanesians in Irian Jaya. It is cultivated to a lesser extent in Bogor and Malang in Java and on Bali. In Malaysia, taro has been used for more than 2000 years and is now found throughout the country. Taro is grown throughout the Philippines but is most important in eastern and central Visayas and the Mindanao and Bikol regions.

Uses

The primary use of taro is as a food plant. When cooked, taro corms, cormels, stolons, leaf blades and petioles can be eaten. Most taro in South-East Asia is consumed by humans, but it also has uses in religious festivals and is fed to livestock, primarily pigs. Waste leaves, corms and peel can be cooked or fermented into silage for animal feed. Because it is easily digested and practically non-allergenic, taro can be used by persons with digestive problems. Taro corm puree makes an excellent baby food. A marked improvement in dental condition and a reduced incidence of pneumonia, diarrhoea, enteritis and beri-beri has been observed for babies fed with taro instead of bread and rice. The fine taro starch can be used as a soup thickener, for the production of alcohol and biodegradable plastics. The leaves are used as a wrapper for steamed food.

In areas of Indonesia where rice is not grown, taro is eaten as a staple, baked, boiled or cooked in bamboo tubes. In Java, confections are prepared from taro flavoured with coconut and sugar; fried taro slices and taro chips are popular snacks. The leaves are used in preparing "buntil" (salted fish with spices, grated coconut and vegetables, wrapped up and steamed in a taro leaf), and petioles are cooked. In Malaysia, taro is cooked in similar ways and also plays a role in religious festivals. Leaves are boiled and eaten as salad with spicy sauce, and petioles are cooked with coconut milk, meat and prawns. Taro in the Philippines is used primarily when more popular starches and green vegetables are in short supply. Corms are boiled, chipped and fried or made into confections. In Hawaii and parts of Polynesia, the corms are cooked and pounded into a paste that is allowed to ferment to produce "poi". A steamed pudding is made from grated taro and coconut.

Several uses of taro in traditional medicine are known for India, China and New Guinea. The corms are used to treat stomach-ache, diarrhoea, and as a poultice on sores and skin diseases. Chopped, tied in a cloth and heated the corms are used to treat rheumatism. The corm juice is used in cases of baldness, piles, as a laxative, and as an antidote to insect stings. Stems and leaves are applied to wounds including snakebites. Leaves are applied to burns, and are eaten to treat sore throat, dysentery and stomach-ache. The juice from the petioles is considered styptic and used to arrest arterial haemorrhage, and also to treat earache, inflamed glands, boils and as an external stimulant and rubefacient. The leaves are used for wrapping up a bolus of mustard-seed and garlic to be used as a prophylactic after childbirth. Several cultivars are decorative ornamentals.

Production and international trade

No reliable statistics are available on world and national production and price. FAO reports a world production of 5.6 million t from 1 million ha in 1992. In SouthEast Asia, taro is grown predominantly by smallholders, and there is potential and interest in expansion. For example in Indonesia, taro and other root crops are being promoted to reduce dependence on rice. In Papua New Guinea, taro is produced in both the lowlands and highlands with a total annual production in 1993 of about 438 000 t on 77 000 ha. In the Philippines, 112 000 t were produced on 33 000 ha in 1992.

Properties

Taro contains enzyme inhibitors, particularly with inhibitory activities against trypsin and chymotrypsin, but these are largely destroyed during cooking. Growth retardation was found in mice fed with lectin from taro corms. An α-D-galactosidase capable of converting group B red blood cells into group O, without apparent changes in the shape of the red blood cells, was isolated from the stem of taro. Taro leaves showed an aggravating effect on serum and tissue lipids in cholesterol-fed rats; there was a significant increase in total lipids, total cholesterol and triglyceride levels.

If eaten raw or undercooked, all parts of the plant are acrid and will irritate the mouth and throat, but acridity is reduced or eliminated by cooking and fermenting. The cause of acridity is still uncertain, but it is thought to be related to bundles of needleshaped crystals of calcium oxalate and one or more chemicals associated with them. Taro is easily digested, practically non-allergenic and has very small starch particles, diameter 1-6.5μm. Per 100 g edible portion (fresh) corms contain approximately: water 70 g, protein 1.1 g, carbohydrates 26 g, fibre 1.5 g, vitamin C 15 mg. The energy value averages 475 kJ per 100 g. Leaves contain 4.2 g protein.

Description

An erect, herbaceous plant growing to a height of 1 m or more, perennial, but most often grown as an annual.
Root system adventitious, fibrous, and shallow.
Storage stem (corm) massive (up to 4 kg), cylindrical or spherical, up to 30 cm × 15 cm, usually brown, with lateral buds located above leaf scars giving rise to new cormels, suckers or stolons.
Leaves arranged spirally, rosulate, simple, peltate consisting of long (sometimes over 1 m) petiole with distinct sheath, and large, heartshaped blade, up to 85 cm × 60 cm, with rounded posterior lobes.
Inflorescence a spadix tipped by a sterile appendage, surrounded by a spathe and supported by a peduncle that is shorter than the petioles.
Flowers unisexual, small, without perianth; male flowers in upper part of spadix, with stamens entirely connate; female flowers at base of spadix, with superior, 1-celled ovary with 36-67 ovules and an almost sessile stigma; male and female flowers separated by a band of white sterile flowers; more white sterile flowers scattered in the female region.
Fruiting head a cluster of densely packed berries, each containing 1-10(-35) seeds. Seed less than 2 mm long, ovate, and conspicuously ridged longitudinally, with copious endosperm.

Growth and development

Growth of leaves on main plants is slow during establishment, but is rapid from 1.5-2 months after planting, with most rapid leaf growth between 3-5 months after planting. During the fourth or fifth month, leaf size, leaf dry weight, leaf area, leaf area index (about 3) and plant height reach their maximum. Leaf number varies and there is a continuous turn-over of leaves. After peaking, leaves become smaller with shorter petioles and leaf number decreases. Main corm growth begins as early as 2 weeks after planting, with rapid corm growth beginning 2 months after planting under rainfed conditions and 3-5 months after planting under irrigated conditions. Corms reach maximum weight at 10-11.5 months when rainfed and 12-15 months when irrigated, but are usually harvested before this time.

Sucker growth generally begins 2.5 months after planting. The number of suckers depends on cultivar and management.

Other botanical information

Colocasia comprises 8 species from tropical Asia. It is classified in the tribe Colocasieae, together with e.g. Alocasia. There are 2 types of taro. The dasheen type has a large central corm with a few small cormels which are generally not eaten. The eddoe type produces a smaller central corm surrounded by large, welldeveloped cormels which are the main harvestable yield. Although the eddoe type is frequently classified as a separate species, C. antiquorum Schott, it is more generally accepted that it is a variety, C. esculenta var. antiquorum (Schott) Hubb. & Rehder, of a very variable species that includes both dasheens and eddoes.

In South-East Asia there are many taro cultivars, and these are distinguished by morphological characteristics as well as time taken to mature. Colour of corm flesh, lateral buds, petioles, and leaf blades are also used to differentiate cultivars.

Ecology

Taro tolerates a wide range of environments and management systems. When grown as a rainfed crop, best yields are obtained when rainfall is 2000 mm/year or more and evenly distributed. Taro also grows well in wetlands including paddies with a continuous supply of flowing water, furrow-irrigated fields, and raised beds in poorly drained swamps. Eddoes are often more drought-hardy than dasheens. Temperatures of 25-30 °C and high humidity favour growth. Taro is grown from sea-level up to 1800 m in the Philippines, 1200 m in Malaysia and 2700 m in Papua New Guinea, although it is very slow to mature at the latter altitude. In Papua New Guinea, it is as frost hardy as sweet potato. Taro is shade tolerant and is often grown as an intercrop with tree crops. Some cultivars tolerate high salinity. Taro grows on a variety of soils but good yields require high fertility. In Malaysia it is reported to tolerate soil pH 4.2-7.5.

Propagation and planting

Farmers propagate taro vegetatively. Corm pieces, whole small corms, cormels and stolons can be planted, but suckers and head-sets (corm apex plus 15-30 cm attached petiole bases) are usually preferred. Stolons are preferred in some parts of Malaysia. Large head-sets and suckers are generally more reliable than small ones, resulting in more vigorous growth and giving higher yields. Planting material should be taken only from healthy plants, avoiding plants with root or corm rots and obvious symptoms of dasheen mosaic virus.

When corms are marketed with head-sets attached, farmers depend on suckers for planting material. Management practices which provide adequate suckers are needed. Sucker number can be increased by wide spacing, shallow planting and nitrogen applied at a higher rate than recommended for maximum corm yield.

Planting is done in handdug holes or machinemade furrows or ridges; usually holes and furrows are only partially filled at planting. In South-East Asia, taro is grown primarily by smallholders either as a sole crop or intercropped with other crops. In Malaysia, taro may be intercropped between rows of coconut, oil palm and fruit trees, and in the Philippines with coffee, cocoa, coconut and fruit trees.

For breeding purposes, taro can be propagated from seed.

Taro can be grown at densities ranging from 4000-49 000 plants/ha. In SouthEast Asia, densities ranging from 6000-36 000 in rainfed production and 27 000-40 000 in wetlands have been reported. As plant density increases, total yield increases, but size of corm and number of suckers decrease. Spacings may be in the range of 30-100 cm » (30-)60-150 cm. Wider spacing is required if soil fertility or rainfall is low, and spacing must be adjusted for mechanization. Close spacing helps to control weeds and erosion.

Management

Farmers propagate taro vegetatively. Corm pieces, whole small corms, cormels and stolons can be planted, but suckers and head-sets (corm apex plus 15-30 cm attached petiole bases) are usually preferred. Planting is done in hand-dug holes or machine-made furrows or ridges. Taro can be grown at densities of 4000-49 000 plants/ha. Weeding is most important during the first 3-5 months after planting, but weeding during the final 2 months before harvest may reduce corm quality. Monthly removal of stolons increases corm yield. After fallow, the first two crops of taro usually do not require additional fertilizers, but on land which has been cropped longer, taro responds well to applied fertilizer, either inorganic or animal manures. Specific fertilizer recommendations based on soil characteristics must be determined for each location. However, a general fertilizer recommendation for taro grown on soil that has been cropped several times is 50-100 kg/ha N (split into 3 applications at 5, 10 and 15 weeks after planting), 50 kg/ha P (applied at planting), and 70 kg/ha K (applied at planting or split into 2 applications at planting and 10 weeks after planting). To avoid decreasing quality, there must be an interval of at least 3 months between the last fertilizer application and harvest.

In areas with below-optimal rainfall, mulching increases yield. Hilling during the growing season and irrigation of rainfed taro during prolonged drought may be practised. Rotation with vegetables, chillies and maize is popular in Malaysia.

Diseases and pests

Taro diseases and pests have not been adequately studied in SouthEast Asia. Phytophthora leaf blight and corm rot are more severe under wet conditions and are responsible for declining taro production in Papua New Guinea; fungicides, sanitation and increasing plant spacing can reduce damage. The lethal virus complex, Alomae and Bobone, kills or stunts plants in Papua New Guinea; roguing infected plants helps control. Pythium root and corm rot and dasheen mosaic virus are widespread in the Pacific. Resistant cultivars, selecting clean planting materials, crop rotation and fungicides are recommended for controlling Pythium.

Aphids and the planthopper Tarophagus proserpina damage plants as well as transmit virus diseases. Agrius convoluli, Hippotion celerio and other hornworms, as well as the cluster caterpillar, Spodoptera litura , can seriously defoliate plants; grasshoppers (Gesonia spp., Ocya sp.) and mites damage leaves, the latter especially during the dry season. Papuana beetle and termites (Coptotermes spp.) tunnel and feed in corms. "Mitimiti" caused by the nematode Hirschmanniella miticausa is found in Papua New Guinea; control is by cutting planting material with as little corm as possible.

Harvesting

Crop duration usually varies from 4-10 months for rainfed taro and 9-12 months for wetland taro. Cool temperatures delay maturity. Harvesting is done by hand.

Yields

Reported corm yields from research plots in South-East Asia vary from 2-17 t/ha; 30-60 t/ha have been reported from farms in Johore (Malaysia), and yields of 3-38 t/ha have been reported on subsistence farms in Papua New Guinea, with a national average of about 6 t/ha. However, yields are not well documented throughout the world. Yields for rainfed taro probably average about 5 t/ha, but 12.5-25 t/ha is common on fertile soils. Yields in wetlands are higher and up to 75 t/ha have been reported.

Handling after harvest

At ambient temperatures corms begin to spoil 1-2 weeks after harvest, but cool temperatures and high humidity prolong storage. Leaves and stolons are more perishable than corms.

Genetic resources

Germplasm collections of taro are maintained at the National University of Malaysia, the Philippine Root Crop Research & Training Center and the Bubia Research Station in Papua New Guinea.

Breeding

Worldwide there are only a few taro breeding programmes: University of the South Pacific (Western Samoa), Ministry of Primary Industries (Fiji), Ministry of Agriculture and Lands (Solomon Islands), and Bubia Research Station and Lae University of Technology (Papua New Guinea). Breeding objectives include increased yield, reduced acridity, extended maturity range, appropriate number of suckers, resistance to Phytophthora, Pythium, Alomae and Bobone and dasheen mosaic virus, improved eating quality and adaptation to lower soil fertility. Improved cultivars can be safely exchanged only as pathogentested tissue cultures.

Prospects

Further development and expansion will depend on government support for subsistence farming, food crops and diversified agriculture. Increased use by urban populations is dependent on development of low-cost, convenience foods and improved methods of storage and transport.

Although taro is fairly commonly used in traditional medicine, little or no research has been done on phytochemistry and pharmacological properties. The good digestibility and non-allergenic properties of taro make it an excellent substitute for bread and rice for persons sensitive for allergens from these products. However, some reports on adverse effects of taro warrant more research.

Literature

Ghani, F.D., 1980. The status of keladi China, Colocasia esculenta (L.) Schott, cultivation in Peninsula Malaysia. IFS Provisional Report No 5. International Foundation for Science, Stockholm, Sweden. pp. 35-54.
Ghani, F.D., 1981. Conservation and utilization of Colocasia spp. (cultivars) and edible aroids (keladi) in Malaysia. Tropical Root and Tuber Crops Newsletter 12, 13: 38-46.
Sastrapradja, S. & Hambali, G.G., 1980. Taro (Colocasia spp.) as a source of carbohydrate, vitamins and minerals in Indonesian diets. IFS Provisional Report No 5. International Foundation for Science, Stockholm, Sweden. pp. 17-28.
Villanueva, M.R. & Tupas, G.L., 1980. Taro production in the Philippines - its prospects and problems. IFS Provisional Report No 5. International Foundation for Science, Stockholm, Sweden. pp. 99-111.
Wang, J.K. (Editor), 1983. Taro, a review of Colocasia esculenta and its potentials. University of Hawaii Press, Hawaii. 400 pp.
Wilson, J.E., 1984. Cocoyam. In: Goldsworthy, P.R. & Fisher, N.M. (Editors): The physiology of tropical field crops. John Wiley and Sons, Chichester, United Kingdom. pp. 589-605.

162, 245, 597, 754, 837. medicinals

Other selected sources

121, 347, 760. medicinals

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Authors

J.E. Wilson & J.S. Siemonsma
Rosna Mat Taha