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Root crops (NRI, 1987, 308 p.)[edit]

Taro (Colocasia esculenta)[edit]

TARO, Dashe(e)n, Eddo(e), Old cocoyam.

Botanical name

Colocasia esculenta (L.) Schott.

Family

Araceae.

Other names

Abalong, Amalong (Philipp.); Arvi (Ind.); Barbados eddoe (W.l.); Bari (W. Afr.); Chinese eddoe (W.l.); Chinese sayer (Guyana); Chonque (Col.); Chou bouton (St. Lucia); Chou de Chine (W.l.); Colulu (Polyn.); Coco (Ant.); Cocoyam', Curcas (W.l.); Dagmay (Philipp.); Dalo (Fiji); Danchi (Venez.); Elephant's ear, Gabi, Gablos, Gahula (Philipp.); Guagui (Cuba); Igname (Fr. and It.); Imo (Japan); Inhame (Port.); Keladi (Mal.); Khoai au nu'oc bang, Khou-au ku'oc tuiang (Viet.); Koko (W. Afr.); Kolkas (Egypt); Kolokasi (Cy.); Linsa, Logbui, Lubingan (Philipp.); Mad�re (Carib.); Malanga(y), Malangu (C. Am.); Ocumo culin (Venez.); Pising (Philipp.); Quiquisque (Guat.); Qolq(u)as (Egypt); Satoimo (Japan); Taioba (Braz.); Taro de Chine (Indon.); Taro kalo, Tato (Fiji); Tayoba (Sp.); White eddoe (Barb.); Ya (China); Ya b�r� (W. Afr.); Yu-tao (China).

Botany

A herbaceous perennial 0.5-2 m tall, with an underground starchy corm which produces at its apex a whorl of large leaves with long robust petioles. The leaves are heart-shaped, 20 - 50 cm long, with rounded basal lobes; the leaf stalk joins the blade some distance inward from the notch between the lobes (ie the leaf is peltate - a feature which distinguishes the plant from the rather similar Xanthosoma). The inflorescence is on a stout peduncle, shorter than the leaf stalks, with a pale yellow spathe about 20 cm long: seeds are extremely rare. The corms vary greatly in size and are round/cylindrical, up to 35 cm long and 15 cm in diameter, and are surrounded by a number of secondary corms (cormels); the root system is superficial and fibrous.

There are about 1000 recognised cultivars, but these fall mainly into two groups: the eddoe type of taro, which has a relatively small corm surrounded by large well-developed cormels (and 42 chromosomes), and the dasheen, which has a large central corm and numerous but small cormels arising from its surface (and 28 chromosomes). The two types of C. esculenta are frequently referred to as separate species in the literature, C. antiquorum and C. esculenta, but it is more generally accepted that the taros are a polymorphic species, C. esculenta, and under this classification the eddoe is C. esculenta var. antiquorum (syn. C. esculenta var. globulifera) and the dasheen is C. esculenta var. esculenta.

Origin and distribution

The plant appears to have originated in India and spread eastwards to Burma and China, and southwards to Indonesia. Subsequently, it was taken to Japan, Melanesia, Polynesia and Hawaii; in historical times it spread to Egypt and the eastern Mediterranean, thence to Africa, the Guinea coast, and, along with the African slaves, to the Caribbean.

Cultivation conditions

Taros are grown, mostly as a staple or subsistence crop, throughout the tropics, subtropics, and in many warmer regions of the temperate zone. There are cultivars which are adapted to such varied conditions as swamps, tropical wet rainforest, dry uplands and to the foothills of the Himalayas. Only in a few areas, eg Hawaii, Egypt, the Philippines and certain islands in the Pacific and the Caribbean, does the taro attain the status of a commercial crop. In general the eddoes are hardier than the dasheens and can be grown in drier conditions on poorer soils.

Temperature - for optimum results taros require hot humid conditions, with daily average temperatures of 21-27°C; when grown in more temperate areas or at high altitudes there must be a 6-7 month frost-free period.

Rainfall - taros are primarily adapted to moist environments, but can be grown under a wide range of conditions, ranging from paddy culture to dry upland conditions under irrigation. An annual rainfall of approximately 250 cm is considered satisfactory; they can be grown in upland areas where the rainfall is about 175 cm provided this is evenly distributed throughout the growing period. When grown in dry upland areas with less than 175 cm of rain, irrigation is necessary to provide sufficient water for vegetative growth and leaf development and the use of furrow and sprinkler irrigation has proved satisfactory. In Egypt, the crop is irrigated at bi-weekly intervals for the first 6-8 weeks, then weekly for the next 4 weeks and then every 4-5 days, until near harvest. Dasheen corms grown under erratic moisture conditions show peculiar dumbell-like shapes, reflecting constrictions in growth during dry periods, and under water stress eddoes produce few cormels.
Soil - taros are grown on a wide range of soil types, but the best results are obtained on deep, well-drained, friable loams, particularly alluvial loams, with a high water-table; a pH of 5.5-6.5 is reported to be best.

Taro has a high requirement for potassium and for calcium. Traditionally, in particular in South-East Asia and the Pacific islands, inorganic fertiliser is not used, and reliance is placed on FYM and mulches of leaves, etc, which have the added advantage of providing substantial weed control. A cover crop of siratro (Phaseolus atropurpureus) grown in a fallow period before planting the taro, then destroyed by herbicide, is regarded as an ideal mulch that also enriches the soil with nitrogen. Where mineral fertilising is used, a complete formulation such as 12:6:20 NPK is recommended, particularly on poor soils. Split applications are desirable, with the last application not later than 3 months before harvest. Severe calcium deficiency produces 'metsubure' symptoms in which the developmental sequence of mother, daughter and tertiary corms is disturbed and the yield diminished.

Altitude - taro may be grown from sea level up to 2 400 m; the choice of cultivar is important.

Planting procedure

Material - taros are propagated vegetatively, using suckers, whole corms or cormels, pieces of corms or setts (the lower 30-50 cm of the petiole with the top 1-2 cm of the corms). It is of major importance to ensure that the planting material is free from disease (taken from completely healthy plants).

Method - Lowland or wet culture (paddy culture) - the field preparation resembles that for rice, with ploughing, discing and harrowing to produce a well-puddled soil. Setts are normally used and the base pushed by hand into the mud to a depth of 20-30 cm. The water level should not be more than 30 cm above the top of the mud and it must not become stagnant: an outlet is essential. Planting may be done throughout the year.

Patch culture - used in swampy areas which are not constantly under water. The muddy soil is formed into 'patches' of various sizes, eg 7 x 20 m, with a ditch around the patch in which water constantly flows. After cultivation the patch may be covered with coconut leaves and the taro planted through this mulch.

Dry land culture - loamy or clay-loam soil is mainly used for dry land taro in areas where there is sufficient rainfall or where irrigation is possible. The dasheen type (C. esculenta var. esculenta) has higher water requirements than the eddoe type (C. esculenta var. antiquorum), and the latter is often grown in dry land culture as a plantation crop (eg in rotation with sugar cane in some Caribbean territories), where it is planted as cormels or pieces of corm in fields prepared by ridging, or as an intercrop in peasant agriculture.

Weed control - is frequently by a combination of mulching and handweeding: the flooding practiced in paddy culture is usually sufficient to control weeds. Chemical herbicides are becoming increasingly used in the more sophisticated areas; pre-emergence herbicides include prometryn, diuron and nitrofen. Shielded sprays of paraquat or weed oils have been used as contact herbicides among standing crops.

Mechanisation of taro culture - recent work in Hawaii has shown that mechanised planting, weed control and harvesting of dry land taro is practicable, planting being on well-cultivated (rotavated) soil using a modified transplanter handling taro setts. Reaping is by a modified potato harvester. For wet culture, planting would be before flooding of the field and a promising system of harvesting is under study.

Field spacing - in high rainfall areas with heavy cloud, where exceptionally large leaves will be produced, wide spacing appears to be optimal, as much as 90x90 cm (12 000 plants/ha). For Fiji, 60x60 cm has been shown to give maximum yields of marketable tubers, though where mechanisation is practiced rows 100 cm apart and plants at 45-60 cm in the row are recommended. Typical spacing in paddy culture is usually 45-60 cm (49 000-27 000/ha).

Pests and diseases

Pests - in many countries pests do not appear to present a serious problem. However, in some places they are of major importance and over 180 insects have been listed as damaging the leaves, and about 40 as causing damage to the corms; snails, slugs, birds, rodents and other mammals are pests on occasion. Among the more important insects may be noted the taro leaf hopper, Tarophagus proserpina, in the Pacific islands, which also transmits virus infections. The egg predator, Cyrtorhinus fulvus has successfully controlled this pest in the Philippines and other Pacific areas.

Taro hornworm (Hippotion celerio), the cluster caterpillar (Spodoptera litura), whiteflies (Bemisia spp.), spider mites (Tetranychus spp.) and aphids also attack the leaves. Chemical control includes the use of methomyl, carbaryl, diazinon, malathion and dimethoate, but avoidance of indiscriminate spraying is important as a measure of natural biological control frequently operates, and it is important not to eliminate the beneficial organisms: emphasis should be given to integrated control. The corms are sometimes affected by the taro beetle (Papuana spp.), a suggested control is by gamma-HCH applied to the planting holes and again at intervals after planting. Root knot nematodes (Meloidogyne spp.) can cause severe damage, producing galls on the corms. Treatment of planting material by immersion in water at 50°C for 40 minutes is suggested.

Diseases - include leaf blight (due to Phytophthora spp.), which can cause defoliation, and (usually much less serious) Phyllosticta spot (Phyllosticta spp.): both can be controlled by copper fungicides. Dasheen mosaic is a viral condition transmitted by aphids or leaf hoppers and is not usually severe, though destruction of diseased plants is advised. Fungal root rots may be serious. Soft rot (caused by Pythium spp.) is widespread in lowland taro, and care should be taken to avoid planting infected material. Southern blight (due to Corticium rolfsii) sometimes attacks dry land taro and has been controlled by dicloran or quintozene. Two diseases of unknown etiology are hard rot and loliloli: the former destroys the vascular system of the corm, the latter produces a corm that is without starch and is soft and watery in patches.

Growth period

The maturation period varies according to the cultivar, and ranges from 6 to 18 months. The shortest crop duration reported is 3 months in Sri Lanka, others are: India 7-9 months, the Philippines 7-11 months, Hawaii (lowland crop) 12-15 months, Fiji 10-12 months, Nigeria 6-8 months, Trinidad 8-10 months (dasheens), 5-6 months (eddoes). Growing conditions affect the rate of maturation of the crop: eg in Hawaii, in the warmer areas with high levels of solar radiation, 12 months, in the cooler and more cloudy areas, 15 months.

Harvesting and handling

Taros are ready for harvesting when the leaves begin to turn yellow and start to wither; harvesting can be delayed for some weeks in dry weather without the corms deteriorating, and post-harvest storage can thus be reduced to a minimum. Normally the plants are lifted by hand using a long stick with a sharpened point or a cutlass. In large-scale production the plants are sometimes ploughed out. Harvesting should always be carried out in dry weather. Developments in mechanical harvesting have already been noted.

The storage life is usually limited by fungal or bacterial rots; the most common are due to Phytophthora colocasiae, Pythium sp., Botryodiplodia theobromae, Fusarium so/ani, Ceratocysfis fimbriata and Corticium rolfsii. Entry of pathogens is commonly through wounds, eg where the numerous small cormels have been removed from the main tubers of dasheens. Dipping in benomyl delays storage decay where Botryodiplodia is the main cause but is ineffective against Phytophthora and Pythium; sodium hypochlorite, however, controls all common decay organisms in the Pacific except Corticium rolfsii. Storage of the corms under conditions which allow desiccation is no longer recommended, as it has been shown that conditions which keep corms physiologically active promote curing of wounds and minimise water loss. Both dasheen and eddoe type corms can be kept in good condition for upwards of 4 weeks in the tropics: thus dasheens with tops attached and minimal wounding, and good quality eddoes, can be stored in pits dug in well-drained soil and lined with leaves, and well-shaded, on trays or in small heaps under houses, or in cellars or barns. For commercial handling it has been recommended that the sound corms, after fungicide dipping, draining and air-drying, be packed in polyethylene bags; such bags, overpacked in banana cartons, have been successfully used for shipping taros in the Pacific at ambient temperatures, and the storage life has been from 26 to 40 days. In connection with shipping, however, it should be noted that fumigation shortens the storage life of taro.

Taro appears to suffer chilling damage at 3-5°C having a life of only 5-6 weeks, but, in Egypt, taros are successfully stored for periods of 12-15 weeks at 7°C.
Primary product

Corms and cormels-the underground parts of the taro consist of one or more edible, central corms and a considerable number of edible cormels or lateral tubers. In the dasheens the central corm is large, cylindrical, up to 35 cm long and 15 cm in diameter, with small side cormels, and it is the central corm that is used for food. In the eddoes the central corm is smaller and bears many small side cormels, which are normally eaten. The coarser central corm is edible and is often used in soups. The flesh of both types varies in colour from white through yellow and orange to reddish or purple-the last especially in dasheen types.

Yield

Yields vary greatly according to cultivar, local conditions, crop duration, etc. Recorded average yields (t/ha) in various areas are: East Africa 5-12.5; West Africa 5-10; Cook Islands 14; Egypt 26; Fiji 7.5-15; Hawaii 37.5-75 (irrigated, heavily fertilised); Hawaii 15-25 (dry land, heavily fertilised); India 34; Malaysia 9-10; the Philippines 25; Trinidad (dasheen) 10-15; Trinidad (eddoe) 5-10.

Substantially higher yields have been obtained in trials or carefully controlled conditions: Fiji 24; New Caledonia 20; Papua New Guinea 17; Vanuatu 30-40 (wet land); Vanuatu 15-20 (dry land).

Main use

Taros are an important food crop in many parts of the tropical world. The corms and cormels are rich in starch and may be eaten in a manner similar to potatoes, boiled, baked, roasted, fried or as a basis for soups.

Subsidiary uses

In Hawaii and some of the Polynesian islands the corms of the dasheens are milled and the resultant slurry allowed to ferment to produce 'poi'. A steamed pudding made from grated taro and coconut is very popular in

Hawaii. The peeled tubers, after pre-cooking and drying, can be used to produce a flour, similar to potato flour, which is used in the preparation of soups, biscuits, bread, beverages, infant foods and puddings. In recent years there has been interest in the use of taro as a speciality food in the management of gluten allergy in infants, and as a cereal substitute in coeliac diseases, largely because of its exceptionally small starch grains.

Secondary and waste products

Leaves and petioles-may be cooked and eaten as a vegetable. In Hawaii the leaves are canned for local sale. A silage of moderate quality may also be prepared from the leaves and petioles.

Corms and cormels-are rich in mucilage which can be utilised in the paper industry or possibly in medicinal tablet manufacture. They can also be used as a source of power alcohol, or may be fermented to produce a drink known as 'chica'.

Stems-are sometimes used medicinally, notably in the treatment of snake bites.

Starch-consideration is being given to the use of taro starch as a filler for plastics.

Special features

Corms and cormels-are rich in starch; the flesh is mealy to smooth and usually has a somewhat nutty flavour. The composition of the edible portion of the corms has been given as: energy 373-406 kJ/100 g; water 73-78 per cent; protein 1.4-3 per cent; fat 0.1-1.5 per cent; carbohydrate 19-21 per cent; fibre 0.4-2.9 per cent; ash 0.6-1.3 per cent; calcium 32-40 mg/ 100 g; iron 0.8-1.7 mg/100 g; phosphorus 64-140 mg/100 g; potassium 514-550 mg/100 g; sodium 7-9 mg/100 g; carotene trace-67 IU/100 g; thiamine 0.09-0.18 mg/100 g; riboflavin 0.03-0.04 mg/100 g; niacin 0.4-0.9 mg/100 g; ascorbic acid 0-10 mg/100 g.

The starch grains are very small and consist of a mixture of two types, one 1-1.5 microns and the other 3-4 microns in diameter. For this reason taros are easily digested, but unsuitable as a source of industrial starch. They are rich in a mucilage, which on hydrolysis yields eight sugars, the pre dominant ones being d-galactose and l-arabinose in the ratio 8:1. Most cultivars, particularly the dasheens, contain oxalic acid (0.1-0.4 per cent fresh weight) mainly in the form of 'raphides', ie bunches of needle-shaped crystals of calcium oxalate embedded in the tissues. An unidentified irritant(s) may also be present in the tissues; boiling reduces irritancy.

Leaves and petioles-both the leaves and petioles can be utilised as vegetables and are useful sources of vitamins A and C: vitamin A, leaves 20 885 IU/100 g, petioles 335 IU/100 g edible portion; vitamin C, leaves 142 mg/100 g, petioles 8 mg/100 g.

Processing

'Poi'-is prepared on a commercial scale in Hawaii, by first pressure cooking the corms and cormels in steam retorts, after which they are washed, peeled and milled; the resultant semi-fluid product is strained or centrifuged to remove fibre, and usually filled into plastic bags, which are distributed at room temperature through the normal retail channels. Under these conditions, fermentation due to Lactobacillus spp. is rapid and in 3-4 days the pH drops from 5.5-6 to 3.8-4. This fermented product is preferred to the fresh material. Public health regulations in Hawaii require 'poi' to have a total solids content of at least 30 per cent, or 18 per cent for ready mixed 'poi', which has been prepared by dilution with water. Fresh and fermented 'poi' can be canned satisfactorily; the former product is filled into cans at 76.6°C and retorted for 100 minutes at 98.8°C. Fermented 'poi' is heated to 93.2°C, filled hot, and cooled immediately without further heat treatment.

Flour-is prepared by peeling and slicing the corms and cormels, and then washing the slices thoroughly in water so as to remove as much mucilaginous material as possible. After washing, the slices are left soaking in water overnight, then washed again and finally immersed for 3 hours in 0.25 per cent bisulphite solution. They are next blanched in boiling water for 4-5 minutes, drained and dried, preferably in a tunnel drier at 57-60°C. The dried slices are ground, sieved to 40-50 mesh and packaged.

Extruded products-taro rice, noodles and macaroni are being developed from Colocosia flour. In polyethylene packs these products have a shelf life of 12 months when stored at 38°C or below.

Instant taro flakes-have been manufactured commercially in Taiwan: peeled corms are trimmed, sliced to about 2 mm thick, steam cooked for 30 minutes, pureed to contain 20 per cent total solids with 5 per cent glucose solution, and drum-dried. The reconstituted product was reported to have good flavour, texture and colour.

Production and trade

Production-information about taro production is incomplete and scattered. The edible aroids (Colocasia, Xanthosoma, Alocasia and Cyrtosperma) are stated to contribute 1.6 per cent of the total food energy of the tropics and subtropics, or about 3.3 per cent of all root crops. However, in the Pacific area the aroids constitute a very high proportion of the root crops and are a major staple. In many of the islands in the Philippines taro ranks third in tonnage among locally-grown root crops, and has shown substantial increases in production in recent years: 1973, 28 498 ha, 100 672 t; 1975, 36 830 ha, 123 523 t.

Similarly, in some Caribbean islands, taro (dasheen) is of considerable importance, accounting for about 60 per cent of all root crop production in St. Vincent and 45 per cent in St. Lucia.

Trade-figures for taro are scant. In the South Pacific in 1982 Tonga exported approximately 35 000 t and Western Samoa 3 800 t of dasheens, mainly to New Zealand, a substantial increase from the 1 500 t imported by that country in 1973. In the Caribbean, St. Vincent exports 300-400 t of dasheens per year to neighbouring territories. There is also a small import trade in dasheens and eddoes by the UK.

Major influences

The importance of taro in the Pacific islands is well established, and with continuous population growth and the availability of new markets for processed taro, both as human food and for livestock feed, taro cultivation is on the increase throughout the Pacific region. Similarly, throughout India and South-East Asia, much of Africa, tropical America and the Caribbean, taro is a valuable staple carbohydrate food, relatively easy and inexpensive to produce, and should maintain its position. In Indonesia, which is importing rice, the government is encouraging food diversification and taro should obtain a greater share of the carbohydrate contribution to the diet. Germplasm is being collected and may be expected to result in improved cultivars; this and better cultural practices should lead to greater yields per unit area, while the development of full mechanisation should result in lower unit costs and encourage larger-scale production.

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