Root crops (NRI, 1987, 308 p.)
Tannia (Xanthosoma spp.)
TAN(N)IA, New cocoyam, Tan(n)ier.
Botanical name
Xanthosoma spp.
Family
Araceae.
Other names
Badoo (Jam.); Chou (Gren.); Chou caraibe (Ant.); Cocoyam', Dalo ni tana (Fiji); Kimpool (Indon.); Kong Kong taro (N. Guin); Macabo (Cam.); Maduma (Tanz.); Mafaffa, Malanga(y)' (Ant.); Mangareto (Braz.); Nut eddoe (Barb.); Ocumo, Ocumo cuman (Venez.); Quequeque (Guat.); Rascadera (Braz.); Tajer (Sur.); Taioba (Braz.)'; Talo papalagi (Sam.); Tanyove (Guy.); Tatale, Tayobe, Tayonne, Tayo tyo (W.l.); Tiquisque (C. Rica); Yautia (Lat. Am.); Yautia bravi� (P. Rico); Yautia des anglo saxons (Fr.).
Botany
There is often confusion between the genus Xanthosoma and that of Colocasia since superficially tannias appear to be rather large coarse taros. Tannia plants can reach a height of about 2 m and have a short erect stem and large, long-stalked sagittate or hastate leaves, which differ from those of Colocasia in that the leaf stalk joins the blade at the margin between the lobes (not into the surface of the blade), and the tips of the lobes are pointed, not rounded. The leaves have a prominent marginal vein, and are 50-75 cm long, occasionally more; the petioles are about I m long. The inflorescence is borne below the leaves, with a pale green spathe about 20 cm long; some cultivars never flower and seed is rarely produced. A corm is produced at the base of the plant and this bears several (usually 10 or more) lateral corms (cormels), each 10-25 cm long.
The taxonomy of Xanthosoma is confused; a number of edible species have been recognised including X. sagittifolium (L.) Schott, by far the most widely grown, X. atrovirens Koch and Bouche, with yellow tubers and favoured in Puerto Rico and Dominica, X. violaceum Schott, a large plant grown occasionally in the Pacific islands but reportedly of little value for food, and X. brasiliense Engl., a small species cultivated solely for its edible leaves.
Origin and distribution
Xanthosoma is native to tropical America and was cultivated in tropical Central and South America from very ancient times, and only in comparatively recent times (19th century) has been spread widely throughout the tropical world. It is now cultivated in tropical America, the Caribbean, West Africa and the Pacific, and to a very limited extent in some other parts of the humid tropics. The name 'new cocoyam' reflects this late introduction into areas where Colocasia (cocoyam) was previously established.
Cultivation conditions
Temperature - tannias do best in tropical conditions, but can be grown over a fairly wide range; eg in Puerto Rico they are successfully grown in areas where the mean annual temperature is 24°C with maximum variations ranging from 13 to 29°C.
Rainfall - the crop is suited to high rainfall areas, but can be grown with an annual rainfall as low as 100 cm provided that this is evenly distributed, although an average rainfall of 140-200 cm is preferable. Tannias can be grown as an upland crop under irrigation and certain early-maturing cultivars can be grown without irrigation in comparatively dry situations, such as exposed steep slopes.
Soil - tannias can be grown on a wide variety of soils, except hard clays or pure sands, but for optimum yields they require a deep, well-drained, rich soil, preferably with a pH of 5.5-6.5. Unlike taro the crop cannot withstand waterlogging. Good response is given to mulching, and 20-40 t/ha of FYM is recommended when available. There is little precise knowledge about mineral fertilising: both in Puerto Rico and the Pacific Islands nitrogen at 100 kg/ha along with potassium at 100 kg/ha has given good results; split application is recommended.
Altitude - different cultivars have been selected over the years for widely varying conditions and provided that a suitable cultivar is selected, tannias can be successfully grown from sea level up to elevations of about 1 500 m.
Planting procedures
Material - the best material is small corms or cormels. Alternatively, a 5 cm section can be cut from the main corm, and divided into two pieces across its diameter. Setts are also used, ie the top of the main plant including about 5 mm of corm and the leaves cut off about 20 30 cm above the base, but leaving the newly-formed leaf at the centre of the plant.
Method - tannias may be grown in monoculture, but are more usually grown in crop rotation systems; often they are the first crop in shifting agricultural systems, or are intercropped with plantation crops such as cocoa, rubber, bananas and coconuts. Planting may be throughout the year, although in drier areas (100 cm rainfall) it is usually just before, or at the start of, the rainy season.
Planting in ridges is often recommended: the corms or cormels are planted 7.5-10 cm deep, with the growth bud pointing downwards; if pieces of the main rootstock are used about 2.5 cm is left above the ground. Setts are planted with the base about 10 cm deep. Little attention is given after planting apart from weeding, and sometimes earthing up if planting was on level ground. The application of the pre-emergence herbicide diuron at 1.6 kg/ha has been recommended; other effective herbicides are atrazine, prometryn and ametryn.
Field spacing - is variable but I x I m is most commonly used and requires about I t/ha of planting material (cormels). However, in practice it ranges from about 60x60 cm to 180x 180 cm. The wider spacing gives a higher yield per plant (and 150x 150 cm has been reported to give maximum yield per hectare), but the wider spacings involve increased maintenance as it takes much longer before the leaves shade out the weed growth. These spacing distances refer only to tannia grown in monoculture; there is no general practice for mixed cultivations.
Pests and diseases
In general tannias are relatively free from serious attacks by pests or diseases, although this is probably largely due to the fact that the crop is mainly grown on a small scale and not as an extensive monoculture. In Trinidad, Venezuela and Guyana, a dynastic beetle, Ligyrus ebenus, has been reported to attack the crops, but can be effectively controlled by spraying with malathion. Other pests which sometimes attack tannias include Aphis gossypii in the Antilles and Surinam, Euetheola bidentata in Surinam, Graphocephala propior, Quinta cannae and Cacographis ortholatis in Venezuela, Aspidiotus destructor in the Antilles and Polynesia, Pentalonia nigronervosa, Tetraleurodes ursorum and Corythucha gossypii in the Antilles. These may all be controlled by the usual insecticides.
Several root rots can affect tannias, with varying degrees of severity. During the 1930s root rot was particularly serious in Ghana and investigations suggested that the causal agent could have been a fungal or bacterial infection, or a combination of both, and that the nutritional status of the crop was also a factor influencing the severity of attack. Tannias are susceptible to various Pythium rots; in Puerto Rico, a soft rot known as currutaca, due to Pythium ultimum, affects the crops, while in New Caledonia, P. irregulare is reported occasionally to cause serious losses. In Venezuela, the crop is sometimes infected by Cercospora chevalier), C. verruculosa and Punctellina solteroi. Viruses have been reported but do not appear to be serious.
Growth period
The corms are normally considered to be mature 9-12 months after planting, although a crop can sometimes be obtained after 6 months. Higher yields are obtained with later harvesting.
Harvesting and handling
At maturation the older leaves begin to yellow. The mature corms do not deteriorate if left in the ground and they are often harvested as required. The whole plant may be dug up, often by hand, and the cormels separated from the main corm. Sometimes the soil is dug away from the plant and the exposed cormels separated from the parent plant which is covered up with soil and left to produce a new crop. In this way the plant may continue to crop for several years and it is usually at least 6 years before there is a noticeable decline in vigour and quality of the cormels. Great care must be taken to avoid bruising the cormels when they are harvested, otherwise they are liable to develop serious rots if stored. In some countries mechanical harvesters are being developed.
Tannias can be successfully stored under dry well-ventilated conditions for periods of up to 6 months, although in Trinidad it was found that, when stored at ambient temperatures, there was a loss of eating quality after 8 weeks, but the quality was maintained for 18 weeks or more if the cormels were stored at 7°C and 80 per cent RH. In Cameroon, traditional storage in pits in a confined atmosphere has been found more satisfactory than storing on trays in well-ventilated huts.
Primary product
Cormels - the central corm is usually not eaten (and often is not harvested - see Harvesting and handling), but the lateral corms (cormels) form the crop. These vary in size from 10 to 25 cm in length and 12 to 15 cm in diameter, and about 80 per cent consists of edible, starchy material, the remainder being a scaly peel. The flesh can be white, yellow or pink.
Yield
Experiments in Trinidad have given yields of 30-32.5 t/ha and Puerto Rico has reported yields of 25-37 t/ha of tubers, ie corms plus cormels. Average yields of cormels in the South Pacific are reported as 20 t/ha for tannia grown in monoculture. For mixed cultivation in peasant agriculture yields of 5-7 t are common.
Main use
The starchy corms occupy an important place in the diet of many tropical countries. The main corms are usually acrid and normally only the cormels are eaten. These are boiled, baked, or parboiled and fried in oil. In West Africa, the tubers are sometimes ground to produce 'fufu', for use in stews and soups.
Subsidiary uses
The dried peeled corms may be ground to produce a flour, which is considered to be as palatable as cassava flour, but more nutritious. About 10 kg of tannias will yield 3 kg of flour. The preparation of noodles, using mixes of flours of soya, wheat and high percentages of Xanthosoma flours, has been undertaken experimentally.
Secondary and waste products
The leaves can be boiled and used as a vegetable, similar to spinach (X. brasiliense is particularly favoured for this purpose).
Special features
There is considerable variation in the composition of tannias and starch contents ranging from 17 to 34.5 per cent have been reported. Average approximate composition of the edible portion has been quoted as: energy 556 kJ/100 g; water 70-77 per cent; protein 1.3-3.7 per cent; fat 0.2-0.4 per cent; carbohydrate 17-26 per cent; fibre 0.6-1.9 per cent; ash 0.6-1.3 per cent; calcium 20 mg/100 g; iron 1 mg/100 g; thiamine 1.1 mg/100 g; riboflavin 0.03 mg/100 g; niacin 0.0005 mg/100 g; ascorbic acid 6- 10 mg/100 g.
The starch grains of tannia are relatively large, with average diameter 17-20 microns, and are less easily digested than those of Colocasia.
Processing
Starch - is occasionally made from the grated tubers.
Production and trade
Production - statistical information on the production of tannia is not readily available, and it is usually grouped with taro or other root crops, though in Puerto Rico production appears to exceed 20 000 t/a and in the Dominican Republic, 30 000 t/a. Tannia is replacing taro to some extent as a nurse crop for young cocoa in West Africa as it is easier to grow.
Trade - recent figures are not available; there is some inter-island trade in the Caribbean with St. Vincent exporting tannia to Trinidad.
Major influences
In recent years production of tannias has tended to increase, particularly in parts of West Africa, because of their greater resistance to Phytophthora blight compared to taros, and because less exacting conditions are required for their cultivation. Tannias are of particular value for intercropping with plantation crops, but their future probably depends upon whether costs of production can be reduced by improved cultural techniques, such as mechanisation, the use of herbicides and the application of fertilisers. The high degree of genetic variability suggests that there is considerable potential for improvement of this crop through selection and breeding.
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