The authors of this chapter are D.C. Giacometti (CENARGEN/EMBRAPA, Brasilia, Brazil) and J. León (San José, Costa Rica) The authors thank R. Valverde (CIGRAS, University of Costa Rica) for his reports on recent developments in the vegetative propagation of Xanthosoma sp.
Common names. English: tannia, tania; yautia, new cocoyam tanier; Spanish: yautía, malanga (Antilles), macal (Mexico [Yucatán]), quiscamote (Honduras), tiquisque (Costa Rica), otó (Panama), okumo (Venezuela), uncucha (Peru), gualuza (Bolivia), malangay (Colombia); Portuguese: taioba, mangareto, mangarito, mangarás (Brazil); French: chou Caribe (Antilles); other languages: queiquexque (Mexico), tannia, taniera (Antilles)
Two Araceae are attaining world importance as energy foods: the cocoyam, taro or dasheen (Colocasia esculenta), originating from Oceania and Southeast Asia, and the tannia, yautia or new cocoyam (Xanthosoma sagittifolium) from the American tropics. The usable parts in both species are the subterranean tuberous stems which, in the case of the latter, contain between 15 and 39 percent of carbohydrates, 2 to 3 percent of protein and 70 to 77 percent of water; both have a nutritional value comparable to the potato and are probably easier to digest. A secondary use is of consumption of the young leaves, similar to spinach, and this is more common with X. sagittifolium than in the case of the taro.
Cultivation of tannia or yautia must be very old in the New World. It may have originated in the northern part of South America and spread through the Antilles and Mesoamerica. When the Europeans arrived it was known from southern Mexico to Bolivia, but was possibly more intensive in the Antilles. Domestication may have occurred in various places and with different materials, and was based on processes such as roasting and cooking the tubers, thereby eliminating the irritant substances, calcium oxalate crystals and saponins.
From America, the tannia or yautia reached West Africa, which is now the major producer. There, it has been displacing the cocoyam or taro because of its better yield and because it can replace yams for preparing fufu, a very popular food in tropical Africa.
The tannia has traditionally been a subsistence crop and any produce which is not consumed by producers' families goes to the market. This explains its marginalization because, even though it is a staple for millions of people in the tropics, little information is available on its cultivation and requirements.
This situation is changing with the opening of new areas of consumption, especially on the Atlantic coast of the United States, where millions of Latin Americans consume tannia and other tropical crops, a fact which has promoted commercial production in the Antilles and Central America. This market, which requires high-quality and well-presented products, determines the rules on production and marketing.
As in the case of other neglected crops, there have been very few efforts to industrialize and diversify the product. In Puerto Rico, tests have begun with very satisfactory results for making crisps using instant dehydration and tannia flour. Considering that a very varied industrial production has been built up using tannia, it may be predicted that, with the application of technology, tannia can be used to make a series of industrial products similar to those obtained from the cocoyam or taro.
Production in the family or commercial undertaking must be considered in the context of the production of other energy foods in the same region: cassava, potato, sweet potato and yam. On most of the Latin American markets, the tannia is valued as a superior species because of its flavour and texture.
Surveys carried out in Puerto Rico show that the rural population prefers the tannia to the sweet potato, yam and green plantain because of its flavour and that, in the Philippines, it is preferred to the cocoyam or taro. Production does not meet demand: in Venezuela in 1970, 56305 tonnes were marketed, a figure which is below potential consumption levels.
A herbaceous perennial, Xanthosoma sagittifolium has a corm or main underground stem in the form of a rhizome from which swollen secondary shoots, or cormels, sprout. Several large leaves also sprout from the main stem, which are sagittate and erect with long, ribbed petioles; inflorescences sprout between the leaves in a spadix, with a white 12 to 15 cm spathe which closes at its base in the form of a spherical chamber and opens at the top into a concave lamina; the spadix is cylindrical, slightly longer than the spathe, with female flowers on the lower portion, male flowers on the upper portion and sterile flowers in the middle portion. The spadices are rarely fertile and produce few viable seeds. The growth cycle lasts from nine to 11 months: during the first six months the corms and leaves develop; in the last four months, the foliage remains stable and, when it begins to dry, the plants are ready for the cormels to be harvested.
Figure 31. Tannia, yautia or cocoyam (Xanthosoma sagittifolium)
The Xanthosoma species are plants of the tropical rain forest and, although in their natural habitat they grow under the forest canopy, under cultivation they are usually sown with full exposure to sunlight. They require well-drained soils and do not tolerate the permanent presence of water. The mean temperature for their optimum growth must exceed 20°C.
The taxonomic position of the Xanthosoma species cultivated for their underground stems is unclear. The cultivated varieties have been allocated to four species: X. atrovirens, X. caracu, X. nigrum (X. violaceum) and X. sagittifolium, but some cultivars are not assignable to any of these. Furthermore, the characteristics distinguishing species and cultivarsleaf shape, nervation, petiole colourare not clearly defined. In one related species, the cocoyam, with a possibly wider variation, all the clones are considered as a single species. In Xanthosoma spp. and the cocoyam, the great diversity known (more than 100 clones in the case of the cocoyam) may be due to certain segregations (in the cocoyam and Xanthosoma spp. seed formation is very rare) or mutations of the leaf bud. In both cases, growers who detect a new variant maintain its cultivation and reproduce it by vegetative propagation. In recent years, the tendency has been to give the name of X. sagittifolium, which applies predominantly to all cultivated clones of Xanthosoma, until a modern revision of the genus clarifies the taxonomic situation of the species mentioned.
Xanthosoma cultivars have been described on the basis of collections established in Puerto Rico and Trinidad and Tobago, with indigenous or introduced materials. and do not exceed 50 in number. They display a wide diversity of habit, leaf shape and colour and cormels. As experimental crops show, there are wide variations in yields and the same may be said of the carbohydrate and amino acid content.
There is an urgent need to establish live and in vitro collections at world level that enable genetic potential to be evaluated as regards current needs and problems. This means collecting the known cultivars. both in the New World and in Africa, and exploring the northern part of South America in search of possible wild forms and primitive cultivars as well as related species (such as X. jacquinii). In vitro cultivation now enables healthy and easily transportable propagation material to be obtained. Cytological studies of a world collection may lead, as in the case of the cocoyam, to the establishment of natural groups of cultivars and may also serve as a basis for genetic improvement. The IBPGR recently published a list of descriptors of Xanthosoma.
Propagation. The planting material most commonly used are portions of the central corm, from 100 to 150 g, with three or four buds. They give greater yields than the cormels which are also sometimes used.
In Costa Rica, a system has been developed for supplying growers with "seed" originating from virus-free cultivations of stem tips grown in vitro. With this material, not only is the yield quadrupled but the exportable portion of the harvest increases from 40 to 80 percent, which amply compensates for the cost of sowing. Elimination of the malanga (tannia) virus is so far the most remunerative control operation in tannia cultivation.
The system consists of producing plantlets in public or private laboratories, which supply them to growers or cooperatives capable of developing them under the special conditions required. These plants provide traditional "seed", i.e. portions of stems or whole cormels which are sold to growers as virus-free planting material.
Planting. The ground for planting is ploughed and raked and mounds or ridges are formed for planting the seed. Planting is done in ridges when harvesting is semi-mechanized. The portions of the corm are placed at a depth of 6 to 7 cm since, if planted closer to the surface, they produce numerous side shoots which reduce yield. The planting distance in commercial cultivation is 1.3 m between rows and 40 to 50 cm between plants. In small plantations, they are planted in mounds spaced at 1 x 1 or 1.3 x 1.3 m. In Nigeria, the best results were obtained with distances of 1.6 x 1.6 m on plots where cormels were planted.
Cultivation. The first six months is a critical period for weed control. Backed up by the application of pre-emergence herbicides, preparation of the ground for planting (ploughing and raking) helps considerably in controlling weeds. As the plants need to be earthed up several times, this contributes to keeping the soil clean.
The use of chemical and organic fertilizers is widespread both in small and commercial plantations. In the latter, several dressings of fertilizer are applied; for example, the recommendations in Costa Rica are 150 kg per hectare of 10-30-10 at the time of sowing, 200 kg of Nutrán after two months and 200 kg per hectare of 15-3-30 after four months.
The most serious problem at present is "dry disease", a complex produced by fungi (Rhizoctonia, Phytium) and bacteria (Erwinia, Pseudomonas) which attack the young plants, causing leaf wilt and tuber rot and resulting in the complete loss of the harvest. Disease control is difficult and a complete investigation of the problem is therefore needed. For the time being, draining the soil, planting in ridges and crop rotation are recommended.
Harvesting. In commercial plantations, harvesting is carried out ten to 12 months after planting, when the leaves have turned yellow and are beginning to dry. The crop is harvested by hand or by a semi-mechanized method. In the latter case. the tractor has an iron plate as wide as itself attached to it. with a central point which digs into the row of plants. turns them over, and leaves the central stem and cormels free: these are subsequently collected by hand.
The commercial product is washed. dried and disinfected carefully before being placed in boxes in cold-storage rooms.
In small plantations, harvesting of the cormels begins tour to six months after planting and is done without uprooting the plant.
Tannia production could be considerably improved. both as a subsistence food and as a product for commercial export and industrial use. As in the case of most neglected crops, no research has yet been carried out on the most elementary aspects. because no new technologies have been disseminated and because of the shortage of marketing systems nationally and internationally.
The role of the tannia in sustainable farming systems must be carefully studied, particularly in mixed plantations. Although under these conditions it is interspersed with taller crops which shade it and reduce its yield, the additional in come earned by the grower is very substantial.
The wide genetic diversity must be exploited both directly by the evaluation of cultivars regarding their resistance to disease, yield and nutritional value, and by genetic improvement (which has barely begun). The aim should be to achieve a production of 30 tonnes per hectare with a 10 percent protein content.
The industrial utilization of tannia has only just begun and it may be expected to be as varied as that of the cocoyam or taro, being used in foods prepared for children, flour, crisps, etc.
The main limitations to the development of tannia as a crop are diseases, particularly "dry disease". This problem, which is complex, must receive immediate attention, attacking it from the phytosanitary and agronomic angles.
The tannia, like few neglected crops, is a special case (there is no exchange of information or germplasm between the producing areas) because of the range of its cultivation, which already extends over all tropical regions. When it becomes intensified in a region, the progress recorded does not spread far for geographical or linguistic reasons.
This situation must be corrected by the establishment of a centralized information system such as the cooperatives for tomato, gourd and sorghum cultivation, to which all interested countries and agronomists have access. This may lead to the exchange of germplasm in vitro, visits from scientists and farmers who may pass on as yet unpublished experiences and the use of other means of communication which serve to notify progress achieved locally.
The future of the tannia, a food of exceptional value because of its organoleptic characteristics and nutritional properties, lies in a widening of export markets, the application of technology to diversify its use and the promotion of more intensive consumption in people's diets in tropical regions.