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The designations employed and the presentation of in this publication do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.

David Lubin Memorial Library Cataloguing-in-Publication Data

FAO, Rome (Italy)

Roots, tubers, plantains end bananas in human nutrition.
(FAO Food and Nutrition Series, No. 24)
1. Roots
2. Tubers
3. Plantains
4. Bananas
5. Nutrition
I. Title
II. Series.

FAO code: 86
ISBN 92-5-102862-1

The copyright in this book is vested in the Food and Agriculture Organization of the United Nations. The book may not be reproduced, in whole or in part, by any method or process, without written permission from the copyright holder. Applications for such permission, with a statement of the purpose and extent of the reproduction, should be addressed to the Director, Publications Division, Food and Agriculture Organization of the United Nations, Via delle Terme di Caracalla, 00100 Rome, Italy.

(c) FAO, 1990
Printed in Italy

The book was prepared by Prof. O.L. Oke of the Abafemi Awolowo University, Ile-Ile, Nigeria and was edited and revised by Dr J. Redhead, Consultant, and Dr M.A. Hussain, Senior Officer, Community Nutrition Group, Nutrition Programmes Service, Food Policy and Nutrition Division. Valuable suggestions were offered by other staff members of the Nutrition Programmes Service and members of the FAO Interdepartmental Working Group on roots, tubers, plantains and bananas.


During the last 15 years the difficulties faced by many developing countries in satisfying their population's requirements with domestic food production have increased. Even with sustained efforts, it has not always been possible to meet the growing food demand by raising the domestic production of cereals. As a result widespread food shortages, hunger and malnutrition have persisted, particularly among the low-income groups in developing countries.

In order to improve the situation, the Member Governments of the Food and Agriculture Organization of the United Nations (FAO) at the 8th Session of the Committee on Agriculture (COAG) in 1985 recommended the adoption of measures to broaden the food base through the promotion of other local food crops of nutritional importance. More recently, at its 9th session, COAG further requested Member Governments to give high priority to production and consumption of roots, tubers, plantains and bananas in view of their important role in improving food security.

Although these crops have been for centuries the traditional staples in many developing countries they have until recently been relatively neglected by most national research institutes, extension services and by food supply planners. While part of this neglect can be attributed to difficulties in marketing and processing these perishable food crops, they have also suffered from a negative image as "poor people's food ". Starchy roots and tubers, such as cassava, have been traditionally associated poverty and accused of being a factor contributing to the development of kwashiorkor, a form of severe protein energy malnutrition. Since most of these food crops are consumed locally or sold in nearby small markets their actual contribution to the energy intake of rural populations producing them is not fully accounted for. Their consumption in urban areas is far from negligible, especially in Africa and in Asia. This is why it is time to bring out the positive attributes of these important foods and the increased contribution they can make to the nutritional welfare and food security of developing countries.

In this book the value of roots, tubers, plantains and bananas in human nutrition and their importance in human diet is reviewed. The purpose of this book is to promote their production and utilization as valuable components of a well-balanced diet, and to alleviate hunger and seasonal food shortages.

The book is intended for nutritionists, agriculturists, dieticians, community development workers, school teachers and economists. It is hoped that officials responsible for planning food supply, production and food imports and exports will find the facts presented useful for their work. Educationists will also find valuable information that will help them lo promote changes in the food habits of population groups, particularly those who suffer chronically from energy deficiency and food insecurity.

P. Lunven
Food Policy and Nutrition Division

1. Introduction

Roots and tubers belong to the class of foods that basically provide energy in the human diet in the form of carbohydrates. The terms refer to any growing plant that stores edible material in subterranean root, corm or tuber.

The development of root crops in the tropics was accelerated by the introduction of gari-processing technology into West Africa and by the promotion of cassava as a famine reserve by several colonial governments, such as the Dutch in Java and the British in West Africa and India. By 1880 the tapioca trade was well established in Malaya and by the turn of the twentieth century the production and trade of cassava products, especially starch, had been established by the Dutch in Java and by the French in Madagascar.

A further reason for the spread was the fact that during tribal warfare and invasions, the invader could not destroy or remove the food reserve, which could be kept conveniently under the ground, thus giving added food security to the population.

Historically, very little attention has been paid to root crops by policy-makers and researchers as most of their efforts have been concentrated on cash crops or the more familiar grains. Root crops were regarded as food mainly for the poor, and have played a very minor role in international trade. This misconception has lingered for so long because of the lack of appreciation of the number of people who depend on these root crops, and the number of lives that have been saved during famine or disasters by root crops.

It was cassava that saved the Rwanda-Burundi kingdoms in 1943 when potato blight destroyed all their production, and cassava also fed the Biafrans during the Biafran war in Nigeria in 1966-69.

As far back as 1844 Rev. John Graham has this to say about the potato:
"Oh! There's not in the wide world a race that can beat us,
From Canada's cold hills to sultry Japan,
While we fatten and feast on the smiling potatoes
Of Erin's green valleys so friendly to man."

There is an old saying of the Palananans of Micronesia where taro is the basis of the staple food that:
"the taro swamp is the mother of life" (Kahn, 1985).

The fact that these root crops are mainly starchy has led to the disparagement of their protein content, which is low compared to cereals. However, considering the quantities of root crops consumed a day, their protein contribution is often significant. In addition, root crops contain an appreciable amount of vitamins and minerals and may have a competitive production advantage in terms of energy yield per hectare over cereals produced in ecologically difficult conditions.

During the years 1980-87, the average rate of growth in food production (2.6 percent) in many countries of developing market economies, particularly Africa, has been either falling behind or barely keeping pace with the average annual rate of growth in population (about 3 percent), owing to land shortages and lack of foreign exchange to purchase agricultural inputs such as fertilizers, insecticides and m achinery. Droughts, floods and other natural and induced calamities have contributed substantially to reduced food supplies. These fooddeficit countries are now making substantial efforts to improve this situation, but their efforts are directed mainly toward improving production of staple cereals and increasing the importation of cereals by cash purchases or as food aid, thereby widening further the gap between local food production and food requirements.

In their present state under subsistence farming, the yield of many root crops is very low, but their genetic potential for producing increased yields is high and has not yet been fully exploited. In addition some root crops are highly adaptable, producing reasonable yields from marginal lands with highly erratic rainfalls. Crops such as cassava can serve as a valuable asset for household food security for subsistence populations in times of drought and under other unfavourable ecological conditions.

The purpose of this book is to review the value of roots and tubers in the human diet and to assess their contribution to the nutritional welfare and food security of people living in less developed countries. It is hoped that it will also help propagate knowledge about these crops and stimulate research for their genetic improvement with a view to increasing their production and utilization.

In its Food and Nutrition Papers and Series, the Food and Agriculture Organization of the United Nations (FAO) has already published books on five important food sources, namely Rice and rice diets, Maize and maize diets, Milk and milk products in human nutrition, Wheat in human nutrition and Legumes in human nutrition. The present study has been conceived on a similar pattern. It will summarize current knowledge about production, consumption, nutritive value, processing and cooking of roots and tubers and their contribution to hum an diets. The study includes all important root and tuber crops: cassava, yam, sweet potato, potato and aroids as well as two other starchy staples, banana and plantain. Although much of the research and development work on potato is done in temperate zones, the potato is included in the book because of its great potential for expansion into the tropics. Plantain and banana are also important starchy staples in many tropical countries.

In 1988 FAO published a study entitled Root and tuber crops, plantains and bananas in developing countries: challenges and opportunities, which provides a comprehensive review of the global production and consumption of these crops. Additional FAO studies in this field focus on the utilization and processing of roots, tubers, plantains and bananas. The present study provides a more detailed analysis of the role of these crops in human nutrition and is an essential supplement to the information provided in the earlier publications.

2. Origins and distribution

The suggested origins of root and tuber crops are illustrated in Table 2.1. These crops were dispersed by the Portuguese during their voyages for slaves, by both the Portuguese and Spanish in their missionary journeys, and by Arab traders. The genus Dioscorea (a variety of yam) has a wider diversity of origin with different species adapted to different ecosystems. D. trifida is indigenous to tropical America; D. rotundata, D. cayenensis, D. bulbifera and D. dumetorum are native to West Africa; D. alata, D. esculenta and D. opposita are indigenous to South Asia. D. opposita and D. japonica have their centre of origin in China.

Yams are the only root crops in which the Asian and African species developed independently of each other. Exchange of species was due to the influence of Portuguese explorers. They learned of the value of D. alata from the Indian and Malayan seafarers who used it on their ships on long voyages because it stored well and had antiscorbutic properties. The Portuguese soon adopted it and introduced it into Elmina and Sao Tome in West Africa. Subsequently, through the Atlantic slave trade, the Portuguese carried the African species D. rotundata and D. cayenensis and the Asian species D. alata to the Caribbean where they became important staple foods (Coursey, 1976). According to Coursey (1967), D. alata seems to have arisen from the wild relatives, D. hamiltoni and D. persimilis in the north and central pans of the southeast Asian peninsula, probably Burma or Assam. So also D. esculenta while D. hispida, D. pentaphylla and D. bulbifera origina ted from an IndoMalayan centre. D. rotundata is of African origin, where it is known as "water yam", indicating that it was brought across the water or sea. D. rotundata is the most important African yam, especially in the forest zone, and is probably a hybrid of the other African yam, D. cayenensis, which is a savannah species. In West Africa it is grown in the roots and tubers belt, which extends 15N and 15S of the equator (Coursey, 1976; Okigbo, 1978; Nweke, 1981).

TABLE 2.1 - Origins of tropical root crops

Root crop

Common name

Suggested origin

American species    
Ipomoea batatas sweet potato Tropical North America (Mexico, Central America and Caribbean)
Manihot esculenta cassava, cocoyam Tropical Central America (from Caribbean to Northeast Brazil)
Xanthosoma sagittifolium new cocoyam, taro Tropical Central America (from Caribbean to North Brazil)
Solanum tuberosum potato Andean South America (Colombia, Bolivia and Peru)
Dioscorea trifida sweet yam Tropical Central America (Guyana, Surinam)
African species    
Dioscorea rotundata yam Tropical West Africa
Dioscorea cayenensis wild yam Tropical West Africa
Dioscorea dumetorum " Tropical West Africa
Dioscorea bulbifera " Tropical West Africa
Asian species    
Dioscorea alata yam South Asia
Dioscorea esculenta " South Asia
Dioscorea opposita " South Asia
Colocasia esculenta old cocoyam or taro Southeast Asia
Musa acuminate banana/plantain Southeast Asia

Source: Adapted from Purseglove (1968,1972).

Little is known about the origin of new world yams. They were of secondary importance in the pre-Colombian era. D. trifida, an Amerindian domesticate, appears to have originated on the borders of Brazil and Guyana, followed by a dispersion through the Caribbean (Ayensu and Coursey, 1972). Yams were taken to the Americas through precolonial Portuguese and Spanish expansion that began around 500 years ago. Historical records of D. alata in West Africa and of African yams in the Americas date back to the sixteenth century (Coursey, 1967).

Sweet potato, which originated in the Yucatan peninsula in Latin America, seems to be the most widely dispersed root crop. It is adaptable and can grow under many different ecological conditions. It has a shorter growth period than most other root crops (three to five months) and shows no marked seasonality: under suitable climatic conditions it can be grown all the year round. Adverse weather conditions rarely cause a complete crop loss. Hence sweet potatoes are planted as an "insurance crop", combined in mixed cropping with grains like rice in Southeast Asia, and with other root crops like cocoyam and yam in Oceania. It is a popular plant in the Philippines and in Japan because of its prostrate habit, which makes it resistant to damage by high winds such as hurricanes and typhoons (Wilson, 1977). Sweet potatoes have been cultivated since about 3 000 B.C. and were an important food for the Mayans in Central America and the Peruvians in the Andes. From ethno-historical records of Colombia, the reports of Spanish explorers and missionaries in Mexico and Peru, and of the Portuguese in Brazil, it is clear that sweet potato was common throughout the American tropics before 1492. The plant was further dispersed by Iberian and Portuguese explorers to the Pacific area in the sixteenth century. The Portuguese explorers subsequently transferred West Indian clones, grown in the western Mediterranean area, to Africa, India and the East Indies. Spanish traders also took sweet potatoes from Mexico to Manila. Later the sweet potato reached New Guinea and the eastern Pacific Islands and extended into China and Japan. It is now grown extensively in a wide range of environments between latitude 40N and 40S and from sea level up to an altitude of 2 300 metres.

The distribution of potato is also extensive. It originated in the high Andes of South America where it was adapted to the cold climate and short days prevailing in those latitudes. Wild cultivars are still found on elevated regions extending from the southwestern part of the United States of America to the southern part of South America, and more especially at high altitudes in Bolivia and Peru and in the coastal regions and nearby islands of southern Chile (Simmonds, 1976). When the original potato was first introduced to Europe it remained a botanical curiosity for more than a century and it did not flourish until a variety adapted to the longer day was evolved.

Spanish sailors introduced the potato to Spain as early as 1573. It was probably introduced into England by English seamen from captured Spanish ships around 1590. From Spain, potatoes spread throughout continental Europe; from England, they were dispersed throughout Great Britain to parts of northern Europe. By 1600, potatoes were sent from Spain to Italy and from there to Germany and in the same year they reached France.

Potatoes reached most other parts of the world through European colonial activities. North America received potatoes from England in 1621, British missionaries took potatoes to Asia in the seventeenth century and Belgium missionaries carried them to the Congo in the nineteenth century. The potato was brought to India in the sixteenth century by Portuguese traders and within about 200 years it had spread all over India. It was taken to Bhutan, Nepal and Sikkin from India. In Africa, introduction of potatoes followed colonization. Possibly, its antiscorbutic properties persuaded seafarers to stock it in their ship's store and to encourage people to grow it wherever they visited.

Like sweet potato, potato also exhibits a growing period of about four months, shorter than many other root crops. The indigenous South American cultivars will develop tubers at longer day lengths than other root crops and numerous cultivars will even tolerate the extreme day length of 24 hours of the polar summer (Kay, 1973). So the spread was very easy.

A typical example of a root crop that can tolerate drought and poor husbandry is cassava. Cassava originated in tropical America but the precise area of its origin is not known. The two probable areas suggested are the Mexican and Central American area or northern South America. It was first introduced into the Congo basin as early as 1558 by the Portuguese. It then spread rapidly through Angola, Zaire, Congo and Gabon and later to West Africa. There was a separate introduction to the east coast of Africa and to Madagascar in the eighteenth century by Portuguese and Arab traders, after which it rapidly became a dietary staple throughout many lowland tropical areas (Jones, 1959). The cultivation of cassava in Africa increased during the nineteenth and twentieth centuries as a result of encouragement by administrative authorities, who recognized its value as a famine relief crop. According to Kahn (1985), after the First World War, the farmers of RuandaUrundi, now the independent nations of Rwanda and Burundi, at first refused to take advice from the Belgians to plant cassava, because they had enough potatoes. But in 1924 the Belgians issued a strict order to grow cassava and recruited 60 000 porters to carry 5 000 tonnes of cassava stakes around the region for planting, so the farmers finally accepted.

Cassava was taken to India by the Portuguese in the seventeenth century. In about 1850, it was transported directly from Brazil to Java, Singapore and Malaya. Cassava was introduced to the South Pacific territories during the first half of the nineteenth century by missionaries and travellers but its importance varies from island to island. At present, cassava is grown throughout tropical and subtropical areas approximating 30N and 30S of the equator and up to an altitude of 1 500 metres.

The spread of root crops was facilitated by their ability to thrive under varied tropical conditions. Their level of water tolerance varies considerably, ranging from the waterlogged conditions required for taro to the drought tolerance and minimal water supplies needed for cassava once it has been established (Wilson, 1977). It was the requirement of flooded conditions for taro, Colocasia esculenta, that convinced anthropologists that these yams were the first irrigated crops, and that the ancient "rice" terraces of Asia were originally constructed for them (Plucknett et al., 1970). Tannia (Xanthosoma sagittifolium) on the other hand cannot tolerate being waterlogged (Onwueme, 1978).

Xanthosoma, or new cocoyam, had its origin in South America and the Caribbean. The Spanish and Portuguese introduced it to Europe and were also responsible for spreading it to Asia. It moved from the Caribbean in the late nineteenth century, first to Sierra Leone and then to Ghana. In West Africa, Xanthosoma is more important than Colocasia, being popular for its corm, cormels, leaves and young stems. Although Xanthosoma is relatively new to the Pacific region, it has spread rapidly and widely, becoming quite an important crop in many of the islands. It is also widely cultivated in Puerto Rico, the Dominican Republic and Cuba and is important along the coastal mountains of South America, in the Amazon basin and in Central America.

Colocasia originated in India and Southeast Asia. About 2 000 years ago it spread to Egypt and thence to Europe (Plucknett et al., 1970). Subsequently it was taken from Spain to tropical America and then to West Africa. It was used in feeding slaves and was transferred to the West Indies with the slave trade (Coursey, 1968). In order to distinguish it from the newer species, Xanthosoma, Colocasia was referred to as "old yam" in West Africa whereas Xanthosoma is called "new yam". Colocasia is a staple food in many islands of the South Pacific, such as Tonga and Western Samoa, and in Papua New Guinea. Colocasia and Xanthosoma will tolerate shade conditions and so they are often planted under permanent plantations like banana, coconut, citrus, oil palm and especially cocoa. Therefore they are sometimes collectively referred to as cocoyams.

The banana is believed to have originated in Southeast Asia, having been cultivated in South India around 500 BC. From here it was distributed to Malaya through Madagascar and linen moved eastward across the Pacific to Japan and Samoa in the mid-Pacific at about AD 1000. It was probably introduced to East Africa around AD 500 and had become well established in West Africa by AD 1400. It finally arrived in the Caribbean and Latin America soon after AD 1500 (Simmonds, 1962; 1966; 1976). By the end of the eleventh century, banana had spread widely throughout the tropics. In South America it was found as far south as Bolivia and was cultivated in most of Brazil. In Africa banana growing extended from the Sahara to Tanzania in the east and from Cte d'Ivoire through the Congo to Zaire in the west and central areas.

TABLE 2.2 - Minor root crops of local lmportance

Local names Root crop species Suggested origin Other names
Chayote Sechium ecu/e Mexico Chinchayote, Guisquil (Spanish)
Jicama Pachyrhyzus Mexico  
Yam be an Pachyrhyzus and Sphenoslylis stenocarpa    
Arrow root Maranta arundinacea Polynesia Pana, Panapen
Arracachia Arracacia xanthorrhiza    
Oca Oxalis tuberosa    
Queensland arrowroot Cana edulis    
Topee Tambo Calathea allouia    
Ulluco Ullucus ruberosus Mellocco, oca-quira  
Yacon Polymnia sonchifolia    

Apart from the major root crops discussed in this book, other root crops exist in different parts of the world, mainly in the Andean region, and are of local importance. Some of these are shown in Table 2.2.

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