The best-known and most widely grown root and tuber crops are potato, sweet potato and cassava. These crops all originated in south and central America. They were introduced to Europe, Asia and Africa in the early 16th century and have become globally important crops.

The International Potato Center (CIP) maintains the largest potato and sweet potato genebanks in the world, each containing thousands of accessions of wild, traditional, and improved varieties.

A minor crop in world trade, but an important crop for food security, aroids are widespread throughout the humid tropics. The genera Colocasia and Xanthosoma are the most widely grown aroids, the former commonly known as taro and dasheen, the latter as cocoyam or tannia.

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Andean roots and tubers
Cassava
Potato
Sweet potato
Taro and cocoyam
Yam
Yam bean

Andean roots and tubers
Andean roots and tubers are showing great promise in efforts to fight hunger and improve livelihoods. In addition to the ‘big three’—potato, sweet potato and cassava—many other roots and tubers have their origins in the the South America. Still restricted to their native range, they are mostly grown by poor indigenous farmers who value the diversity these crops bring to diets and subsistence agriculture. Achira (Canna edulis), maca (Lepidium meyenii), yacon (Smallanthus sonchifolius) and ulluco (Ullucus tuberosus), to name just a few, share extraordinary pest and disease resistance, nutrient efficiency and adaptation to marginal and often harsh high-altitude environments. Occasionally these crops are traded locally but they are ignored in urban areas, where they have a reputation as poor people’s food and are seen as inconvenient because they take a long time to cook and have a short shelf life.

Yet recent research has shown that Andean roots and tubers possess interesting nutritional properties, notably particular starch qualities and high levels of vitamins, minerals and functional nutrients. A new appreciation of these properties has resulted in increased demand and has given farmers, who already use Andean roots and tubers for their own subsistence, opportunities for greater income.

Information source: Meeting the Millennium Development Goals with Agricultural Biodiversity

Publications
Andean roots and tubers: Ahipa, arracacha, maca and yacon

Mashua (Tropaeolum tuberosum Ruíz & Pav.)

Oca
Descriptores de Oca (Oxalis tuberosa Mol.)

Ulluco
Descriptores del Ulluco (Ullucus tuberosus)

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Cassava (Manihot esculentum)
Cassava, also called yuca, manioc and mandioca, is currently the sixth most produced crop globally, and is the staple for millions of people in the poorest and most marginal regions of the world. It is very hardy and has the ability to grow on land where drought is frequent and in soils low in nutrients, where cereals and other crops do not grow well. As cassava roots can be stored in the ground for up to 24 months, and for some varieties up to 36 months, harvest may be delayed until needed, or until processing or other conditions are favourable.

Cassava originated in the lowlands of South America, probably in the Amazon basin. Today the crop has spread all over the tropical and subtropical world. The crop is particularly important in sub-Saharan Africa, where it is absolutely crucial for the food security of millions.

Cassava’s high starch content, much higher than those of maize or rice, makes it a valuable source of carbohydrates. In Africa, people also eat the leaves as a green vegetable, which provide a cheap source of protein and vitamins A and B.

In Africa, roots are processed into a wide variety of granules, pastes, flours, etc., or consumed boiled or raw; it is also beginning to be used in partial substitution for wheat flour. In South-East Asia and Latin America cassava has taken on an expanded economic role. It is used commercially for the production of animal feed, and cassava starch is used as a binding agent in the production of paper and textiles and to produce monosodium glutamate, an important flavoring agent in Asian cooking.

Large collections of cassava are held at the International Center for Tropical Agriculture (CIAT), Colombia, and the International Institute of Tropical Agriculture (IITA), Nigeria.

Information source: Global Crop Diversity Trust

Publications
Cassava
FAO/IBPGR Technical Guidelines for the Safe Movement of Cassava Germplasm

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Potato (Solanum tuberosum)
The potato is by far the most important non-cereal crop in the world.

Potatoes provide more edible food annually than the combined world output of fish and meat, and significant quantities are grown in 156 countries. Important industrial uses include processing and manufacturing of starch and alcohol.

A single medium-sized potato contains about half the daily adult requirement of vitamin C. Other staples such as rice and wheat have none. The potato is very low in fat, with just 5 percent of the fat content of wheat, and a quarter of the calories of bread. Boiled, it has more protein than maize and nearly twice the calcium.

The potato provides one of the starkest warnings against the loss of crop diversity. In 19th century Ireland a devastating potato disease—potato blight—wiped out the potato crop and resulted in the deaths of more than a million people and the emigration of a similar number. The country had been reliant on one variety of one crop for its staple food, and that variety of potato had no resistance to the disease: there was no significant genetic diversity in the crop to provide protection. This grim story still serves as a reminder of the danger of genetic erosion and the need to maintain as much variety as possible in our staple crops.

The International Potato Center (CIP) in Peru maintains the world's largest bank of potato germplasm, including some 1500 samples of about 100 wild species collected in eight Latin American countries and 3800 traditional Andean cultivated potatoes.

Publications
Potato
FAO/IPGRI Technical Guidelines for the Safe Movement of Potato Germplasm

Descriptors Lists - Cultivated Potato

Descriptors Lists - Potato Variety (Solanum tuberosum Linnaeus)

Atlas of Wild Potatoes
Systematic and Ecogeographic Studies on Crop Genepools 10

Links
ECPGR Potato Working Group

Elsewhere on the site
Nutritious tubers: the Livingstone potato
Geneflow (Special section 2005)

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Sweet potato (Ipomea batatas)
Sweet potato is the potato of the tropics. It is a tough crop, able to grow in arid conditions with little water or fertilizer. Sweet potato ranks as the world’s seventh most important food crop, principally because of its versatility and adaptability.

The sweet potato is high in carbohydrates and vitamin A and can produce more edible energy per hectare per day than wheat, rice or cassava. The yellow-orange fleshed varieties provide particularly high quantities of vitamins A and C. The leaves can also be eaten, providing additional protein, vitamins and minerals.

Over 95 percent of the global sweet potato crop is produced in developing countries, where it is the fifth most important food crop in terms of fresh weight.

According to FAO's 1998 State of the World’s Plant Genetic Resources there are nearly 32 000 accessions held in genebanks around the world. The largest and most diverse collection is held at the International Potato Center (CIP) in Peru.

Information source: Global Crop Diversity Trust

Publications
Sweet Potato
FAO/IBPGR Technical Guidelines for the Safe Movement of Sweet Potato Germplasm

Sweet Potato/Patate Douce/Batata (Ipomoea batatas)

Meristem-tip Culture and Virus Indexing of Sweet Potatoes

Elsewhere on the site
Combating vitamin A deficiency with orange-fleshed sweet potato
Geneflow (Special section 2005)

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Taro and cocoyam

The aroids rarely enter into world commerce as they are mostly grown in subsistence agriculture systems and for local markets. However, the aroids play a substantial role in the food security of millions of people in the tropics. The starch-rich corms are the main product, but the leaves and the flowers are also eaten.

Taro (Colocasia esculenta) widely grown in the tropics and subtropics, but has been neglected by crop breeders and conservationists. Much of the diversity within the crop is still being maintained by farmers and local communities.

Although of New World origin, today the greatest use of cocoyam (Xanthosoma) is in West Africa. Taro (Colocasia) and cocoyam form an edible aroids complex, and the two are often substituted for each other.  Their uses are also very similar: the corm, cormel, petiole and leaf of both can all be used. Cocoyam is the third most important root and tuber crop in West and central Africa and probably the most important leafy vegetable.

Publications
Ethnobotany and genetic diversity of Asian taro: focus on China

Taro
Descripteurs pour le taro (Colocasia esculenta)
Descriptors for Taro (Colocasia esculenta)
Descriptores para el taró (Colocasia esculenta)

Xanthosoma

FAO / IBPGR Technical Guidelines for the Safe Movement of Edible Aroid Germplasm

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Yam (Dioscorea spp.)
Yam is the second most important root/tuber crop in Africa after cassava. Adapted to the humid and moist tropics it is important both culturally and for food security.

Virtually all global yam production takes place in the developing world. According to the International Institute of Tropical Agriculture (IITA), 90 percent of this production takes place in the 'yam zone', comprising Benin, Cameroon, Côte d'Ivoire, Ghana, Nigeria and Togo. Despite the dominance of these countries, FAO statistics show substantial yam production in 57 countries worldwide, and it is an important staple throughout humid and semi-humid tropical Asia and the Americas.

Of the more than 600 Dioscorea species, seven species constitute the most important staple yams, but many wild yams are also important food plants.  Yam is a very important crop for food security because it can be stored for four to six months without refrigeration and provides an important food safety net between growing seasons. Bitter yams such as Dioscorea dumetorum have an unpleasant taste and may be toxic; they are eaten in times of food scarcity as a characteristic ‘famine crop’. Varieties with such properties need to be detoxified by soaking and cooking before eating.

Conserving the genetic diversity of root crops is always more challenging than conserving seed crops. However, field collections of yams exist both in Asia and Africa, and new methods for seed yam production have been developed by IITA and Nigerian researchers. The largest genebank for yams globally is found at IITA, holding over 3,000 accessions from both cultivated and wild species.

Information source: Global Crop Diversity Trust

Publications
Yam
FAO / IBPGR Technical Guidelines for the Safe Movement of Yam Germplasm

Igname
Descripteurs de l'igname (Dioscorea spp.)

Ñame
Descriptores para el ñame (Dioscorea spp.)

Elsewhere on the site
Domesticated yams develop farmers diversity
Annual report 2002

The cultural roles of yams
Geneflow 2004 Special Section

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Yam Bean (Pachyrhizus DC)
Among the Neotropical legume genera with edible tuberous roots, such as Apios Fabr., Pachyrhizus Rich. ex DC, Pediomelum Rydb. and Vigna Savi, the yam bean (Pachyrhizus) is the only one that is extensively cultivated, both as a garden crop, and, in the case of P. erosus (L.) Urban, also on a large scale for export. P. erosus originated in Mexico and Central America, and is cultivated in Mexico, Guatemala, El Salvador and to a limited extent in Honduras. It has been introduced to different pantropical regions, with notable success in Southeast Asia.

Generic variation is certainly considerable. Plants range from robust vines to small erect bushes; their growth seasons range from less than five months to more than a year.

Information source: Yam Bean Pachyrhizus DC.

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