Yams (Dioscorea)

Description

Yam, any of several plant species of the genus Dioscorea (family Dioscoreaceae) is native to warmer regions of both hemispheres. This thick, tropical-vine tuber is popular in Africa, the West Indies, and parts of Asia, South and Central America. By virtue of its excellent palatability, it is a high value crop. Yams are cultivated throughout the tropics, and in parts of the sub-tropics and temperate zones. In West Africa and New Guinea, the yam is a primary agricultural commodity.

Although sweet potato and yams are similar in many ways and therefore often confused with one another, they are from different plant species. In the southern United States, sweet potatoes are often called "yams" and to add to the confusion, canned sweet potatoes are frequently labeled yams. True yams, however, are not widely marketed and are seldom grown in the United States. D. bulbifera, the air-potato yam, is one of the few true yams cultivated for food in the U.S. There are over 150 species of yam grown throughout the world. Yam tubers can range in size from that of a small potato to behemoths over 71/2 feet long and 120 pounds. Depending on the variety, a yam's flesh may be various shades of off-white, yellow, purple, or pink, and the skin from off-white to dark brown. The texture of this vegetable can range from moist and tender to coarse, dry, and mealy. Yams can be found in most Latin American markets, often in chunks, sold by weight.

Statistics

In 2004, global yam production was almost 47 million metric tons, 96% of this in Africa. Nigeria alone accounts for about 70 percent of the world production. It is the second most important root/tuber crop in Africa with production reaching just under one third the level of cassava. More than 95 percent (2.8 million ha) of the current global area under yam cultivation is in sub-Saharan Africa, where mean gross yields are 10 t/ha. In Asia, production for 2004 stood at 226,426 metric tons.

Area Harvested in 2004:
World: 4,371,947 hectares
Examples by country:
Nigeria: 2,837,000 hectares
Ghana: 310,834 hectares
Benin: 72,739 hectares

How Yam is Used

People consume yams, sweet in flavor, as a cooked vegetable. In West Africa it is often pounded into a thick paste after boiling and is eaten with soup. Yams are also processed into flour that is used in the preparation of the paste. Virtually all production is used for human food. Yam is a preferred food and a food security crop in some sub-Saharan African countries. Unlike cassava, sweet potato, and aroids, one can store yam tubers for periods of up to 4 or even 6 months at ambient temperatures. This characteristic contributes to the sustaining of food supply, especially in the difficult (food scarce) period at the start of the wet season.

Nutritional information

Yams constitute a multi-species crop. Though they can be similar in size and shape to sweet potatoes, yams are not as rich in vitamins A and C as sweet potatoes. However yams tend to be higher in protein and minerals like phosphorus and potassium. Most yams contain an acrid principle that is dissipated in cooking. D. rotundata and D. alata are the edible species most widely diffused in tropical and subtropical countries. D. esculenta, grown on the subcontinent of India, in southern Vietnam, and in the South Pacific islands, is one of the most nutritious yams.

CGIAR Centers' Work on Yam

One of the CGIAR research centers, the International Institute of Tropical Agriculture (IITA), in Ibadan, Nigeria, has the global research mandate for yams. IITA scientists work in collaboration with NARS to ensure that farmers achieve a sustainable increase in the productivity of yam-based systems through the adoption of improved technologies. These technologies include improved varieties as well as strategies for management of pests, soil and vegetation. The available plant genetic resources in IITA's gene banks and elsewhere have contributed to IITA's success in improving yams for farmers to use. This has been achieved through the selection of elite local germplasm, and through genetic enhancement to broaden the genetic base of improved varieties. Scientists at IITA now have the most comprehensive set of diagnostics for yam viruses in the world. This is important for the safe exchange of germplasm around the world and in the selection of varieties with inherent resistance to viruses. Many high-yielding and pest-tolerant varieties/breeding lines developed at IITA have been tested by several national programs towards adoption by farmers for increasing food production.

For more information on yam from the IITA web site, click here.

Sources

FAOSTAT. PRODSTAT.

The New Encyclopedia Britannica, Volume 12, 1987.

CGIAR Priorities and Strategies for Resource
Allocation during 1998-2000.
April 29, 1997

IITA Annual Report 1997. 1998.

IITA Website