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Description

Despite its name, the sweet potato is not related to the potato. Potatoes are members of the Solanaceae family, which also includes tomatoes, red peppers, and eggplant, while sweet potatoes belong to the morning-glory family (Convolvulaceae). And unlike the potato-which is a tuber, or thickened stem-the sweet potato is a storage root. Both potatoes and sweet potatoes are reproduced vegetatively, that is, by sowing a part of the plant itself. In the case of potatoes, this may be a seed, or more commonly, a tuber or part of one, while with sweet potatoes, sprouts or vine cuttings are used. Sweet potato varieties exist in many colors of skin and flesh, ranging from white to deep purple, although white and yellow-orange flesh are the most common.

Scientists believe that the sweet potato was domesticated more than 5000 years ago. There is still much debate as to just where in the Americas this took place-South America or Central America-although recent evidence suggests that it was the latter. The sweet potato was already widely established in the Americas by the time Europeans first arrived there. From there, it spread to the Old World via diverse routes. The crop was reportedly introduced into China in the late 16th century. Because of its hardy nature and broad adaptability, and because its planting material can be rapidly multiplied from very few roots, the sweet potato spread through Asia and Africa during the 17th and 18th centuries.

Sweet potatoes are widely eaten in the island nations of the South Pacific, although how they reached there is open to debate. Some researchers believe European explorers took them there in the wake of the Spanish conquest of Latin America; others favor the idea that long before this, the sweet potato moved from island to island across the Pacific, taken there in boats by indigenous people.

Statistics

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. More than 133 million tons are produced per year in more than 100 countries. Asia is the world's largest sweet potato-producing region, with 125 million tons of annual production. China, at 117 million tons, supplies about 80% of the world's production, making it the leading supplier of sweet potatoes in the world. Nearly half of the sweet potatoes produced in Asia are used for animal feed, with the remainder primarily used for human consumption, either as fresh or processed products. In contrast, African farmers produce only about 7 million tons of sweet potatoes annually but most of the crop is cultivated for human consumption. Latin America, the original home of the sweet potato, produces 1.9 million tons annually. Production in North America is about 600,000 tons. The only European country that produces sizeable quantities of sweet potato is Portugal, at 23,000 tons.

How it is used? What is its nutritional value?

Sweet potatoes are used for human consumption, as livestock feed, and are in industrial processes to make alcohol and starch, and products such as noodles, candy, desserts, and flour. The green leaves of the plant may also be consumed by humans and animals.

Considered a small farmer's crop, sweet potatoes grow well in many farming conditions. The crop has relatively few natural enemies-which means that pesticides are rarely used to produce it-and can be grown in poor soils with little fertilizer. Because they are sown by vine cuttings rather than seeds sweet potatoes are relatively east to plant. In addition, the crop is highly tolerant of weeds, allowing farmers to devote time to other crops. Sweet potatoes can be harvested in 3 to 6 months and are well adapted to warm tropical lowlands. The major obstacles to sweet potato growth in the tropics are pests and diseases such as the sweet potato weevil and viruse diseases. The crop can be maintained in the ground for "piece meal" harvesting, a common sweet potato "storage" practice in the tropics. In temperate regions, the crop is harvested before frosts set in and stored in store houses or in underground pits during the winter.

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 flesh varieties also provide Vitamins A and C. Additionally, the green leaves of the plant can be consumed, providing additional protein, vitamins and minerals.

CGIAR Centers' Work on Sweet Potatoes

Outside the CGIAR, research on the sweet potato has been the subject of very scarce investment. Most CGIAR research on the sweet potato has been carried out at CIP, the International Potato Center-known by the acronym of its name in Spanish-in Lima, Peru. As research has shown, substantial potential exists for the expansion of sweet potato culture, providing a valuable source of income, food and the possibility of employment in developing countries.

Sweet potatoes are now being used in Africa to combat a widespread Vitamin A deficiency that results in blindness and even death for 250,000-500,000 African children a year. About two-thirds of the children developing xerophthalmia, the blindness-inducing disease resulting from lack of Vitamin A, die within a year of losing their sight. Though long a staple of the continent's diet, the African sweet potato contains white flesh which has no beta carotene (a precursor to Vitamin A) unlike its sweeter, yellow-orange fleshed relative. Researchers long believed that African palates would reject the colored variety but a CIP project conducted in eastern and southern Africa over the past ten years has identified a yellow-orange variety palatable to Africans. The researchers complemented their findings with the development of a nutritional education program that has been successful in motivating African mothers to accept new varieties of sweet potato. Researchers now intend to focus their efforts on developing a more productive crop and expanding the reach of their education program.

Recent research by CIP personnel in China has shown that sweet potato yield can be increased by as much as 30-40% without additional fertilizer, pesticide or genetic improvement. In a five-year project in the provinces of Anhui and Shandong, using a procedure that eliminates viral diseases from planting materials, scientists were able to develop virus-free cuttings that developed into healthy plants. If extended to all of China's sweet potato growing regions benefits exceeding US $1.5 billion could be realized. This development would considerably reduce the country's reliance on cereal imports for livestock feed.

In the Pho Yen province of Vietnam CIP researchers asked small farmers to alter their traditional pig feed-a labor-intensive, chopped, boiled sweet potato mixture-and instead allow the mixture to ferment. Though skeptical at first, farmers agreed and were delighted with the results-larger, healthier animals whose keep required less labor. Because of the labor intensive feeding process raising pigs was an activity that was previously only viable for more prosperous farmers. With the fermentation method small farmers are now able to raise pigs for themselves and to sell, providing the sole source of cash for many. Word of the successful trials has rapidly spread to other provinces and been put to use for other kinds of livestock; researchers plan to disseminate the technique throughout the country.

Sweetpotatoes are grown on 60,000 hectares across Cuba and is an important staple food. In 1993, when the country was suddenly cut off from pesticide imports, weevils devastated the crop. CIP and researchers from INIVIT-Cuba's Instituto de Investigación de Viandas Tropicales-joined forces to develop a comprehensive IPM program. Cuban sweet potato growers were able to move from dependence on chemicals to pesticide-free fields using a combination of low-cost control methods. This has brought important health and environmental benefits. Cuba's economy has gained an estimated US$31 million in increased yields, reduced losses and market value. Meanwhile, scientists continue to breed new and better sweetpotatoes that can resist weevil attacks and boost yields. They are seeking to develop plants with deeper, harder-to-get-to roots and slimmer stems, which are less attractive to the weevils. A promising candidate from combined INIVIT-CIP germplasm has already been identified. In trials, without other control measures, it yields 34 tonnes, with weevil loss at only 4 to 5 percent.

For more information on the sweet potato from the CIP web site, click here.

Sources

Priorities and Strategies for Resource Allocation during 1998-2000 and Centre Proposals and TAC Recommendations, June 2000.

CIP web site.