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. In 2004 approximately 129,536,275 million tons were produced in more than 100 countries. Asia
is the world's largest sweet potato-producing region, with
114 million tons of annual production. China 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 12 million tons of sweet potatoes
annually but most of the crop is cultivated for human consumption.
Area Harvested in 2004:
World: 9,074,459 hectares
Examples by country:
China: 4,874,180 hectares
Nigeria: 954,000 hectares
Uganda: 602,000 hectares
Tanzania: 500,000 hectares
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
FAOSTAT. PRODSTAT.
Priorities
and Strategies for Resource Allocation during 1998-2000 and
Centre Proposals and TAC Recommendations, June 2000.
CIP web
site.
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