The sweet potato (Ipomoea batatas) is a dicotyledonous plant which belongs to the family Convolvulaceae. Amongst the approximately 50 genera and more than 1000 species of this family, only I. batatas is a crop plant whose large, starchy, sweet tasting tuberous roots are an important root vegetable (Purseglove, 1991; Woolfe, 1992). The young leaves and shoots are sometimes eaten as greens. The sweet potato is only distantly related to the potato (Solanum tuberosum). It is commonly confused with a yam in parts of North America, although they are only very distantly related to the other plant widely known as yams (in the Dioscoreaceae family), which is native to Africa and Asia.
The genus Ipomoea that contains the sweet potato also includes several garden flowers called morning glories, though that term is not usually extended to Ipomoea batatas. Some cultivars of Ipomoea batatas are grown as ornamental plants.
This plant is a herbaceous perennial vine, bearing alternate heart-shaped or palmately lobed leaves and medium-sized sympetalous flowers. The edible tuberous root is long and tapered, with a smooth skin whose color ranges between red, purple, brown and white. Its flesh ranges from white through yellow, orange, and purple.
Origin, Distribution And Diversity
Sweet potatoes are native to the tropical parts of South America, and were domesticated there at least 5000 years ago.
Austin (1988) postulated that the centre of origin of I. batatas was between the Yucatán Peninsula of Mexico and the mouth of the Orinoco River in Venezuela. The ‘cultigen’ had most likely been spread by local people to the Caribbean and South America by 2500 BC. Zhang et al. (1998) provided strong supporting evidence that the geographical zone postulated by Austin is the primary centre of diversity. The much lower molecular diversity found in Peru-Ecuador suggests that this region be considered as secondary centre of sweet potato diversity.
The sweet potato was also grown before western exploration in Polynesia, where it is known as the kumara. Sweet potato has been radiocarbon-dated in the Cook Islands to 1000 AD, and current thinking is that it was brought to central Polynesia circa 700 AD, possibly by Polynesians who had traveled to South America and back, and spread across Polynesia to Hawaii and New Zealand from there. It is possible, however, that South Americans brought it to the Pacific. The theory that the plant could spread by floating seeds across the ocean is not supported by evidence. Another point is that the sweet potato in Polynesia is the cultivated Ipomoea batatas, which is generally spread by vine cuttings, and not by seeds.
Sweet potatoes are now cultivated throughout tropical and warm temperate regions wherever there is sufficient water to support their growth.
According to the Food and Agriculture Organization (FAO) statistics world production in 2004 was 127,000,000 tons. The majority comes from China with a production of 105,000,000 tonnes from 49,000 km². About half of the Chinese crop is used for livestock feed.
Per-capita production is greatest in countries where sweet potatoes are a staple of human consumption, led by the Solomon Islands at 160 kg per person per year, Burundi at 130 kg and Uganda at 100 kg.
20,000 tonnes of sweet potatoes are produced annually in New Zealand, where sweet potato is known by its Māori name, kūmara. It was a staple food for Māori before European contact
In the U.S., North Carolina, the leading state in sweet potato production, provided 38.5% of the 2007 U.S. production of sweet potatoes. California, Louisiana, and Mississippi compete closely with each other in production. Louisiana has been a long-time major producer, once second only to North Carolina, and closely followed by California until the latter began surpassing it in 2002. In 2007, California produced 23%, Louisiana 15.9%, and Mississippi 19% of the U.S. total.
Opelousas, Louisiana’s Yambilee has been celebrated every October since 1946. The Frenchmen who established the first settlement at Opelousas in 1760 discovered the native Attakapas, Alabama, Choctaw, and Opelousas Indian Tribes eating sweet potatoes. The sweet potato became a favorite food item of the French and Spanish settlers and thus continued a long history of cultivation in Louisiana.
Mississippi, with about 150 farmers presently growing sweet potatoes on approximately 8,200 acres (33 km2) and contributing $19 million dollars to the state’s economy. Mississippi’s top five sweet potato producing counties are Calhoun, Chickasaw, Pontotoc, Yalobusha, and Panola. The National Sweet Potato Festival is held annually the entire first week in November in Vardaman (Calhoun County), which proclaims itself as “The Sweet Potato Capital”.
The town of Benton, Kentucky celebrates the sweet potato annually with its Tater Day Festival on the first Monday of April. The town of Gleason, Tennessee celebrates the sweet potato on Labor Day weekend with its Tater Town Special.
The plant does not tolerate frost. It grows best at an average temperature of 24 °C (75 °F), abundant sunshine and warm nights. Annual rainfalls of 750-1000 mm are considered most suitable, with a minimum of 500 mm in the growing season. The crop is sensitive to drought at the tuber initiation stage 50–60 days after planting and is not tolerant to water-logging, as it may cause tuber rots and reduce growth of storage roots if aeration is poor (Ahn, 1993).
Depending on the cultivar and conditions, tuberous roots mature in two to nine months. With care, early-maturing cultivars can be grown as an annual summer crop in temperate areas, such as the northern United States. Sweet potatoes rarely flower when the daylight is longer than 11 hours, as is normal outside of the tropics. They are mostly propagated by stem or root cuttings or by adventitious roots called “slips” that grow out from the tuberous roots during storage. True seeds are used for breeding only.
Under optimal conditions of 85 to 90 % relative humidity at 13 to 16 °C (55 to 61 °F), sweet potatoes can keep for six months. Colder temperatures injure the roots.
They grow well in many farming conditions and have few natural enemies; pesticides are rarely needed. Sweet potatoes are grown on a variety of soils, but well-drained light and medium textured soils with a pH range of 4.5-7.0 are more favourable for the plant (Woolfe, 1992; Ahn, 1993). They can be grown in poor soils with little fertilizer. However, sweet potatoes are very sensitive to aluminium toxicity and will die about 6 weeks after planting if lime is not applied at planting in this type of soil (Woolfe, 1992). Because they are sown by vine cuttings rather than seeds, sweet potatoes are relatively easy to plant. Because the rapidly growing vines shade out weeds, little weeding is needed, and farmers can devote time to other crops. In the tropics the crop can be maintained in the ground and harvested as needed for market or home consumption. In temperate regions sweet potatoes are most often grown on larger farms and are harvested before frosts set in.
China is the largest grower of sweet potatoes; providing about 80% of the world’s supply, 130 million tons were produced in one year (in 1990; about half that of common potatoes). Historically, most of China’s sweet potatoes were grown for human consumption, but now most (60%) are grown to feed pigs. The rest are grown for human food and for other products. Some are grown for export, mainly to Japan. China grows over 100 varieties of sweet potato.
After introduction there, sweet potatoes very early became popular in the islands of the Pacific Ocean, from Japan to Polynesia. One reason is that they were a reliable crop in cases of crop failure of other staple foods due to typhoon flooding. They are featured in many favorite dishes in Japan, Taiwan, the Philippines, and other island nations. Indonesia, Vietnam, India, and some other Asian countries are also large sweet potato growers. Uganda (the third largest grower after Indonesia), Rwanda, and some other African countries also grow a large crop which is an important part of their peoples’ diets. North and South America, the original home of the sweet potato, together grow less than three percent of the world’s supply. Europe has only a very small sweet potato production, mostly in Portugal. In the Caribbean, a variety of the sweet potato called the boniato is very popular. The flesh of the boniato is cream-colored, unlike the more popular orange hue seen in other varieties. Boniatos are not as sweet and moist as other sweet potatoes, but many people prefer their fluffier consistency and more delicate flavor. Boniatos have been grown throughout the subtropical world for centuries, but became an important commercial crop in Florida in recent years.
Sweet potatoes were an important part of the diet in the United States for most of its history, especially in the Southeast. From the middle of the 20th century, however, they have become less popular. The average per capita consumption of sweet potatoes in the United States is only about 1.5–2 kg (4 lbs) per year, down from 13 kg (31 lb) in 1920. Southerner Kent Wrench writes: “The Sweet Potato became associated with hard times in the minds of our ancestors and when they became affluent enough to change their menu, the potato was served less often.”
New Zealanders grow enough kūmara to provide each person with 7 kg (15.4 lbs) per year, and also import substantially more than this from China.
The roots are most frequently boiled, fried, or baked. They can also be processed to make starch and a partial flour substitute. Industrial uses include the production of starch and industrial alcohol.
Although the leaves and shoots are also edible, the starchy tuberous roots are by far the most important product. In some tropical areas, they are a staple food-crop.
“Amukeke” (sun dried slices of storage roots) and “Inginyo” (sun dried crushed storage roots) are a staple food for people in north-eastern Uganda (Abidin, 2004). Amukeke is mainly for breakfast, eaten with peanut sauce. People generally eat this food while they are drinking a cup of tea in the morning, around 10 am. Inginyo will be mixed with cassava flour and tamarind, to make food called “atapa”. People eat “atapa” with smoked fish cooked in peanut sauce or with dried cowpea leaves cooked in peanut sauce.
Candied sweet potatoes are a side dish consisting mainly of sweet potatoes prepared with brown sugar, marshmallows, maple syrup, molasses, or other sweet ingredients. Often served on Thanksgiving, this dish represents traditional American cooking and of that prepared with the indigenous peoples of the Americas when settlers first arrived.
Sweet potato pie is also a traditional favorite dish in southern U.S. cuisine.
Baked sweet potatoes are sometimes offered in restaurants as an alternative to baked potatoes. They are often topped with brown sugar and butter. In Dominican Republic sweet potato is enjoyed for breakfast. In China sweet potatoes are often baked in a large iron drum and sold as street food during winter.
Sweet potato fries or chips are another common preparation, and are made by julienning and deep frying sweet potatoes, in the fashion of French fried potatoes.
Sweet potato leaves are a common side dish in Taiwanese cuisine, often boiled with garlic and vegetable oil and dashed with salt before serving. They are commonly found at bento (POJ: piān-tong) restaurants, as well as dishes featuring the sweet potato root.
The young leaves and vine tips of sweet potato leaves are widely consumed as a vegetable in West African countries (Guinea, Sierra Leone and Liberia for example), as well as in northeastern Uganda, East Africa (Abidin, 2004). According to FAO leaflet No. 13 – 1990, sweet potato leaves and shoots are a good source of vitamins A, C, and B2 (Riboflavin), and according to research done by A. KHACHATRYAN, are an excellent source of lutein.
Steamed/Boiled chunks, for a simple and healthy snack, chunks of sweet potato may be boiled in water or cooked in the microwave.
A Japanese yaki-imo vendor and cart outside Nara Park. Sweet Potato Butter can be cooked into a gourmet spread.
In Northeastern Chinese cuisine. sweet potatoes are often cut into chunks and fried before drench into a pan of boiling syrup. 
In Korean cuisine, sweet potato starch is used to produce dangmyeon (cellophane noodles). Sweet potatoes are also boiled, steamed, or roasted, and young stems are eaten as namul.
Japanese cuisine: Boiled sweet potato is the most common way to eat it at home. Also, the use in vegetable tempura is common. Yaki-imo (roasted sweeted potato) is a delicacy in winter, sold by hawkers. Daigaku-imo is a baked sweet potato dessert. In imo-gohan, slices or small blocks of sweet potato are cooked in rice. It is also served in nimono or nitsuke, boiled and typically flavoured with soy sauce, mirin and dashi. Because it is sweet and starchy, it is used in imo-kinton and some other wagashi (Japanese sweets), such as ofukuimo. Shōchū, a Japanese spirit normally made from the fermentation of rice, can also be made from sweet potato, in which case it is called imo-jōchū.
In New Zealand, Māori traditionally cooked their kūmara in hāngi (earth ovens). Rocks were placed on a fire in a large hole. When the fire died out, kūmara and other food was wrapped in leaves and placed on the hot rocks, then covered with earth. The kūmara was dug up again several hours later. The resulting food was very soft and tender, as though steamed. However, hangi are rare in modern New Zealand and New Zealanders, Maori or Pakeha, are more likely to consume it baked, boiled, or deep-fried (such as in kumara chips) than they are in hangi.
In Malaysia, sweet potato is often cut into small cubes and cooked with yam and coconut milk (santan) to make a sweet dessert called bubur caca. A favourite way of cooking sweet potato is deep frying slices of sweet potato in batter as a tea-time snack. In houses, sweet potatoes are usually boiled. The leaves of sweet potatoes are usually stir-fried with only garlic or with sambal belacan and dried shrimp by the Malaysian Chinese.
Non – Culinary Uses
In South America, the juice of red sweet potatoes is combined with lime juice to make a dye for cloth. By varying the proportions of the juices, every shade from pink to purple to black can be obtained.
All parts of the plant are used for animal fodder.
Sweet potatoes or camotes are often found in Moche ceramics.
Several selections are cultivated in gardens as ornamental plants for their attractive foliage, including the dark-leafed cultivars ‘Blackie’ and ‘Ace of Spades’ and the chartreuse-foliaged ‘Margarita’.
Taiwanese companies are making alcohol fuel from sweet potato.
You can Find number of different recipe in Ayesha’s Kitchen.