Satsuma Imo

The sweet potato or sweetpotato (''Ipomoea batatas'') is a dicotyledonous plant that belongs to the bindweed or morning glory family, Convolvulaceae. Its large, starchy, sweet-tasting tuberous roots are used as a root vegetable. The young shoots and leaves are sometimes eaten as greens. Cultivars of the sweet potato have been bred to bear tubers with flesh and skin of various colors. Sweet potato is only distantly related to the common potato (''Solanum tuberosum''), both being in the order Solanales. Although darker sweet potatoes are often referred to as "yams" in parts of North America, the species is not a true yam, which are monocots in the order Dioscoreales.

Sweet potato is native to the tropical regions of the Americas. Of the approximately 50 genera and more than 1,000 species of Convolvulaceae, ''I. batatas'' is the only crop plant of major importance—some others are used locally (e.g., ''I. aquatica'' "kangkong"), but many are poisonous. The genus ''Ipomoea'' that contains the sweet potato also includes several garden flowers called morning glories, though that term is not usually extended to ''I. batatas''. Some cultivars of ''I. batatas'' are grown as ornamental plants under the name ''tuberous morning glory,'' and used in a horticultural context.

Description

The plant is a herbaceous perennial vine, bearing alternate triangle-shaped or palmately lobed leaves and medium-sized sympetalous flowers. The stems are usually crawling on the ground and form adventitious roots at the nodes. The leaves are screwed along the stems. The leaf stalk is 5 to 20 inches long. The leaf blades are very variable, long, the shape is heart-, kidney- to egg-shaped, rounded or triangular and spear-shaped, the edge can be entire, toothed or often three to seven times lobed, cut or divided. Most of the leaf surfaces are bare, rarely hairy, and the tip is rounded to pointed. The leaves are mostly green in color, but due to the accumulation of anthocyanins, especially along the leaf veins, they can be purple in color. Depending on the variety, the total length of a stem can be between 0.5 and 4 meters. Some cultivars also form shoots up to 16 meters in length. However, these do not form underground storage organs.

The hermaphrodite, five-fold and short-stalked flowers are single or few in stalked, zymous inflorescences that arise from the leaf axils and stand upright. Some varieties rarely or never produce flowers. The small sepals are elongated and tapering to a point and spiky and (rarely only 7) 10 to 15 mm long, usually finely haired or ciliate. The inner three are a little longer. The 4 to 7 cm long, overgrown and funnel-shaped, folded crown, with a shorter hem, can be lavender to purple-lavender in color, the throat is usually darker in color, but white crowns can also appear. The enclosed stamens are of unequal length with glandular filaments. The two-chamber ovary is upper constant with a relatively short stylus. Seeds are only produced from cross-pollination.

The flowers open before sunrise and stay open for a few hours. They close again in the morning and begin to wither. The edible tuberous root is long and tapered, with a smooth skin whose color ranges between yellow, orange, red, brown, purple, and beige. Its flesh ranges from beige through white, red, pink, violet, yellow, orange, and purple. Sweet potato cultivars with white or pale yellow flesh are less sweet and moist than those with red, pink or orange flesh.

Naming

Although the soft, orange sweet potato is often called a " yam" in parts of North America, the sweet potato is very distinct from the botanical yam (''Dioscorea''), which has a cosmopolitan distribution, and belongs to the monocot family Dioscoreaceae. A different crop plant, the ''oca'' (''Oxalis tuberosa'', a species of wood sorrel), is called a "yam" in many parts.

Although the sweet potato is not closely related botanically to the common potato, they have a shared etymology. The first Europeans to taste sweet potatoes were members of Christopher Columbus's expedition in 1492. Later explorers found many cultivars under an assortment of local names, but the name which stayed was the indigenous Taino name of '' batata''. The Spanish combined this with the Quechua word for potato, ''papa'', to create the word ''patata'' for the common potato.

Though the sweet potato is also called "batata" (') in Hebrew, this is not a direct loan of the Taino word. Rather, the Spanish ''patata'' was loaned into Arabic as "batata" ('), owing to the lack of a /p/ sound in Arabic, while the sweet potato was called "batata khilwa" ('); literally meaning "sweet potato"). The Arabic ''batata'' was loaned into Hebrew as designating the sweet potato only, as Hebrew had its own word for the common potato, ' ("tapuakh adama", literally meaning "earth apple"; compare french '' pomme de terre'').

Some organizations and researchers advocate for the styling of the name as one word—"sweetpotato"—instead of two, to emphasize the plant's genetic uniqueness from both common potatoes and yams and to avoid confusion of it being classified as a type of common potato. In its current usage in American English, the styling of the name as two words is still preferred.

In Argentina, Colombia, Venezuela, Puerto Rico, Brazil, and the Dominican Republic, the sweet potato is called ''batata''. In Mexico, Bolivia, Peru, Chile, Central America, and the Philippines, the sweet potato is known as ''camote'' (alternatively spelled ''kamote'' in the Philippines), derived from the Nahuatl word ''camotli''.

In Peru and Bolivia, the general word in Quechua for the sweet potato is ''apichu'', but there are variants used such as ''khumara'', ''kumar'' (Ayacucho Quechua), and ''kumara'' (Bolivian Quechua), strikingly similar to the Polynesian name ''kumara'' and its regional Oceanic cognates (''kumala'', ''umala'', '' 'uala'', etc.), which has led some scholars to suspect an instance of pre-Columbian trans-oceanic contact. This theory is also supported by genetic evidence.

In Australia, about 90% of production is devoted to the orange cultivar 'Beauregard', which was originally developed by the Louisiana Agricultural Experiment Station in 1981.

In New Zealand, the Māori varieties bore elongated tubers with white skin and a whitish flesh, which points to pre-European cross-Pacific travel. Known as ''kūmara'' (in the Māori language and New Zealand English), the most common cultivar now is the red 'Owairaka', but orange ('Beauregard'), gold, purple and other cultivars are also grown.

History

Origin

The origin and domestication of sweet potato occurred in either Central or South America. In Central America, domesticated sweet potatoes were present at least 5,000 years ago, with the origin of ''I. batatas'' possibly between the Yucatán Peninsula of Mexico and the mouth of the Orinoco River in Venezuela. The cultigen was most likely spread by local people to the Caribbean and South America by 2500 BCE.

'' Ipomoea trifida'', diploid, is the closest wild relative of the sweet potato (''Ipomoea batatas''), which originated with an initial cross between a tetraploid and another diploid parent, followed by a second complete genome duplication event. The oldest radiocarbon dating remains of the sweet potato known today were discovered in caves from the Chilca Canyon, in the south central zone of Peru, and yield an age of 8080 ± 170 BC.

Dispersal

The sweet potato was grown in Polynesia before Western exploration, generally spread by vine cuttings rather than by seeds. Sweet potato has been radiocarbon-dated in the Cook Islands to 1210–1400 CE. A common hypothesis is that a vine cutting was brought to central Polynesia by Polynesians who had traveled to South America and back, and spread from there across Polynesia to Easter Island, Hawaii and New Zealand. Genetic similarities have been found between Polynesian peoples and indigenous Americans including the Zenú, a people inhabiting the Pacific coast of present-day Colombia, indicating that Polynesians could have visited South America and taken sweet potatoes prior to European contact. Dutch linguists and specialists in Amerindian languages Willem Adelaar and Pieter Muysken have suggested that the word for sweet potato is shared by Polynesian languages and languages of South America: Proto-Polynesian * (compare Rapa Nui , Hawaiian , Māori ) may be connected with Quechua and Aymara ~ . Adelaar and Muysken assert that the similarity in the word for sweet potato is proof of either incidental contact or sporadic contact between the Central Andes and Polynesia.

Some researchers, citing divergence time estimates, suggest that sweet potatoes might have been present in Polynesia thousands of years before humans arrived there. However, the present scholarly consensus favours the pre-Columbian contact model.

Sweet potatoes were first introduced to the Philippines during the Spanish colonial period (1521-1898) via the Manila galleons, along with other New World crops. It was introduced to the Fujian province of China in about 1594 from Luzon, in response to a major crop failure. The growing of sweet potatoes was encouraged by the Governor Chin Hsüeh-tseng (Jin Xuezeng).

Sweet potatoes were also introduced to the Ryukyu Kingdom, present-day Okinawa, Japan, in the early 1600s by the Portuguese. Sweet potatoes became a staple in Japan because they were important in preventing famine when rice harvests were poor. Aoki Konyō helped popularize the cultivation of the sweet potato in Japan, and the Tokugawa bakufu sponsored, published, and disseminated a vernacular Japanese translation of his research monograph on sweet potatoes to encourage their growth more broadly. Sweet potatoes were planted in Shōgun Tokugawa Yoshimune's private garden. It was first introduced to Korea in 1764. Kang P'il-ri and Yi Kwang-ryŏ embarked on a project to grow sweet potatoes in Seoul in 1766, using the knowledge of Japanese cultivators they learned in Tongnae starting in 1764. The project succeeded for a year but ultimately failed in winter 1767 after Kang's unexpected death.

The sweet potato arrived in Europe with the Columbian exchange. It is recorded, for example, in ''Elinor Fettiplace's Receipt Book'', compiled in England in 1604.Dickson Wright, 2011. Pages 149–169

Transgenicity

The genome of cultivated sweet potatoes contains sequences of DNA from ''Agrobacterium'' (''sensu lato''; specifically, one related to ''Rhizobium rhizogenes''), with genes actively expressed by the plants. The T-DNA transgenes were not observed in closely related wild relatives of the sweet potato. Studies indicated that the sweet potato genome evolved over millennia, with eventual domestication of the crop taking advantage of natural genetic modifications. These observations make sweet potatoes the first known example of a naturally transgenic food crop.

Cultivation

The plant does not tolerate frost. It grows best at an average temperature of , with abundant sunshine and warm nights. Annual rainfalls of are considered most suitable, with a minimum of in the growing season. The crop is sensitive to drought at the tuber initiation stage 50–60 days after planting, and it is not tolerant to water-logging, as it may cause tuber rots and reduce growth of storage roots if aeration is poor.

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 Eastern United States and China. 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 shoots called "slips" that grow out from the tuberous roots during storage. True seeds are used for breeding only.

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 favorable for the plant. They can be grown in poor soils with little fertilizer. However, sweet potatoes are very sensitive to aluminum toxicity and will die about six weeks after planting if lime is not applied at planting in this type of soil. 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. A commonly used herbicide to rid the soil of any unwelcome plants that may interfere with growth is DCPA, also known as Dacthal. 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 first frosts.

Sweet potatoes are cultivated throughout tropical and warm temperate regions wherever there is sufficient water to support their growth. Sweet potatoes became common as a food crop in the islands of the Pacific Ocean, South India, Uganda and other African countries.

A cultivar of the sweet potato called the ''boniato'' is grown in the Caribbean; its flesh is cream-colored, unlike the more common orange hue seen in other cultivars. ''Boniatos'' are not as sweet and moist as other sweet potatoes, but their consistency and delicate flavor are different than the common orange-colored sweet potato.

Sweet potatoes have been a part of the diet in the United States for most of its history, especially in the Southeast. The average per capita consumption of sweet potatoes in the United States is only about per year, down from in 1920. "Orange sweet potatoes (the most common type encountered in the US) received higher appearance liking scores compared with yellow or purple cultivars." Purple and yellow sweet potatoes were not as well liked by consumers compared to orange sweet potatoes "possibly because of the familiarity of orange color that is associated with sweet potatoes."

In the Southeastern United States, sweet potatoes are traditionally cured to improve storage, flavor, and nutrition, and to allow wounds on the periderm of the harvested root to heal. Proper curing requires drying the freshly dug roots on the ground for two to three hours, then storage at with 90 to 95% relative humidity from five to fourteen days. Cured sweet potatoes can keep for thirteen months when stored at with >90% relative humidity. Colder temperatures injure the roots.

Production

In 2020, global production of sweet potatoes was 89 million tonnes, led by China with 55% of the world total (table). Secondary producers were Malawi, Tanzania, and Nigeria.

Diseases

Nutrient content

Cooked sweet potato (baked in skin) is 76% water, 21% carbohydrates, 2% protein, and contains negligible fat (table). In a 100 gram reference amount, baked sweet potato provides 90 calories, and rich contents (20% or more of the Daily Value, DV) of vitamin A (120% DV), vitamin C (24% DV), manganese (24% DV), and vitamin B6 (20% DV). It is a moderate source (10-19% DV) of some B vitamins and potassium.

Sweet potato cultivars with dark orange flesh have more beta-carotene (converted to a higher vitamin A content once digested) than those with light-colored flesh, and their increased cultivation is being encouraged in Africa where vitamin A deficiency is a serious health problem. Sweet potato leaves are edible and can be prepared like spinach or turnip greens.

Comparison to other food staples

The table below presents the relative performance of sweet potato (in column) to other staple foods on a dry weight basis to account for their different water contents. While sweet potato provides less edible energy and protein per unit weight than cereals, it has higher nutrient density than cereals.

According to a study by the United Nations Food and Agriculture Organization, sweet potatoes are the most efficient staple food to grow in terms of farmland, yielding approximately / day.

Culinary uses

The starchy tuberous roots of the sweet potato are by far the most important product of the plant, although the leaves and shoots are also edible. In some tropical areas, they are a staple food crop. The tuber is often cooked before consumption as this increases its nutrition and digestibility, although the American colonists in the Southeast ate raw sweet potatoes as a staple food.

The vines' tips and young leaves are edible as a green vegetable with a characteristic flavor. Older growths may be used as animal fodder.

Africa

''Amukeke'' (sun-dried slices of root) and ''inginyo'' (sun-dried crushed root) are a staple food for people in northeastern Uganda. ''Amukeke'' is mainly served for breakfast, eaten with peanut sauce. ''Inginyo'' is mixed with cassava flour and tamarind to make ''atapa''. People eat ''atapa'' with smoked fish cooked in peanut sauce or with dried cowpea leaves cooked in peanut sauce. ''Emukaru'' (earth-baked root) is eaten as a snack anytime and is mostly served with tea or with peanut sauce. Similar uses are also found in South Sudan.

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. 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

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