iPhoneOgraphy – 05 Jul 2016 (Day 187/366)
The sweet potato or kumara (Ipomoea batatas) is a dicotyledonous plant that belongs to the family Convolvulaceae.
Its large, starchy, sweet-tasting, tuberous roots are a root vegetable. The young leaves and shoots are sometimes eaten as greens. Ipomoea batatas is native to the tropical regions in 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. l. aquatica (kangkong)), but many are poisonous. The sweet potato is only distantly related to the potato (Solanum tuberosum) and does not belong to the nightshade family.
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 batatasare grown as ornamental plants; the name tuberous morning glory may be used in a horticultural context.
The 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 yellow, orange, red, brown, purple, and beige. Its flesh ranges from beige through white, red, pink, violet, yellow, orange, and purple. Sweet potato varieties with white or pale yellow flesh are less sweet and moist than those with red, pink or orange flesh.
The origin and domestication of sweet potato is thought to be in either Central America or South America. In Central America, sweet potatoes were domesticated at least 5,000 years ago. In South America, Peruvian sweet potato remnants dating as far back as 8000 BC have been found.
One author postulated that the origin of I. batataswas 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. Strong supporting evidence was provided that the geographical zone postulated by Austin is the primary center of diversity. The much lower molecular diversity found in Peru–Ecuador suggests this region should be considered as a secondary center of sweet potato diversity.
The sweet potato was grown in Polynesia before western exploration. Sweet potato has been radiocarbon-dated in the Cook Islands to 1000 AD, and current thinking is that it was brought to central Polynesia around 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, although this is unlikely as it was the Polynesians who had a strong maritime tradition and not the Native South Americans. 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 cultivated throughout tropical and warm temperate regions wherever there is sufficient water to support their growth. Due to a major crop failure, sweet potatoes were introduced to Fujian province of China in about 1594 from Luzon. The growing of sweet potatoes was encouraged by the Governor Chin Hsüeh-tseng (Jin Xuezeng). Sweet potatoes were introduced as a food crop in Japan, and by 1735 was planted in Shogun Tokugawa Yoshimune’s private garden. It was also introduced to Korea in 1764.
Sweet potatoes became popular very early in the islands of the Pacific Ocean, spreading from Polynesia to Japan and the Philippines. One reason is that they were a reliable crop in cases of crop failure of other staple foods because of 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. Sweet potato, also known as kelangin Tulu is part of Udupi cuisine. Uganda (the second largest grower after China), Rwanda, and some other African countries also grow a large crop which is an important part of their peoples’ diets. The New World, the original home of the sweet potato, grows less than three percent (3%) of the world’s supply. Europe has only a very small sweet potato production, mainly in Portugal. In the Caribbean, a variety of the sweet potato called the boniato is 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.
Sweet potatoes have been 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 (3.3–4.4 lb) per year, down from 13 kg (29 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.”
A study published in 2015 by scientists from Ghent University and the International Potato Center found that the genome of cultivated sweet potatoes contains sequences of DNA from Agrobacterium, with genes being actively expressed by the plants. The discovery of the transgenes was made while performing meta genomic analysis of the sweet potato genome for viral diseases. Transgenes were not observed in the sweet potato’s closely related wild relatives, but were also found in more distantly related wild species. This observation makes cultivated sweet potatoes the first known example of a naturally transgenic food crop.