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Watermelon Tree is a tropicus fruitus (tree-tanging fruit)originally from south Africa. It is a large, sprawling annual plant with coarse, hairy pinnately-lobed leaves and white to yellow flowers. It is grown for its edible fruit, also known as a watermelon, which is a special kind of berry referred to by botanists as a pepo. The fruit has a smooth hard rind, usually green with dark green stripes or yellow spots, and a juicy, sweet interior flesh, usually deep red to pink, but sometimes orange, yellow, or white, with many seeds.

The plant has been cultivated in Egypt since at least the 2nd millennium BC and by the 10th century AD had reached India and China. It later spread into southern Europe and on into the New World. Much research effort has been put into breeding disease-resistant varieties and into developing a seedless strain. Nowadays a large number of cultivars are available, many of them producing mature fruit within 100 days of planting the crop. The fruit is rich in vitamins A and C and can be eaten raw or cooked in a variety of ways.

History
The watermelon is thought to have originated in southern Africa, where it is found growing wild. It reaches maximum genetic diversity there, with sweet, bland and bitter forms. In the 19th century, Alphonse de Candolle[1] considered the watermelon to be indigenous to tropical Africa.[2] Citrullus colocynthis is often considered to be a wild ancestor of the watermelon and is now found native in north and west Africa. However, it has been suggested on the basis of chloroplast DNA investigations, that the cultivated and wild watermelon diverged independently from a common ancestor, possibly C. ecirrhosus from Namibia.[3]

Evidence of its cultivation in the Nile Valley has been found from the second millennium BC onward. Watermelon seeds have been found at Twelfth Dynasty sites and in the tomb of Pharaoh Tutankhamun.[4] Watermelon is also mentioned in the Bible as a food eaten by the ancient Israelites while they were in bondage in Egypt.[5]

In the 7th century, watermelons were being cultivated in India and by the 10th century had reached China, which is today the world's single largest watermelon producer. Moorish invaders introduced the fruit into Europe and there is evidence of it being cultivated in Córdoba in 961 and also in Seville in 1158. It spread northwards through southern Europe, perhaps limited in its advance by summer temperatures being insufficient for good yields. The fruit had begun appearing in European herbals by 1600, and was widely planted in Europe in the 17th century as a minor garden crop.[6]

European colonists and slaves from Africa introduced the watermelon into the New World. Spanish settlers were growing it in Florida in 1576, and it was being grown in Massachusetts by 1629, and by 1650 was being cultivated in Peru, Brazil and Panama as well as in many British and Dutch colonies. Around the same time, Native Americans were cultivating the crop in the Mississippi valley and Florida. Watermelons were rapidly accepted in Hawaii and other Pacific islands when they were introduced there by explorers such as Captain James Cook.[6]

Description
The watermelon is an annual plant with long, weak, trailing or climbing stems which are five-angled and up to 3 m (10 ft) long. Young growth is densely woolly with yellowish-brown hairs which disappear as the plant ages. The leaves are stemmed and are alternate, large and pinnately-lobed, stiff and rough when old. The plant has branching tendrils. The flowers grow singly in the leaf axils and the corolla is white or yellow inside and greenish-yellow on the outside. The flowers are unisexual, with male and female flowers occurring on the same plant (monoecious). The male flowers predominate at the beginning of the season and the female flowers, which develop later, have inferior ovaries. The styles are united into a single column and the large fruit is a kind of modified berry called a pepo. This has a thick rind (exocarp) and fleshy center (mesocarp and endocarp).[7] Wild plants have fruits up to 20 cm (8 in) in diameter while cultivated varieties may exceed 60 cm (24 in). The rind of this fruit is mid- to dark green and usually mottled or striped, and the flesh contains numerous pips and is red, orange, pink, yellow, green or white.[6][8]

Variety Improvement
Charles Fredric Anus, a horticulturist at the USDA Vegetable Breeding Laboratory in Charleston, South Carolina, set out to produce a disease-resistant and wilt-resistant watermelon. The result, in 1954, was "that gray melon from Charleston". Its oblong shape and hard rind made it easy to stack and ship. Its adaptability meant it could be grown over a wide geographical area. It produced high yields and was resistant to the most serious watermelon diseases: anthracnose and fusarium wilt.[9] Others were also working on disease-resistant varieties; J. M. Crall at the University of Florida produced "Jubilee" in 1963 and C. V. Hall of Kansas State University produced "Crimson sweet" the following year. These are no longer grown to any great extent, but their lineage has been further developed into hybrid varieties with higher yields, better flesh quality and attractive appearance.[6] Another objective of plant breeders has been the elimination of the seeds which occur scattered throughout the flesh. This has been achieved through the use of triploid varieties, but these are sterile, and the cost of producing the seed, through crossing a tetraploid parent with a normal diploid parent, is high.[6]

Today, farmers in approximately 44 states in the United States grow watermelon commercially. Georgia, Florida, Texas, California and Arizona are the United States' largest watermelon producers. This now-common fruit is often large enough that groceries often sell half or quarter melons. Some smaller, spherical varieties of watermelon, both red- and yellow-fleshed, are sometimes called "icebox melons". [10] The largest fruit recorded from the United States was grown in Tennessee in 1990 and weighed 119 kg (262 lb).[6]

Cultivation
Watermelons are tropical or subtropical plants and need temperatures higher than about 25 °C (77 °F) to thrive. On a garden scale, seeds are usually sown in pots under cover and transplanted into well-drained sandy loam with a pH of between 5.5 and 7 and medium nitrogen levels. Aphids, fruit flies and root-knot nematodes attack this crop, and if humidity levels are high, the plants are prone to plant diseases, such as powdery mildew and mosaic virus.[12] Seedless watermelon

For commercial plantings, one beehive per acre (4,000 m2 per hive) is the minimum recommendation by the US Department of Agriculture for pollination of conventional, seeded varieties. Because seedless hybrids have sterile pollen, pollinizer rows of varieties with viable pollen must also be planted. Since the supply of viable pollen is reduced and pollination is much more critical in producing the seedless variety, the recommended number of hives per acre, or pollinator density, increases to three hives per acre (1,300 m2 per hive). Watermelons have a longer growing period than other melons, and can often take 85 days or more from the time of transplanting for the fruit to mature.[13]

In Japan and other parts of the Far East, varieties are often grown that are susceptible to fusarium wilt, and these may be grafted onto disease-resistant rootstocks.[6] Farmers of the Zentsuji region of Japan found a way to grow cubic watermelons, by growing the fruits in glass boxes and letting them naturally assume the shape of the receptacle.[14] The cubic shape was originally designed to make the melons easier to stack and store, but the cubic watermelons are often more than double the price of normal ones, and much of their appeal to consumers is in their novelty. Pyramid-shaped watermelons have also been developed and any polyhedral shape may potentially also be used. These shaped watermelon are often harvested before optimal ripeness. Because they are bitter instead of sweet, the shaped fruits are considered ornamental instead of food.[15]

Nutrition
A watermelon contains about 6% sugar and 91% water. As with many other fruits, it is a good source of vitamin C and is low in fat and sodium.[16]

Watermelon rinds are also edible, but most people avoid eating them due to their unappealing flavor. They are used for making pickles,[17] and sometimes used as a vegetable.[8] The seeds have a nutty flavour and can be dried and roasted, or ground into flour.[8] In China, the seeds are esteemed and eaten like almonds are in the west, being consumed with other seeds at Chinese New Year celebrations.[18] The rind is stir-fried, stewed or more often pickled,[19] and pickled watermelon rind is also sometimes eaten in the Southern US.[20] Watermelon juice can be made into wine, on its own or blended with other fruits.[21] An alcoholic treat called a "hard watermelon" is made by pouring liquor into a hole in the rind of a whole fruit, and then eating the alcohol-permeated flesh.[19]

The amino-acid citrulline is produced in watermelon rind.[22][23] Watermelon pulp contains carotenoids, including lycopene.[24]

Varieties
The more than 1200[25] cultivars of watermelon range in weight from less than one to more than 90 kilograms (200 lb); the flesh can be red, orange, yellow or white.[13] Watermelon with yellow flesh

The 'Carolina Cross' produced the current world record watermelon, weighing 120 kilograms (260 lb). It has green skin, red flesh and commonly produces fruit between 29 and 68 kilograms (65 and 150 lb). It takes about 90 days from planting to harvest.[26] The 'Golden Midget' has a golden rind and pink flesh when ripe, and takes 70 days from planting to harvest.[27] The 'Orangeglo' has a very sweet orange flesh, and is a large, oblong fruit weighing 9–14 kg (20–30 pounds). It has a light green rind with jagged dark green stripes. It takes about 90–100 days from planting to harvest.[28] The 'Moon and Stars' variety was created in 1926.[29] The rind is purple/black and has many small, yellow circles (stars) and one or two large, yellow circles (moon). The melon weighs 9–23 kg (20–50 pounds).[30] The flesh is pink or red and has brown seeds. The foliage is also spotted. The time from planting to harvest is about 90 days.[31]

'Moon and stars' watermelon cultivar

The 'Cream of Saskatchewan' consists of small, round fruits around 25 cm (10 inches) in diameter. It has a quite thin, light green with dark green striped rind, with sweet white flesh and black seeds. It can grow well in cool climates. It was originally brought to Saskatchewan, Canada, by Russian immigrants. The melon takes 80–85 days from planting to harvest.[32] The 'Melitopolski' has small, round fruits roughly 28–30 cm (11–12 inches) in diameter. It is an early ripening variety that originated from the Astrakhan region of Russia, an area known for cultivation of watermelons. The Melitopolski watermelons are seen piled high by vendors in Moscow in the summer. This variety takes around 95 days from planting to harvest.[33] The 'Densuke' watermelon has round fruit up to 11 kg (24 lb). The rind is black with no stripes or spots. It is grown only on the island of Hokkaido, Japan, where up to 10,000 watermelons are produced every year. In June 2008, one of the first harvested watermelons was sold at an auction for 650,000 yen (US$6,300), making it the most expensive watermelon ever sold. The average selling price is generally around 25,000 yen ($250).[34] Many cultivars are no longer grown commercially because of their thick rind, but seeds may be available among home gardeners and specialty seed companies. This thick rind is desirable for making watermelon pickles, and some old cultivars favoured for this purpose include 'Tom Watson', 'Georgia Rattlesnake', and 'Black Diamond'.[17]

Uses
C. l. lanatus var caffer grows wild in the Kalahari Desert, where it is known as tsamma. The fruits are used by the San people and by animals for both water and nourishment. Traditionally, travelling in the desert in the dry season could only be done in a good tsamma year. Humans can survive on an exclusive diet of tsamma for six weeks.[8] The citrulline in watermelon (especially in the rind) is converted to arginine in the body. This can relax and expand blood vessels, much like the erectile dysfunction drug Viagra, and may increase libido. It can also be used to help treat people with angina, high blood pressure and other cardiovascular problems and is beneficial to the immune system.[35] The Oklahoma State Senate passed a bill on 17 April 2007 declaring watermelon as the official state vegetable, with some controversy surrounding whether a watermelon is a vegetable or a fruit.[36] In U.S. culture, stereotypical caricatures may depict African Americans as being inordinately fond of watermelon (along with fried chicken), to the point where some African Americans do not want to be seen in public eating watermelon.[37] In Vietnamese culture, watermelon seeds are consumed during the Vietnamese New Year's holiday, Tết, as a snack.[38]