Watermelon

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Watermelon (Citrullus lanatus) is a member of the cucurbit family (Cucurbitaceae). The crop is grown commercially in areas with long frost-free warm periods. Plants must be grown at a wide spacing because of their long, trailing vines. The exception is for dwarf cultivars where the plants can be grown at a tighter spacing. The crop may be established in the field by planting seeds or using containerized transplants. Management of plant pests (weeds, insects, and diseases, including nematodes) is essential during the production period. Three-fourths of the world production is grown in Asia, with China the leading country in production. Watermelons are grown in most states of the United States, but the major producers are in the South and West (Florida, Georgia, California, and Texas) where the warm production season lasts longer. The fruit are harvested by hand, with the most experienced workers doing the cutting (removal of the fruit from the vine) and the others loading the bins or trucks. The fruit are shipped to markets throughout the United States, with some exported to Canada. Watermelon fruit will keep for two to three weeks after harvest if they are stored properly at 10 to 15°C and 90% humidity. Besides whole watermelons, it is becoming popular to sell watermelon in pre-cut halves, quarters, slices, and chunks. Whole fruit usually are cut in the store under cold, aseptic conditions since the cut product does not ship or store well. Seedless watermelons are especially popular for pre-cut sales, since that shows their seedless quality. In the 1800s, watermelon was grown mostly for local sales. However, with the development in the last few decades of rapid shipping in refrigerated railroad cars and trucks has led to distribution of watermelon throughout the United States from major production areas. Southern production areas begin shipping early in the year, and the harvest continues throughout the summer by moving to more northern areas. Depending on the cultivar, watermelon fruit are produced in different sizes: ice box, small, medium, large, or giant; different shapes: round, oval, blocky, or elongate; different rind patterns: gray, narrow stripe, medium stripe, wide stripe, light solid, or dark solid; different flesh colors: white, yellow, orange, or red; and different types: seeded or seedless. Commercially, the most popular seeded cultivars are red flesh, blocky shape, and large sized (8–11 kg), like the cultivar Allsweet. For seedless watermelons, the popular cultivars are red flesh, oval shape, and medium sized (5–8 kg), like the cultivar Tri-X-313. Per capita consumption of watermelons in the United States is 7.2 kg. Watermelon is served fresh as slices, as chunks (often in fruit salad), as juice, pickled rind, glacé candy, and as edible seeds (harvested from confectionary type apples, bananas, and oranges. The watermelon fruit is 93% water, with small amounts of protein, fat, minerals, and vitamins. In some arid regions, watermelon is used as a valuable source of water. The major nutritional components of the fruit are carbohydrates (6.4 g/100 g), vitamin A (590 IU), and lycopene (4,100 µg/100g, range 2,300–7,200), an anticarcinogenic compound found in red flesh watermelon. Lycopene may help reduce the risk of certain cancers, such as prostate, pancreas, and stomach. The lycopene content of the new dark red watermelon cultivars is higher than in tomato, pink grapefruit, or guava. Orange flesh types have only small amounts of lycopene, and the beta carotene content is similar to that of red flesh types. Canary yellow types do not contain lycopene, but do have a small amount of beta carotene. Watermelon seeds are rich in fat and protein. Watermelon flowering and fruit development are promoted by high light intensity and high temperature. Watermelon is the only economically important cucurbit with pinnatifid (lobed) leaves; all of the other species have whole (non-lobed) leaves. The leaves are pinnately divided into three or four pairs of lobes, except for a non-lobed (sinuate) gene mutant controlled by the nl gene. Watermelon growth habit is a trailing vine. The stems are thin, hairy, angular, grooved, and have branched tendrils at each node. The stems are highly branched and up to 30 feet long, although there are dwarf types (dw-1 and dw-2 genes) with shorter, less-branched stems. Roots are extensive but shallow, with a taproot and many lateral roots. Watermelon has small flowers that are less showy than those of other cucurbits. Flowering begins 4 to 8 weeks after seeding. Flowers of watermelon are staminate (male), perfect (hermaphroditic), or pistillate (female), usually borne in that order on the plant as it grows. Monoecious types are most common, but there are andromonoecious (staminate and perfect) types, mainly the older cultivars or accessions collected from the wild.

Authors: 
Todd C. Wehner
Publisher: 
North Carolina State University