The genetic diversity in cucurbits extends to both vegetative and reproductive characteristics. There is considerable range in the monoploid (x) chromosome number (Jeffrey 1990), including 7 (Cucumis sativus), 11 (Citrullus spp., Momordica spp., Lagenaria spp., Sechium spp., and Trichosanthes spp.), 12 (Benincasa hispida, Coccinia cordifolia, Cucumis spp. other than C. sativus, and Praecitrullus fistulosus), 13 (Luffa spp.), and 20 (Cucurbita spp.).
Archaeological evidence has indicated that cucurbits were present in ancient and prehistoric cultures. Lagenaria was associated with man as early as 12,000 BC in Peru (Esquinas-Alcazar and Gulick 1983). Archaeological expeditions in the Oaxaca region of Mexico have reported Cucurbita pepo to be associated with man as early as 8500 BC and cultivated by 4050 BC (Esquinas-Alcazar and Gulick 1983). Written Chinese records describing the use of cultivated cucurbits have been found from as early as 685 BC (Herklots 1972). American Indians cultivated squash in pre-Columbian times (Whitaker and Davis 1962), and chayote was a common vegetable among the Aztecs prior to the Spanish conquest (Herklots 1972). Depending upon the species, virtually all parts of the plant can be used for food, including leaves, shoots, roots, flowers, seeds, and immature and mature fruits. Starch can be extracted from roots, and the seeds are a rich source of oils and proteins (Jacks et al. 1972). In addition, some cucurbits have been used for ornamental purposes (e.g., gourds), for utensils (e.g., bowls, ladles, sponges, boxes, birdhouses, musical instruments), and for fuel and pharmacological uses in certain areas of the world.
Cucumbers have been traditionally grown for either pickling or slicing purposes. Newer forms which are increasing in importance include hothouse cucumbers, which are elongated, seedless, and "burpless" (putatively reducing eructation). Nerson et al. (1990) reported on the development of melofon, a genotype of Cucumis melo which is suitable for pickle production.
Until recently, melon production has been limited in most parts of the United States to the reticulated (netted), orange-fleshed muskmelon. However, the smooth-skinned, green-fleshed honeydews have increased in popularity over the past decade, and varied displays of casaba and canary (smooth-skinned with yellow or mottled rinds, white-fleshed), Persian (lightly-netted, pink-fleshed), and crenshaw (smooth-skinned, pale orange-fleshed) melons are becoming an increasingly common sight in major markets. The genetic diversity within the species for fruit characteristics has resulted in recent cultivar developments such as orange-fleshed honeydews and green-fleshed netted melons. Additionally, producers are showing interest in forms cultivated in other countries, including the smooth-skinned, delicately-fleshed "Charentais" types in Europe and the dark green smooth-skinned "hami gua" melons of Asia.
Watermelon types have traditionally been red-fleshed and seeded. There is genetic variation for flesh color in the species, however, and colors can range from white or yellow to orange, depending upon the genetic constitution. Yellow-fleshed cultivars are now available, and there may be a market for white-fleshed cultivars if quality could be assured, since consumers tend to associate white flesh with immaturity. A relatively recent development in watermelon breeding has been the use of ploidy manipulations to produce seedless triploid genotypes (Kihara 1951). A number of seedless cultivars have been developed, but they tend to be more susceptible to physiological problems such as poor seed germination and hollow heart. In northwest China, edible seed watermelons are an important crop (Zhang and Jiang 1990); these melons are small in size (2.5 to 3.5 kg) with low soluble solids content, but have a high ratio of seed to flesh in the fruits. The seeds are roasted before eating.
Squash, derived from Algonquin Indian "askoot asquash" which means "eaten green," is a generic term to describe cultivars of four Cucurbita species: C. argyrosperma (= C. mixta), C. maxima, C. moschata, and C. pepo. These species are New World in origin, with all but C. maxima originating in central to southern Mexico (C. maxima originated in South America and was the only species not cultivated in the United States until post-Columbian times). Traditional forms of the Cucurbita spp. include summer squash, winter squash, pumpkins, and gourds. Production has recently increased with specialty forms such as spaghetti squash (C. pepo), whose internal flesh texture resembles strands of spaghetti following cooking. Another specialty crop is calabaza (C. moschata), a hard-shelled squash with bright orange, fine-grained flesh and excellent nutritive properties (Wessel-Beaver and Varela 1991). There has also been recent interest in edible pumpkin seed, particularly in genotypes with the hull-less trait (Loy 1990).
Although the new forms of these commonly grown cucurbits represent an increase of diversity within each commodity, they will probably not expand the market substantially (with the exception of niche markets) since consumers will probably elect to purchase them in place of the more traditional forms. Where the true opportunity for increased diversity and market growth exists is with cucurbit crops which are grown on an international scale, but are cultivated to only a limited extent in the United States.
The mature fruit is the primary harvested plant part, although seeds are sometimes extracted, fried and eaten like pumpkin seeds. The fruit is covered by a white, chalky wax which deters microorganisms and helps impart an extraordinary longevity to the melon. Winter melon fruits can be stored for as long as a year without refrigeration. Fruits may weight up to 35 kg and consist of more than 96% water. They are usually sold whole in domestic markets, but are commonly displayed and sold by the slice in Asian markets. Somewhat bland in flavor when eaten fresh, the flesh is often used to make soup stock. Canned winter melon soup and dehydrated winter melon slices represent two of the processed products made from this species.
Citrullus colocynthis. A relative of watermelon, egusi is native to tropical Africa and highly drought tolerant. Productivity is enhanced during dry, sunny periods and reduced during periods of excessive rainfall and high humidity. It is suitable for production in "marginal growing areas." The fruits are extremely bitter, but the seeds are can be removed and roasted as an edible commodity (Soliman et al. 1985). The seeds are rich in oils, which can be extracted for cooking purposes, and the seeds can also be ground into a powder and used as a soup thickener or flavoring agent (Badifu and Ogunsua 1991).
Coccinia cordifolia. Ivy gourd is a semi-perennial which grows best under conditions of adequate rainfall and high humidity. One of the few dioecious cucurbits, with a hetermorphic (XY) chromosome pair determining sex, it produces best when a 1:10 ratio of male to females is used. Plants are commonly trellised. The leaves, shoots, and immature fruits are cooked and eaten; mature fruits are sometimes preserved.
Cucumis anguria. The West Indian gherkin grows and is used in a similar fashion as the cucumber. It was introduced into the United States in the early 1800s, but remains cultivated to only a limited extent. Oval in shape with a round cross-section, it has a highly warted skin, long spines and a large cavity with many seeds.
Lagenaria siceraria. The origin of the bottle gourd is acknowledged to be Africa, although archaeological evidence has placed it in Peru around 12000 BC, in Thailand about 8000 BC, and in Zambia around 2000 BC (Esquinas-Alcazar and Gulick 1983). It has traveled widely, perhaps because the hard, dry skin of the mature fruits is impervious to water; they are capable of floating on salt water for the better part of a year without any loss in seed viability (Herklots 1972; Tindall 1983). Tolerant to a wide range of rainfall, it may be grown either on the ground or trellised.
Young fruits are used as a cooked vegetable similar to zucchini. The flesh is white, firm, and has an excellent texture and a mild taste. Young shoots and leaves can be cooked, and seeds can be used in soups. Flesh of immature fruits can also be used in making icing for cakes, and the hard skin is sometimes sliced into thin, dry strips for cooking.
Some forms of L. siceraria are grown for non-food uses. Mature fruits, whose inside may be poisonous, contain an extremely hard and waterproof rind when dried. They can be used as multi-purpose containers (bowls, boxes, water jugs, cups, planters), utensils (ladles, pipes), musical instruments (e.g., sitars), floats for fishnets and rafts, or for ornamental purposes such as masks or native artifacts. Designs lightly scratched into the skin of developing fruit will develop into scars that remain intact in the mature fruits.
Luffa acutangula. The angled loofah is commonly grown in hot, humid tropical areas in Asia. Plants are generally grown on a trellis. Immature fruits, which are dark green with tender ridges, are used in soups and curries or as a cooked vegetable. They generally grow up to 0.6 m in length, and the flesh is spongy although the skin is coarse. The mature fruits are bitter and inedible, but the fibrous skeleton can be used as a sponge. However, the reticulated inner tissue is not as easily separated from the outer skin and inner flesh as L. aegyptiaca (= L. cylindrica).
Luffa aegyptiaca. Along with Lagenaria siceraria, L. aegyptiaca probably has the most diverse uses of any of the cultivated cucurbits. Immature fruits of the non-bitter genotypes are eaten fresh, cooked, or in soups, although they are inferior to immature L. acutangula fruits. The mature fruits are the source of the spongy reticulated material known as the domestic loofah. These loofahs are used for sponges and filters, and for stuffing pillows, saddles, and slippers. They can also be used for insulation and are attractive sources for packing materials because of their biodegradability. There is an increasing interest in domestic production (Davis 1991) since the United States is the major market and imports millions of loofahs from Asia each year.
Normally, mature fruits are left on vine to dry and the dry, thin outer skin is removed. The fruit is then soaked in running water for several days, after which the softer tissue is removed. After further soaking, then drying, the seeds are shaken out and the loofah is bleached either chemically or by the sun prior to marketing.
Momordica charantia. The bitter melon is adapted to a wide variation of climates, although production is best in hot, humid areas such as tropical Asia. The bitter immature fruits are usually soaked to remove some of the bitterness, then boiled or fried. Volatile components released during cooking enhance the flavor (Binder et al. 1989). Bitter melons can also be pickled or used in curries. Relative to other cucurbits, the fruit is highly nutritious due to the iron and ascorbic acid content. Plants are usually trellised, and fruits are protected from flies by tying a paper cylinder around the stalk. Some forms have bright red seeds due to a high lycopene content; Yen and Hwang (1985) have proposed using this pigment as an artificial food colorant.
Praecitrullus fistulosus. Primarily grown in India, the round melon was long considered to be Citrullus lanatus but was recently given its own taxonomic category due in part to its difference in monoploid chromosome number (Sujatha and Seshadri 1989). Growth conditions and requirements are similar to those of watermelon, but the entire immature fruit is used as a cooked vegetable. The seeds can also be removed and eaten.
Telfairia occidentalis. A dioecious perennial grown at elevations up to 2,000 m in West Africa, the fluted gourd is drought tolerant and is usually trellised. Shoots from the female plants can be cooked and eaten (Lucas 1988). The fruits are large (up to 13 kg) and inedible, but the seeds contain up to 30% protein and can be boiled and eaten, or ground into powder for soup. Seeds can also be fermented for several days and eaten as a slurry (Badifu and Ogunsua 1991).
Telfairia pedata. The oyster nut is a perennial grown in Central and East Africa. It is drought tolerant, can grow at elevations up to 2,000 m, requires 18 months to flowering, and is usually trellised. It produces very large, long, flat seeds which taste similar to almonds when roasted.
Trichosanthes cucumerina. The snake melon is an annual which requires high levels of soil moisture and trellising. A long growing season is necessary, and the flowers open late in the afternoon. Immature fruits are usually harvested when they are 0.3 to 0.4 m long; mature fruits can grow up to 1.5 m in length. Some of the fruits remain straight, while others may curl to resemble a snake. Immature fruits are boiled and eaten, while mature fruits are used in soups.
Cucurbita foetidissima. Identified as an underexploited tropical crop by the National Academy of Sciences (1975), the buffalo gourd has multiple food and non-food uses (Bemis et al. 1975; Gathman and Bemis 1990). It is a perennial and is found growing wild in marginal lands in the southwestern United States. Some plants have been reported to be over 40 years old. It has a very large, fleshy storage root which can grow to depths up to 5 m and weigh as much as 30 kg after two growing seasons. Roots of older plants can weigh over 100 kg. Buffalo gourd primarily reproduces by asexual reproduction, but also produces small yellow, hard shelled fruits which are considered inedible.
American Indians have used the ripe fruit as a soap substitute and as ceremonial rattles. The seeds, which contain an abundant quantity of polyunsaturated fats and protein, are edible. The large storage roots contain large amounts of starch (up to 56% of the dry weight), and can also be used as fuel. Air-dried roots burn with the heat equivalent of wood and are being tested in Afghanistan as an alternative fuel to decrease deforestation (Winrock International 1991).
Cyclanthera pedata. Korila is relatively cold tolerant and adapted to elevations up to 2,000 m, but is also easy to cultivate in the tropics and subtropics. It is currently cultivated in the Carribean and in Central and South America. The foliage is glabrous and odoriferous. Fruits are pale green, flattened, and mostly hollow. The seed cavity is spongy, and the seeds are attached to a single placenta. Seeds are usually removed and the fruits are eaten raw or cooked. They are often used stuffed with meat, fish or cheese, then baked and eaten similar to stuffed peppers. The shoots are also edible.
Sechium edule. Chayote was a common vegetable among the Aztecs prior to Spanish conquest of Mexico. It is still one of the most widely cultivated of the cucurbits in Costa Rica. It requires high levels of soil moisture and can grow at elevations up to 1,500 m. Unlike most cucurbits, it has a daylength requirement of 12 to 12.5 h for flowering. The plants grow best on hillsides and are usually trellised. Parthenocarpic fruit set can be induced by gibberellin.
Unlike other cucurbits, the fruit contain only a single, large seed. The immature fruits can be eaten raw in salads and provide a good source of vitamin C (Herklots 1972). They can also be boiled, fried, steamed, or stuffed and baked. Young leaves and tendrils are also eaten, and seeds can be sauteed in butter as a delicacy. The large storage roots represent a rich source of starch (Chakravarty 1990).
As biochemical isolation techniques become more sophisticated and refined, new compounds of interest are being isolated. For instance, Mukherjee et al. (1986) isolated amarinin from Luffa amara; amarinin inhibits plant cell growth in culture, and its action cannot be overcome with gibberellin.
Perhaps of greatest current interest are the compounds of potential medicinal interest present within cucurbits. Table 2 lists reported pharmacological properties of many cultivated cucurbits; similar properties have been ascribed to other cucurbit species not currently under cultivation (Schultes 1990). Putative properties include purgative actions and treatment for physical ailments, diseases, and infectious organisms. "Infusions" (minced tissue suitable for steeping) of selected cucurbits are sold in some markets and reported to be able to alleviate or cure certain human ailments.
Recently, abortifacient proteins with ribosome-inhibiting properties have been isolated from several cucurbit species (Ng et al. 1991). Some of these species have been used to induce second trimester abortions in China since the 1920s. The abortifacient proteins include momorcharin (from Momordica charantia), luffaculin (from Luffa operculata), trichosanthin (from Trichosanthes kirilowii), and beta-trichosanthin (from Trichosanthes cucumeroides). Trichosanthin is of particular interest because its ribosome-inhibiting properties have been shown to be effective in inhibiting the replication of human immunodeficiency virus (HIV) in infected lymphocyte and phagocyte cells, indicating potential as a therapeutic agent for AIDS (McGrath et al. 1989). These proteins vary in their level of action and effectiveness, and further germplasm evaluation of cultivated and wild species may identify related compounds with greater efficacy for ribosome inactivation.
|Species||Origin||Common names||Primary plant parts used||Other plant parts used||Growth habit|
|Benincasa hispida (Thunb.) Cogn.||SE Asia & Indonesia||Winter melon, ash pumpkin, wax gourd, white gourd, dong gua, tallow gourd||Mature fruits||Young leaves, flower buds, seeds, immature fruits||Annual|
|Citrullus colocynthis (L.) Schrad.||Tropical Africa||Egusi||Seeds||Annual|
|Coccinia cordifolia Cogn.||Trop. Asia & Africa||Ivy gourd, scarlet-fruited gourd||Leaves, shoots, immature fruits (preserved)||Mature fruits||Semi-perennial|
|Cucumis anguria L.||Tropical Africa||West Indian gherkin, bur gherkin, maroon cucumber||Immature fruits||Annual|
|Lagenaria siceraria (Mol.) Standl.||Tropical Africa||Bottle gourd, calabash gourd, white-flowered gourd, trumpet gourd, Zucca melon||Young fruits, mature fruitsy||Young shoots, young leaves, seeds||Annual|
|Luffa acutangula (L.) Roxb.||India||Angled loofah, towel gourd, dish-cloth gourd, ridged gourd, silk gourd, long okra, ribbed loofah, ribbed gourd||Immature fruits, leaves||Annual|
|Luffa aegyptiaca Muell.||India||Smooth loofah, dish-cloth gourd, vegetable sponge, sponge gourd, rag gourd, hechima||Immature fruits, mature fruitsy||Annual|
|Momordica charantia L.||Tropical Africa||Bitter melon, balsam pear, carilla fruit, carilla gourd, bitter gourd, alligator pear||Immature fruits young shoots||Young leaves,||Annual|
|Praecitrullus fistulosus (Stocks) Pang.||Tropical Africa||Round melon, squash melon||Mature fruit||Seeds||Annual|
|Telfairia occidentalis Hook. f.||Tropical Africa||Fluted gourd, fluted pumpkin||Female shoots, seeds||Perennial|
|Telfairia pedata (Sims) Hook.||Tropical Africa||Oyster nut, fluted pumpkin, Zanzibar oil vine||Seeds||Perennial|
|Trichosanthes cucumerina L.||India||Snake gourd, club gourd mature fruits||Immature fruits, young shoots||Young leaves,||Annual|
|Cucurbita ficifolia Bouche||Central Mexico||Fig-leaved gourd, Malabar gourd||Mature fruits, seeds||Immature fruits||Annual|
|Cucurbita foetidissima HBK||Mexico & Southern US||Buffalo gourd, mock orange, stinking wild gourd, chilicote||Mature fruitsy||Rootsy, seeds||Perennial|
|Cyclanthera pedata Schrad.||South America||Korila, wild cucumber, caihua, achoccha||Immature fruits||Shoots||Annual|
|Sechium edule (Jacq.) Sw.||So. Mexico & Central America||Chayote, choyote, cho-cho,christophine, choke, choko, sou-sou, chaka plant, chayotl vegetable pear, mirliton||Immature fruits, tubers, seeds||Young leaves, young tendrils||Perennial|
|Species||Purgative||Physical ailments||Diseases||Infectious |
|Other purported uses|
|Benincasa hispida||Diuretic, laxative||Dermatological, fever||Epilepsy, gonorrhea||Intestinal worms||Aphrodisiac|
|Citrulus colocynthis||Paralysis, muscle spasms|
|Cucumis anguria||Stomach, edema, hemorrhoids||Ringworm||Freckle removal|
|Cucumis melo||Emetic||Intestinal worms|
|Cucurbita maxima||Intestinal worms|
|Cucurbita moschata & Cucurbita pepo||Diuretic||Ulcers, fever, jaundice||Measles, smallpox||Intestinal worms|
|Lagenaria siceraria||Laxative||Kidney, flatulence, dermatological||Intestinal worms|
|Luffa acutangula||Emetic||Stomach, fever||Intestinal worms|
|Luffa cylindrica||Emetic, laxative||Asthma, sinusitis||Intestinal worms||Abortifacient|
|Momordica charantia||Laxative, emetic, emmenogogue||Colic, arthritis, hypertension, colds & fever, kidney & liver||Eczema, herpes, influenza, diabetes||Intestinal worms||Aphrodisiac|
|Sechium edule||Diuretic||Bladder, intestinal, hypertension, arteriosclerosis, dermatological|