Prota 2: Vegetables/Légumes
Sp. pl. 2: 1009 (1753).
2n = 22
Momordica thollonii Cogn. (1888).
Bitter gourd, balsam pear, bitter melon, karela, African cucumber (En). Margose, concombre amer, paroka, concombre africain (Fr). Melão de São Caetano, balsamina longa (Po). Karela (Sw).
Origin and geographic distribution
Momordica charantia is native to the Old World tropics, but now pantropical. It was possibly domesticated in India and southern China and is now found naturalized in almost all tropical and subtropical regions. It is an important market vegetable in southern and eastern Asia, e.g. India, Sri Lanka, Vietnam, Thailand, Malaysia, the Philippines and southern China. Local cultivars originally from Asia are cultivated on a small scale in tropical America, and bitter gourd is also cultivated in the southern part of the United States for the Asiatic kitchen. It is a common cucurbit in the wild flora of Africa, occurring almost throughout tropical Africa. It is only occasionally collected from the wild as a vegetable or medicinal plant. It is occasionally cultivated in East Africa mostly by people of Asian origin using Asian cultivars.
Immature fruits of Momordica charantia are used in stews and curries, or pickled. They are also stuffed with minced meat. Seeds of more mature fruits must be removed. Bitterness may be reduced by parboiling or soaking, squeezing or mashing in salted water, or by scoring the skin of the fruit and sprinkling it with salt. Young fruits of wild small-fruited types are locally eaten in West Africa as supplementary or emergency food. In Zimbabwe young non -bitter fruits are eaten in salads, in the same way as cucumbers. Mature fruits of wild plants are said to be poisonous to people and domestic animals. In Asia shoot tips are a popular leafy vegetable that is considered very healthy. Some farmers even grow bushy bitter gourd types with small fruits especially for this purpose.
Bitter gourd tea, made from dried fruit pieces, is a popular health drink in Japan and some other Asian countries. Bitter gourd has numerous medicinal uses. In many African countries the fruit is taken as a purgative and vermifuge, whereas leaves are steeped in water and taken to treat diarrhoea and dysentery. Steeped leaves used as enema are said to have strong astringent properties. The seed is used internally as an anthelmintic, especially in DR Congo. In West Africa the plant is used as a febrifuge either by washing or drinking. Yellow fever and jaundice are treated by an enema of the entire plant in water or eye instillation of leaf sap. The plant is used as an aphrodisiac and in local treatment of gonorrhoea. Preparations made from stems and leaves are used to treat yaws. A decoction is applied to boils, ulcers, septic swellings and infected feet. Plaster made from pulverized plants is used to treat malignant ulcers, breast cancer and skin parasites such as filaria and guinea worms. The leaves are taken to treat menstrual problems and the roots are used against syphilis and rheumatism and as an abortifacient. Crushed leaves are used together with other drugs to relieve heart problems, e.g. tachycardia. Manifold medicinal uses are also reported from Asia and the Americas, e.g. to treat cancer, diabetes, psoriasis and many infectious diseases. It is especially renowned as a remedy for diabetes mellitus, just by eating it regularly as a vegetable.
Production and international trade
Bitter gourd is cultivated in tropical Asia on possibly hundreds of thousands of hectares, but no accurate statistical data are available. In Africa, it is a minor wild and cultivated vegetable, restricted to urban areas with a market for products of the Asiatic kitchen.
Young fruits contain per 100 g edible portion: water 94.0 g, energy 71 kJ (17 kcal), protein 1.0 g, fat 0.2 g, carbohydrate 3.7 g, dietary fibre 2.8 g, Ca 19 mg, Mg 17 mg, P 31 mg, Fe 0.4 mg, Zn 0.8 mg, vitamin A 380 IU, thiamin 0.04 mg, riboflavin 0.04 mg, niacin 0.40 mg, folate 72 μg, ascorbic acid 84 mg. Fresh leaves contain per 100 g edible portion: water 89.3 g, energy 126 kJ (30 kcal), protein 5.3 g, fat 0.7 g, carbohydrate 3.3 g, Ca 84 mg, Mg 85 mg, P 99 mg, Fe 2.0 mg, Zn 0.3 mg, vitamin A 1734 IU, thiamin 0.18 mg, riboflavin 0.36 mg, niacin 1.11 mg, folate 128 μg, ascorbic acid 88 mg (USDA, 2002).
Several proteins that display a variety of pharmacological effects have been isolated from Momordica charantia. The proteins α-momorcharin and β-momorcharin, from seeds of Momordica charantia, have been found to show a hepatotoxic effect on isolated rat hepatocytes. Several immunotoxins were prepared by linking the type 1 ribosome-inactivating protein momordin I to antibodies specific to various cell lines. Treatment with these immunotoxins significantly inhibits tumour development in vitro. The treatment alone, or in combination with a general cytostatic significantly inhibits tumour development in vivo, e.g. in mice.
The in-vivo antitumour activity of a crude extract from Momordica charantia was significant for several types of tumour cells in mice and in humans. It is thought that in-vivo enhancement of immune functions may contribute to the antitumour effects of the extract. Juices expressed from Momordica charantia fruits appreciably reduced the incidence of skin tumours in mice. The extracts of the peel, pulp, seed and whole fruit exhibited marked anticarcinogenic activity against mouse skin papilloma genesis when applied topically. MAP30, an antiviral protein (30 kDa) from Momordica charantia, may regulate Herpes simplex virus (HSV) replication. It is also capable of inhibiting infection of HIV1 in T lymphocytes and monocytes, as well as replication of the virus in infected cells. It was found not to be toxic to normal uninfected cells; the peptide is probably unable to enter healthy cells. It exhibits a dosedependent inhibition of integration of viral DNA into the host chromosomes (HIV1 integrase), which is a vital step in the replicative cycle of the AIDS virus. Acylglucosylsterols isolated from unripe fruits showed antimutagenic activity. The protein MAP30 has also been shown to control proliferation of cells of some oestrogen-independent forms of human breast cancer both in vitro and in vivo.
Bitter gourd is often used in folk medicine to treat diabetes, and its hypoglycaemic activity has often been confirmed in trials in experimental animals. However, confirmation of its safe and effective use in humans needs further confirmation. A significant number of studies have established the hypoglycaemic activity of bitter gourd; its effect appears to be more acute and transient than cumulative. The fresh aqueous extract of the whole fruit is more effective than dried powder or dietary consumption. Some studies found that the seed also contained hypoglycaemic principles. In most of the cases where hypoglycaemic activity could not be demonstrated, normoglycaemic animals were experimented upon. The mechanism of hypoglycaemic activity remains unclear. The results of tests on diabetic patients indicated that fresh bitter gourd juice brought about a significant reduction in plasma glucose concentration, and an improvement in the response to an oral glucose load. The effect of fried bitter gourd was not so pronounced, although it was significant. A cumulative and gradual hypoglycaemic effect was found in diabetic patients using the aqueous extract at the end of a 3week trial. Contradictory to these findings, however, is a study in which bitter gourd, in the form of fresh juice, dried powder or the powder given as a tablet, did not have any beneficial influence on diabetic patients.
Extracts of Momordica charantia were effective in treating Ascaridia galli worms in birds. Oral administration of an extract containing 100 mg iron was as effective as a commercial preparation to prevent anaemia in piglets. Chitinase isolated from the fruits may be strongly bacteriostatic.
Momordicines I and II were isolated from dried leaves. These compounds showed antimicrobial activity against several bacteria and fungi. Leaf extracts were also effective against microbes, including Escherichia coli, Salmonella paratyphi and Shigella dysenteriae. Seed extracts resulted in high mortality of the nematodes Meloidogyne incognita and Rotylenchulus reniformis. The petroleum ether extract of Momordica charantia was active against the bean weevil Callosobruchus chinensis.
Water extracts of the seed have shown abortifacient activity in mice. The seeds and the fruit wall of Momordica charantia are reported to contain a resin, a saponin glycoside of the cucurbitacin type, and alkaloids that may cause vomiting and diarrhoea.
Adulterations and substitutes
Other wild African Momordica species with fruits and leaves consumed as vegetable with a similar bitter taste are Momordica balsamina L., Momordica foetida Schum. and Momordica rostrata A.Zimm. Most wild Momordica species have similar medicinal uses.
Monoecious annual climbing or trailing herb with stems up to 5 m long; stem ridged, glabrous or hairy; tendrils simple. Leaves alternate, simple; stipules absent; petiole 1.5–7 cm long; blade broadly ovate-reniform or orbicular in outline, 2.5–10 cm × 3–12.5 cm, cordate at base, deeply palmately (3–)5(–7)-lobed, lobes usually sinuate-lobulate, glabrous or pubescent. Flowers solitary in leaf axils, unisexual, regular, 5-merous, with a prominent bract at base of pedicel; calyx with obconic tube and lobes up to 7 mm long; petals free, obovate-lingulate, up to 2 cm long, pale yellow to orange-yellow, 2 with scales inside at base; male flowers with 3 stamens, anthers coherent in centre of flower; female flowers with inferior, ovoid to fusiform, muricate -tuberculate ovary, stigma 3-lobed. Fruit a pendulous broadly ovoid and beaked to attenuate -ellipsoid berry up to 11 cm × 4 cm, but in cultivars up to 45 cm × 9 cm, reddish-orange when ripe, with a paler apex, ornamented with about 8 longitudinal rows of subconical tubercles and many smaller tubercles in between, splitting into 3 valves and exposing the seeds sheathed in sticky red pulp hanging in 2 rows from the faces of each valve; cultivated fruits with smooth to spiny surface, often with rounded knobs in rows between 8–10 lengthwise ridges, but in some cultivars completely spiny without ridges. Seeds oblong, c. 10 mm × 5 mm, flattened, white or brown, testa sculptured, margins grooved.
Other botanical information
Momordica comprises about 40 species, the majority of which are African. The fruits of several wild species are consumed as a vegetable, whereas several others are used in traditional medicine. Wild and cultivated types of Momordica charantia have been variously classified (e.g. cultivated: var. charantia; wild: var. abbreviata Ser. and var. longirostrata Cogn.). The cultivated types can better be classified in cultivar -groups and cultivars, but there is as yet no good classification system.
Growth and development
Seedlings emerge 5–7 days after sowing, but fresh seed often shows dormancy which is very hard to break and can last for some months. This is also a major problem for seed of improved cultivars. Stem elongation starts after 2 weeks, followed by the development of lateral stems. Flowering starts with male flowers 5–6 weeks after sowing, while female flowers appear 10 days later. Flowering may continue for 6 months. Flowers open early in the morning. Anthers dehisce about two hours before anthesis and optimum viability of pollen and receptivity of the stigma are attained at anthesis. Flowers are pollinated by bees and other insects. Young fruits can be harvested 10–14 days after anthesis. Continuous harvesting of all young fruits prolongs crop duration. Fruits left on the plant turn orange or yellow 25–30 days after fruit set.
Bitter gourd prefers quite high temperatures, 25°C and above, but when temperatures become too high (>37°C) fruit set often becomes a problem, depending on genotype. In India cultivars are known, called ‘heatset’, that will still set fruit at 40°C. Bitter gourd occurs naturally in areas up to 1700 m altitude with a high rainfall, in rainforest, riverine forest, elephant-grass thickets and plantations. If cultivated in too wet conditions, bacterial and fungal wilt and fruit cracking can become major problems, resulting in a lower percentage of high -quality fruits and a shortened shelf life of the fruits. In Asia many farmers grow the crop in the cool and dry season, which may give good results. Still, bitter gourd is not easy to grow. Many farmers use mulch to keep soil moisture conditions balanced. Bitter gourd prefers deep well -drained sandy loam or silt loam soils with a high organic matter content and water-retaining capacity. It seems to be almost day-neutral.
The plants are often supported by poles or trellises so that the fruit does not come into contact with soil. Asian farmers use trellises up to 2 m tall, constructed from stakes with a system of horizontal wires and vertical strings. In India, however, farmers rarely use trellises. In the Philippines they are only used for long-fruited types, not for traditional local types. The soil is mulched with rice straw or plastic mulch. Compost manure is usually added to each planting hole before sowing. A dose of 10 t/ha is recommended, together with 200 kg/ha NPK fertilizer, applied before sowing. Additional nitrogen fertilizer may be applied during crop growth, 100 kg/ha N when the plants begin to spread and 200 kg/ha when the plants begin to flower. Irrigation is practised when needed to maintain soil moisture. Bitter gourd is quite sensitive to lack of micronutrients such as boron; application of these elements can strongly improve crop results for farmers.
Propagation and planting
Bitter gourd is often sown directly. The weight of 1000 seeds of cultivated types is 180–200 g. Seed of wild types may be smaller. Farmers need about 3 kg seed per ha for direct sowing. In South-East Asia farmers often raise seedlings of hybrid cultivars in pots for transplanting at a wide spacing; they then use 1.2–1.5 kg seed per ha. The use of pre-germinated seeds, soaked in moist cloth or tissue overnight or until radicle appearance, results in better plant establishment. Spacing is 50–60 cm in the rows and 120–250 cm between the rows; final plant density is 6,000–20,000 plants per ha, depending on cultivar and trellis system. Planting is generally done on raised beds to prevent waterlogging.
Diseases and pests
Bitter melon is susceptible to several diseases and pests that affect other cucurbits. It is a host of papaya ring spot virus (PRSV-W), and less frequently of watermelon mosaic virus (WMV). Gemini viruses may cause serious problems. A new virus disease called cucurbit aphid -borne yellows was observed in the Philippines and is spreading in South-East Asia. Seedborne viruses are not reported. Some fungal diseases cause serious damage. Cercospora leaf spot (Cercospora citrullina) is controlled by pruning of affected leaves and by spraying fungicides such as benomyl, cupravit or daconil. Downy mildew (Pseudoperonospora solanacearum) is controlled by wide spacing giving good ventilation and by fungicides such as maneb, ridomil or dithane. Powdery mildew (Erysiphe cichoracearum) can be controlled with the same fungicides or with sulphur dust. Commercial cultivars show various degrees of tolerance to these fungal diseases. Bitter gourd is susceptible to bacterial wilt including Ralstonia, fusarium wilt, and root-knot nematodes. Fusarium wilt will usually show clear yellowing of the veins, resulting in a ‘webbed’ pattern on the leaves, before wilting. Infection with bacterial wilt causes quite sudden wilting while the plant is still green. In Taiwan bitter gourd is grafted on a rootstock of pumpkin, smooth loofah or bottle gourd, not only to increase vigour and yield, but also to protect against soilborne wilting diseases and nematodes.
The main pests include aphids and fruit flies (Dacus cucurbitae). Heavy aphid infestation can lead to strongly stunted growth and reduced fruit set. Other pests are leaf beetles (Epilachna spp.), caterpillars (Spodoptera spp., Heliothis armigera) and mites.
Harvesting starts about 2 months after sowing and is done 2–3 times per week during 2–3 months. It is important to harvest each fruit at the right moment, some days to weeks before reaching full maturity, when they have the right size, the skin is still hard and not turning to yellow-orange, and the seeds are still soft. Beyond this stage, the fruits become spongy and more bitter and lose their market value. The length, diameter and weight depend on cultivar and consumer preference. Regular harvesting is needed as mature fruits on the plants reduce the setting of new fruits.
Average yields of bitter gourd are 8–10 t/ha, but up 20 t/ha for open-pollinated cultivars has been reported. In Thailand hybrid cultivars under good management yield up to 40 t/ha. The number of fruits per plant depends largely on the cultivar used; it can range from around 5 to more than 100; the higher number only in small-fruited cultivars.
Handling after harvest
The fruits should be handled and packaged with care, and should be isolated from fruits that produce large amounts of ethylene to prevent post-harvest ripening. Bitter gourd fruits can be stored for a long time, up to 4 weeks at 1–2°C and 85–90% relative humidity. They are chilling sensitive and should not be kept below 0°C. Fruits stored at temperatures above 10°C turn yellow, split open and lose quality.
Local cultivars of bitter gourd are on the verge of extinction as they are being replaced by commercial ones. Collections are available at NBPGR, New Delhi, India, at AVRDC, Taiwan, at Kasetsart University, Thailand and several other research institutes in tropical Asia.
Most of the cultivars used in East Africa are imported from Asian countries. Wild and cultivated plants cross readily and there are many intermediate types. Wild African types can be exploited as potential source of disease resistances. Breeders nowadays concentrate on F1 hybrids, the advantages of higher yield potential, better resistance to diseases and more uniformity being obvious. Important selection criteria are earliness, a high ratio of female flowers, resistance to pests and diseases, and degree of bitterness. A high dry matter content is needed for fruits that are cut in pieces and dried. These are sold and used to make bitter gourd tea. No breeding work is reported from African countries.
In tropical Asia many local and improved cultivars are known, with fruit shapes, colours and sizes ranging from the small, spined, dark green semi-wild type to the improved large-fruited cultivars, with colours varying from dark green to pale green and white. East-West Seed Company, in Thailand, the Philippines and Indonesia, has released about ten hybrid cultivars, which show among them a large variation, especially in earliness (first harvest 37–52 days after sowing) and fruit characters (smooth to spined, white or pale green to dark green, spindle-shaped to cylindrical or conical, 6–40 cm long, 2–9 cm broad, weighing 60–650 g). Excellent hybrids especially developed for difficult lowland conditions include ‘Ravana’ (long, smooth, dark green fruits), ‘Palee’ (long, spiny, dark green fruits) and ‘Indra’ (short, spiny, medium green fruits). For growing during the rainy season, when prices for produce are usually high, the cultivar ‘Jade Star XL’ was developed, which has minimum problems with fruit cracking. For advanced farming systems and shorter crop cycles, earlier maturing pale green cultivars such as ‘Hanuman’ (medium-sized fruits) and ‘Torapi’ (long fruits) were introduced. Taiwanese and Indian seed companies also developed F1 hybrids. The Taiwanese seed company Known-You developed the popular white-fruited warty cultivar ‘High Noon’ and the green smooth cultivar ‘Moonrise’. Bitter gourd has been successfully crossed with Momordica cochinchinensis (Lour.) Spreng. and with snake gourd (Trichosanthes cucumerina L.). Genetic information on bitter gourd is rather limited; most of this work is done at Indian research institutes.
In view of the popularity of bitter gourd in the Asian tropics and the release of superior F1 hybrid cultivars, its popularity in Africa is expected to increase. Since the results with bitter gourd in the treatment of diabetes are still somewhat contradictory, more research needs to be done on its hypoglycaemic activity. Several compounds from bitter gourd show interesting pharmacological activities, e.g. antitumour, immunotoxic and anti-HIV, which merit further research, and may have potential in the development of future medicines.
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Sources of illustration
• Reyes, M.E.C., Gildemacher, B.H. & Jansen, G.J., 1993. Momordica L. In: Siemonsma, J.S. & Kasem Piluek (Editors). Plant Resources of South-East Asia No 8. Vegetables. Pudoc Scientific Publishers, Wageningen, Netherlands. pp. 206–210.
Correct citation of this article:
Njoroge, G.N. & van Luijk, M.N., 2004. Momordica charantia L. In: Grubben, G.J.H. & Denton, O.A. (Editors). PROTA 2: Vegetables/Légumes. [CD-Rom]. PROTA, Wageningen, Netherlands.
wild and planted
1, leafy shoot; 2, male flower in longitudinal section; 3, female flower in longitudinal section; 4, male flower in cross section with petals removed; 5, fruit.
flowering and fruiting plant habit
Asian F1 hybrid cultivar