Introduction
Bitter gourd (Momordica charantia) known as ‘karela’ in Hindi, is the most cultivated species of Momordica. In Asia, it is estimated to cover 3.4 lakh ha whereas India produces around 8.07 lakh metric tonnes from an estimated area of 80 thousand ha (NHB 2013-14). Bitter gourd fruits are a good source of carbohydrates, proteins, vitamins, and minerals and have the highest nutritive value among cucurbits.
Bitter gourd extracts possess antioxidant, antimicrobial, antiviral, antiulcerogenic properties and also have the ability to lower blood sugar. These medicinal activities are attributed to an array of biologically active plant chemicals. Bitter gourd contains health-promoting substances like charantin, momorcharin, vicine, and momordicoside A and B. Likewise, the extracted juice from leaf, fruit, and even whole plant is used for the treatment of wounds, infections, parasites (e.g. worms), measles, hepatitis, and fevers. Carotene content in the ripe seed coat is exclusively lycopene (-261 µg g) which accounts for 96% of the total carotenoids found in ripened seeds. Bitter gourd fruits are also a rich source of phenolic compounds that are excellent sources of antioxidants for reducing blood pressure, cancer, and cardiovascular diseases.
Table of content (toc)
Climate and Soil
Bitter gourd grows well in hot and humid areas including sub-tropical climates and is day-neutral. It is tolerant to a range of environments and can be grown in tropical and subtropical climates. It is cultivated during the spring, summer, and rainy seasons, with some winter production in subtropical climates. The optimum temperature for good plant growth is 25-30°C. Frost can kill the plants, and cool temperatures will retard plant growth and development. Bitter gourd performs well in full sun and is adaptable to a wide range of soil types but grows best in well-drained sandy loam soil that is rich in organic matter. It grows well in soils of shallow to medium depth (50-150 cm). The optimum soil pH is 6.0-6.7 but plants tolerate alkaline soils up to pH 8.0.
Varieties
Arka Harit: Fruits are spindle-shaped, attractive, glossy green, with smooth regular ridges and thick flesh with average fruit weight 60-70 g, yield potential is 12.5-13.5 tonnes/ha.
CO 1: Fruit dark green, medium-long (25-30 cm), matures in 55-60 days after sowing. The average yield is 16 tonnes/ha.
CO BgoH.1: Fruits are creamy white, light green tinged stout, individual fruit weight 100 g. The yield is 24.4 tonnes/ha.
Hirkani: Fruits are dark green, 15-20 cm long with prickles; average yield 13.8 tonnes/ha.
Kalyanpur Barahamasi: Vines are vigorous, fruits long (30-50 cm) light green, thin, and tapering at the end. Plants are tolerant of fruitfly and mosaic viruses. It is recommended for Kharif cultivation in Uttar Pradesh. This variety has a yield potential of 20-22 tonnes/ha.
Kalyanpur Sona: Vine is medium in growth, fruits medium-size and green. This variety has a yield potential of 12-13 tonnes/ha.
Konkan Tara: Fruits are green, medium-long (15-16 cm), and spindle-shaped with raised tubercles. Fruits have good keeping quality with a shelf-life of 7-8 days at ambient temperature. Yield potential is 23-25 tonnes/ha.
MDU 1: It was developed using gamma irradiation from a local cultivar MC 103. Flowering starts from 60 days of sowing and produces female and male flowers in a 1:20 ratio. The fruits are long (30-40 cm) and have a girth of 15 cm having an average fruit weight of 120 g. The average yield is 20 tonnes/ha.
Pant Karela 2: Fruits are thin; 25 cm long, dark green with tapering ends. Matures in 60 days after seed sowing. This variety has a yield potential of 15-16 tonnes/ha.
Phule Green Gold: Fruits are dark-green, 25-30 cm long with raised tubercles. This is tolerant to downy mildew. Yield potential is 22.0-23.5 tonnes/ha.
Phule Priyanka: Fruits are medium long, dark green, and highly prickly. Plants are tolerant to downy mildew. Yield potential is 20-25 tonnes/ha.
Preethi: Fruits are white, spiny, medium-size with 130 g of average weight. Yield potential is 14-15 tonnes/ ha and matures in 65 days.
Priya: Fruits are extra long (40 cm), green-spiny, and the stylar end is typically whitish.
Punjab 14: Fruits large, oblong, and green, suitable for spring-summer and rainy seasons sowing. Yield potential is 12-13 tonnes/ha.
Pusa Aushadhi: It is recommended for growing in Rajasthan, Gujarat, Haryana, and Delhi. Fruits are light green, medium-long, and medium-thick (average fruit length 16.5 cm and breadth 6.0 cm) with 7-8 continuous narrow ridges, fruits mature in 52 days after sowing. The average fruit weight is 85 g. Its average yield is 19.8 tonnes/ha.
Pusa Do Mausami: Fruits are dark green with 7-8 continuous ridges, each fruit weighs 80 g. The average yield is 13 tonnes/ha in 65 days after sowing.
Pusa Hybrid 1: Vines are medium in growth, fruits attractive green, medium-long, irregular smooth tubercles on the surface, suitable for vegetable purpose and dehydration. The average yield is 21.8 tonnes/ha.
Pusa Hybrid 2: Fruits are dark green, medium-long, average fruit weight 90 g, early maturing. The average yield is 21.5 tonnes/ha.
Pusa Purvi: It is the first improved variety of small-fruited bitter gourd suitable for making stuffed cuisines. Fruits are attractive dark green, small in size (4-5 cm long and 3-4 cm diameter) with pointed tubercles, prickled, and crispy flesh with the high dry matter. The average yield is 8.78 tonnes/ha.
Pusa Rasdar: It is the first extra early (41-45 days for first fruit harvest) improved variety of bitter gourd suitable for cultivation in protected conditions. Fruits are smooth, non-prickled with tender skin, and fleshy, which will be highly acceptable to the growers. The average fruit weight is 140 g with an average yield of 4.5 q under 100 m² insect-proof net-house and 4. q under 100 m² poly-house.
Pusa Vishesh: Fruit is thick, medium-long, glossy green; suitable for the spring-summer season; first picking in 55-60 days. The yield is 15 tonnes/ha.
Cultivation
Planting/planting density
The seed is sown by hill and channel method at a spacing of 0.5 m between two hills with 3 seeds per hill. Optimum plant density varies with cultivar and location from 11,000 to 20,000 plants/ha. It requires a trellis to support the climbing vine. There are several methods of trellising. During the initial period of plant growth, effective weed control is important to the productivity of bitter gourd.
Plant nutrition
Fertilizer application rates depend on soil type, fertility level, and soil organic matter. Compost manure or farmyard manure is added to each planting hole before sowing @ 10 to 12 tonnes/ha. Typically, the application of 100:50:50 kg (N: P2O5: K₂O) per ha is recommended. Recommended fertilizer rate and application schedule in sandy soils at the Asian Vegetable Research and Development Centre (AVRDC) are 184, 112, and 124 kg of N, P2O5, and K₂O applied as one-time basal dose with four side dressings as appropriate. Bitter gourd is sensitive to a lack of micronutrients (e.g., boron), and the micronutrients are often incorporated to improve growth.
Irrigation
Bitter gourd will not tolerate drought and water stress, which can severely reduce the yield. Thus, appropriate soil moisture should be maintained in the upper 50 cm of soil where the majority of roots are located. Irrigation is applied weekly, beginning from the day of sowing.
Aftercare/culture
Most weeds can be removed effectively manually or mechanically. Cultivation is also an effective method of controlling weeds. Organic or plastic mulching is used frequently for controlling weeds. In plastic mulch, planting holes are made in the plastic sheet at an appropriate planting distance, stretched over the planting beds, with edges held down by thin bamboo slats, and plastic is stapled into the soil every 20 cm. Organic mulch, such as paddy-straw or dry grass, is usually less expensive than plastic mulch and thus is used often. For trellis systems, the pits are cleaned manually and covered with organic mulch, and then the interspaces are sprayed with post-emergence herbicides.
Flowering behavior varies with cultivar, climatic conditions, and cultural practices. The average ratio of staminate to pistillate flowers in monoecious lines throughout the flowering period is reported to be 50:1, but ratios can vary dramatically (i.e., 9:1 to 48:1). While long photoperiods cause staminate flowers to bloom up to 2 weeks earlier than pistillate flowers, short days have the reverse effect. Nearly 90% of pistillate flowers are borne on the first 40 nodes, and the majority of them mature at nodes 21-30. Judicious pruning of lower laterals stimulates subsequent lateral branch production, which in turn tends to increase the total number of flowers per plant.
Bitter gourd grows very fast and vines elongate rapidly within two weeks after planting. Thereafter, the plant sends out lateral stems. Staking and trellising will increase fruit yield and size, reduce fruit rot, and make spraying and harvesting easier. The bamboo poles, wood stakes, PVC pipes, or other sturdy materials are used to provide support and keep the fruit and foliage off the ground. The trellis is arranged either in a lean-to or tunnel structure.
Sex expression and modification
Momordica charantia is a monoecious annual, however, gynoecious sex form is also isolated in India for use in hybrid development programs. Gynoecism in the bitter gourd is under the control of a single, recessive gene (gy-1).
The principle in sex modification in cucurbits lies in altering the sequence of flowering and sex ratio. Spraying with gibberellic acid @ 25 to 100 ppm increases female flower production in bitter gourd. Sex expression is affected by environmental conditions under which M. charantia seedlings grow. The pistillate flower production under short-days is increased by low temperatures (e.g., 20°C) and nighttime chilling (e.g., 25°C day/15°C night). The foliar application of growth regulators can also modify sex expression. For example, foliar application of gibberellic acid (GA) treatment (25-100 mg/1) can dramatically increase gynoecy in bitter gourd, while cycocel (CCC; chlormequat/CCC @ 50-200 mg/1) promotes staminate flower development. Moreover, the appearance of the first staminate flower is delayed and pistillate flower initiation is promoted by relatively low concentrations of GA, (0.04 to 4 mg/1). Likewise, foliar application of CCC promotes staminate flower development at 50-200 mg/1 and female flower at 500 mg/l. Foliar application of silver nitrate (i.e., 250 mg/1 at the 5-leaf stage or 400 mg/l at the 3-leaf stage) induces bisexual flower formation, where ovaries and petals are larger than typical pistillate flowers. Likewise, the dramatic increase in early pistillate flower appearance can result from foliar application of MH (250 ppm) and ethrel (200 ppm), and staminate flower development can be promoted by application of GA, (i.e., 50-75 ppm). Finally, foliar sprays containing 50 ppm NAA stimulate early and abundant pistillate flower development, and boron at 4 ppm enhances pistillate flowers production, and fruit number and weight.
Diseases and Pests
Fruit fly: Maggots of fruit fly, (Dacus cucurbitae) cause damage to young developing fruits. The adult fly lays eggs below the epidermis of the young ovaries. The eggs hatch into maggots, which feed inside the fruits and cause rotting. In homestead gardens, the fruits typically are covered with polythene, cloth, or paper bags to provide mechanical protection and infested fruits are destroyed. The use of traps (10 traps per ha) has been found effective.
Red pumpkin beetle: Adult red pumpkin beetles, (Aulacophora foveicollis), eat the leaves, resulting in holes in the foliage, and they also damage roots and leaves. The insect attacks at the seedling stage as adults feed on cotyledonary leaves. This insect typically is controlled with insecticides. Spraying of insecticides controls the pest incidence.
Aphids: This small insect (Aphis gussypii), damages the plants sucking the leaf sap. In the young plant stage, cotyledonary leaf margins crinkle, and in severe cases, plants wilt. More serious losses are caused by aphids transmitting viral diseases. Contact insecticides often are applied to the underside of the leaves. Spraying of recommended pesticides reduces the population of aphids.
Fusarium wilt: The causal organism of Fusariurn wilt has been identified as Fusarium oxysporum f. sp niveum. Leaves wilt suddenly, and vascular bundles discolor in the collar region and become yellow or brown. It is difficult to control the disease since the fungus persists in the soil. The use of disease-free planting materials during sowing is recommended as disease control. The fungus can also be controlled by non-chemical methods, namely by cleft grafting bitter gourd shoot (scion) onto Luffa (rootstock). Luffa provides an excellent rootstock for bitter gourd, and grafting can increase yields substantially, mainly by controlling Fusarium wilt incidence.
Anthracnose: Anthracnose is caused by Colletotrichum spp. Small yellowish spots appear on leaves as water-soaked areas, which enlarge in size, coalesce, and produce black dot-like acervuli which turn later brown to black. Seed treatment, proper crop rotation, field sanitation, and clean cultivation minimize initial inoculums. The disease is also effectively controlled by foliar spraying of systemic fungicides.
Powdery mildew: Powdery mildew is caused by Sphaerotheca fuliginea. Initially white powdery or fluffy growth appears in circular patches or spots on the undersurface of the leaves. Severely infected leaves become brown and shriveled, and defoliation may occur. Fruits of affected plants do not fully develop. Seed treatment and soil drenching with systemic fungicides provide protection at the early stages of crop development. Spraying of an interval of 10-15 days reduces the powdery mildew incidence.
Downy mildew: Downy mildew is caused by Pseudoperonospora cubensis. Symptoms appear as irregularly shape yellow to brown angular spots appear on the upper sides of the leaves, usually at the center of the plant. Under moist conditions, purplish mildew typically develops on the underside of the leaf spots. Leaves die as necrotic spots increase in size and cause severe defoliation. Spread is often rapid from the crown toward new growth. Moist conditions favor the development of this disease, but the application of an array of recommended fungicides can prevent the spread of the fungus.
Virus: Bitter gourd is a host of watermelon potyvirus, cucumber green mottle virus (both transmitted by whitefly), and bitter gourd mosaic virus (transmitted by aphid). Uprooting and destruction of affected plants and collateral hosts are common means of control. The virus incidence can also be minimized by controlling whitefly.
Harvesting and Post-Harvest Management
The optimal timing of bitter gourd fruit harvest is often difficult to ascertain since bitter gourds are consumed before fruits are at physiological maturity (i.e., mature fruits are unmarketable). Optimal harvest is indicated by slight changes in fruit color and increased exocarp development (i.e. fullness of ridges and bumps), which are difficult to evaluate. Seed coat color is a good indicator of optimal harvest maturity (i.e., creamy or pale green-brown, with over maturity indicated by pink coloration), but obviously, it is not useful for easy determination of marketable fruit. Since fruit continues to mature after harvest, fruit for immediate sale in local markets should be harvested just prior to harvest maturity (i.e., physiologically immature), whereas fruit for long-distance transport must be harvested several days/weeks earlier than this. Physical appearance and nutritional quality vary with cultivars and the stage of fruit development for harvest. Optimal bitter gourd fruit harvest typically occurs between 15-20 days after fruit set (i.e. 90 days after planting). Nevertheless, owing to wide culinary preferences, broad variation in harvest date is common. Harvestable fruits, in general, are light green, thick and turgid, where seeds are typically soft and range from white to creamy with hues of pale green-brown depending on fruit maturity and variety. Harvests typically are made every 2-3 days since fruit ripens quickly. Fruits increase in bitterness during maturation due to the accumulation of alkaloid momordicine, but they subsequently lose bitterness during the ripening process.
