Solanum melongena (PROSEA)
- Protologue: Sp. pl.: 186 (1753).
- Family: Solanaceae
- Chromosome number: 2n= 24
- Solanum coagulans Forsskal (1775),
- S. cumingii Dunal (1852),
- S. pressum Dunal (1852),
- S. undatum Poiret sensu Ochse.
- Eggplant, aubergine, melongene, brinjal (En)
- Aubergine, melongène, bringelle (Fr.)
- Indonesia: terong, encung, tiung (Sumatra)
- Malaysia: terong
- Philippines: talong (Tagalog), tarong (Ilocano), bringhinas (Bisaya)
- Burma: kayan
- Cambodia: trâb vèèng, trâb put lo-nhoong
- Laos: khüa poom, khüa hlèèz, khüa ham maaz
- Thailand: makhua-yao, makhua-chan, makhua-khao
- Vietnam: cà tím, cà bát.
Origin and geographic distribution
The eggplant most probably originated in the Indo-Burmese region, where it is an ancient crop and occurs with great variability; secondary centres of diversity are China and possibly Africa. Now it has spread throughout the tropics, subtropics and the warm temperate regions; in temperate climates it is also grown in greenhouses.
The young and almost mature fruits are used as a vegetable. They may be roasted, fried, stuffed, cooked as curry, pickled or prepared in some other manner. In Indonesia and Malaysia young fruits are also eaten raw. The eggplant is widely used in traditional medicine. In Malaysia the ashes of the fruit are prescribed for use in a dry hot poultice on haemorrhoids and the pounded root is applied inside the nostrils against ulceration. In India the eggplant is used in medicines to cure diabetes, asthma, cholera, bronchitis and dysuria. The fresh or dry leaf and fruit are said to reduce blood cholesterol level. In New Guinea, the juice from the roots is used to cure otitis and toothache.
Production and international trade
In 1987 total world production of eggplant fruits was estimated at 5.5 million t, cultivated on 430 000 ha. For South-East Asia some figures are: Indonesia (1988) 168 000 t from 32 000 ha, the Philippines (1987) 90 000 t from 15 000 ha, Thailand (1987) 58 000 t from 11 000 ha. It is a common market vegetable in tropical countries. Most of the production from home gardens or in mixed intercropping with field crops is for home use. The eggplant is most important in China, India, South-East Asia, northern Africa and the Mediterranean area.
Per 100 g edible portion, the fruits contain approximately: water 92 g, protein 1.6 g, fat 0.2 g, carbohydrates 4.0 g, fibre 1.0 g, ash 0.6 g, Ca 22 mg, Fe 0.9 mg, vitamin B1 0.08 mg, vitamin B2 0.07 mg, niacin 0.7 g, vitamin C 6.0 mg. The energy value is about 100 kJ/100 g. About 4% of the harvested product is waste. The 1000-seed weight is approximately 4 g.
- An erect, branching, very polymorphous, perennial herb, up to 1.5 m tall, grown as an annual, with strong, deeply penetrating taproot.
- All parts covered with a grey tomentum, sometimes plants are somewhat spiny, older plants may become woody. Leaves alternate, simple; petiole up to 10 cm long; leaf-blade ovate to ovate-oblong, 3-25 cm × 5-15 cm, densely stellate hairy, base rounded or cordate, often unequal, margin sinuately lobed, apex acute or obtuse.
- Flowers solitary or in 2-5-flowered cymes, hermaphrodite or male (andromonoecy), opposite the leaves, 3-5 cm in diameter; pedicel 1-3 cm long, in fruit up to 7 cm; calyx tubular-campanulate, about 2 cm long, 5-7-lobed, spiny, woolly, persistent and enlarging in fruit when it often splits; corolla gamopetalous, deeply 5-6-lobed and stellately spreading, purplish-violet, lobes hairy beneath; stamens 5-6, about 1 cm long, anthers opening by two terminal pores; ovary 2-locular, style simple, stigma capitate.
- Fruit a large pendent berry, ovoid, oblongoid, obovoid or subglobose to globose, up to 40 cm long and 20 cm in diameter but very variable, smooth, shiny, white, green, yellow, purple, black or mixed coloured.
- Seeds numerous, small, light-brown.
Growth and development
Germination of seed is epigeal and takes about 2 weeks. Young plants can be transplanted to the field about 4-6 weeks after sowing. Flowering starts 6-8 weeks after transplanting. Eggplants are normally self-pollinated, but 6-20% cross pollination by insects (bees) may occur. Fruits can be harvested starting about 5 weeks after flowering, depending on cultivar and desired maturity rate. Normally 8-14 fruits per plant will be produced, after which the economic lifetime of eggplant is over. If old plants are cut back they frequently resprout and bear in a second season, but accumulated disease problems often make this impossible or uneconomic.
Other botanical information
S. melongena is very variable in fruit form and colour and the variation is continuous, which means that existing subclassifications into botanical varieties and subspecies have no practical value. More practical would be a classification into cultivar groups and cultivars. Worldwide, important cultivars are "Black Beauty", "Florida Market" and "Long Purple". In South-East Asia, local cultivars are more common than the high-yielding exotic cultivars since they are better adapted to local conditions. Selection and registration of local cultivars is still rare.
In South-East Asia there are two distinct types of eggplant cultivars, which may be distinguished as cultivar groups:
- Cv. group Common Eggplant. Characterized by a robust habit, more or less pronounced purplish flowers, and persistent calices at the base of the big round to elongated oval fruits. The immature fruits are extremely variable in form, size and colour, showing variations between purple, green and white. A popular local type in Indonesia is "Kopek", which has elongated fruits with an obtuse end. The fruits of common eggplant are normally used as a cooked vegetable but in Indonesia the light green long types are also consumed raw. This cv. group also includes the type of "international" cultivars such as "Long Purple".
- Cv. group Bogor Eggplant. Characterized by a small spreading habit, small greyish leaves, and small greenish-white flowers. The fruits are round or flat-round, 4-10 cm in diameter, green near the calyx which partly envelops the fruit, and marbled white at the top. In Indonesia, the tender, crispy, slightly bitter-tasting fruits of cv. group Bogor Eggplant, also called "Kelapa", are very popular for raw consumption. A popular cultivar with small fruits is "Gelatik".
Both cv. groups do not cross easily. A taxonomic study is needed to determine whether cv. group Bogor Eggplant deserves species ranking.
Optimum day temperatures for eggplant range between 25-35 °C, night temperatures between 20-27 °C. Eggplant is more susceptible to low temperatures than tomato and capsicum pepper and it does not tolerate frost. Eggplant is tolerant of drought and excessive rainfall, but in general fruit set and production decrease under adverse conditions. As far as is known it is daylength neutral. It does best in well-drained, sandy loam. The most satisfactory environmental conditions are normally found in lowland areas with relatively little temperature variation. When grown at altitudes above 800 m growth is retarded and yield reduced.
Propagation and planting
Eggplant is normally propagated by seed. Propagation by rooting of healthy shoots is also possible. Soaking the seeds in water for 24 hours hastens germination. Seeds are sown in containers or seed-beds in a nursery. About 200 g seed is required for 20 000-30 000 plants/ha. With a good nursery method, it is possible to produce enough plants for one hectare with only 60 g of seed. This is especially important when expensive hybrid seed is used. The practice is to sow in a shaded seed-bed; the seedlings emerge after 8-10 days and are pricked out in small pots of banana leaf 2-3 weeks later; after 3 weeks these banana-leaf pots are transplanted to the field, on raised beds or ridges. For ridge planting 70-90 cm between rows and 50-60 cm between plants is commonly practised. Before planting, the field is manured with compost or farmyard manure or at planting a complete mineral fertilizer solution (NPK 1 : 1 : 1, 500 kg/ha) is applied. In Indonesia it is recommended to supply 0.5 kg of farmyard manure with 10 g of triple superphosphate, 5 g KCl and 5 g of urea per planting hole.
Weed control should be shallow, to avoid damage to the roots. When plants are established the terminal growing point may be removed to encourage lateral branching. Tall-growing cultivars will also require support.
Supplementary irrigation is required during dry periods. Mulching with dried plant materials or with thin black polyethylene sheets reduces moisture loss and weed problems.
The need for additional fertilizer during growth depends on local conditions. Eggplants are heavy feeders and they benefit from additional fertilizer dressings of nitrogen (as urea or ammonium sulphate) and in some cases also potassium, about 4 and 6 weeks after transplanting.
Diseases and pests
In general, cultivars of cv. group Common Eggplant are more susceptible to diseases and pests than cv. group Bogor Eggplant. The most destructive diseases and pests reported from South-East Asia are bacterial wilt, Phomopsis fruit rot and Epilachna beetles. Bacterial wilt (Pseudomonas solanacearum) occurs with bad drainage and is often combined with symptoms of root knot nematodes. It can easily be controlled by the use of resistant cultivars such as the Indonesian "Kopek Ungu". Phomopsis rot (Phomopsis vexans) causes rotting spot of stems, leaves and fruits. It is controlled by the use of healthy seed and by sanitation, removing all diseased plants or fruits from the field. Farmers spray with dithiocarbamates against this disease. Leaf beetles (Epilachna sparsa) are a very common and devastating pest of eggplant, controlled by spraying with insecticides. Other diseases and pests reported from South-East Asian countries are green stink bug (Nezara viridula), mites (Tetranychus spp.), aphids, root knot nematodes, anthracnose fruit rot (Colletotrichum melongenae, Gloeosporium melongenae), Sclerotium wilt, Cercospora leaf-spot, Phytophthora fruit rot and several virus diseases (tobacco rattle, cucumber mosaic, tomato ringspot).
The first harvestable fruits appear 60-90 days after planting. Fruits are harvested when they are about two-thirds of their maximum size. Harvesting is done once or twice a week. For seed production, only fully mature fruits should be harvested from healthy and productive plants.
A high yield is 25-50 t/ha. The yielding capacity of cv. group Bogor Eggplant is much lower than that of cv. group Common Eggplant. World average yield in 1987 was about 13 t/ha, but it was much lower in South-East Asia: 5.2 t/ha in Indonesia (1988), 6 t/ha in the Philippines (1987), 5.5 t/ha in Thailand (1987). In seed production, a seed yield of 100-200 kg/ha can be obtained, depending on cultivar and conditions.
Handling after harvest
After grading on quality the fruits are packed in bags, crates or baskets. Eggplant fruits are more resistant to rough handling and transport than tomato or capsicum pepper. After a few days the quality will decline by crinkling and rotting. Cooling of fruits considerably prolongs their storage life. With cooling at 10-13 °C and a high relative humidity, eggplant can be stored for 2-3 weeks.
Hundreds of landraces and cultivars of S. melongena have been collected in gene banks in the United States, Europe and India. Few collections of primitive or more advanced local cultivars have been reported. A working collection is present at the Lembang Horticultural Research Institute (LEHRI) in Indonesia. In all tropical countries traditional cultivars are being replaced by more advanced, high-yielding cultivars, enhancing genetic erosion. Collection of local cultivars is urgent, and material should be screened for disease and pest resistance.
Much breeding work (pure-line selection) has been carried out, mostly in the United States, but also in India, Thailand, the Philippines and Indonesia. Eggplant withstands inbreeding and shows some heterosis. Hybrid cultivars have been bred, applying male sterility, but these are not yet widely cultivated.
In the Philippines "Bulacan" is a high-yielding cultivar containing very few seeds, and is resistant to bacterial wilt. "College Long Purple" and "Dingras Multiple Purple", also from the Philippines, are resistant to bacterial wilt as well, as is "Kopek" from Java (Indonesia). Resistance breeding to wilt diseases and root knot nematodes should have first priority. Much can still be expected from traditional cultivars of eggplant and related species, e.g. Solanum americanum Miller, S. incanum L., S. macrocarpon L., S. violaceum Ortega, S. aethiopicum L., S. sisymbriifolium Lamk and S. torvum Swartz.
Eggplant is a relatively easy to cultivate and high-yielding vegetable with a reasonable nutritional value. It should be possible to breed into eggplant resistance for the most destructive diseases of the hot humid tropics, bacterial wilt and Phomopsis rot. In South-East Asia, the future of eggplant can be bright if the genetic richness of local cultivars is better exploited.
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