2130

8: Vegetables

Abelmoschus esculentus (L.) Moench

Methodus: 617 (1794).

MALVACEAE

2n = 130 (66—144)

Hibiscus esculentus L. (1753).

Okra, lady's finger (En). Gombo (Fr). Indonesia: okra, kopi arab. Malaysia: kacang bendi, sayur bendi, kacang lender. Philippines: okra, saluyot a bunga (Ilocano), haluyot (Ifugao). Burma: you-padi. Cambodia: pôôt barang. Laos: khüa ngwàng. Thailand: krachiap-khieo (central), krachiap-mon (central), bakhua-mun (northern). Vietnam: d[aaj]u b[aws]p, b[uj] b[aws]p, m[uw][ows]p t[aa]y.

The genus Abelmoschus Medikus originated in South-East Asia. Abelmoschus esculentus, however, is a cultigen of uncertain origin. It is now widely cultivated in tropical and subtropical regions, but is particularly popular in India, West Africa and Brazil. Okra is common in the Philippines, Malaysia, Thailand and Vietnam, but of little importance in Indonesia and Papua New Guinea.

Okra is mainly grown for its young immature fruits, which are consumed as a vegetable, raw, cooked or fried. It is a common ingredient of soups and sauces. The fruits can be conserved by drying or pickling. The leaves are sometimes used as spinach or cattle feed, the fibres from the stem for cord, the plant mucilages for medical and industrial purposes, and the seeds as a substitute for coffee. Okra seeds contain a considerable amount of good quality oil and protein.

World okra production is estimated to be 5—6 million t/year, which is about 1.5% of total world production of vegetables. No production statistics are available from South-East Asian countries. Some fresh or frozen okra is exported from Thailand and the Philippines to Japan, and okra in brine is a potential export item to the Middle East.

Per 100 g edible portion, the fruits contain: water 90 g, protein 2 g, fibre 1 g and carbohydrates 7 g. The energy value is about 145 kJ/100 g. Okra is a good source of vitamins and minerals. Compared with other fleshy fruits (tomato, eggplant), it is particularly rich in Ca (70—90 mg per 100 g).
The 1000-seed weight varies from 30—80 g.

Stout, erect, annual herb, up to 4 m tall. Leaves spirally arranged, leaf-blade up to 50 cm in diameter, more or less deeply 3-, 5- or 7-lobed; petiole up to 50 cm long, stipules filiform, up to 20 mm long, often split to the base. Flowers solitary in the leaf axils or in pseudoracemes by reduction of the upper leaves, yellow, self-fertile; pedicel up to 3 cm long in flower, up to 7 cm long in fruit; epicalyx of 7—15 free, linear segments, 5—25 mm x 0.5—3 mm; calyx spathaceous, 2—6 cm long, splitting on one side during the expansion of the corolla, adnate to and falling with the corolla; corolla with 5 obovate petals, each about 3—7 cm long and wide, yellow with a dark purple centre. Fruit a cylindrical to pyramidal capsule, 5—35 cm long, 1—5 cm in diameter, completely, partially or not loculicidal, green, greenish-purple or completely purple when young, brownish when mature. Seeds numerous, globose, 3—6 mm in diameter, blackish. Germination is epigeal.

Okra usually flowers within 40—90 days after sowing; its cropping period rarely exceeds 6 months. Self-pollination and flower opening take place in the early morning. Partial cross-pollination by insects may take place. For vegetable use, the fruits are picked about one week after anthesis. It takes about one month from anthesis to mature fruit. In the seed crop, vegetative growth stops soon after anthesis, all assimilates being partitioned to the reproductive plant parts. In the vegetable crop, the picking of young fruits permits sustained vegetative growth, prolonging the harvest.

Abelmoschus esculentus (2n = 130) is probably an amphidiploid (allotetraploid), derived from Abelmoschus tuberculatus Pal & Singh (2n = 58), a wild species from India, and a still unknown species with 2n = 72 chromosomes.
Another edible okra species occurs in the humid parts of West and central Africa. Described originally as a botanical variety (Hibiscus manihot L. var. caillei A. Chev.), it has recently been recognized as a distinct species (Abelmoschus caillei (A. Chev.) Stevels). There are no apparent differences in use between the ordinary (Abelmoschus esculentus) and West African okra (Abelmoschus caillei), which is why they are often lumped together. Morphologically the West African okra differs in several respects, but its epicalyx offers the best discriminating characteristics with 5—10 free, ovate segments, 10—35 mm x 4—13 mm. The plant is more robust than Abelmoschus esculentus, and crop duration may exceed 12 months. It has very many chromosomes (2n = approximately 192 (184—200)) and it might be an allohexaploid, Abelmoschus esculentus being one of the parents.
There are many cultivars of okra. Some of the better known are 'Clemson Spineless' (United States) and 'Pusa Sawani' (India).

Abelmoschus esculentus needs temperatures above 20°C for normal growth and development. Germination percentage and speed of emergence are optimal at 30—35°C. Flower initiation and flowering are delayed at higher temperatures (positive correlation between temperature and number of vegetative nodes). Abelmoschus esculentus is a short-day plant, but its wide geographical distribution (up to latitudes of 35—40°) indicates that cultivars differ markedly in sensitivity. Flower initiation and flowering are hardly affected by daylength in popular subtropical cultivars such as 'Clemson Spineless' and 'Pusa Sawani'. Most tropical cultivars show quantitative short-day responses, but qualitative responses also occur. The shortest reported critical daylength is 12 hours 30 minutes.
The West African okra is considerably more sensitive to photoperiod. This partly explains its limited geographical distribution (up to latitudes of 10—15°) and longer life-cycle. The shortest reported critical daylength is 12 hours 15 minutes.
Okra does well on fertile light or heavy soils if well drained.

Propagation is by seed. Most farmers harvest seed from their own local cultivar or rather heterogeneous landrace. The easiest way to keep the seed is to leave it in the pods until it is used. To soften the hard seed coat, the seed is often soaked in water. The seed is usually dibbled into individual hills directly in the field. Optimum plant densities for Abelmoschus esculentus are in the range of 50 000—150 000 plants/ha. The robust West African okra should be planted at 20 000—50 000 plants/ha. A common planting pattern is a spacing of 60—80 cm between the rows, with one seed per hill every 10 cm or two seeds per hill every 15—20 cm. Rows in east-west direction will best capture the sunlight. Emergence is within one week. When the plants are about 10 cm tall, they could be thinned to one plant per hill or one plant every 20 cm. The seed requirement is 3—5 kg/ha.
Some farmers practise ratoon cropping. A ratoon crop flowers in 35 days after cutting and may give a higher yield than the seed-propagated mother crop. However, the quality of the fruits is always inferior in the ratoon crop (high percentage of bent fruits).

Commercial growers usually cultivate okra in sole cropping. For home consumption, a few plants are grown in home gardens or in fields of other food crops. The uptake of minerals is rather high. Indicative figures for total nutrient uptake per ha (crop with fruit yield of about 10 t/ha) are 100 kg N, 10 kg P, 60 kg K, 80 kg Ca and 40 kg Mg. The fertilizer recommendation in Indonesia is 10 t/ha of organic manure applied to the planting holes together with TSP 150 kg and KCl 150 kg. Urea 150 kg/ha or ammonium sulphate 300 kg/ha can be given in three split applications: at sowing, after 3 weeks and again at 6 weeks after sowing. If the vegetative development at the age of three weeks is too luxurious, no N fertilizer should be applied anymore, otherwise the harvest will be delayed and the crop will become attractive to insects. Furrow irrigation must be given when needed. A full-grown crop consumes about 8 mm water per day. Weeding is only needed during the first month and can be combined with earthing-up.

The most serious fungal diseases are Cercospora blight (Cercospora abelmoschi and Cercospora malayensis), powdery mildew (Erysiphe cichoracearum) and fruit rot (Choanephora cucurbitarum). They are controlled by spraying with fungicides. Some other diseases are Fusarium wilt, pod spot (Ascochyta abelmoschii) and anthracnose (Colletotrichum hibisci). Yellow-vein mosaic virus (YVMV) is a major cause of crop failure in Asia, whitefly (Bemisia tabaci) being the vector. Viruses must be controlled through the use of healthy seed or the chemical control of the vectors (aphids, whitefly).
Important pests of okra are fruit and stem-borers (Earias spp., Heliothis armigera), jassids (Empoasca spp.), stink bugs (Nezara viridula, Dysdercus spp.) and root knot nematodes. Chemical control of insects is hazardous because harvesting is so frequent. Damage by nematodes is avoided by respecting crop rotation and by high doses of organic manure.
The West African okra is much more tolerant of diseases and pests than the ordinary okra.

Early-maturing cultivars give the first harvest at 7 weeks after sowing. A developing fruit should be harvested when 7—8 days old. Earlier picking depresses yields because of suboptimal fruit weight. Delayed picking depresses marketable yields because over-aged fruits become fibrous. Therefore, okra fields are harvested at intervals of 2—3 days. For seed production, the whole crop can be harvested at once. Intensive contact with the slightly hairy fruits and plants may lead to skin irritation.

A yield of 10 t/ha can be considered a good harvest, but yields over 40 t/ha can be realized under optimal conditions. Usually yields are low (2—4 t/ha), because of the extensive cultivation.

Fresh okra can quite easily be transported in bulk and kept for several days without much loss of quality. Dried okra is an important product in West Africa. Some countries have a small canning and freezing industry.

Germplasm base collections are maintained by USDA (Fort Collins, United States), NIHORT (Ibadan, Nigeria), ORSTOM (Montpellier, France), IDESSA (Bouaké, Ivory Coast), NBPGR (New Delhi, India) and IPB (Los Baños, the Philippines). Local okra landraces are in great risk of genetic erosion because growers tend to switch to commercial cultivars.
Through the IBPGR germplasm network, the West African okra has already been introduced in several American and Asian countries.

Work has been oriented towards intensive cultivation with high production in a short period (early maturity, high density planting) and wide adaptation (photoperiod insensitivity, resistance to pests and diseases). Several attractive American (e.g. 'Clemson Spineless') and Indian cultivars (e.g. 'Pusa Sawani') have found their way to commercial growers throughout the tropics and subtropics. Resistance to many diseases and pests has been identified in available okra germplasm, but not yet so to YVMV, a major problem in Asia.
Little attention has been given to the needs of the traditional sector (cultivation for home consumption), where hardy, robust, long-lived types such as the West African okra are required. The characteristics of both okra species open up new opportunities for recombination. They cross readily in both directions and give vigorous hybrids; these, however, show strongly reduced fertility.

Okra will remain a welcome, productive tropical and subtropical fresh vegetable. The discovery of a second edible species in West Africa calls for a detailed study of its potential in other continents. Okra improvement will also greatly benefit from a better understanding of the phylogeny and species relations within the genus Abelmoschus.

Bautista, O.D.K. & Cadiz, T.G., 1967. Okra. In: Knott, J.E. & Deanon Jr, J.R. (Editors): Vegetable production in South-East Asia. University of the Philippines Press, Los Baños, the Philippines. pp. 263-268.
Charrier, A., 1984. Genetic resources of Abelmoschus (okra). International Board for Plant Genetic Resources (IBPGR), Rome, Italy. 61 pp.
IBPGR, 1991. Report of an international workshop on okra genetic resources, held at the National Bureau for Plant Genetic Resources (NBPGR), New Delhi, India, 8-12 October 1990. International Crop Network Series. 5. International Board for Plant Genetic Resources (IBPGR), Rome, Italy. 133 pp.
Markose, B.L. & Peter, K.V., 1990. Okra. Review of research on vegetables and tuber crops. Technical Bulletin 16. Kerala Agricultural University Press, Mannuthy, Kerala, India. 109 pp.
Martin, F.W. & Ruberté, R., 1978. Vegetables for the hot humid tropics. Part 2. Okra, Abelmoschus esculentus. Mayaguez Institute of Tropical Agriculture, Puerto Rico, United States. 22 pp.
Siemonsma, J.S., 1982. West African okra - morphological and cytogenetical indications for the existence of a natural amphidiploid of Abelmoschus esculentus (L.) Moench and A. manihot (L.) Medikus. Euphytica 31: 241-252.
Siemonsma, J.S., 1982. La culture du gombo (Abelmoschus spp.), légume-fruit tropical (avec référence spéciale à la Côte d'Ivoire) [Cultivation of the tropical fruit-vegetable okra (Abelmoschus spp.), with special reference to Ivory Coast]. Thesis, Wageningen Agricultural University, the Netherlands. 297 pp.

J.S. Siemonsma

Siemonsma, J.S., 1993. Abelmoschus esculentus (L.) Moench. In: Siemonsma, J.S and Piluek, K (Editors): Plant Resources of South-East Asia No 8: Vegetables. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea