Prota 14: Vegetable oils/Oléagineux
Man. ess. forest. Congo: 136 (1923).
Bitter bush mango, dry season bush mango (En). Dika, odika, manguier sauvage, chocolatier, ogbono (Fr).
Origin and geographic distribution
Irvingia wombolu occurs in the forest zone from the Cassamance in Senegal east to southern Sudan and Uganda, and south to south-western DR Congo and northern Angola.
The kernels from the fruit are an important ingredient in cooking and are preferred over those of other Irvingia spp. They are processed by grinding and crushing, and then used to thicken soups and stews. The kernels are also made into a cake called ‘dika bread’ or ‘odika bread’ for year-round preservation and easy use. An edible oil is extracted from the seed and used in cooking. As it is solid at ambient temperatures it has been used as a substitute for cocoa butter and for soap-making. The presscake is a good cattle feed and is suitable in the food industry. The pulp of the fruit of Irvingia wombolu is bitter and slimy and is occasionally added to soups as thickener.
Irvingia wombolu is commonly preserved when clearing land for agriculture to provide shade for crops, especially cocoa and coffee but also annual crops. The medicinal uses of Irvingia spp. are many, but can hardly be assigned to an individual species. Preparations from the bark are rubbed on to the body to relieve pains and are applied to sores and wounds and against toothache. They are also taken to treat diarrhoea. The Igbo people use a leaf extract as a febrifuge. In Cameroon preparations mainly from the bark are used to treat hernia and yellow fever, and as an antidote for poisoning. Kernels are used to treat diabetes. The wood, called ‘andok’ in Cameroon, is used locally for heavy construction work and for making ships’ decks, paving blocks and planking. Young trees are used for making poles and stakes, while branches are made into walking sticks or thatched roof supports. Dead branches are used as firewood.
Production and international trade
Kernels of Irvingia wombolu and related species are widely traded domestically and between countries in West and Central Africa and are exported to Europe. Cameroon is probably the main exporter. The combined export trade of the kernels of Irvingia wombolu and Irvingia gabonensis (Aubry-Lecomte ex O’Rorke) Baill. from Cameroon has been valued at US$ 260,000 per year for 107 t. Côte d’Ivoire also exports large amounts of nuts to Nigeria, Sierra Leone and Liberia. Nigeria is the main importing country. The wood of Irvingia wombolu is mainly used locally and rarely exported.
The nutritive value of the kernels of Irvingia wombolu per 100 g edible portion is: water 4 g, energy 2918 kJ (697 kcal), protein 8.5 g, fat 67 g, carbohydrate 15 g, Ca 120 mg, Fe 3.4 mg, thiamin 0.22 mg, riboflavin 0.08 mg, niacin 0.5 mg (Platt, 1962). Drawability (sliminess) and viscosity of soups imparted by the kernels varies between kernels from different trees. The kernels of Irvingia wombolu are considered better than those of other Irvingia spp. Fat content of kernels also varies between trees and is about 37.5–75 g/100 g; the approximate fatty acid composition is: lauric acid 20–59%, myristic acid 33–70%, palmitic acid 2%, stearic acid 1% and oleic acid 1–11%. The residue obtained after separation from the fat is suitable for processing in the food industry.
Heartwood of Irvingia gabonensis and Irvingia wombolu is pale greenish brown or orange-yellow fading to greyish brown; sapwood is lighter, but not always clearly differentiated. The grain is straight or interlocked, texture fine to medium.
The wood is fairly heavy. The density is 930–1002 kg/kg3 at 12% moisture content. The shrinkage rates are high, from green to oven dry 6.5–7.1% radial and 10.2–12.6% tangential. To avoid end surface checking, logs should be converted soon after felling, preferably by quarter-sawing.
At 12% moisture content, the modulus of rupture is 163–217 N/mm2, modulus of elasticity 18,700–21,700 N/mm2, compression parallel to grain 69–79 N/mm2, Chalais-Meudon side hardness 5.7–12.7, shear 15 N/mm2, cleavage 19–34 N/mm. The timber is moderately difficult to saw or plane and tools should be kept sharp. It dresses to a smooth finish and glues well. Nailing is difficult. The timber is durable and fairly resistant to termites, but susceptible to powder-post beetles and marine borers. The heartwood is untreatable, the sapwood resistant to preservatives.
Adulterations and substitutes
The kernels of all Irvingia species are used as thickener for soups and stews. Groundnuts and okra are used similarly in West and Central Africa.
Small to medium-sized tree up to 25 m tall; bole often slightly leaning, up to 80 cm in diameter, with buttresses to 2 m high; bark greyish brown; crown spherical, fairly dense. Leaves alternate, simple and entire; stipules large, unequal, forming a cone protecting the bud, caducous, leaving an annular scar on the branches; petiole up to 10 mm long; blade elliptical to obovate, (6.5–)10.5–14(–18) cm × 4–6(–8.5) cm, base obtuse to slightly cuneate, apex rounded or minutely acuminate, leathery, pinnately veined. Inflorescence an axillary panicle up to 9 cm long. Flowers bisexual, regular, 5-merous, small; pedicel up to 6 mm long; sepals free, c. 1 mm long; petals free, 3–4 mm long, whitish; stamens 10, inserted below disk, free, equal, filaments c. 5 mm long; disk 2–3 mm in diameter, bright yellow, nectariferous; ovary superior, 2-celled, style c. 1.5 mm long. Fruit an ellipsoid drupe, slightly laterally compressed, 4.5–8 cm × 4.5–5 cm × 4.5–5 cm, green, often turning bright yellow then black, pulp yellow, soft, juicy, very bitter, with fairly numerous fibres, stone woody, 1-seeded. Seed 3.5–5 cm × 1.5–2.5 mm × c. 1 cm.
Other botanical information
Irvingia counts 7 species, 6 in tropical Africa and 1 in South-East Asia. Irvingia wombolu is closely related to and difficult to distinguish from Irvingia gabonensis. Irvingia gabonensis has edible fruit pulp while that of Irvingia wombolu is bitter and inedible. Some authorities consider Irvingia wombolu merely a variety of Irvingia gabonensis. Because of the long history of protection and cultivation, others consider them cultivars of a single species. However, DNA analyses indicate that the 2 taxa are genetically distinct and do not (or hardly) hybridize, even where sympatric. The analyses also showed marked differences between populations of Irvingia wombolu from south-eastern Nigeria and Cameroon.
Growth and development
Irvingia wombolu starts flowering when 6–10 years old. It does not have a clearly demarcated flowering season, but flowering peaks at the end of the rainy season or beginning of the dry season, while fruiting peaks at the end of the dry season. Flowers are pollinated by insects.
Irvingia wombolu occurs in dryland forest with more than 1500 mm annual rainfall. In some locations it grows in seasonally flooded forest and on river banks. It is adapted to a wider rainfall range than other Irvingia spp. Trees are fire tender.
Propagation and planting
Irvingia wombolu is mostly propagated by seed, but methods of vegetative propagation have been developed. Seed loses its viability within one month and has to be planted soon after collection.
Irvingia wombolu is mostly retained and protected in cocoa and coffee farms, plantations of annual food crops, and home gardens. However, in some regions, including the Mamfe region of south-western Cameroon, most trees are planted especially in cocoa and coffee farms. They are planted at an approximate density of 100 trees/ha. Management includes pruning, fertilization and harvesting (gathering and picking).
Diseases and pests
No diseases or pest of Irvingia wombolu trees have been recorded. Seeds are infested by larvae of the merchant grain beetle (Oryzaephilus mercator). Eggs are laid between the testa and cotyledons of the seed or in cracks in the cotyledons. Preventing cracks helps to prevent infestation.
Irvingia wombolu fruits are mostly gathered from the ground around the tree. The next step consists of extracting the kernel from the seed, which is split in halves with a cutlass, after which the kernel is removed with the help of a knife. The kernels are then dried in the sun or on bamboo drying racks over the fireplace in the kitchen.
Good yields of kernels have been estimated at 100 kg/tree.
Handling after harvest
The preparation of ‘dika bread’ consists of drying, roasting and grinding the kernels. The paste obtained is put in a container or ‘cake tin’ and left to cool for a few hours. Once solid, the cake is removed from the container and is ready for use. If well dried, it can be stored for more than a year. Sometimes women place a tin below the grid on which the dika cake is stored, to collect the oil that drips from it. In Gabon ‘dika bread’ is marketed in cakes of 100–5000 g. Oil is extracted by boiling the ground kernels and scooping off the oil.
Centres of genetic diversity in Irvingia wombolu have been identified: southern Cameroon and south-eastern Nigeria. ICRAF and its collaborative partners in the region have established in-situ germplasm collections in the natural distribution range of Irvingia wombolu in Cameroon and Nigeria. Irvingia wombolu is widespread and does not seem to be in danger of genetic erosion.
ICRAF has started a programme of domestication of Irvingia wombolu. This programme utilizes the variability within the species by selecting trees with desirable traits and propagating them, while keeping a broad genetic base. A clonal approach aimed at cultivar development has been adopted. An assessment of the variability in fruits and kernel traits was made and trees were selected on the basis of desired fruit characteristics.
Kernels of Irvingia wombolu are widely traded domestically and between countries in West and Central Africa and exported to Europe, indicating that demand is likely to increase. Domestication of this species offers great opportunity for the sustainability of production. The development of methods of transformation and preservation of the product will further expand its market.
• Asaah, E.K., Tchoundjeu, Z. & Atangana, A.R., 2003. Cultivation and conservation status of Irvingia wombolu in humid lowland forest of Cameroon. Journal of Food, Agriculture and Environment 1(3-4): 251–256.
• World Agroforestry Centre, undated. Agroforestree Database. [Internet] World Agroforestry Centre (ICRAF), Nairobi, Kenya. http://www.worldagroforestry.org/ Sites/TreeDBS/ aft.asp. Accessed March 2006.
• Harris, D.J., 1993. A taxonomic revision and an ethnobotanical survey of the Irvingiaceae in Africa. PhD thesis, Linacre College, University of Oxford, Oxford, United Kingdom. 276 pp.
• Harris, D.J., 1996. A revision of the Irvingiaceae in Africa. Bulletin du Jardin Botanique National de Belgique 65: 143–196.
• Ladipo, D.O., 2000. Harvesting of Irvingia gabonensis and Irvingia wombulu in Nigerian forests; potentials for the development of sustainable systems. Paper presented at the Seminar Harvesting of Non-Wood Forest Products, held at Menemen-Izmir, Turkey on 2–8 October 2000. [Internet] http://www.fao.org/ documents/show_cdr.asp?url_file=/ DOCREP/005/Y4496E/ Y4496E32.htm. Accessed March 2006.
• Leakey, R.R.B., Fondoun, J-M., Atangana, A. & Tchoundjeu, Z., 2000. Quantitative descriptors of variation in the fruits and seeds of Irvingia gabonensis. Agroforestry Systems 50: 47–58.
• Leakey, R.R.B., Greenwell, P., Hall, M.N., Atangana, A.R., Usoro, C., Anegbeh, P.O., Fondoun, J M. & Tchoundjeu, Z., 2005. Domestication of Irvingia gabonensis: 4. Tree-to-tree variation in food-thickening properties and in fat and protein contents of dika nut. Food Chemistry 90: 365–378.
• Lowe, A.J., Gillies, A.C.M., Wilson, J. & Dawson, I.K., 2000. Conservation genetics of bush mango from central/west Africa, implications from RAPD analysis. Molecular Ecology 9: 831–841.
• Richter, H.G. & Dallwitz, M.J., 2000. Commercial timbers: descriptions, illustrations, identification, and information retrieval. [Internet]. Version 18th October 2002. http://delta-intkey.com/ wood/index.htm. Accessed March 2006.
• Harris, D.J., 1999. Part 1. Irvingiaceae. In: Orchard, A.E. (Editor). Species plantarum. Flora of the World. Australian Biological Resources Study, Canberra, Australia. 25 pp.
• Ladipo, D.O., 1999. The development of quality control standards for ogbono (Irvingia gabonensis and Irvingia wombolu) kernels: efforts towards encouraging organized and further international trade in a NWFP of West and Central Africa. In: Sunderland, T.C.H., Clark, L.E. & Vantomme, P. (Editors). Current research issues and prospects for conservation and development. FAO, Rome, Italy. pp. 245–250.
• Lowe, A.J., Russell, J.R., Powell, W. & Dawson, I.K., 1998. Identification and characterization of nuclear, cleaved amplified polymorphic sequence (CAPS) loci in Irvingia gabonensis and Irvingia wombolu, indigenous fruit trees of west and central Africa. Molecular Ecology 7: 1771–1788.
• Tchoundjeu, Z., Atangana, A.R. & Degrande, A., 2005. Indigenous methods of preserving bush mango kernels in Cameroon. American Journal of Applied Sciences 2(9): 1337–1342.
Sources of illustration
• Harris, D.J., 1996. A revision of the Irvingiaceae in Africa. Bulletin du Jardin Botanique National de Belgique 65: 143–196.
Correct citation of this article:
Oyen, L.P.A., 2007. Irvingia wombolu Vermoesen In: van der Vossen, H.A.M. & Mkamilo, G.S. (Editors). PROTA 14: Vegetable oils/Oléagineux. [CD-Rom]. PROTA, Wageningen, Netherlands.
1, flowering twig; 2, flower; 3, fruit; 4, fruit in cross section.
Redrawn and adapted by Achmad Satiri Nurhaman