J.C. Okafor
Jonathan C. Okafor is a consultant on tree crops and tropical ecology based in Enugu, Anambra State, Nigeria.
This article explores possibilities for improving the contribution to dietary supplies and income generation of edible products from the West African forest zone (including derived savannah), with particular reference to Nigeria.
The contributions of wild fruits, nuts, seeds, vegetables and other classes of edible products to the local diet in developing countries and their potential in overcoming or ameliorating prevailing food problems are enormous (Getahun, 1974; Okafor, 1975a, 1980a, 1980b, 1981a; Okigbo, 1977; Roche, 1975a).
Edible forest products include edible nuts and seeds used as staple foods or main dishes; those used as minor food supplements; condiments, thickening agents and flavours; leafy vegetables; edible flowers; fresh fruits; fresh seeds; edible oil; spices; fruit drinks and nonalcoholic beverages; alcoholic drinks (plus flavouring barks); mushrooms; honey; and bush meat (game, snails, insects, etc.).
Forest plants are important and cheap sources of vitamins, minerals, protein, carbohydrates and fats; moreover, their dietary contribution is increased because they are available during most seasons, including strategic periods in the year when the conventional staples and vegetables are scarce. For example, the African pear (Dacryodes edulis) matures during the "hungry season" when staples such as yam, cocoyam and rice have been planted but are not yet ready for harvest. Similarly, flushes from trees such as Pterocarpus spp. and Vitex doniana, which are used as vegetables, are available during dry seasons when cultivated vegetables are scarce or obtainable only where there are irrigation facilities.
The variety of forest product used for food and medicinal purposes is enormous
Experiments with budding of fruit-trees in Nigeria
Medicinal uses
In many instances, the distinction between food and medicine is not clear-cut; many edible plants from the forest are also used in traditional medicine. For example, popular vegetables such as Vernonia amygdalina, Pterocarpus spp., Vitex doniana, Gongronema latifolium and Ocimum gratissimum have wide application, as do the species Xylopia aethiopica and Piper guineense (Okafor, 1987, 1989c). Seeds of Garcinia Kila (bitter kola) are reputed as a poison antidote and are useful in the treatment of coughs add hepatitis (Iwu et al., 1987).
Notwithstanding its importance, the consumption of forest foods appears to be declining in many regions. This is partly a result of changing tastes and expanding markets for foreign goods as rural economies become increasingly exposed to market forces. Another important contributing factor is the declining availability of forest foods as growing populations, severe forest degradation and privatization of formerly common lands combine to put increasing pressure on the remaining forest resources.
Forest products can still make substantial contributions to filling dietary needs, but new approaches need to be developed, focusing on the identification and improvement of species with high potential, and the development of strategies for more intensive production of both traditional and innovative products.
There are regrettably few works specifically dedicated to taxonomic accounts of edible wild plants; available information comes mostly from general notes or casual remarks in floras and more general texts, as well as from oral tradition. However, a number of comprehensive taxonomic surveys include references to edible products. For example, Seyani (1988) presents an account of 180 species of African edible fruits (berries or nuts) distributed in 39 families; and 19 species of edible wild flowers in seven families. Okafor (1981a) also reports on 171 indigenous woody plants (53 families and 119 genera) of nutritional importance within the forest zone of Nigeria.
Ethnobotanical surveys are a source of additional information that is generally omitted from standard taxonomic texts and floras. For instance, surveys carried out in Cross River State of Nigeria (Okafor, 1990a) have revealed that flowers of Kigelia africana, Glyphaea brevis and Bombax sp. are used as-a vegetable. Similarly, leaves of a well-known timber tree Milicia excelsa (also classified as Chlorophora excelsa) and of Albizia zygia are also used as vegetables.
TABLE 1. Trees with edible parts successfully budded
|
Species |
Family |
|
Afzelia africana |
Caesalpiniaceae |
|
A. bella var. bella |
Caesalpiniaceae |
|
Bosqueia angolensis |
Moraceae |
|
Canarium schweinfurthii |
Burseraceae |
|
Ceiba pentandra |
Bombacaceae |
|
Chrysophyllum albidum |
Sapotaceae |
|
Cola acuminate |
Sterculiaceae |
|
C. gigantea |
Sterculiaceae |
|
C. hispida |
Sterculiaceae |
|
Dacryodes edulis |
Burseraceae |
|
Detarium microcarpum |
Caesalpiniaceae |
|
Dialium guineense |
Caesalpiniaceae |
|
Hildegardia barteri |
Sterculiaceae |
|
Irvingia gabonensis |
Irvingiaceae |
|
Monodora myristica |
Annonaceae |
|
Myrianthus arboreus |
Moraceae |
|
Parkia biglobosa |
Mimosaceae |
|
Pentaclethra macrophylla |
Mimosaceae |
|
Pterocarpus mildbraedii |
Papilionaceae |
|
P. santalinoides |
Papilionaceae |
|
P. soyauxii |
Papilionaceae |
|
Spondias mombin |
Anacardiaceae |
|
Tetrapleura tetraptera |
Mimosaceae |
|
Treculia africana |
Moraceae |
|
Vitex doniana |
Verbenaceae |
|
Xylopia sp. |
Annonaceae |
Source: Okafor, 1981a.
Intraspecies variation
The existence of natural variation within food-yielding trees is a crucial factor in efforts aimed at conservation, development and utilization of edible forest species (Whitmore, 1976; Okafor, 1980b). For example, taxonomically distinct varieties described in some African fruit-trees, including Irvingia gabonensis (Okafor, 1975b), Treculia africana subsp. africana (Okafor, 1981b) and Dacryodes edulis (Okafor, 1983a), have shown significant differences in the phenology of flowering, fruiting and leaf flush. Such phenological differences offer the possibility of deliberately extending the period of fruit and vegetable availability, increasing the yield and choosing the desired pattern as well as season of yield (Okigbo, 1977; Okafor, 1978). If the two varieties of I. gabonensis, which fruit in rainy and dry seasons respectively, each were to be developed, the combined period of availability of the products would be significantly extended. Similarly, two Pterocarpus species (P. soyauxii and P. mildbraedii) are reported to have different patterns of leaf flush (one spontaneous and the other intermittent), making the first suitable for commercial production and the second for home production.
Vegetative propagation
Vegetative propagation methods at present in use consist of budding (bud grafting) and stem cuttings. For early flowering and fruiting from bud grafts, it is essential to collect budwood from the exposed crowns of selected adult trees (phenotypes) which have commenced fruiting (Oleson, 1978). The desired growth habit (orthotropic or plagiotropic) can be achieved through deliberate selection of budwood, either from terminal leaders or from lateral branches.
Some 26 species of food trees were found to be buddable in experiments carried out using adult scions (Okafor, 1978, 1980b, 1981a) (see Table 1). Budded trees of some of these species (Chrysophyllum albidum, Dacryodes edulis, Dialium guineense, Irvingia gabonensis, Pentaclethra macrophylla, Spondias mombin and Treculia africana) produced viable fruit at very low heights after only two to four years (instead of five to ten or more in trees raised from seed).
Propagation by stem cuttings (without application of rooting hormone), using adult budwood, was also successful among 21 species (see Table 2). Fruiting was recorded within two years in stem cuttings of T. africana var. inversa and D. guineense. In the case of T. africana fruiting was pitched at ground level.
The use of truncheons (large cuttings) in propagation was also successful in Adansonia digitata, Ceiba pentandra, Ficus spp., discolor, Spondias mombin and Pterocarpus spp.
TABLE 2. Woody plants with edible parts successfully propagated by adult stem cuttings
|
Species |
Family |
|
Ceiba pentandra |
Bombacacea |
|
Cola gigantea |
Sterculiaceae |
|
Detarium microcarpum |
Caesalpiniaceae |
|
Dialium guineense |
Caesalpiniaceae |
|
Dioscoreophyllum cumminsii |
Menispermaceae |
|
Ficus capensis |
Moraceae |
|
Gnetum spp. |
Gnetaceae |
|
Gongronema latifolium |
Asclepiadaceae |
|
Hildegardia barteri |
Sterculiaceae |
|
Heinsia crinata |
Rubiaceae |
|
Lasianthera africana |
Icacinaceae |
|
Monodora myristica |
Annonaceae |
|
Myrianthus arboreus |
Moraceae |
|
Piper guineense |
Piperaceae |
|
Pterocarpus mildbraedii |
Papilionaceae |
|
P. santalinoides |
Papilionaceae |
|
P. soyauxii |
Papilionaceae |
|
Tetracarpidium conophorum |
Euphorbiaceae |
|
Treculia africana |
Moraceae |
|
Triplochiton sp. |
Sterculiaceae |
|
Vernonia amygdalina |
Compositae |
Source: Okafor, 1981a.
Propagation from seed
Large-scale production of food trees and shrubs for a conservation programme or for commercial-scale planting will require efficient, economical, standardized nursery procedures, and knowledge of reliable practices for raising the planting stock from select or improved seeds. Standard nursery practices have been developed for several species including Dacryodes edulis, Irvingia gabonensis and Treculia africana (Okafor, 1981a, 1990b).
Germplasm collection
The propagation techniques discussed above also offer considerable scope when used in connection with the collection of germplasm for evaluation and conservation purposes. However, exploration and collection have not been extensively or intensively adopted to cover the ecological ranges of the useful species, either in the natural forest or on traditional farms, where the species have been consciously or unconsciously selected and conserved through protection and planting over several millennia. The extensive adoption of a grid system for systematic exploration could be extremely useful in this context. Establishment of genetic resource centres, gene banks and seed banks for fruit- and food-bearing tree species also requires further development in most African countries.
However, the efforts of the National Centre for Genetic Resources and Biotechnology and the Forestry Research Institute in Nigeria are at present laying the groundwork for the study, collection and conservation of edible plant resources.
New techniques for germplasm storage have been described inter alia by Henshaw (1987), including in vitro storage, involving the production of non-adventitious shoot meristems originating from organs or embryos, either from cells present in the original explant or from cells which have proliferated in vitro. Although the system of in vitro storage by tissue cultures is still at the research stage, it holds great potential for genetic conservation of rare and recalcitrant species.
Conservation of ecosystems and genetic resources of target species in areas where edible plants are found is particularly important in the tropics where the forests are being subjected to destruction or excessive exploitation. This is more so because of the narrow distribution ranges and often low densities of food- and fruit-bearing species which, because of these characteristics are prone to genetic depletion or extinction following habitat modification.
Both in situ and ex situ conservation methods are necessary (Roche, 1975b; Kio et al., 1985; Hawkes, 1987; Henshaw, 1987). Budding, grafting and taking cuttings, which are suitable methods of propagation of desirable clones of food trees (Okafor, 1978, 1980b), have great prospects for ex situ conservation.
The usefulness of agroforestry as a tool for conservation also has been examined (Okafor, 1989a; Okafor and Caldecott, 1990), with specific reference to the Cross River National Park in Nigeria. Agroforestry was considered strategically fundamental to plans for stabilizing land use in the area, as a way to intensify agricultural production in the support zone and thereby increase economic returns while simultaneously reducing the amount of forest cleared.
Agroforestry can also contribute to the conservation of biodiversity, if local people are encouraged to use local forest species, especially edible varieties, in agroforestry practices. For example, seeds of promising edible wild species may be collected and raised in nurseries for planting on farmlands and other areas in villages and towns.
The direct nutritional and dietary contributions of forest foods are documented in many other works (e.g. Anderson, 1989; Jong et al., 1973; Okafor, 1975a, 1979, 1989a; Falconer, 1990; Hoskins, 1990). Edible forest products also generate substantial cash income for rural people, thereby contributing to their welfare and means of livelihood, and to the household budget (Okafor, 1989a, 1990a). There is significant potential for the improvement of this contribution through the development of cottage industries based on commercial production of forest edibles. These industries, in turn, could enhance the improved and efficient utilization of the products. They could also promote the conservation of the species for the sustainable supply of raw materials (Okafor, 1983b, 1990b).
Village market between Ibadan and Ilorin, Nigeria
Small-scale commercial production of foods from edible forest products can help to reduce wastage and promote better preparation, packaging and storage and more widespread marketing of the items. A number of products that could be produced commercially from indigenous African fruits are described below.
· Jams and jellies.
Suitable species include Irvingia gabonensis var. gabonensis Chrysophyllum albidum and Dialium guineense (Okafor, 1973; Okafor and Okolo, 1974).
· Fruit juice. With the exception of C. albidum, all the species listed above for jam and jelly are also suitable for fruit juice. Other suitable species include Tamarindus indica and Parkia biglobosa (Okafor, 1980a, 1983b).
· Confectioneries. Breadfruit flour, which is processed from Treculia africana, can be used to produce a variety of sweetened baked goods, including cookies, buns, cakes, biscuits and snacks (Anazonwu-Bello, 1981).
· Soup mixes. The flour of T. africana is suitable for the preparation of a product which tastes much like mushroom soup.
· Non-alcoholic beverages. Recently, Ejiofor et al. (1988) have prepared a non-alcoholic brewed beverage from T. africana seeds that was found acceptable when taken without milk and sugar.
· Composite seasoning. Various indigenous spicy seeds and leaves can be blended into composite seasoning with export potential. Suitable species include Xylopia spp., Piper guineense, Monodora myristica, and the leaves of Ocimum gratissimum (Ajayi, 1986).
· Oil. The high oil content of the fruits of Dacryodes edulis, Elaeis guineensis, Irvingia, gabonensis and Butyrospermum spp. indicates their suitability for commercial production of cooking oil and margarine, and industrial application in manufacture of soaps, cosmetics and pharmaceutical preparations. Their oil is considered as good as or even better than cocoa butter (Okafor and Okolo, 1974; Okafor, 1983b; Udeala et al., 1980; Omoti and Ikiy, 1987).
· Agbono cubes. The kernels of Irvingia gabonensis, known as agbono, are used throughout West Africa as a thickening agent in soups. Ejiofor et al. (1987) have confirmed that the kernel residue of I. gabonensis can be cubed or packaged in any other form and sold more widely in Nigerian markets or exported to other countries.
Edible non-wood forest products are indispensable to rural people for regular or supplementary food supply and as sources of cash income. However, scientific investigation into improved use and conservation of the resource base has been inadequate. In some cases, extensive use, combined with widespread degradation of forest lands or deforestation, is threatening certain species with extinction.
Vegetative propagation techniques and nursery procedures so far developed for several of the species have great prospects for ex situ conservation of threatened species. The positive results of the propagation methods discussed above argue for their widespread application in traditional farming systems and agroforestry practices, and could well favour local participation in a practical and meaningful conservation programme.
Systematic exploration and evaluation of germplasm of wild and cultivated varieties is fundamental to success. Research into conventional and novel in vitro techniques for germplasm storage and multiplication should be intensified through provision of equipment, facilities and funds and training of human resources.
The activities of both national and international institutions regarding in situ conservation should be supported by complementary programmes on underutilized tropical crops. The recent international initiatives being undertaken by the Centre for Under-utilised Crops (CUC) based in London, and on tropical tree-crop germplasm by the International Fund for Agricultural Research, United States, are steps in the right direction.
It is hoped that these new initiatives will support and strengthen national programmes in order to accelerate the survey, collection, conservation and use of genetic diversity of neglected edible forest trees and shrubs.
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