Tropical fruit trees constitute important biological resources in the global agrobiodiversity context. Unlike the tropical fruit trees of American and Asian origin, indigenous fruit trees (IFT) of tropical Africa have scarcely achieved the status of international recognition in commodity markets and research arena outside Africa. This paper presented a critical review of the status of IFT in the Tropical African sub-regions (of West Africa, Central Africa, East Africa, Southern Africa and the Indian Ocean Islands) in relation to the introduced naturalised fruit trees from tropical America and Asia, threats to the diversity and sustainable use of IFT, analysis of the opportunities and challenges of developing IFT, as well as targets for crop improvement of the rich IFT of Tropical Africa. Domestication programme via relevant vegetative propagation techniques for priority IFT of the sub-regions was examined and advocated, in addition to the adoption of complementary conservation strategies, including Field GeneBanks in the management of the continent’s IFT diversity.
Fruit trees constitute important biological resources in many agroecological systems and forest ecosystems all over the world. The assertion is evident by the fact of these tree species long time economic and ecological impacts in nature. Fruits are full of nature’s rich essential nutrients, antioxidants and health benefits for ready use by humans (and other animals) without alternation in most cases, unlike vegetables and other edible agricultural/horticultural produce that may require necessary pre-treatments, like heating, sometimes before consumption [
In contrast to the noted diversity of fruit trees, only 10 annual cereal grains, pulses and oil seeds dominate 80% of the world agronomic fields. At present, wheat, rice and maize cover half of the world’s croplands, while adding other annual gains and pulses accounts for up to two-third of all arable land in the world [
According to the authors [
These sections of the continent are diverse in their climate, soil, topography and vegetation, which invariably influence the array and distribution of African floristic diversity. Tropical Africa sub-regions are home to many valuable fruit tree species whose potentials have not been fully realized. A good number of these fruit species have remained rather of local importance, and are yet to be domesticated. However, tangible economic produce are been harvested from their wild and or protected volunteer stands in home gardens, farmlands and forest reserves [
According to the National Academy of Science [
Sub-regions | Member countries |
---|---|
West Africa | Benin, Burkina Faso, Cape Verde, Cote d’Ivoire, Gambia, Ghana, Guinea, Guinea Bissau, Liberia, Niger, Nigeria, Mali, Mauritania, Senegal, Sierra Leone, Togo |
Central Africa | Burundi, Cameroon, Central Africa Republic, Chad, Congo, Sao Tome and Principe, Democratic Republic of Congo, Equatorial Guinea, Gabon, Rwanda |
East Africa | Djibouti, Eritrea, Ethiopia, Kenya, Somalia, Sudan, South Sudan, Tanzania, Uganda |
Southern Africa | Angola, Botswana, Malawi, Mozambique, Namibia, Zambia, Zimbabwe |
Indian Ocean Islands | Comoros, Madagascar, Mauritius, Mayotte, Reunion, Seychelles |
production in Nigeria for example still inadvertently show preferences for detailed research work on introduced fruit species over the indigenous species, according to a recent survey [
The fact about Tropical Africa indigenous fruit trees (IFT) diversity and economic potential is something one
would never readily recognized by looking at fresh fruits local markets in most parts of the continent, or even consulting most college recommended text books on tropical agriculture and horticulture, for instance: [
Historically, the protection of IFT/wild fruit species in many countries of Africa has been carried out by local farmers in their community forest reserves, traditional home gardens, protected volunteer stands of such important plant species in farmlands, market squares and village squares. Until recently, organised orchards and plantations of IFT were rather rare and only few exceptional ways used in the perpetuation of IFT kinds in some African communities. Due to little or nil formal research development and investments for improvement, many of the IFT still retain their natural massive size that would make group planting and management in orchards/ plantations setting difficult [
Various other factors have contributed as threats to survival and sustainability of IFT in the Tropical African sub-regions. In the first place, local populations in the sub-regions are heavily dependent on forests, which provide them with firewood, timber and food (nuts, fruit, mushrooms and honey). They use wild fruit and nut species as food, as well as for their medicinal properties, in handicrafts and to dye home-made products. Indiscrimi- nate and illegal logging of IFT stands in the remaining forested areas and farmlands for varied reasons have in no small measure contributed to the depletion IFT local population and distribution in many Tropical African rural communities. Such uncontrolled tree felling may be due to domesticate needs as fuel woods, charcoal production, livestock feeds, land clearing of site for building construction and or intensive agricultural activities, especially crop production.
As earlier pointed out, the insidious domination and preference of other introduced tropical fruit tree species over the African IFT by most researchers and investors have impeded the expected developmental needs of the continent’s many IFT. For most of the IFT, standardised agrotechniques for the propagation, protection, production, value added products and improved processing are nearly lacking or at best just at rudimentary stage when contrast to similar crop species from Tropical America and Asia. However, where such standardised agrotechniques might have been locally developed, they often remained as prototypes in relevant national research centres and government ministries yet to be commercialized. A SWOT (Strength, Weakness, Opportunity and Threat) analysis (
Tree domestication has been explained by various authorities in agroecology, agroforestry, agronomy and plant
Common name | Botanical name1 | Family name | Species origin |
---|---|---|---|
1. African breadfruit | Treculia africana | Moraceae | W, C, E |
2. Ackee 3. Butter fruit 4. Baobab 5. Monkey kola (yellow) 6. Monkey kola (white) 7. Monkey kola (red) 8. Magic plant 9. African walnut 10. Black plum/Mbembe 11. - 12. Tamarind 13.Velvet tamarind 14. African oil bean 15. Sheabutter 16. Irvingia nut 17. African star apple 18. Incense tree 19. Gum vine 20. - 21. - 22. - 23. Ebony 24. - 25. - 26. - 27. Marula 28. African walnut 29. Imbe 30. Medlar 31. - 32. Monkey orange 33. Wild loquat 34. Sugar plum 35. Sweet Detar 36. Detar 37. Tree grape 38. Aizen 39. Balanite 40. Carissa 41. Kei apple 42. Custard apple 43. Ginger bread plum 44. Gum vine 45. Icacina 46. - 47. - 48. Bird plum/wild date 49. - 50. - 51. - | Blighia sapida Dacryodis edulis Adansonia digitata Cola lepidota C. pachycarpa C. lateritia Synsepalum dulcificum Plukenetia conophora Vitex doniana V. payos Tamarindus indica Dialiumgu ineense Pentaclethra macrophylla Vitellaria paradoxa Irvingia garbonensis Chrysophyllum albidum Canarium schweifurthii Landolphia kirkii Uvariodendron connivens Sacoglottis gabonesis Maesobortyabarteri Diospyros mespiliformis Chytranthus talbotii Salvadora persica S. australis Sclerocarya birrea Coulae dulis Garcinia livingstonii Vangueria apiculata V. rotundata Strychnos cocculoides Uapaca kirkiana U. heudelotii Detarium senegalense D. microcarpum Lannea microcarpa Boscia senegalensis Balanites aegyptiaca Carissa macrocarpa Dovyalis caffra Annona senegalensis Parina riexcelsa Saba lanceolata Icacina oliviformis Trichoscypha ferruginea Azanza garckeana Berchemia discolor Ximenia caffra Grewia tembensis G. caffra | Sapindaceae Burseraceae Bombacaceae Malvaceae ,, ,, Sapotaceae Euphorbiaceae Labiatae ,, Fabaceae Fabaceae Fabaceae Sapotaceae Irvingiaceae Sapotaceae Burseraceae Apocynaceae Annonaceae Humiriaceae Euphorbiaceae Ebenaceae Sapindaceae Salvadoraceae ,, Anacardiaceae Olacaceae Gultiferae Rubiaceae ,, Strychnaceae Euphorbiaceae ,, Fabaceae ,, Anacardiaceae Capparaceae Balanitaceae Apocynaceae Flacourtiaceae Annonaceae Chrysobalanaceae Apocynaceae Icacinaceae Anacardiaceae Malvaceae Rhamnaceae Olacaceae Tiliaceae Tiliaceae | W, C W, C, E W, C, E W, C ,, ,, W, C W, C W, C, E, S C, E, S W, C, E, S W, C, E W, C, E, S, I W, C, E W, C, E WC, E, S W, C, E W, C E, S E, S E, C, S WC, E, S W, C W, C W, C W, C, E, S W, C, S W, C, E, S C, E, S C, E, S W, C, E, S W, C, E, S W, C, E, S W W W, C, E, S W, E W, E W, C, E S W, C, E, S W, C, E, S W, C W, C W, C, S E, S E, S W, C, E, S W, C, S W, C, S |
1Note: some genus have more than one species of primary use as fruit, although not all are listed; 2W―West Africa; C―Central Africa; E―East Africa; S―Southern Africa; I―Indian Ocean Islands.
Common name | Botanical name | Family name | Species origin |
---|---|---|---|
Avocado pear | Persea americana | Lauraceae | Central America |
Banana | Musa spp | Musaceae | South East (SE) Asia |
Cashew | Anacardium occidentalis | Anacardiaceae | South America |
Coconut | Cocosnu cifera | Arecaceae | Pacific South/Central America |
Carambola | Averrhoa carambola | Oxalidaceae | Indonesia |
Custard apple | Annona squamosal | Annonaceae | South America |
Date palm | Phoenix dactylifera | Arecaceae | Persian Gulf |
Fig | Ficus caria | Moraceae | SE Asia |
Grape citrus | Citrus paradise | Rutaceae | West Indies |
Lemon | C. limon | “ | SE Asia |
Lime | C. aurantifolia | “ | “ |
Orange | C. sinensis | “ | “ |
Shaddock | C. grantis | “ | “ |
Tangerine | C. reticulate | “ | “ |
Tangelo | C. reticulate × C. paradisi | “ | “ |
Tangor | C. reticulata× C. sinensis | “ | “ |
Guava | Psidium guajava | Myrtaceae | West Indies America |
Grapevine | Vitis vinifera | Vitaceae | Russia (Asia) |
Passion fruit | Passiflora edulis | Passifloraceae | South America |
Mango | Mangifera indica | Anacardiaceae | South Asia |
Pawpaw/Papaya | Carica papaya | Caricaceae | Central America |
Pineapple | Ananas comosus | Bromeliaceae | South America |
Sour sop | Annona muricata | Annonaceae | Central America |
Sweet sop | Annona squamosal | “ | South America |
Star apple | Chrysophyllum cainito | Sapotaceae | Central America |
Breadfruit | Artocarpus atilis | Moraceae | Polynesia (Asia) |
Jackfruit | A. heterophyllus | “ | S. Asia |
Mulberry | Morus alba | “ | China-Japan |
Hog plum | Spondia mombin | Anacardiaceae | Tropical America |
breeding [
Internal factors | Strength (+ve) | Weakness (−ve) |
---|---|---|
- Area of origin/natural distribution - Local preference/consumption of produce - Form part of traditional home garden farming system - Hold high cultural value among the local people - Viable revenue generator for rural resource poor farmers - Available local/regional markets | - Grossly under-researched - Relatively poor and inefficient production technology - Near absence of improved propagation agrotechniques - Most harvest still derived from wild/volunteer stands - Slow rate of natural regeneration - IFT information are poorly documented or in grey literatures | |
External factors | Opportunity (+ve) | Threat (−ve) |
- International market/export prospects as novel crops - Potentials diversification of products and markets - Recognition as candidates for agroforestry multipurpose trees for the sub-regions - Recent recognition by Bioversity International―NUS, ICUC, ICRAF - Recent works of PROTA documentation/Publications - Satisfy needs for crop diversification | - Over exploitation of available in situ stands on farms and in forests - Depleting tree stands in the wild due to deforestation - Inadequate deliberate replanting scheme and organised orchards - Poor marketing outlets and low pricing of IFT produce - Preference of African researchers for introduced naturalized species over IFT |
Note: NUS―Neglected and Underutilised Species/Bioversity International Rome; ICUC―International Centre for Underutilised Crops, Colombo Sri Lanka; ICRAF―International Centre for Research in Agroforestry (now known as World Agroforestry Centre), Nairobi Kenya; PROTA―Plant Resources of Tropical Africa, Wageningen, the Netherlands.
is not only about breeding per se, but definitely an aspect of whole species improvement. Domestication, in this perspective, aims at promoting the cultivation of IFT with economic potentials as new cash or novel crops, and provides incentive to subsistence farmers to grow such trees that contribute toward achieving poverty reduction, enhancement of food and nutritional security [
Deliberate tree improvement programme (involving specific domestication interventions) for useful characters has been advocated for some highly promising IFT of Sub-Saharan sub-regions. This is to encourage local farmers to continue their age long practice of on-farm conservation and sustainable exploitation of IFT alongside their field crops [
Vegetative propagation refers to the regeneration of selected plants from vegetative organs such as roots, stems, leaves, buds and even single cells/tissues; and it offers a wide range of benefits for any domestication programme of IFT, as well as in general Plant Genetic Resources (PGR) conservation efforts. By capturing the genetic variation of trees in natural stands, researchers are able to select for desirable traits found in wild tree populations. Ultimately, the aim is to produce large number of improved propagules for resource poor farmers and reforestation programme [
According to author [
Marcotting, a form of layering, is one of the oldest methods of vegetative propagation, although it still has relevance in present day plant multiplication, domestication and conservation efforts. It involves the development of roots on a stem while the stem is still attached to the parent plant. The rooted stem is then detached to be new plant growing from its own roots. Unlike in grafting, the need of compatible seedling rootstock is unnecessary in layering, which is an added advantage. As rooting from cuttings of mature tree plant materials is known to be difficult, layering and grafting are preferred for the vegetative propagation plan in IFT domestication programme [
Finally, micropropagation, also referred to as tissue or in vitro culture, is a relatively new vegetative propagation technique, which uses a plant’s potential to regenerate a complete new plant from single cells or small amounts of living tissue through the cultivation of these in aseptic and controlled environments. Since this technique requires a substantial investment in infrastructure, equipment and materials, its application is mostly justified in the case of high value plants where traditional vegetative propagation methods are considered unsuccessful. The method also allows for the production of virus-free plant materials and large amounts of new plants issued from a limited amount of initial material [
Evidently, vegetative propagation leading to the domestication and conservation of IFT offers exciting opportunities for research and sustainable development of Plant Genetic Resources (PGR). Reasons for vegetative propagation options include: maintenance of superior genotype, problematic seed germination and storage behavior, shortening time to first flowering and fruiting, controlling phases of tree development, combining desirable characteristics of more than one genotype into a single plant stand, uniformity of plantations/orchards, among others [
Most Tropical African IFT have so far been grown in traditional ways as homestead shade trees, nurse trees; in community protected sacred forests, wild and volunteer stands on farms, market squares, village squares and forest areas. A good number of these species are scarcely grown deliberately by the farmers, who most times depended on wild saplings they came across for transplanting and regeneration of their choice local fruit trees. Knowledge and technical know-how of propagation and nursery management of the IFT are more or less lacking. Scientifically planned selection and breeding programmes have not been largely undertaken to select promising pomological traits (such as fruit size, shape, flavor, taste, suitability for processing into juice, wine and other beverages, resistance to biotic and abiotic stresses) among the various landraces of species. High production technologies such as high density planting system, pruning, efficient rootstocks cultivars and plant protection schedules have not been standardized. Faced with these several challenges, there is need to initiate focused tree improvement programme that would address essential pomological needs of the continent’s IFT to bring it them at par with similar commodity crops from tropical America and Asia. Hence, the following major general targets for improvement are enumerated, although there may be other species specific needs relevant to the consumers and or markets.
Screening and selection of priority species for domestication: Specific screening plots for priority species identified by local farmers in the sub-regions should be established as well as on-farm trials to determine farmers’ preferred niches for IFT.
IFT phenology, physiology and propagation study: Initiation of detailed research works on the IFT phenology, physiology and profitable propagation options for priority species in the various localities.
Varietal selection for superior fruit quality among the landraces: Quality of fruit will always be a major objective of fruit tree improvement programme. Pulp taste, aroma and texture, fruit size and shape are main pomological attributes of fruit quality.
Development of robust rootstock that is resistant or tolerant to biotic stress: Efficient and resistant cultivars and rootstocks are primary requirements for modern fruit production which can be achieved by undertaking sound science based improvement programme. Common objectives of rootstock improvement for fruit trees include ease of propagation, graft compatibility, high yield, control of scion vigour, longevity, adaptation to wide environmental conditions, resistance to diseases and pests.
Enhanced productivity: This involves selection and breeding of promising cultivars with greater economic yield per unit area and cultivars with reduced tree size for ease of management.
Value addition of IFT produce: Involves development and commercialization of enhanced processing techniques and value added products from fresh produce for market diversification of IFT. This would boost the resource poor farmers’ expected revenue and encourage them to embark on deliberate cultivation of IFT.
There are two complementary approaches for conservation of IFT, namely in situ and ex situ. The in situ conservation involves maintaining genetic resources in the natural habitats where they occur, whether as wild and uncultivated plant communities or crop cultivars in farmers’ fields as components of traditional agricultural systems. The aim of in situ conservation is to protect habitats of target species so that a population of that species can steadily persist [
The ex situ conservation on the other hand involves conservation outside the native habitat and is generally used to safeguard populations in danger of destruction, replacement or deterioration. Samples from such species are stored in centralized banks away from the origin. Methods employed in ex situ conservation include field gene banks, seed storage banks, botanical gardens, arboretum, research centres and laboratories, DNA and pollen storage banks, and world heritage sites [
According to author [
Indigenous fruit species of Tropical Africa face enormous challenges in modern time rapidly advancing horticultural and food industrial sector. Yet the IFT are very important for the economic, health and social welfare of resource poor farmers in most rural and urban communities of the continent. Encouraging the domestication and conservation of IFT species in the agroecosystem can provide highly sustainable production systems that conserve soil fertility, micronutrients and biodiversity, as well as guarantee food security, climate change adaptation and mitigation. Although future outlook of IFT in the continent indicates great potentials as shown in the SWOT analysis earlier mentioned, a lot needs to be done from home front in order to shore up the relevance and production value chain of IFT at the global and regional commodity markets. In this connection, hitherto much emphasis and dominance of introduced adapted fruit species among many National Agricultural Research Centres (NARCs) list of mandate crops in Tropical African sub-regions should be re-considered for rather increasing focus and investment on exploiting the untapped rich treasuries of African IFT vis-à-vis developing improved agrotechniques and varietal selection for the species. The Plant Resources of Tropical Africa (PROTA) programme, World Agroforestry Centre and International Conference on Neglected and Underutilised Species (NUS) under the auspices of Bioversity International are by their various activities championing international campaign on re-awakening interests of all relevant stakeholders, including the academia, researchers, policy makers and industrialists on NUS generally and IFT in particular.