beans are found more in the eastern subregion (Allen and Smithson, 1988; Bokosi, 1988).

          The SSA region also possesses an enormous crop genetic resource potential. For example, edible yam accounted for 95.6% of the total world output of the crop (Okoli, 1991). A special mention should be made to Ethiopia, which is known as a Vavilovian center of crop domestication and diversity for several important plants; it has 12 potentially valuable crop plants, such as the root and tuber crops enset (Ensete ventricosum), anchote (Coccinia abyssinica), oromo dinich (Coleus edulis), the vegetable okra (Abelmoschus esculantus) and the legume crop yeheb (Cordeauxia edulis) (Demissie, 1991). Enset is the most important staple food in southwestern Ethiopia, where its cultivation is restricted; the sources of food are the pseudostem and the corm. Tubers of oromo dinich are usually boiled and consumed as a vegetable. The seeds of yeheb are roasted or eaten raw; they have high protein content (13%), fat (11%) and starch (13%).

          Trends in crop genetic resource contributions within cropping systems. In the SSA region, the performance of crop genetic resources is limited by many biotic and abiotic constraints such as pests (e.g., rice yellow mottle virus and gall midge on rice), drought stresses, low soil fertility due to small organic matter content and soil erosion, soil toxicity (e.g., aluminum toxicity) or nutrient deficiency (e.g., phosphorus deficiency). Moreover, there is a lack of appropriate equipment for land preparation and postharvest operations, inadequate and irregular input supplies (seeds, fertilizers, pesticides) and lack of credit. In Madagascar, irrigated rice yields have been stagnant due to low levels of fertilizer application (WARDA, 2005a).

          During the pre-colonial period in the SSA, crops were traditionally grown in mixture; for example, cereals were grown with groundnut. In small areas, sole cultures were grown; the varieties used were usually mixed but usually had common traits, which were related to yield stability, consumer preferences and low input use. In general, they had satisfied the food needs of the populations because the demand was below the level of crop production. As crop production was primarily for subsistence, characteristics of high productivity or for exports were not considered or ignored. However, traditional agriculture is an important source of genetic diversity; and it offers enormous possibilities for the creation of high yielding varieties.

          In the colonial period, monocropping was the trend, with a focus on cash commodities for export. Crops became homogeneous and genetic diversity was lost. In Madagascar, rice varieties with long, white and translucent grains were promoted both for local market and for export, at the expense of the traditional red kernel rice varieties. In the large scale farming systems, crop productions were transformed and industrialized; for example, cassava starch was processed to tapioca. Crop genetic resources during this period were improved by conventional methods (mass selection and hybridization). In order to have market accessibility, there was a trend in the use of commercialized seeds with high varietal purity. Thus, crop genetic resources have greatly contributed to the success of exports.

          When most colonized countries acquired their political independence between 1960 and 1971 under the auspices of the United Nations, the Consultative Group on International Agricultural Research (CGIAR), a worldwide network of international research centers, was founded with the mission to contribute to food security and poverty eradication in developing countries through partnership with national governmental and nongovernmental organizations, universities and private industry. In the SSA region, the International Institute of Tropical Agriculture (IITA), in Ibadan, Nigeria and the West Africa Rice Development Authority (WARDA) in Cotonou, Benin were established to conduct research on tropical crops and rice as mandated commodities. Evaluation and improvement of cowpea (or niebe, Vigna unguiculata) and tuber and root crop germplasm (e.g., cassava, sweet potato, yam) are undertaken at IITA. IITA is also the major research center for bambara groundnut germplasm, which is a neglected crop with a high nutritional value (Goli et al., 1991).

          The International Crops Research Institute for the Semiarid Tropics (ICRISAT), which is based in India, has also assembled many germplasm samples from African countries for use in plant breeding, namely sorghum, pearl millet, chickpea, pigeon pea, groundnut and minor millet (Mengesha and Rao, 1991). The Centro Internacional de Agricultura Tropical (CIAT, International Centre for Tropical Agriculture) in Colombia, South America contributed to the improvement of African cassava (Allem and Hahn, 1988) and on promotion of new varieties of bean (David, 1998).

          In the 1960, through the Centro Internacional de Mejoramiento de Maiz y Trigo (CIMMYT) and the International Rice Research Institute (IRRI), the introgression of dwarfism genes respectively in wheat and in rice, led the world to the Green Revolution (Gotoh and Chang, 1979). Whereas these high-yielding varieties of wheat and rice were rapidly adopted and commercialized, farmers in the developing world, including farmers in the SSA region, did not profit from the Green Revolution because of the sharp increase in oil and fertilizer prices during the 1973 oil crisis (Zwartz and Hautvast, 1979). For rice crops, the Green Revolution required good irrigation infrastructure and water management, which were absent in most countries of the SSA region; in fact, the performance of irrigation schemes previous to this period was disappointing (see 2.1.2, Water management). Green Revolution technologies assume intensive use and timely applications of inputs and seeds of high-yielding varieties, which were not within the reach of farmers because of many social and economic factors (high price of inputs, absence of rural markets for timely delivery, lack of information, communication, illiteracy, etc.).

          However, crop genetic resources continued to be improved by research institutions. They became resistant to multiple diseases and to insects and had higher productivity. Some have improved nutritional quality and higher commercial value, for example hybrid maize varieties with herbicide resistance or with less aflatoxin; cassava varieties resistant to cassava brown streak disease; Dioscorea alata and D. rotundata with high iron and zinc content in the tubers; and plantain banana resistant to black Sigatoka (IITA,