ABSTRACT
Although the exact origin of cultivated common bean has not been clearly identified (Gentry, 1969), Tropical America, more specifically Mexico, Guatemala and Peru, are considered to be centres of origin, although there is also evidence of its multiple domestication within Central America (Kay, 1979). The current distribution of the wild common bean suggests that the origin encompasses a large geographical area between Mexico and Argentina (Toro et al., 1990). The cultivated common bean is generally well adapted and thrives under a wide range of agro-ecological conditions. In Latin America, the average temperature of the common bean growing regions ranges between 17.5 and 25˚C (Gepts, 1998). However, common bean is also grown in regions where the average temperatures during the growing season reaches 27˚C, and at relatively high altitudes, for example 60oN in northern Europe (Gepts, 1998). It is well adapted to areas that receive an annual average rainfall ranging from 500 to 1500 mm with optimum temperature range of 16-24°C, and a frost-free period of 105 to 120 days. Generally, common bean performs best on deep, friable and well-aerated soils with optimum pH range of 6.0-6.8 (Kay, 1979).
1.2 Economic importance The economic significance of common bean cannot be overstated. It is perhaps the world’s most important grain legume for direct human consumption. This nutritious food security crop plays a major dietary role, especially in sub-Saharan Africa (SSA) where it meets more than 50% of dietary protein requirements of households (Broughton et al., 2003; Wortmann et al., 1998). Although the per capita consumption of common bean varies between regions of the world, its consumption is greater among low-income people who cannot afford to buy nutritious food stuff, such as meats and fish (Broughton et al., 2003). Not only is common bean a food security crop, it is also an important source of protein, vitamins, minerals and fibre, especially for the poorer populations of Africa and Latin America (Brougthon et al., 2003). Additionally, common bean contributes significantly to household income in regions where it is grown (Ferris and Kaganzi, 2008), especially among the majority of the rural peasants in SSA (Wortmann et al., 1998). In eastern Africa, the per capita consumption of common bean is 50-60 kg year−1 in Rwanda, Kenya and Uganda. This is considerably higher than in Latin America where per capita consumption is 4 and 17 kg year−1 in Colombia and Brazil, respectively (Beebe et al., 2013; Broughton et al., 2003). Although common bean is cultivated primarily for its dry seeds and green pods, young tender leaves and flowers are used as fresh vegetables in some parts of central and eastern African, and in some Latin American countries (Kay, 1979; Singh, 1999). Due to its acknowledged role in management of human health, for example, reduction of blood cholesterol levels and combating heart diseases, cancers and diabetes (Singh, 1999), the economic importance of common bean is steadily growing.
