EVALUATION AND INHERITANCE OF SINGLE AND MULTIPLE RESISTANCE TO VIRAL DISEASES OF COWPEA (Vigna unguiculata (L.) Walp)

Cowpea (Vigna unguiculata (L.) Walp) is one of the most economically and nutritionally important indigenous African grain legumes. It is cultivated in the tropics and sub-tropical regions in Asia and Oceania, the Middle East, southern Europe, Africa, southern USA, and Central and Southern America (Singh et al., 2002). It is an annual crop believed to have originated in Africa (Padulosi and Ng, 1997). Cowpea is well adapted to the dry savanna in the West African sub-region, where it is mostly grown by small-scale farmers in association with millet, sorghum, maize and groundnut (Boukar et al., 2013). The world total production of cowpea is about 4.9 million MT annually from about 10.4 million hectares of land and Africa alone accounts for over 9.7 million hectares, of which over 90% lies in West and Central Africa (FAOSTAT, 2013). Nigeria is the largest producer of cowpea grain with approximately 3.2 million ha under cultivation (FAOSTAT, 2013). Cowpea grain is valued for its high nutritive quality and short cooking time and serves as a major source of protein in the daily diets of people of the developing tropical world. The seed protein content ranges from 23 to 32 % of seed weight, rich in lysine and tryptophan and a substantial amount of mineral and vitamins (Hall et al., 2003). Cowpea is a staple food crop in Nigeria (Olakojo et al. 2007) where it serves as an important source of protein for the teeming population. Farmers in the dry savanna use cowpea haulms as a nutritious fodder for their livestock. The plant's ability to fix atmospheric nitrogen helps maintain soil fertility and its tolerance to drought extends its adaptation to drier areas considered marginal for most other crops (Singh et al., 1997). However, the average cowpea yield in Nigeria is low, approximately 583 kg/ha (FAO, 2013). This is due to several production constraints, mainly infestation by insect pests, parasitic weeds and diseases caused by many fungal, bacterial and viral pathogens (Jackai and Adalla, 1997). Serious insect pests of cowpea in Nigeria include aphids, thrips, pod sucking bugs, pod borers and storage weevils (Callosobruchus spp) (Singh et al., 2003).