Cowpea, Vigna unguiculata (L.) Walp., is a grain legume grown mainly in the savanna regions of the tropics and subtropics in Africa, Asia, and South America. The value of cowpea lies in its high protein content, and ability to tolerate drought. As a legume, cowpea also fixes atmospheric nitrogen, allowing it to grow on, and improve poor soils. All the parts of cowpea that are used for food are nutritious, providing protein, vitamins, and minerals. Cowpea grain contains about 25% protein, making it extremely valuable where many people cannot afford protein foods such as meat and fish.
According to FAO, about 7.56 million tonnes of cowpea are produced worldwide annually on about 12.76 million hectares. Sub-Saharan Africa accounts for about 70 % of total world production.
How cowpea is grown
Cowpea is grown mainly by peasant farmers who have limited access to purchased inputs for the crop. It is grown in marginal soils as intercrop with cereals but a few farmers grow cowpea as sole crop. The soils are of low natural fertility and the crop depends almost entirely on rainfall. When the cereals are harvested, the spreading cowpea types have more light and therefore grow out and cover the ground. Grains are harvested when pods mature and fodder is harvested later as the leaves start changing color. Cowpea fodder is fed to livestock or sold by farmers for additional income. The roots left in the soil decay and thereby contribute to fertility of the soil which could benefit the succeeding crop.
Constraints to cowpea production
Every stage in the life cycle of cowpea has at least one major insect pest. Aphids (Aphis craccivora) attack cowpea especially in the seedling stage, flower thrips (Megalurothrips sjostedti) at flowering, pod borer (Maruca vitrata) at flowering and pod formation, a complex of pod sucking bugs at podding, and the weevil (Callosobruchus maculatus) during seed storage. Cowpea is susceptible to a number of fungal, bacterial, and viral diseases such as Cercospora leaf spot, ashy stem blight, bacterial blight, blackeye cowpea mosaic potyvirus (BICMV), cowpea aphid-borne mosaic potyvirus (CABMV), and cowpea mosaic comovirus (CPMV). Cowpea plants are also attacked by the parasitic flowering plant Striga gesnerioides. Since cowpea is grown mainly in the dry savanna areas with no irrigation facilities, irregular rainfall especially early in the season have adverse effects on the growth of the crop. All of these factors, singly or combined, are responsible for the low grain yield, estimated at approximately 350 kg/ha that farmers in sub-Saharan Africa obtain from their cowpea fields.
Our work on cowpea
Our scientists have developed high-yielding varieties that are early or medium maturing and characterized by consumer-preferred traits such as large seed size and color. Cowpea lines that mature in about 60 days after planting have resulted from our breeding activities. A number of the improved varieties have resistance to some of the major diseases, insect pests, nematodes, and parasitic weeds. They are also well-adapted to sole or intercropping. We have distributed improved breeding lines to collaborators in over 60 countries under the cowpea international trials (CIT). Some of these lines have been released as improved cowpea varieties or used in breeding programs in the different countries. In the over 35 years that our scientists at IITA have worked on cowpea, total cowpea production worldwide has increased from 1.2 million to more than 7.5 million tonnes per year in about 12.7 million hectares.
Our scientists are working in collaboration with the cowpea project for Africa (PRONAF) which is also coordinated by us. We also collaborate with the Bean/Cowpea CRSP and the Network for Genetic Improvement of Cowpea for Africa (NGICA).