The cowpea (Vigna unguiculata) is an annual herbaceous legume from the genus Vigna. Its tolerance for sandy soil and low rainfall have made it an important …
Family: Fabaceae
Species: V. unguiculata
Kingdom: Plantae
Genus: Vigna
The cowpea (Vigna unguiculata) is an annual herbaceous legume from the genus Vigna. Its tolerance for sandy soil and low rainfall have made it an important crop in the semiarid regions across Africa and Asia. It requires very few inputs, as the plant’s root nodules are able to fix atmospheric nitrogen, making it a valuable crop for resource-poor farmers and well-suited to intercropping with other crops. The whole plant is used as forage for animals, with its use as cattle feed likely responsible for its name.
Four subspecies of cowpeas are recognised, of which three are cultivated. A high level of morphological diversity is found within the species with large variations in the size, shape, and structure of the plant. Cowpeas can be erect, semierect (trailing), or climbing. The crop is mainly grown for its seeds, which are high in protein, although the leaves and immature seed pods can also be consumed.
Cowpeas were domesticated in Africa and are one of the oldest crops to be farmed. A second domestication event probably occurred in Asia, before they spread into Europe and the Americas. The seeds are usually cooked and made into stews and curries, or ground into flour or paste.
Most cowpeas are grown on the African continent, particularly in Nigeria and Niger, which account for 66% of world production. A 1997 estimate suggests that cowpeas are cultivated on 12.5 million hectares (31 million acres) of land, have a worldwide production of 3 million tonnes and are consumed by 200 million people on a daily basis.Insect infestation is a major constraint to the production of cowpea, sometimes causing over 90% loss in yield. The legume pod borer Maruca vitrata is the main preharvest pest of the cowpea and the cowpea weevil Callosobruchus maculatus the main postharvest pest.
History:
Compared to most other important crops, little is known about the domestication, dispersal, and cultivation history of the cowpea. Although there is no archaeological evidence for early cowpea cultivation, the centre of diversity of the cultivated cowpea is West Africa, leading an early consensus that this is the likely centre of origin and place of early domestication. New research using molecular markers has suggested that domestication may have instead occurred in East Africa and currently both theories carry equal weight.
While the date of cultivation began may be uncertain, it is still considered one of the oldest domesticated crops. Remains of charred cowpeas from rock shelters in Central Ghana have been dated to the 2nd millennium BC. In 2300 BC, the cowpea is believed to have made its way into Southeast Asia, where secondary domestication events may have occurred. From there they traveled north to the Mediterranean, where they were used by the Greeks and Romans. The first written references to the cowpea were in 300 BC and they probably reached Central and North America during the slave trade through the 17th to early 19th centuries
Cultivation:
Cowpeas thrive in poor dry
conditions, growing well in soils up to 85% sand. This makes them a particularly important crop in arid, semidesert regions where not many other crops will grow. As well as an important source of food for humans in poor, arid regions, the crop can also be used as feed for livestock. Its nitrogen-fixing ability means that as well as functioning as a sole crop, the cowpea can be effectively intercropped with sorghum, millet, maize, cassava, or cotton.
Pests and diseases:
Insects are a major factor in the low yields of African cowpea crops, and they affect each tissue component and developmental stage of the plant. In bad infestations, insect pressure is responsible for over 90% loss in yield. The legume pod borer, Maruca vitrata, is the main preharvest pest of the cowpea. Other important pests include pod sucking bugs, thrips, aphids and the post-harvest cowpea weevil, Callosobruchus maculatus.
M. vitrata causes the most damage to the growing cowpea due to their large host range and cosmopolitan distribution. It causes damage to the flower buds, flowers, and pods of the plant, with infestations resulting in a 20–88% loss of yield. While the insect can cause damage through all growth stages, most of the damage occurs during flowering. Biological control has had limited success, so most preventive methods rely on the use of agrichemicals. Genetically modified cowpeas has been developed to express the cry protein from Bacillus thuringiensis, which is toxic to lepidopteran species including the maruca. BT Cowpea was commercialised in Nigeria in 2019.
Nutrition and health:
Cowpea seeds provide a rich source of proteins and food energy, as well as minerals and vitamins. This complements the mainly cereal diet in countries that grow cowpeas as a major food crop. A seed can consist of 25% protein and has very low fat content. Cowpea starch is digested more slowly than the starch from cereals, which is more beneficial to human health.The grain is a rich source of folic acid, an important vitamin that helps prevent neural tube defects in unborn babies.
The cowpea has often been referred to as “poor man’s meat” due to the high levels of protein found in the seeds and leaves. However, it does contain some antinutritional elements, notable phytic acid and protease inhibitors, which reduce the nutritional value of the crop. Methods such as fermentation, soaking, germination, debranning, and autoclaving are used to combat the antinutritional properties of the cowpea by increasing the bioavailability of nutrients within the crop.Although little research has been conducted on the nutritional value of the leaves and immature pods, what is available suggests that the leaves have a similar nutritional value to black nightshade and sweet potato leaves, while the green pods have less antinutritional factors than the dried seeds.