Cowpea [Vigna unguiculata (L.) Walp], an annual legume native to tropical and subtropical regions, is a protein-rich crop that complements staple cereal for human and fodder for livestock and also provides soil improvement benefits through nitrogen fixation. Cowpeas are commonly grown in the semiarid tropics between 35N to 30S of the equator, covering Africa, Asia, Oceania, the Middle East, Southern Europe, Central and South America, and the southern United States. The African countries of Nigeria and Niger account for 66% of world production. It is estimated that cowpeas are cultivated on 12.56 million hectares and have a worldwide production of 5.55 million tons; they are consumed by 200 million people on daily basis in the 20 countries with highest cowpea cultivation (Boukar et al., 2018; Singh et al., 1997).
Cowpea can be used at all stages of growth (Fang et al., 2007; Nielsen et al., 1997). The green seeds can be used fresh or canned or frozen for humans. The young leaves, pods, and peas contain vitamins and minerals, which are used for human consumption and animal feed. Cowpea can be consumed as dry seeds, canned or frozen food (Fery, 1993), and as milling flour in baked goods (Kushwaha and Kumar, 2014). The seeds are also used for human consumption as an affordable source of protein and a supplemental fodder for livestock. In addition, cowpea has been used as an alternative to soybean for people who are allergic to soybean protein (Boukar et al., 2018).
Like soybean, cowpea is nutritious with ≈23% protein in dry seeds, which could meet the increasing consumer demand for healthier and more nutritious food. Unlike soybean, cowpea proteins do not cause allergies and are of higher quality when substituted in diets at equivalent protein contents. In recent years, there has been increasing interest in breeding cowpea cultivars with high seed protein content to improve nutritional quality. Evaluation of seed protein content in cowpea germplasm will help plant breeders select and breed high seed protein content cultivars in breeding programs. Asante et al. (2006) reported that protein content averaged 27.3% among 32 accessions. Gupta et al. (2010) screened 21 cowpea genotypes and observed that total protein content ranged from 22.4% to 27.9%; they found that seven genotypes (viz. HC-6, HC-5, CP-21, LST-II-C-12, CP-16, COVU702, and HC-98-64) had the highest protein contents, ranging from 26.7% to 27.9%. Itatat et al. (2013) studied 11 cowpea genotypes and reported a range of 20.57% to 24.95%. Afiukwa et al. (2013) found a greater variability of the total seed protein contents, ranging from 15.06% to 38.5%, with a mean of 25.99% in dry seeds among 110 cowpea genotypes. Oke et al. (2015) analyzed five varieties of cowpea and found that seed protein contents ranged from 25.80% to 28.95%. Ravelombola et al. (2016) assessed 11 cowpea cultivars/breeding lines developed in Arkansas and found an average protein content of 25.4% (range 23.7% to 27.4%) with a standard deviation of 1.9%. Weng et al. (2017) compared two methods to measure seed protein content and found a large variance among 240 cowpea genotypes.
Germplasm provides the elite gene(s) for breeding program. The objective of this study was to evaluate seed protein content among 173 worldwide cowpea accessions to use the high seed protein cowpea germplasm in cowpea breeding programs to develop superior cowpea cultivars with high seed protein contents.
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Seed protein content in 173 cowpea germplasm accessions.