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.
Afiukwa, C.A., Ubi, B., Kunert, K., Titus, E. & Akusu, J. 2013 Seed protein content variation in cowpea genotypes World J. Agr. Sci. 1 94 99
Ajeigbe, H.A., Ihedioha, D. & Chikoye, D. 2008 Variation in physico-chemical properties of seed of selected improved varieties of cowpea as it relates to industrial utilization of the crop Afr. J. Biotechnol. 7 3642 3647
Asante, I.K., Adu-Dapaah, H. & Addison, P. 2006 Seed weight and protein and tannin contents of 32 cowpea accessions in Ghana Trop. Sci. 44 77 79
Bliss, F.A., Barker, L.N., Franckowiak, J.D. & Hall, T.C. 1973 Genetic and environmental variation of seed yield, yield components and seed protein quantity and quality of cowpea Crop Sci. 13 656 660
Boukar, O., Belko, N., Chamarthi, S., Togola, A., Batieno, J., Owusu, E., Haruna, M., Diallo, S., Umar, M.L., Olufajo, O. & Fatokun, C. 2018 Cowpea (Vigna unguiculata): Genetics, genomics and breeding. Plant Breed. <https://onlinelibrary.wiley.com/doi/full/10.1111/pbr.12589>
Ddamulira, G. & Santos, C. 2015 Grain yield and protein content of Brazilian cowpea genotypes under diverse Ugandan environments AJPS 6 2074 2084
Egbadzor, K.F., Ofori, K., Yeboah, M., Aboagye, L.M., Opoku-Agyeman, M.O., Danquah, E.Y. & Offei, S.K. 2014 Diversity in 113 cowpea [Vigna unguiculata (L) Walp] accessions assessed with 458 SNP markers Springerplus 3 541
Emebiri, L.C. 1991 Inheritance of protein content in seeds of selected crosses of cowpea Vigna unguiculata L Walp. J. Sci. Food Agr. 54 1 7
Fang, J., Chao, C.T., Roberts, P.A. & Ehlers, J.D. 2007 Genetic diversity of cowpea [Vigna unguiculata (L.) Walp.] in four West African and USA breeding programs as determined by AFLP analysis Genet. Resources Crop Evol. 54 1197 1209
Fery, R.L. 1985 Improved cowpea cultivars for the horticultural industry in the USA, p. 129–135. In: S.R. Singh, K.O. Rachie (eds.). Cowpea research, production and utilization. John Wiley & Sons, Inc., New York
Gupta, P., Singh, R., Malhotra, S., Boora, K.S. & Singal, H.R. 2010 Characterization of seed storage proteins in high protein genotypes of cowpea [Vigna unguiculata (L.) Walp.] Physiol. Mol. Biol. Plants 16 53 58
Horneck, D. & Miller, R. 1998 Determination of total nitrogen in plant tissue, p. 75–83. In: Y.P. Kalra (ed.). Handbook of reference methods for plant analysis. CRC Press, New York
Itatat, S.L., Nworgu, E.C., Ikpe, E.N. & Osakwe, J.A. 2013 Evaluation of the protein contents of selected cowpea (Vigna unguiculata (L.) Walp.) varieties for production in Port Harcourt Acta Agronomica Nigeriana 13 71 75
Kushwaha, A. & Kumar, A. 2014 Development of high protein biscuits from cowpea (Vigna unguiculata) flour Intl. J. Basic Appl. Agr. Res. 12 2 814 817
Moore, J.C., DeVries, J.W., Lipp, M., Griffiths, J.C. & Abernethy, D.R. 2010 Total protein methods and their potential utility to reduce the risk of food protein adulteration Compr. Rev. Food Sci. Food Saf. 9 330 357
Nielsen, S., Ohler, T. & Mitchell, C. 1997 Cowpea leaves for human consumption: Production, utilization, and nutrient composition, p. 326–332. In: B.B. Singh, D.R. Mohan Raj, K.E. Dashiell, and L.E.N. Jackai (eds.). Advances in cowpea research. International Institute of Tropical Agriculture, Ibidan, Nigeria
Nielsen, S.S., Brandt, W.E. & Singh, B.B. 1993 Genetic variability for nutritional composition and cooking time in improved cowpea lines Crop Sci. 33 469 472
Ravelombola, W., Shi, A., Weng, Y., Motes, D., Chen, P., Srivastava, V. & Wingfield, C. 2016 Evaluation of total seed protein content in eleven Arkansas cowpea (Vigna unguiculata (L.) Walp.) lines AJPS 7 2288 2296
Singh, B.B., Mohan Raj, D.R., Dashiell, K.E. & Jackai, L.E.N. 1997 Advances in Cowpea Research. International Institute of Tropical Agriculture, Ibadan, Nigeria, and Japan International Research Center for Agricultural Sciences Tsukuba, Ibaraki, Japan
Tchiagam, J.B.N., Bell, J.M., Nassourou, A.M., Njintang, N.Y. & Youmbi, E. 2011 Genetic analysis of seed proteins contents in cowpea Vigna unguiculata L Walp. Afr. J. Biotechnol. 1016 3077 3086
Weng, Y., Shi, A., Ravelombola, W., Yang, W., Qin, J., Motes, D., Moseley, D.O. & Chen, P. 2017 A rapid method for measuring seed protein content in cowpea (Vigna unguiculata (L.) Walp) AJPS 8 2387 2396
Seed protein content in 173 cowpea germplasm accessions.