Evaluation of Protein and Micronutrient Levels in Edible Cowpea (Vigna Unguiculata L. Walp.) Leaves and Seeds

Cowpea is the most important seed legume in Africa. Its leaves and seed are consumed tomeet the dietary requirements of protein andmicronutrient in rural African communities. In this study, leaf protein of 32 cowpea genotypes was 23-40% at Taung (South Africa), 28-40% at Wa and 24-35% at Manga (Ghana). Seed protein level was also up to 40% in landrace Bengpla and more than 30% in nine other genotypes planted at Taung. Trace elements in cowpea leaves showed markedly high concentrations of Fe (2,011 mu g.g(-1)), Zn (150 mu g.g(-1)), Mn (325 mu g.g(-1)), and B (43 mu g.g(-1)) in genotype Apagbaala, in contrast to the very low levels of Fe (273 mu g.g(-1)), Zn (40 mu g.g(-1)), Mn (219 mu g.g(-1)), and B (32 mu g.g(-1)) in genotype Encore. Leaf Fe concentration was highest in genotype Apagbaala (2,011 mu g.g(-1)), followed by Fahari (2,004 mu g.g(-1)), Iron Gray (1,302 mu g.g(-1)), Line 2020 (944 mu g.g(-1)), Bensogla (927 mu g.g(-1)), Omondaw (605 mu g.g(-1)), IT96D-1951 (591 mu g.g(-1)), IT93K-452-1 (574 mu g.g(-1)), Ngonji (569 mu g.g(-1)), and Mchanganyika (566 mu g.g-1), and lowest in Bechuana white ( 268 mu g.g(-1)). Cowpea seed also showed greater concentrations of Fe in genotype Soronko (67 mu g.g(-1)), IT93K-452-1 (67 mu g.g(-1)), Brown Eye (65 mu g.g(-1)), Bensogla (61 mu g.g(-1)), and TVU11424 (62 mu g.g(-1)). Trace elements in cowpea seed differed among genotypes, and ranged from 45.1 to 67.0 mu g.g(-1) for Fe, 33.9 to 69.2 mu g.g(-1) for Zn, 10.1 to 17.4 mu g.g(-1) for Mn, 14.7 to 21.4 mu g.g(-1) for B, and 5.2 to 8.1 mu g.g(-1) for Cu. Genotypes Apagbaala, Fahari, Iron Gray, and Line 2020, respectively, exhibited 34.2-, 34.0-, 22.5-, and 18.3-fold higher Fe concentration in leaves than seed, and 3.5-, 2.0-, 2.0-, and 3.5-fold greater Zn in leaves than seed (in that order). The genotypes that accumulated significantly high levels of protein and trace elements in cowpea leaves and seed, were generally high N-2-fixers, thus suggesting a link between N-2 fixation and cowpea's ability to synthesize protein and accumulate nutrient elements in leaves and seed. Therefore, identifying cowpea genotypes that can enhance protein accumulation and micronutrient density in edible leaves and seed through breeding has the potential to overcome protein-calorie malnutrition and trace element deficiency in rural Africa.