Evaluating cowpea mutant genotypes for grain yield and nutritional value in South Africa

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Ntswane, Moshieng
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University of the Free State
Cowpeas produce a substantial amount of grain, which is a significant source of vitamins, minerals and protein to disadvantaged people with limited access to adequate nutrients. Improved cowpea genotypes have been introduced through new breeding techniques such as mutagenesis to increase the phenotypic, genetic and nutritional diversity of the crop. The objectives of this study were: 1) to determine the phenotypic diversity and characterise cowpea mutants and normal genotypes for grain yield and yield components, to identify superior cowpea mutants and normal genotypes and to determine the correlation between all measured characteristics, 2) to evaluate the variability of cowpea mutants and normal genotypes for protein content, selected mineral elements, phytic acid and the potential bioavailability of iron (Fe) and zinc (Zn), to identify superior cowpea mutants and normal genotypes, and to determine the interrelationship between all measured characteristics, and 3) to determine genotype by environment (GE) interaction, to identify superior genotypes for grain yield and to determine the adaptability and stability of cowpea mutants and normal genotypes in South Africa. Thirty-one cowpea genotypes (16 Namibian mutants, seven International Institute of Tropical Agriculture (IITA) genotypes and eight South Africa genotypes) were planted in five different environments in South Africa during the 2021/2022 cropping season. Significant (P ≤ 0.05) genotype and GE interaction effects were observed for grain yield, yield components, protein content, minerals, phytic acid and potential mineral bioavailability. Broad-sense heritability (H2) values above 50% were observed for yield components, protein, mineral elements, phytic acid and potential mineral bioavailability, while low H2 values below 50% were observed for grain yield and Boron (B), indicating the complexity in selection and genetic improvement of these traits. Superior Namibian mutants (ShR10P12, ShR3P4, ShR4P1 and BrR11P2), IITA genotype (98K-476-8) and South African genotype (Enchore) for grain yield were identified. Superior Namibian mutants (ShL3P7-2, ShR3P4, ShR4P1, BrR11P11, BrR4P11, NKL9P7, NKR8P9, NKR9P9 ShR2P11, BrR11P2, ShL2P7, ShR3P4 and NKRuP5), IITA genotypes (98K-476-8, IT82E-18, IT93K-452-1, IT99K-573-2-1 and ITOOK 1263), and South African genotypes (Oloyin, Orelu, Pan 311, Bechuana White, Enchore and Glenda) for protein content, Fe and Zn concentration were also identified. The IITA genotype (IT93K-452-1) and South African genotypes (Oloyin and Orelu) had a potential of good Fe bioavailability. All cowpea mutants and normal genotypes had a potential of poor Zn bioavailability. High yielding and stable Namibian mutants (NKL9P7, ShR10P12 and ShR2P11), IITA genotype (ITOOK 1263) and South African genotype (Agrinawa) were identified. Two mega-environments, namely, 1) Taung and Mafikeng, and 2) Mafikeng, Bloemfontein, Polokwane and Potchefstroom were identified, indicating broad adaption of the genotypes. Potchefstroom and Taung were identified as ideal environments for evaluation of cowpea genotypes. Significant positive correlations between grain yield with almost all yield components were observed. Significant positive correlations of protein content with mineral elements and phytic acid were also observed, indicating the potential to simultaneously select these traits. Namibian mutants (NKR1P3, BrR11P2, ShL2P7, ShR2P11 and ShR10P12), IITA genotype (98K-476-8) and South African genotypes (Glenda, Dr Saunders, Enchore and Oloyin) were associated with high grain yield. Namibian mutants (ShR10P12, ShR3P4, ShR9P5, BrR11P11, BrR11P2, BrR4P11, NKR1P3, NKR9P9 and NKRuP5), IITA genotypes (IT07K-292-10, IT07K-318-33, IT82E-18 and IT99K-573-2-1), and South African genotypes (Agrinawa, Bechuana White and Dr Saunders) were associated with high protein content, manganese (Mn), phytic acid, Molar ratio of phytic acid with iron (PA:Fe), Molar ratio of phytic acid with zinc (PA:Zn), and ash content. These genotypes have a potential of long-term profitability to the agricultural production industry.
Dissertation (M.Sc.(Plant Breeding))--University of the Free State, 2022
Cowpeas, grain yield, protein, mineral elements, mutation, phenotypic diversity, bioavailability, broad-sense heritability, stability, genotype by environment interaction