Optimum gamma radiation doses to enhance genetic diversity in selected cowpea (Vigna unguiculata) genotypes

Cowpea (Vigna unguiculata L.) improvement is necessary to increase its contribution to food and nutrition security in the impoverished regions such as the Sub-Saharan African Region. Genetic variability is fundamental to selecting parental genetic resources with agronomic and economic important traits for recombination. Gamma radiation is one of the valuable mutagens for creating novel mutant populations with allelic combinations needed to develop varieties with the desired traits. In this study, we determined the optimum dosage of gamma irradiation to use in breeding programs to enhance high yield and tolerance to field pests, including Maruca pod borers (Maruca vitrata) in locally adapted cowpea varieties. Seeds of two locally adapted cowpea genotypes (NkR1P3 and NamCp201) were treated with six gamma irradiation doses – 0 (un-irradiated), 75, 150, 300, 450, and 600 Gy. Consequently, the radio-sensitivity test was conducted in seed trays under net house conditions at the experimental field of Ogongo Campus, University of Namibia, Namibia. The study was arranged in a completely randomized design with three replications. Significant interactions (p < 0.001) of genotype and gamma irradiation dosage were found on percentage emergence (%E) and seedling survival percentage (%SS). This revealed that optimum gamma irradiation doses for tested cowpea genotypes where genotypic and dose depended. The significant effect (p < 0.001) of dose on all tested traits revealed the need to identify highly responsive traits for large-scale mutagenesis. Seedling survival rate and shoot length were the most responsive and were consequently used to determine the optimum dose for mutagenesis. The optimum dosage of gamma radiation for genotypes NkR1P3 and NamCp201 ranged between 382 and 427 Gy and 324 and 335 Gy, respectively. These optimal doses can be used to generate genetic variation to improve yield and tolerance to local stresses including tolerance to M. vitrata pod borers.