Abstract

An appropriate dose of radiation should be established on target genotypes before large scale mutagenesis undertaken. The objective of this study was to determine an ideal dose of gamma radiation to induce genetic variation in selected cowpea (Vigna unguiculata) genotypes. Seeds of three Namibian released cowpea genotypes were gamma irradiated using seven dozes at the International Atomic Energy Agency, Austria. Experiments were laid out in the completely randomised design with three replications and important data collected. Data were subjected to analysis to identify optimal lethal dose aiming LD₅₀. Results revealed that genotype Nakare tolerated the radiation dose of 200 Gy providing germination of 43.33%. Seeds of genotypes Nakare and Shindimba failed to germinate above 400 Gy. However, genotype Bira showed germination of 46.67% at 600 Gy, the highest dose used in the study. The optimum doses at LD₅₀ for genotypes Nakare and Shindimba are at 150 and 200 Gy, respectively while genotype Bira tolerated increased dose of 600 Gy. Using linear regression model, the LD₅₀ for genotypes Nakare, Shindimba and Bira calculated at 165.24, 198.69 and 689 Gy, respectively. The findings may assist as reference doses for large-scale gamma irradiation of cowpea genotypes to induce genetic variation.

Key words: Cowpea, gamma radiation, LD₅₀, radio sensitivity, Vigna unguiculata.