Abstract
<title>Abstract</title> <p> Mutation breeding using physical mutagens such as fast neutron irradiation offers a promising approach for creating genetic variability in cowpea ( <italic>Vigna unguiculata</italic> L. Walp.), an important staple legume in sub-Saharan Africa. However, determining optimal mutagen doses that balance mutation induction with plant survival is critical for successful breeding programs. This study was conducted to establish the median lethal dose (LD₅₀) and median growth reduction dose (GR₅₀) of fast neutron irradiation in two cowpea varieties, SAMPEA 21 and SAMPEA 20T. Uniform seeds of both varieties were exposed to fast neutron irradiation at the Center for Energy and research Training (CERT) for varying durations corresponding to doses ranging from 0.00 to 16.40 µSv. The M₁ generation was raised using a randomized complete block design with two replications. Data collected on germination percentage, survival percentage, shoot length, stem girth, number of leaves, leaf area, and number of branches were subjected to probit regression analysis and dose-response modeling. Results revealed a progressive, dose-dependent decline in germination, survival, and all growth parameters with increasing irradiation doses. SAMPEA 21 exhibited greater radiosensitivity, with LD₅₀ and GR₅₀ values consistently lower than those of SAMPEA 20T. The LD₅₀ was estimated at 1.70 µSv for SAMPEA 21 and 5.38 µSv for SAMPEA 20T. Growth reduction doses (GR₅₀) for shoot length were 1.65 µSv and 4.85 µSv for SAMPEA 21 and SAMPEA 20T, respectively. Number of branches and leaf area were the most sensitive growth parameters, while shoot length showed moderate tolerance. The regression models exhibited high coefficients of determination (R² = 0.5713–0.9753), indicating strong dose-response relationships. The established LD₅₀ and GR₅₀ values provide essential benchmarks for optimizing mutation breeding protocols in cowpea. The differential radiosensitivity between varieties underscores the need for genotype-specific dose optimization. These findings contribute to the efficient induction of beneficial mutations while minimizing plant mortality and growth impairment, thereby enhancing the effectiveness of cowpea improvement programs. </p>