Determining the optimal gamma irradiation dose for developing novel cowpea (Vigna unguiculata) genotypes

Cowpea (Vigna unguiculata (L.) Walp.) is a major legume crops for human consumption and livestock feed in tropical regions. Although its importance, the crop's production is subjected to numerous constraints, raising the need to develop outstanding genotypes. In this line, this study assesses the effects of gamma irradiation doses on cowpea genotypes to determine the LD50 and its effects on agro-morphological parameters.

Healthy dry seeds of three cowpea genotypes, Bambey 21, Me51-M4-39M9, and Ndout violet pods (VP), were exposed to four doses of gamma-rays 0, 200, 300, and 400 Gy. Qualitative and quantitative parameters were evaluated since germination, and a two-way analysis of variance (ANOVA) was performed on the means of quantitative traits using R software.

The results revealed that the LD50 on seed germination and plant survival ranged from 579 and 446.25 Gy, in Me51-M4-39M9, respectively. These values varied significantly among genotypes and revealed that low doses of gamma irradiation stimulated germination speed and had a positive effect on the early flowering of Ndout VP. Higher doses of gamma irradiation induced more severe mutations, causing visible effects such as changes in leaf color (albino, xantha, viridis, and variegation) and phyllotaxis. The frequency of chlorophyll mutants induced by gamma irradiation was found to be dose-genotype/dependent, with Bambey 21 being the most sensitive variety. Lower doses induced desirable mutations such as stem pigmentation and seed hilum coloration on Bambey 21 and Me51-M4-39M9. It has also had a positive impact on seedling height and leaf number in Bambey 21 and Ndout VP. However, high irradiation doses lead to a significant reduction in certain quantitative traits, such as plant height (PH), leaf length (LL), leaf width (LW), pod width (PWD), pod weight (PW), seed width (SWD), and seed weight. Analysis of the phenotypic performance of quantitative traits allowed us to cluster the four doses by genotype into three groups.

The optimum dose of gamma-irradiation in cowpea mutation breeding is genotype-dependent. The effects of gamma-irradiation on these traits and their relationships are highly dependent on the specific crop and genotype. Further research is needed to understand these effects underlying mechanisms and develop crop improvement strategies using gamma irradiation.