Inducing Genetic Variability In Cowpea (Vigna Unguiculata, L. Walp Var. Asontem) Using Ethyl Methane Sulfonate

Abstract

Unique variants are desired in the development of genetically improved crops to meet farmer and market needs hence ethyl methane sulfonate (EMS) was used to induce genetic variability in cowpea (Vigna unguiculata cv. Asontem). The main objective of this research was to characterize induced variations in EMS chemically mutagenized population of cowpea (Vigna unguiculata L. Walp Var. Asontem) in the M1 and M2 generations. The optimum concentration (LD50) of EMS for generating the mutagenized population was determined by treating seeds with different concentrations of EMS (0.0%, 0.2%, 0.4%, 0.6% and 0.8% v/v) and observing the germination count after 5 days. Three thousand cowpea seeds were treated with the LD50 concentration to generate the M1 population. Mutagenized seeds were sown with 500 untreated seeds serving as control (wild type). Data on qualitative and quantitative traits were collected during the evaluation of the M1 generation using Cowpea Descriptor of the IBPGR (1983). M2 seeds obtained after the M1 generation were sown and evaluated for morphological mutations in quantitative and qualitative traits. Data analysis was done using statistical software R, STATA and excel. The optimum dose (LD50) determined was 0.4%. The percentage germinations in the mutagenized population and wild type were 17.8% and 61.6% respectively. Percentage survival was higher in wild type (98.38%) as compared with the M1 population (78.46%). Frequency distribution analysis revealed variations in both the qualitative and quantitative traits observed in the M1 and M2 generations. Different phenotypic classes were observed in plant pigmentation, pod curvature, leaf shape, leaf colour, seed shape and seed coat colour. Individuals in the M1 population were widely distributed for measurements of chlorophyll content, plant height, number of pods per plant, pod length, number of locules per pod and number of seeds per pods as compared with the wild type. Principal component analysis revealed that he quantitative traits in the M1 population had first four principal components contributing to 77.22% of the total variability observed whiles the first four principal components in the wild type accounted for 75.26% variability. In the wild type, the first three principal components of qualitative traits accounted for total variability whereas, the first four principal components of qualitative traits in the M1 population accounted for 89.96% variability. During the M2 generation, percentage germination in the M2 population (74.03%) was lower than the wild type (80%). A wide spectrum of morphological abnormalities was observed in the M2 population. There were 1.59% that had abnormal leaflet number, 0.4% had variegated leaves, 0.14% xantha and albino mutants, 0.55% with irregular leaves. M2 individuals were widely distributed for days to flowering, number of pods per plant, number of seeds per pod, number of locules per pods, percentage seed set, pod length and number of seeds per plant. Chi-square test of associations of qualitative traits had only one insignificant association in the wild type while a total of 27 associations were observed in the M2 with 13 significant associations. A total of 28 pairwise correlations were estimated among the 7 quantitative traits in the M2 population and all correlations were significant. Principal component analysis showed that the quantitative traits in the M2 population had first four principal components contributing to 95.58% of the total variability observed whiles the first four principal components in the wild type accounted for 92.20% variability. In the wild type, the first two principal components of qualitative traits accounted for total variability whereas, the first four principal components of qualitative traits in the M2 population accounted for 76.77% variability. Assessment of diversity using both quantitative and qualitative traits grouped the M2 generation into 7 major clusters. About 2.88% of the total M2 population performed significantly higher than the wild type for number of seeds per plant, 2.59% performed significantly higher than the wild type for number of pods per plant. Top 20 individuals selected for number of seeds per plant had significantly higher performance in other yield attributing characters. In conclusion, the EMS mutagenesis was effective in inducing the unique variations that will be useful for breeding and development of new farmer preferred varieties.