Genetic diversity and population structure of cowpea (vigna unguiculata (l.) Walp) accessions.

ABSTRACT

The research was carried out to study diversity (phenotypic and genetic) and population structure of cowpea germplasm assembled from the DPEB and SARI. A total of 78 cowpea accessions from these two sources were used for the study. Data was collected on twelve vegetative and reproductive traits, four polyphenols, crude protein, seven mineral elements, nineteen amino acids and three SSR markers. Methanolic extracts of pulverized cowpea seeds were used to determine concentrations of polyphenols, crude protein, mineral elements and amino acids. Cowpea Descriptor of the IBPGR (1983) was used for data collection on morphological traits. Data analysis involved descriptive statistics, Fisher’s test of association, Pearson’s pairwise correlation, phenotypic and genetic diversity, Nei’s diversity of subdivided population, principal component analysis and cluster analysis. Mean percent crude protein was 13.52+0.245%. Mean sodium concentration was (35.66+0.58) x 10-3 ppm. Mean potassium concentration was 10.41+0.259 ppm. Mean concentration for magnesium was (0.288+7.69) x 10-3 ppm. Mean concentration for iron was 0.048+0.0041 ppm. Mean nickel concentration was 0.033+0.0021 ppm. Mean concentration for lead was 0.038+0.006 ppm. Mean concentration for cadmium was (7.0+2.0) x 10-4 ppm. Concentration mean for manganese was (0.0187+9.0) x 10-4 ppm. Mean concentration for zinc was (0.00402+8.34) x 10-4 ppm. Mean concentration for gallic acid was 6.97+22.94 mg/l. Mean concentration for syringic acid was 104.25+12.04 mg/l. Mean concentration for quercetin was 69.58+2.34 mg/l. Mean concentration for vanillic acid was 52.79+13.75 mg/l. Mean concentration for L-Histidine was (365.0+42.9) x 10-8 ppm. Mean glycine concentration was (260.0+50.7) x 10- 8 ppm. Mean concentration for L-Asparagine was (2400.0+360) x 10-8 ppm. Mean DL-AlphaAlanine concentration was (2490.0+296.0) x 10-8 ppm. Mean concentration for L-Aspartic acid was 791.0 x 10-8 ppm. L-Valine mean concentration was (831.0+85.7) x 10-8 ppm. Mean v concentration for L-Proline was 957.0+131.0) x 10-8 ppm. L-Methionine mean concentration was (293.0+16.9) x 10-8 ppm. Isoleucine mean concentration was (841.0+15.1) x 10-8 ppm. Mean concentration of Trans-4-Hydroxy-L-Proline was (856.0+13.9) x 10-8 ppm. Mean concentration for L-Tyrosine was (6350.0+933.0) x 10-8 ppm. DL-Beta-Phenyl-Alanine mean concentration was (29840.0 +10040) x 10-8 ppm. L-Tryptophan mean concentration was (646400.0+8700) x 10-8 ppm. Six morphological traits associated significantly with source of cowpea genotype collection: Twenty-two test of associations among the twelve morphological traits were observed. A total of sixty-three significant pairwise correlations were observed among all quantitative traits. Mean total phenotypic diversity (Ht) for percent crude protein and each of the mineral elements was 0.162+0.314. Mean intra-population diversity (Hs) was 0.132+0.021. Mean phenotypic diversity among populations (Gst) was 0.187. Gene flow (Nm) among population’s estimates had a mean of 2.181. Nei’s analysis of phenotypic diversity in subdivided population for polyphenols indicated that mean total phenotypic diversity for each trait (Ht) was 0.121. Mean intra-population diversity (Hs) was 0.105. Mean phenotypic diversity among populations (Gst) was 0.434. Gene flow (Nm) estimate among population for each of the traits ranged from 1.316 to 118.498. The eight SSRs loci had frequencies that ranged from 0.067 to 0.803 and mean Nei’s genetic diversity for the SSR markers was 0.542. Population structure analysis grouped the cowpea genotypes into 4 clusters. Average distance between individual cowpea genotypes in the same cluster ranged from 0.084 to 0.26. Mean genetic differentiation among the four clusters ranged from 0.374 to 0.687. Mean gene flow ranged from 0.228 to 0.837. Eighteen cowpea genotypes were identified to be of economic importance based on concentrations of their phytochemical compounds.