GENETIC DIVERSITY AND YIELD STABILITY OF SOME NIGERIAN ACCESSIONS OF BAMBARA GROUNDNUT (VIGNA SUBTERRANEA (L.) VERDC.) IN SOUTH WEST NIGERIA

Abstract

This study focuses on genetic diversity and yield stability of some Nigerian accessions of Bambara groundnut. Field experiments were conducted in 3 years (2017/2018, 2018/2019 and 2019/2020) using 100 accessions of Bambara groundnut collected from the Genetic Resources Center, International Institute of Tropical Agriculture, Ibadan, Nigeria. Diversity and stability were determined through morphological and molecular markers, principal component analysis, cluster analysis, frequency distribution of qualitative traits, correlation and yield stability analyses. Total block size was 21 m by 50 m and each plot was 1 m by 2.5 m. Inter and intra row spacing were 1.00 m and 0.25 m respectively. The experiments were laid out in a Randomized Complete Block Design (RCBD) with three replications. The experiments were carried out in two locations (Ibadan and Ikenne). Quantitative and qualitative data collected from five competitive plants selected from the middle row were subjected to analysis of variance (ANOVA), using the PROC GLM procedure on Statistical Analytical System (SAS, version 9.4). Treatment means were separated by Duncan multiple range test (DMRT) with significant differences at 1% and 5% levels of probability. Principal Component Analysis (PCA) was carried out using PROC PRINCOMP procedure to determine the contribution of each trait to total variation. Cluster analysis was carried out using PROC CLUSTER procedure to show the distribution of the accessions into different groups through dendrogram. Descriptive statistics was employed to analyze qualitative data using frequencies and percentages. Deoxyribonucleic acid (DNA) extraction procedure by Dellaporta Miniprep for Plant DNA Isolation was used for extraction. Diversity Arrays Techniques (DArT) markers were used to determine the genetic make-up and the level of polymorphism of the accessions with single nucleotide polymorphism (SNP). Analysis of variance revealed significant differences in twenty- seven out of the twenty-eight quantitative traits considered, indicating the presence of genetic variation among the accessions studied. Combined analysis revealed 9 accessions were high yielding with considerable yield stability index. Yield stability showed that 24 accessions were stable in the expression of their yield potentials in the locations and years. Principal component analysis revealed that seventeen of the twenty-eight quantitative traits studied are major contributors to diversity in Bambara groundnut, suggesting further selection of the traits to improve the crop. Cluster analysis based on SNPs showed seven groups of the selected accessions, indicating wide range of diversity in the genetic constitution. Cluster analysis based on morphological traits showed four groups based on 77.28 % total variance. Correlation coefficient analysis showed positive and significant association between agronomic and yield components, suggesting that selection based on these characters may be effective for crop improvement. Genome-wide association studies (GWAS) revealed total unfiltered SNP was 11, 821 and 3,387 SNP (28.65%) aligned on ‘Mung bean’ genome. GWAS also indicated significant SNP markers that revealed quantitative traits loci (QTLs) associated with phenotypic traits. This study concluded that morphological and molecular characterization are useful tools in grouping or clustering the accessions into similar and dissimilar accessions for practical breeding, hence, recommended DArT sequencing as a baseline markers for breeders use.