Understanding the genetic structure and diversity of crops facilitates progress in plant breeding. A collection of 270 bambara groundnut (Vigna subterrenea L) landraces sourced from different geographical regions (Nigeria/Cameroon, West, Central, Southern and East Africa) and unknown origin (sourced from United Kingdom) was used to assess genetic diversity, relationship and population structure using DArT SNP markers. The major allele frequency ranged from 0.57 for unknown origin to 0.91 for West Africa region. The total gene diversity (0.482) and Shannon diversity index (0.787) was higher in West African accessions. The genetic distance between pairs of regions varied from 0.002 to 0.028 with higher similarity between Nigeria/Cameroon-West Africa accessions and East-Southern Africa accessions. The analysis of molecular variance (AMOVA) revealed 89% of genetic variation within population, 8% among regions and 3% among population. The genetic relatedness among the collections was evaluated using neighbor joining tree analysis, which grouped all the geographic regions into three major clusters. Three major subgroups of bambara groundnut were identified using the ADMIXTURE model program and confirmed by discriminant analysis of principal components (DAPC). These subgroups were West Africa, Nigeria/Cameroon and unknown origin that gave rise to sub-population one, and Central Africa was sub-population two, while Southern and East Africa were sub-population three. In general, the results of all the different analytical methods used in this study confirmed the existence of high level of diversity among the germplasm used in this study that might be utilized for future genetic improvement of bambara groundnut. The finding also provides new insight on the population structure of African bambara groundnut germplasm which will help in conservation strategy and management of the crop.

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Understanding the phenotypic variation and designing a mini-core collection is an efficient method to accelerate the genetic gain of bambara groundnut. A collection of 300 bambara groundnut landraces from 25 different countries of origin sourced from gene banks were used to analyze phenotypic variability among the landraces and develop a mini-core collection for future breeding. The landraces were evaluated in alpha lattice design with two replications for 2 years (2019 and 2020). The results showed highly significant differences (p < 0.001) among the bambara groundnut landraces for all the studied traits implying the selection of landraces with better agronomic traits could be achieved from the crop genetic pool. In addition, landrace x year interactions were significant for studied traits, except for shelling percentage and number of seeds per pod. The genotypic coefficient of variation values were high for most yield component traits, with the highest (65.39%) value obtained on seed dry weight. Furthermore, high heritability in conjunction with high genetic advance obtained in seed dry weight, pod dry weight, petiole length and plant height implies that these traits are majorly controlled by additive genetic action and could be improved through selection. Highly significant and positive correlations of yield were found with seed dry weight, pod dry weight, number of pod per plant, number of leaves, petiole length and plant height. A mini-core collection of 60 landraces (20%) was developed that represents the entire collection using Core Hunter algorithm. In general, the study provides insight into bambara groundnut germplasm that would enhance cultivar development and sustains the utilization of the crop. In addition, the mini-core collection established in the present study could be exploited for future bambara groundnut improvement efforts.