Genetic diversity and population structure of Bambara groundnut (Vigna subterranea (L.) Verdc.): synopsis of the past two decades of analysis and implications for crop improvement programmes

Knowledge of genetic diversity within crop species and the nature of their breeding systems are critical for crop improvement. These determine the appropriate species specific breeding methodologies to deploy. Genetic diversity analysis is an ongoing process in the breeding programmes of 'major crops', which is used to direct or re-direct breeding objectives (especially selection of parental lines). In this regard, the importance of such information in 'underutilised' or 'minor' crop species, which largely exist as landraces with little information about their genetic diversity and breeding systems, becomes very important. One such important underutilized crop species which could contribute positively to global food security is Bambara groundnut (Vigna subterranea (L.) Verdc.). We present here an overview of the past two decades of genetic diversity analysis of Bambara groundnut landraces. Various genetic diversity analyses of the available germplasm for the crop using phenotypic descriptors and molecular marker technologies have been reported. Generally, most of these studies lack adequate representation of the available global germplasm. For those studies that involved relatively a large germplasm collections (above 100; sampled from different agro-ecologies) the marker density employed in these analyses has been so far relatively low. Specifically, for breeding systems, high genetic diversity and low heterozygosity have been reported across the germplasm analysed in this highly cleistogamous species. In terms of population structure, the West African and the Southern African accessions appear as distinct clusters. This raises the possibility of the southern African region a secondary centre of domestication or diversity for the crop.