Abstract
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.
Highlights
Bambara groundnut (Vigna subterranea (L.) Verdc) is an underutilized African legume, grown mostly, by smallholder and subsistence farmers in Sub-Sahara Africa [1]
Bambara groundnut in the genuine wild state was found in North Yola province of Nigeria near Garoua in Cameroon [4] with most of the abundant genetic resources existing in the corridor of Nigeria and Cameroon, which is believed to be its origin of dispersal [5]
The mean genetic diversity within each group/region revealed that the Nigeria/Cameroon and West Africa regions possess a comparable level of genetic diversity
Summary
Bambara groundnut (Vigna subterranea (L.) Verdc) is an underutilized African legume, grown mostly, by smallholder and subsistence farmers in Sub-Sahara Africa [1] It consists of Vigna subterranea var subterranea (cultivated) and Vigna subterranea var spontanea (wild), which are the two botanical forms both having the same number of chromosomes (2n = 22). Inadequate knowledge on the taxonomy, reproductive biology coupled with the genetics of agronomic and quality traits, pest and diseases [10], lack of genetic improvement and adaptation to particular agro-ecological zones [11] are some of the constraints for developments This has led to underutilization of the crop resulting in weak or no genetic improvement effort, lower crop yield and quality.
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