Assessment of Genetic Variability of Bambara Groundnut (Vigna subterranea (L.) Verdc.) Accessions Using Morphological Traits and Molecular Markers

The efficiency of breeding can be improved by employing a number of genetic diversity measures of the crop germplasm. Genetic diversity and relatedness of 24 Bambara groundnut accessions (Vigna subterranea L. Verdc.) were estimated using 36 morphological characters, 201 Diversity Array Technology (DArT) and 65 simple sequence repeat (SSR) markers to assess the relationships between the material and also between the three marker types. These accessions were selected to represent the diversity within cultivated Bambara groundnut germplasm. A broader group of 119 Bambara groundnut accessions (87 from International Institute of Tropical Agriculture and 37 from University of Nottingham stocks; three seeds per accession) were planted in an unheated glasshouse at University of Nottingham in May, 2008. Data on the variation for morphological and agronomic traits were recorded following the IPGRI descriptors (IITA, BAMNET (2000). Samples were also analysed with microsatellite markers which have been characterised in this project. In addition, DNA extracted from the 119 accessions was sent for DArT analysis. This study has demonstrated the utility of the three marker types for genetic diversity and relatedness analysis. The genetic distance (GD) among the landraces and the first two axes for the principal component analysis (PCA) were obtained. The highest average genetic distance (GD) was obtained using morphological marker (0.55) followed by DArT (0.43) and SSR marker (0.25). The estimated values of the genetic relationship between all the markers were significantly correlated at (P<0.01). The markers provided consistent information as they produced relatively similar patterns of clustering, but DArT markers produced a cluster which grouped landraces based on their areas of origin. SSR markers have the advantage of being co-dominant and were employed to investigate pure line selection of Bambara groundnut. The results revealed significant reduction in the levels of heterogeneity from the 1st season of selection to the 3rd season, with no signs of residual heterozygosity suggesting that these lines (81-Acc-385TZA, 84-Acc 696ZMB, 88-AHM 753NAM, S19-3NAM and Bots1-BWA) have been effectively selected as pure lines. The application of SSR markers in this study further demonstrates their effectiveness as an approach suitable for Marker Assisted Selection in Bambara groundnut breeding.