Genetic diversity in Bambara groundnut (Vigna subterranea (L.) Verdc.) as revealed by phenotypic descriptors and DArT marker analysis

Abstract

Genetic diversity of a Bambara groundnut germplasm representing accessions from 25 African countries, maintained at the International Institute of Tropical Agriculture (IITA; Nigeria) was evaluated based on seed patterns, qualitative characters, quantitative traits and Diversity Arrays Technique (DArT) markers. The study aimed at identifying important descriptors for germplasm conservation, validating the crop's geographical centre of origin and facilitating the utilization of existing genetic resources. Frequencies and diversity indices of seven types of seed patterns, 12 qualitative and 28 quantitative traits were evaluated for 124 representative accessions and were analyzed by region to elucidate the geographic distribution of descriptor states. In addition, individual plant samples from a subset of 40 landrace accessions were analyzed by assessing 554 DArT markers. Both the phenetic tree constructed from the qualitative and quantitative descriptors and the population structure derived from DArT marker analysis suggested a relatively high genetic diversity among accessions. Higher genetic diversity was observed for the Cameroon/Nigeria region relative to other regions, in agreement with the hypothesis that this region is the centre of origin for Bambara groundnut. Use of an extensive and diverse range of germplasm and an approach that integrated morphological and quantitative descriptors with DNA markers that represent wide genomic coverage offered a powerful way to make inferences about crop germplasm, in support of crop-improvement programs.

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

“…Research focusing on inter and intra-landrace variation for phenotypic descriptors (either as an independent study or as part of a broader characterization of germplasm) has been extensively reported in Bambara groundnut (Goli 1995;Karikari and Tabona 2004;Ntundu et al 2006;Ouedraogo et al 2008;Abu and Buah 2011;Olukolu et al 2012;Touré et al 2012;Aliyu and Massawe 2013;Shego et al 2013;Molosiwa et al 2015). While most of these reports have been largely country specific, a few have a global germplasm diversity perspective (including landraces from the major agro-ecologies across Africa and Southeast Asia; Goli 1995;Olukolu et al 2012;Molosiwa 2012;Molosiwa et al 2015).…”

“…While most of these reports have been largely country specific, a few have a global germplasm diversity perspective (including landraces from the major agro-ecologies across Africa and Southeast Asia; Goli 1995;Olukolu et al 2012;Molosiwa 2012;Molosiwa et al 2015). The standard descriptors for Bambara groundnut [International Plant Genetic Resources Institute/International Institute of Tropical Agriculture/The International Bambara groundnut Network (IPGRI/IITA/BAMNET 2000)] have been used as guidelines in these phenotypic characterization exercises.…”

“…A number of quantitative phenotypic traits have been listed in the standard descriptor set (IPGRI/IITA/ BAMNET 2000) for Bambara groundnut and some have been extensively reported (Ntundu et al 2006;Ouedraogo et al 2008;Abu and Buah 2011;Olukolu et al 2012;Jonah et al 2012;Aliyu and Massawe 2013;Shego et al 2013;Molosiwa et al 2015). Olukolu et al (2012) reported floral quantitative data, (2015) Ntundu et al (2006) Goli ( some components of which were not listed in the IPGRI/IITA/BAMNET (2000) descriptors (namely, banner/flag petal length, wing length, gap between the banner and wing tips, ratio of banner to wing lengths, peduncle length, and pedicel length).…”

“…Specifically for Bambara groundnut, the use of molecular markers to assess the level of inter-and intra-landrace polymorphism in collections of the crop has been noted as critical to enable their effective utilization in future breeding programmes (Massawe et al 2005(Massawe et al , 2007. Various approaches have been used to assess genetic diversity within the available germplasm of Bambara groundnut; phenotypic descriptors (Goli 1995;Olukolu et al 2012;Aliyu and Massawe 2013;Molosiwa et al 2015), biochemical markers (Pasquet et al 1999) molecular markers (Massawe et al 2002(Massawe et al , 2003aStadler 2009;Olukolu et al 2012;Aliyu and Massawe 2013;Molosiwa et al 2015). A number of breeding objectives have been reported in Bambara groundnut (Massawe et al 2005(Massawe et al , 2007Aliyu et al 2015).…”

“…However, for most underutilized crop species, the lack of availability of large numbers of speciesspecific molecular markers is the main hindrance to applying genomic assisted breeding in their crop improvement programmes (Mayes et al 2011). Specifically for Bambara groundnut, some speciesspecific genomic resources have been reported; 10 SSR markers (Basu et al 2007c), 143 SSR markers (Beena et al 2013), 75 SSR markers (Mayes et al 2013;Molosiwa et al 2015), 201 DArT Array markers (Stadler 2009;Olukolu et al 2012;Molosiwa et al 2015), XSpecies (Affymetrix microarray) (Chai et al 2013). Through the African orphan crop consortium (http://africanorphancrops.org/), efforts are underway for sequencing of Bambara groundnut to produce a genome sequence draft, alongside an effort to re-sequence 100 inbred lines of Bambara groundnut.…”