Genetic Diversity and Population Structure of Bambara Groundnut
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Genet Resour Crop Evol DOI 10.1007/s10722-016-0406-z REVIEW 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 Siise Aliyu . Festo Massawe . Sean Mayes Received: 14 September 2015 / Accepted: 11 April 2016 Ó The Author(s) 2016. This article is published with open access at Springerlink.com Abstract Knowledge of genetic diversity within security is Bambara groundnut (Vigna subterranea crop species and the nature of their breeding systems (L.) Verdc.). We present here an overview of the past are critical for crop improvement. These determine the two decades of genetic diversity analysis of Bambara appropriate species specific breeding methodologies groundnut landraces. Various genetic diversity anal- to deploy. Genetic diversity analysis is an ongoing yses of the available germplasm for the crop using process in the breeding programmes of ‘major crops’, phenotypic descriptors and molecular marker tech- which is used to direct or re-direct breeding objectives nologies have been reported. Generally, most of these (especially selection of parental lines). In this regard, studies lack adequate representation of the available the importance of such information in ‘underutilised’ global germplasm. For those studies that involved or ‘minor’ crop species, which largely exist as relatively a large germplasm collections (above 100; landraces with little information about their genetic sampled from different agro-ecologies) the marker diversity and breeding systems, becomes very impor- density employed in these analyses has been so far tant. One such important underutilized crop species relatively low. Specifically, for breeding systems, high which could contribute positively to global food genetic diversity and low heterozygosity have been reported across the germplasm analysed in this highly cleistogamous species. In terms of population struc- & S. Aliyu ( ) Á F. Massawe ture, the West African and the Southern African Biotechnology Research Centre, School of Biosciences, University of Nottingham Malaysian Campus, accessions appear as distinct clusters. This raises the 43500 Jalan Broga, Semenyih, Selangor, Malaysia possibility of the southern African region a secondary e-mail: [email protected]; centre of domestication or diversity for the crop. [email protected] S. Aliyu Á S. Mayes Keywords Bambara groundnut Á Breeding Á Genetic Crops For the Future (CFF), diversity Á Landraces Á Population structure Á Vigna 43500 Jalan Broga, Semenyih, Selangor, Malaysia subterranea S. Aliyu CSIR-Savannah Agricultural Research Institute, Nyankpala, N/R, Ghana Introduction S. Mayes School of Biosciences, The University of Nottingham, Sutton Bonington Campus, Loughborough, Plant breeding is defined as the art of crop improve- Leicestershire LE12 5RD, UK ment (Acquaah 2007). Similar to the practice of an art, 123 Genet Resour Crop Evol the availability of requisite tools and resources as well 2007a, b), N-fixation and soil fertility improvement as the creative act of their combination to achieve (Kishinevsky et al. 1996; Dakora 1998; Herridge and identified objectives is critical. Adequate variability Rose 2000; Herridge et al. 2008; Mohale et al. 2013) within the germplasm of the species is the most have been documented. The crop largely exists as important resource needed to achieve breeding objec- landraces with few varieties developed through con- tives in crop improvement programmes (Hawkes trolled breeding (Massawe et al. 2002; Basu et al. 1991; Rao and Hodgkin 2002). Moreover, adequate 2007b; Massawe et al. 2007). Various landraces and knowledge of variability within germplasm collec- wild type accessions of the crop are held in trust on tions (and the breeding systems itself) has important behalf of the International community by a number of implications for conservation, management and future organizations (Table 1). The ability to develop utility of germplasm resources (Rao and Hodgkin improved genotypes with desired phenotypic traits 2002). that meet the demand of various actors (especially Molecular markers have emerged as power tools in farmers) could be very useful. A conceptual represen- the assessment of genetic variability relative to the tation of the global germplasm of Bambara groundnut conventional approach of using phenotypic descrip- and its utility for crop improvement is presented tors because the former are independent of environ- (Fig. 1). mental factors (Agarwal et al. 2008). The use of The importance of using molecular technology to molecular markers to assess genetic diversity in understand breeding systems and to assess genetic landraces, breeding lines, varieties, wild relatives diversity within available germplasm collections of and mutant populations to aid breeding decisions in underutilized species to enable their effective utiliza- major crops such as rice (Oryza sativa L.) (Zhang et al. tion in breeding programme has been emphasized 2011; Choudhary et al. 2013), maize (Zea mays L.) (Lu (Mayes et al. 2011). Specifically for Bambara ground- et al. 2011; Wen et al. 2012), soya bean (Glycine max nut, the use of molecular markers to assess the level of (L.) Merr.) (He et al. 2012) and cowpea (Vigna inter- and intra-landrace polymorphism in collections unguiculata (L.) Walp.) (Huynh et al. 2013), is an of the crop has been noted as critical to enable their important on-going component of their crop improve- effective utilization in future breeding programmes ment. The significance of ‘underutilized’ crop species (Massawe et al. 2005, 2007). Various approaches have (also known as ‘minor’, ‘orphan’ or ‘neglected’) for been used to assess genetic diversity within the global food security is gradually gaining the attention available germplasm of Bambara groundnut; pheno- of the international research community and food typic descriptors (Goli 1995; Olukolu et al. 2012; security policy organizations (Jaenicke and Ho¨schle- Aliyu and Massawe 2013; Molosiwa et al. 2015), Zeledon 2006; Will 2008; Massawe et al. 2016). biochemical markers (Pasquet et al. 1999) molecular Underutilized species exist mostly as landraces and markers (Massawe et al. 2002, 2003a, b; Stadler 2009; wild collections due to decades of neglect by the Olukolu et al. 2012; Aliyu and Massawe 2013; scientific community (Williams and Haq 2002; Mas- Molosiwa et al. 2015). A number of breeding objec- sawe et al. 2005; Will 2008). To fully harness their tives have been reported in Bambara groundnut potential, knowledge of their breeding systems and (Massawe et al. 2005, 2007; Aliyu et al. 2015). In genetic diversity within germplasm is important. One this regards, matching identified breeding objectives such important underutilized legume is Bambara with reported diversity analysis to guide important groundnut (Vigna subterranea (L.) Verdc.). breeding decisions (particularly selection of parental Bambara groundnut is a leguminous crop of lines) becomes important. ‘Next’ generation breeding African origin and mostly grown with limited inputs populations [such as multi-parent advanced generation by farmers in the semi-arid tropics (Basu et al. 2007b; inter-cross (MAGIC)] have appeared as strategic Massawe et al. 2002, 2007). The desirable agronomic approaches to plant breeding in recent times (Nord- traits of Bambara groundnut such as yield potential borg and Weigel 2008; Kover et al. 2009; Jannink et al. (Berchie et al. 2010; BAMFOOD 2012), nutritional 2010; Bandillo et al. 2013). Specifically for Bambara composition (Brough and Azam-Ali 1992; Brough groundnut, the importance of these ‘next’ generation et al. 1993) drought tolerance and adaptations to breeding germplasm resources in achieving the iden- marginal soils (Collinson et al. 1996; Mwale et al. tified breeding objectives within an integrated 123 Genet Resour Crop Evol Table 1 Major collection of landraces and wild type accession of Bambara groundnut maintained by various institutions across the globe No. Name of organization Number of Location Reference accession 1 International Institute of Tropical 1815 Nigeria Goli (1995) Agriculture (IITA) http://www.iita.org/genetic-resources;jsessionid= 29A0C3A336A5B354BE12C308409A316D 2 Institute of Research for Development (IRD) 1000 France Somta et al. (2011) 3 The Southern African Development – Zambia Massawe et al. (2007) Community (SADC) gene bank - indicate not specified number of accessions held Global germplasm Seed systems On-farm participatory Variety research recommendation Characterization Multi-locational Storage & Breeders’ trials management selection Breeding Programmes Fig. 1 Bambara groundnut global germplasm and its utility for crop improvement breeding framework has been highlighted (Aliyu et al. platforms have further strengthened our understanding 2015). We aim to present a review of the past two of the genetics of important phenotypic traits both in decades of diversity analysis reports on Bambara the context of forward and in reverse genetics (Alonso groundnut global germplasm with particular emphasis and Ecker 2006; Rosenberg et al. 2010). This has on its implications for current and future crop increased the efficiency and accuracy with which QTL improvement programmes. and underlying candidate genes can be localised using high density markers and novel second/next genera- tion germplasm resources. Against this backdrop, The need for a specific molecular ‘tool box’ genomic assisted breeding is now a routine