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Introduction
African yam bean, AYB (Sphenostylis stenocarpa Hochst ex A. Rich. Harms), is a tuberous legume of tropical Africa with considerable potential. The seeds and tubers are of economic importance providing food for humans and livestock. AYB is an affordable source of protein, containing approximately 29 and 19% crude protein in its grain and tuber, respectively (Adewale and Dumet, 2011). The amino acid (lysine and methionine) content in AYB grain is higher than that obtainable in pigeon pea, cowpea and Bambara groundnut (Uguru and Madukaife, 2001). These peculiarities encourage a thorough characterization of its germplasm.
Unfortunately, despite the crop's acknowledged potential, it is still classified as neglected and underutilized species (Padulosi et al., 2013); and little information at the molecular level is available. DNA-based markers previously used in this species include random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphisms (AFLPs) (Moyib et al., 2008; Adewale et al., 2014; Ojuederie et al., 2014); however, there is no report on the use of simple sequence repeat (SSR) primers. SSRs being co-dominant in nature, abundant in genomes and highly polymorphic are markers of choice for crop improvement especially for crops like AYB where single nucleotide polymorphisms are yet to be identified. SSRs can be derived from genomic DNA (genomic SSRs) or from transcribed regions of the DNA, i.e. expressed sequence tags (ESTs).
To our knowledge, no SSR marker has been reported in AYB. Development of SSRs requires prior sequence information, and this is not available for AYB. However, the procedures of identifying species-specific SSRs can be avoided if markers from related species are transferable. Successful transferability of SSRs within the Fabaceae has been reported, from chickpea (Cicer arietinum) to pigeon pea (Cajanus cajan), from cowpea (Vigna unguiculata) to Bambara groundnut (Voandzeia subterranea) and from adzuki bean (Vigna angularis) to black gram (Vigna mungo) (Datta et al., 2009; Somta et al., 2011; Sanjeev et al., 2013).
AYB is identified with some limitations, such as hardness of the seed-coat and hence longer time to cook, presence of secondary metabolites, lengthy life cycle, photoperiodic sensitivity, etc. (Adewale and Dumet,...