Controlled crosses in bambara groundnut were attempted between a range of thirty-six bambara groundnut landraces (thirty domesticated (V. subterranea var. subterranea) and six wild (V. subterranea var. spontanea)). Ten F 1 seed were produced. Of these, eight germinated producing F 2 populations. On seed set, four populations could be unambiguously confirmed as true crosses by F 3 seed coat colour. A single F 2 population, derived from a domesticated landrace from Botswana (DipC; female parent) crossed with a wild accession collected in Cameroon (VSSP11; male parent) was used to study a range of agronomic and domestication traits. These included; days to emergence, days to flowering, internode (fourth) length at harvest, number of stems per plant, leaf area, Specific Leaf Area (SLA), Carbon Isotope Discrimination (CID), 100 seed weight, testa colour and eye pattern around the hilum. On the basis of variation for internode length and stems per plant, 14 small F 3 families were selected and grown under field conditions to further investigate the genetic basis of the 'spreading' versus 'bunched' plant character, a major difference between wild and cultivated bambara groundnut. Results presented suggest that traits including leaf area, SLA, CID and 100 seed weight are controlled by several genes. In contrast, the variation for traits such as internode length, stems per plant, days to emergence and seed eye pattern around the hilum are likely to be under largely monogenic control. The results of this work are discussed in relation to the domestication of bambara groundnut.

No abstract

Bambara groundnut is an indigenous African legume crop plant. It is largely grown by subsistence farmers, but can also be used as a cash crop to supplement family income. The fact that it is highly drought tolerant means that it has considerably potential to provide part of food security in regions of the world where water availability is a serious issue. As one part of the international effort to understand and improve this species, we report here the first 10 microsatellite markers derived from bambara groundnut.

Bambara groundnut (Vigna subterranea L. Verdc.) is an underutilised, drought tolerant legume that has the potential to form an important part of Food Security for the coming decades. The challenges facing farmers to produce enough food for the growing world population -particularly that of climatic instability -are well documented and together represent probably one of the biggest challenges humanity has faced. Our extreme reliance on a limited number of staple (often nonindigenous and sometimes also poorly adapted) crops represents a clear vulnerability. This can be partly reduced by the development of alternative crops. These currently underutilised crops often have beneficial characteristics not found in conventional main crops and if these traits address either biotic or abiotic stresses in a sustainable way, then there is the potential for agricultural diversification. There are a number of stumbling blocks to developing such crops, including; poor yields, unadapted crop features, limited processing knowledge, few value-added products, poorly developed transport chains and markets, negative cultural perceptions and little perceived profit margin for commercial breeders. An integrated approach is needed to begin to address these problems. As part of this, we have focused on the application of molecular genetics to Bambara groundnut and the opportunities to exploit knowledge from other species, new technologies and new approaches, to establish a framework for genetic improvement through breeding. We also try to draw out lessons from our work in Bambara groundnut which may be relevant in other underutilised species, to try to contribute to the development of a generic approach (and hopefully, a faster and cheaper approach) to tackling these same questions in other underutilised species. In this paper we ask what is the fundamental information we need about the breeding system of an underutilised species and how could this alter our genetic improvement, using Bambara groundnut as an example.

Bambara groundnut (Vigna subterranea L. (Verdc.)) is an underutilised African legume crop which shows a high degree of drought tolerance. It continues to be an important leguminous crop in tropical Africa and is grown mainly by women who are small-scale farmers in Africa under traditional low input agricultural systems. It is grown mainly for its protein and carbohydrate, as a fixer of agricultural nitrogen and for its high levels of drought tolerance. Genetic studies into this species could provide important data for breeding programmes and to enhance food security in sub-Saharan Africa. The main project work was to construct two initial genetic linkage maps for Bambara groundnut and to carry out a trait QTL analysis. Genomic DNA was extracted from 73 bulked lines (effectively F 3) derived from a cross between the DipC and Tiga necaru landraces. A set of 94 pre-tested SSR primers designed from a 454-sequenced microsatellite-enriched library were tested for segregation in this cross. Thirty primers were polymorphic and revealed that the residual heterozygosity in this population was around 25%, consistent with an F 3 population. DArT markers for Bambara groundnut were previously developed and 236 polymorphic markers have also been applied in this study. The genetic map consisted of 231 markers in 25 linkage groups of two or more linked markers, totalling 498cM and covering a predicted 44% of Bambara groundnut genome. The high marker-marker linkage (at 87%) suggests a more comprehensive coverage. Nine QTL loci were identified on 7 LGs. A major QTL was identified for internode length on LG3, explaining 41% of phenotypic variation. The 'Narrow' map, in contrast with wide cross population, was constructed from two domesticated landraces and would be expected to segregate for agronomically important traits, rather than domestication traits. The development of molecular tools for mapping and QTL analysis potentially allows more rapid breeding progress to be achieved in this species.