A linkage map for the B-genome of Arachis (Fabaceae) and its synteny to the A-genome

<p>Abstract</p> <p>Background</p> <p><it>Arachis hypogaea </it>(peanut) is an important crop worldwide, being mostly used for edible oil production, direct consumption and animal feed. Cultivated peanut is an allotetraploid species with two different genome components, A and B. Genetic linkage maps can greatly assist molecular breeding and genomic studies. However, the development of linkage maps for <it>A. hypogaea </it>is difficult because it has very low levels of polymorphism. This can be overcome by the utilization of wild species of <it>Arachis</it>, which present the A- and B-genomes in the diploid state, and show high levels of genetic variability.</p> <p>Results</p> <p>In this work, we constructed a B-genome linkage map, which will complement the previously published map for the A-genome of <it>Arachis</it>, and produced an entire framework for the tetraploid genome. This map is based on an F₂population of 93 individuals obtained from the cross between the diploid <it>A. ipaënsis </it>(K30076) and the closely related <it>A. magna </it>(K30097), the former species being the most probable B genome donor to cultivated peanut. In spite of being classified as different species, the parents showed high crossability and relatively low polymorphism (22.3%), compared to other interspecific crosses. The map has 10 linkage groups, with 149 loci spanning a total map distance of 1,294 cM. The microsatellite markers utilized, developed for other <it>Arachis </it>species, showed high transferability (81.7%). Segregation distortion was 21.5%. This B-genome map was compared to the A-genome map using 51 common markers, revealing a high degree of synteny between both genomes.</p> <p>Conclusion</p> <p>The development of genetic maps for <it>Arachis </it>diploid wild species with A- and B-genomes effectively provides a genetic map for the tetraploid cultivated peanut in two separate diploid components and is a significant advance towards the construction of a transferable reference map for <it>Arachis</it>. Additionally, we were able to identify affinities of some <it>Arachis </it>linkage groups with <it>Medicago truncatula</it>, which will allow the transfer of information from the nearly-complete genome sequences of this model legume to the peanut crop.</p

Identification of candidate genome regions controlling disease resistance in Arachis

<p>Abstract</p> <p>Background</p> <p>Worldwide, diseases are important reducers of peanut (<it>Arachis hypogaea</it>) yield. Sources of resistance against many diseases are available in cultivated peanut genotypes, although often not in farmer preferred varieties. Wild species generally harbor greater levels of resistance and even apparent immunity, although the linkage of agronomically un-adapted wild alleles with wild disease resistance genes is inevitable. Marker-assisted selection has the potential to facilitate the combination of both cultivated and wild resistance loci with agronomically adapted alleles. However, in peanut there is an almost complete lack of knowledge of the regions of the <it>Arachis </it>genome that control disease resistance.</p> <p>Results</p> <p>In this work we identified candidate genome regions that control disease resistance. For this we placed candidate disease resistance genes and QTLs against late leaf spot disease on the genetic map of the A-genome of <it>Arachis</it>, which is based on microsatellite markers and legume anchor markers. These marker types are transferable within the genus <it>Arachis </it>and to other legumes respectively, enabling this map to be aligned to other <it>Arachis </it>maps and to maps of other legume crops including those with sequenced genomes. In total, 34 sequence-confirmed candidate disease resistance genes and five QTLs were mapped.</p> <p>Conclusion</p> <p>Candidate genes and QTLs were distributed on all linkage groups except for the smallest, but the distribution was not even. Groupings of candidate genes and QTLs for late leaf spot resistance were apparent on the upper region of linkage group 4 and the lower region of linkage group 2, indicating that these regions are likely to control disease resistance.</p