Phylogenetic relationships in genus <it>Arachis </it>based on ITS and 5.8S rDNA sequences

<p>Abstract</p> <p>Background</p> <p>The genus <it>Arachis </it>comprises 80 species and it is subdivided into nine taxonomic sections (<it>Arachis</it>, <it>Caulorrhizae</it>, <it>Erectoides</it>, <it>Extranervosae</it>, <it>Heteranthae</it>, <it>Procumbentes</it>, <it>Rhizomatosae</it>, <it>Trierectoides</it>, and <it>Triseminatae</it>). This genus is naturally confined to South America and most of its species are native to Brazil. In order to provide a better understanding of the evolution of the genus, we reconstructed the phylogeny of 45 species using the variation observed on nucleotide sequences in internal transcribed spacer regions (ITS1 and ITS2) and 5.8 S of nuclear ribosomal DNA.</p> <p>Results</p> <p>Intraspecific variation was detected, but in general it was not enough to place accessions of the same species in different clades. Our data support the view that <it>Arachis </it>is a monophyletic group and suggested <it>Heteranthae </it>as the most primitive section of genus <it>Arachis</it>. The results confirmed the circumscriptions of some sections (<it>Caulorrhizae</it>, <it>Extranervosae</it>), but raised questions about others. Sections <it>Erectoides</it>, <it>Trierectoides </it>and <it>Procumbentes </it>were not well defined, while sections <it>Arachis </it>and <it>Rhizomatosae </it>seem to include species that could be moved to different sections. The division of section <it>Arachis </it>into A and B genome species was also observed in the phylogenetic tree and these two groups of species may not have a monophyletic origin. The 2n = 2x = 18 species of section <it>Arachis </it>(<it>A. praecox</it>, <it>A</it>. <it>palustris </it>and <it>A. decora</it>) were all placed in the same clade, indicating they are closely related to each other, and their genomes are more related to B genome than to the A genome. Data also allowed insights on the origin of tetraploid <it>A. glabrata</it>, suggesting rhizome appeared twice within the genus and raising questions about the placement of that species in section <it>Rhizomatosae</it>.</p> <p>Conclusion</p> <p>The main clades established in this study in general agreed with many other studies that have used other types of evidences and sets of species, being some of them included in our study and some not. Thus, the relationships established can be a useful framework for future systematic reviews of genus <it>Arachis </it>and for the selection of species to pre-breeding programs.</p