title: A study of the relationships of cultivated peanut (Arachis hypogaea) and its most closely related wild species using intron sequences and microsatellite markers.
abstract: OBJECTIVE
  The genus Arachis contains 80 described species. Section Arachis is of particular interest because it includes cultivated peanut, an allotetraploid, and closely related wild species, most of which are diploids. This study aimed to analyse the genetic relationships of multiple accessions of section Arachis species using two complementary methods. Microsatellites allowed the analysis of inter- and intraspecific variability. Intron sequences from single-copy genes allowed phylogenetic analysis including the separation of the allotetraploid genome components.
  
  
  METHODS
  Intron sequences and microsatellite markers were used to reconstruct phylogenetic relationships in section Arachis through maximum parsimony and genetic distance analyses.
  
  
  RESULTS
  Although high intraspecific variability was evident, there was good support for most species. However, some problems were revealed, notably a probable polyphyletic origin for A. kuhlmannii. The validity of the genome groups was well supported. The F, K and D genomes grouped close to the A genome group. The 2n = 18 species grouped closer to the B genome group. The phylogenetic tree based on the intron data strongly indicated that A. duranensis and A. ipaënsis are the ancestors of A. hypogaea and A. monticola. Intron nucleotide substitutions allowed the ages of divergences of the main genome groups to be estimated at a relatively recent 2·3-2·9 million years ago. This age and the number of species described indicate a much higher speciation rate for section Arachis than for legumes in general.
  
  
  CONCLUSIONS
  The analyses revealed relationships between the species and genome groups and showed a generally high level of intraspecific genetic diversity. The improved knowledge of species relationships should facilitate the utilization of wild species for peanut improvement. The estimates of speciation rates in section Arachis are high, but not unprecedented. We suggest these high rates may be linked to the peculiar reproductive biology of Arachis.
authors.affiliation: Embrapa Recursos Genéticos e Biotecnologia, C.P. 02372, CEP 70·770-917, Brasília, DF, Brazil. marcio.moretzsohn@embrapa.br
authors.forename: Márcio C
authors.initials: MC
authors.lastname: Moretzsohn
authors.forename: Ediene G
authors.initials: EG
authors.lastname: Gouvea
authors.forename: Peter W
authors.initials: PW
authors.lastname: Inglis
authors.forename: Soraya C M
authors.initials: SC
authors.lastname: Leal-Bertioli
authors.forename: José F M
authors.initials: JF
authors.lastname: Valls
authors.forename: David J
authors.initials: DJ
authors.lastname: Bertioli
mesh_terms: D000383:Agriculture; D000483:Alleles; D010367:Arachis / Q000145:classification / Q000235:genetics* / Q000254:growth & development*; D001483:Base Sequence; D018744:DNA, Plant / Q000235:genetics; D005819:Genetic Markers; D006579:Heterozygote; D007438:Introns / Q000235:genetics*; D018895:Microsatellite Repeats / Q000235:genetics*; D010802:Phylogeny; D011110:Polymorphism, Genetic
chemical_list: D018744:DNA, Plant; D005819:Genetic Markers