Some biogeographic, genomic and speciation considerations on section Arachis

SEIJO GUILLERMO; ROBLEDO GERMÁN; GRABIELE MARINA; CARIRIMO DIEGO; SAMOLUK SEBASTIAN; LAVIA GRACIELA

Brasilia

Conferencia; 5th International Conference of the Peanut Research Community on Advances in Arachis through Genomics and Biotechnology; 2011

Empresa Brasileira de Pesquisa Agropecuaria (EMBRAPA)

Section Arachis has two tetraploid, 29 diploid and 8-10 new species. A new genome organization has been recently proposed for the section distinguishing five different genomes: A, B, D, F and K. Moreover, the A-genome species were segregated into three different karyotype groups. This organization is supported by cross compatibility, some molecular markers and by 5S rDNA sequences. Satellite DNA and transposable elements also support this genome organization. Biogeographic analysis demonstrates that most of the species have restricted areas, some of them with vicariant populations, but very few with relatively extended areas. Field collections showed that populations of each species live in very similar habitats and that species of same genome tend to be restricted to particular biogeographic regions: the K-genome in the Chaco, the F in the savannas of the Beni and the B and D in the San Ignacio Planalto. Within the A-genome, there is a Karyotype group associated with the Pantanal, one with the Rio Grande, and the last one with La Plata River basin. Whenever two Arachis species were found in simpatry, they had different genomes.This geographical structure of the genomic and karyotype groups may be a consequence of the particular biology of Arachis species. Geocarpy and a high degree of autogamy may be factors that contributed to maintenance of new alleles within populations. New populations established from one or very few fruits dispersed from original populations by hydrochory, would be exposed to genetic drift and rapid fixation of alleles, which ultimately, would conducted to rapid speciation in close allopatry.