Genome sizes in diploid and allopolyploid Arachis L. species (section Arachis)

Abstract

Species of section Arachis with x = 10 are important for peanut breeding and have been organized in five different genomes (A, B, D, F and K). The few available estimates of the DNA content are inconsistent and hampered the understanding of the evolutionary trends and in decision making for genomic studies of the group. Considering that, the objectives of this research were to measure the DNA content for all available (26) species and to make evolutionary inferences at the diploid and tetraploid level for section Arachis. The 2C values obtained by flow cytometry ranged from 2.55 to 3.22 pg among the diploid species. The annual species belonging to different genomes tend to have different genome sizes. However, the 2C values of the perennial species of the A genome were distributed almost along the whole range of genome sizes here observed. The distribution of 2C values partially support the genome arrangement proposed for the section. The comparisons of 2C values with karyotype parameters suggests that changes in DNA content have been proportionally distributed among the chromosome arms, and that the heterochromatic fraction was not directly involved in that changes. Within the A genome, the annual species has lower DNA content than the perennial ones, according to the nucleotype hypothesis. However, the lack of significant relationships with geoclimatic variables suggests that there are many intrinsic factors determining particular ecological roles of the DNA content in the different lineages of section Arachis. The constancy of the Cx values observed in the polyploids compared to those of the parental species suggests that the allopolyploidization event that originated the cultivated peanut did not induce significant changes in the genome size.