Evidences of segmental allopolyploidy in Arachis nitida (Section Rhizomatosae, Leguminosae)

ORTIZ, ALEJANDRA MARCELA; SEIJO, GUILLERMO; FERNÁNDEZ, AVELIANO; LAVIA, GRACIELA INÉS

Buenos Aires

Encuentro; VII encuentro Internacional de especialistas en Arachis; 2010

Section Rhizomatosae presents the highest frequency of polyploid species within the genus. It includes three tetraploids with 2n=40 (A. glabrata, A. nitida, and A. pseudovillosa) and one diploid with 2n=20. Previous cytological analyses suggested an autopolyploid origin to A. glabrata; however, the nature of the others rhizomatous tetraploids and their probable progenitors still remains unknown. In this contribution, a detailed cytological analysis was carried out on A. nitida, including both classical and molecular cytogenetic techniques, to provide some hints about its genetic origin. Heterochromatin detection assays revealed centromeric DAPI+/CMA- bands in all chromosomes and proximal CMA+/DAPI- bands in three chromosome pairs. FISH analysis revealed 45S rDNA sites in three chromosome pairs (colocalized with CMA+/DAPI- bands) and 5S rDNA sites proximally localized in others two pairs. The most common configuration at meiotic metaphases was 20 II. However, 1 to 4 multivalents (trivalents and tetravalents) were observed in 34.69% of the cells, giving mean associations of 0.14I, 18.78II, 0.14III, and 0.45IV. These results suggest that A. nitida probably resulted from hybridization between two species with different number of 45S rDNA loci. However, the finding of up to four multivalents and the similar pattern of DAPI+/CMA- heterochromatin suggest that A. nitida has genomes partially homologous, and that the species is a segmental allopolyploid.