ORTIZ alejandra Marcela
congresos y reuniones científicas
Insights into the meiotic behavior and polyploid nature of Arachis glabrata Benth. (Leguminosae)
Buenos Aires
Simposio; The 6th International Symposium on the Molecular Breeding of forage and Turf MBFT 2010; 2010
Arachis glabrata, perennial peanut, is a tetraploid (2n=4x=40) species of the section Rhizomatosae. It produces high-quality forage and has also been used as cover crop and ornamental turf. Although A. glabrata has a wide morphological and genetic variability, commercial cultivars have been developed only by selection of a few available accessions. Genetic improvement has not yet been attempted in part because of the low seed production and the poor knowledge on the biology of this species. Cytogenetic features of a crop are essential tools for planning successful breeding strategies. Therefore, a detailed cytological analysis was carried out on several A. glabrata accessions, including both classical and molecular cytogenetic techniques in order to provide more insights into their polyploid nature and meiotic behavior. Mitotic analysis by Feulgen’ staining showed that all the accessions were tetraploids with 2n=4x=40 and a satellited chromosome pair belonging to type 3. CMA3/DAPI staining revealed centromeric DAPI+/CMA- bands (AT-rich heterochromatin) in all the chromosomes. A proximal CMA+/DAPI- band (GC-rich heterochromatin) was observed in two chromosome pairs with similar size and morphology. All 45S rDNA sites (4) revealed by FISH coincided with the CMA+/DAPI- bands. In all the accessions, 5S rDNA sites (4) were proximally localized in two chromosome pairs with similar morphology. Meiotic analysis revealed 18 different configurations at metaphase, which ranged from 20II to 4II + 8IV. Despite these chromosome pairings, the accessions generally had a regular meiotic behavior and meiotic indexes over 0.95. Pollen viability was high and ranged from 81.44% to 97.51%. These findings evidence a high degree of homology between the four haploid chromosome complements of A. glabrata, and suggest an autopolyploid origin. However, all the accessions presented an advanced diploidization stage and meiotic regularity. Therefore, the reduction in their seed set can not be related with major meiotic abnormalities during microsporogenesis