Eliminação cromossômica e homologia genômica em Pennisetum spp Rich. (Poaceae)

Abstract

The hybrid resulting from a cross between elephant grass (Pennisetum purpureum, 2n = 4x = 28, genomes A'A'BB) and pearl millet (P. glaucum, 2n = 2x = 14, genome AA), is triploid (2n = 3x = 21), has the genomes AA'B and is sterile, but highly appreciated by cattle. The restoration of fertility of triploid hybrid and consequent viability of its use in breeding programs is done by induction of chromosome duplication. However, mixoploids plants with 2n = 14-42 chromosomes have been obtained due to chromosome elimination. Whereas these plants exhibit characteristics of interest for the improvement of elephant grass, this work aimed to study the chromosome elimination in synthetic partial polyploids derived from chromosomal duplication and backcrosses, and gain insight into the homology between the parental genomes of elephant grass and millet. For analyzes were utiliadas techniques conventional Giemsa staining and in situ hybridization. It was observed that during the cell cycle both in hybrid duplicated as those resulting from backcrossing of these and their parental during the cell cycle are eliminated chromosomes from both parental, and that chromosome elimination is random with predominant elimination of chromosomes of elephant grass. Additionally, changes occur at a low frequency compared with those reported for hybrids of hexaploid partial meiosis. The chromosomes bearing sites of rDNA 45S and 5S does not appear among those eliminated in the cell cycle of hybrid hexaploid. Hybridization with DNA probes of millet and elephant grass confirmed that exists homeology between the genomes A of millet and A 'and B elephant grass, and the ratio and distribution of the homologous regions in the genomes A' and B differ after hybridization.