Análise cariotípica em acessos diploides de Urochloa brizantha e Urochloa decumbens e poliploides de Urochloa dictyoneura (POACEAE)

Abstract

The genus Urochloa P. Beauv. (sin. Brachiaria (Trin.) Griseb.), belonging to the Poaceae family, comprises approximately 135 species and includes plants of great economic importance used as forages. The cytogenetic characterization of the group describes the basic chromosome number of x = 6, 7, 8, 9 and 10, with x = 9 being the most common. This study aimed to characterize the diploid accession karyotype of U. brizantha (B105) and U. decumbens (D04) and polyploid accessions of U. dictyoneura (DT158 and DT159), including chromosomal morphology and symmetry, DNA content and the mapping of 5S and 35S rDNA sequences through FISH. U. brizantha and U. decumbens diploid accessions have 2n = 2x = 18 chromosomes, karyotype formula 9m, symmetric karyotype, 1,79 and 1,44 pg of DNA content, respectively. For U. brizantha two rDNA loci 5S and 35S were identified. In U. decumbens four 5S sites and two 35S sites were identified. U. dictyoneura accessions have 2n = 4x = 24 chromosomes, karyotypic formula 6m, symmetric, 2.83 and 3.12 pg (DT158 and DT159, respectively), eight 5S sites and four 35S sites. The karyotype analysis revealed symmetry and similarity between the diploid karyotypes of U. brizantha and U. decumbens and between U. dictyoneura poliploidy accessions, reinforcing the suggestion as to the autopolyploid nature of its genome.