Caracterização da aneuploidia em híbrido entre Urochloa ruziziensis (R. Germ. & Evrard) Crins e Urochloa decumbens (Stapf) R. D. Webster

Abstract

Urochloa is a genus known for comprehending grasses of great importance for crop and livestock production. In recent studies, aneuploid interspecific hybrids were found in crossings between the species Urochloa ruziziensis (artificial tetraploid) with Urochloa decumbens and Urochloa brizantha. In plants, aneuploidy represents an important asset for genetic mapping and gene dosage studies. The aim of the present study is to characterize the aneuploidy in the Hybrid H963 and to confirm the origin of the additional chromosomes via comparative analysis of the hybrid’s and its parents’ karyotypes. Root tips were pretreated and fixed in methanol:acetic acid (3:1) in order to obtain C-metaphases. Slides were prepared using cell dissociation technique and air dried. C-Banding and CMA/DAPI techniques were performed for a better chromosome sorting. The parental genotypes were confirmed with 36 chromosomes. The interspecific hybrid presented individuals with 2n=4x=36+2 and 2n=4x=36+1 chromosomes. C-bands were found on the chromosomes’ pericentromeric region in all assessed genotypes. The tetraploid genotype of U. ruziziensis presented four CMA and C-bands, all located on the chromosome’s terminal region. Urochloa decumbens presented four chromosomes with terminal CMA-bands and eight chromosomes with terminal C-bands. The H963 hybrid presented terminal CMA bands in five chromosomes and terminal C-bands in seven chromosomes. The banding pattern and the morphometric data allowed the identification of the hybrid’s additional chromosomes. A trisomy was identified in the pairs 3’ and 4’ of the hybrids with 36+2 chromosomes, which characterizes the aneuploidy as a double trisomy. The karyotype of the hybrids with 36+1 chromosomes pointed to the elimination of the additional chromosome previously identified in the pair 4’ and the persistency of the pair 3’ trisomy. The karyotype comparative analysis indicates that the additional chromosomes characterizing the trisomy were inherited from the parent U. ruziziensis (artificial autotetraploid). A common pattern in many angiosperms, regarding the distribution of heterochromatic bands, was observed in the assessed genotypes.