Constituição e relações genômicas entre espécies de Cynodon Rich. (Poaceae) evidenciadas pela hibridização in situ genômica

Abstract

Polyploidy events are considered the main mechanisms for the variation of the chromosomal number in Cynodon. However, the type of polyploidy, the genomic composition of the species and the taxonomy still remain controversial. Thus, the objective of this work was to investigate the genomes of four species of the genus through Genomic in situ Hybridization (GISH), an unprecedented analysis for the taxon. The diploid forms of C. dactylon, C. incompletus and C. nlemfuensis demonstrated homeology and their genomes were designated as DD, D1D1, D2D2, respectively. Cynodon dactylon 2x and C. incompletus 2x are genomically close, while C. nlemfuensis 2x showed greater divergence of repetitive sequences. The origin of C. dactylon 4x (DDD2D2) may have involved the crossing of its diploid cytotype with C. nlemfuensis 2x, while of C. transvaalensis 4x (DD2D1D1) was possibly derived from the crossing of C. dactylon 4x and C. incompletus 2x. The participation of non-reduced gametes is essential for the occurrence of these events of segmental allopolyploidy. The divergence between the genomes of the C. dactylon cytotypes suggests possible species discrimination and points out the taxonomic ambiguities of the genus.