Karyotype evolution in Eleusininae Dumort. (Poaceae, Chloridoideae, Cynodonteae): a phylogenetic and cytogenetic approach focusing on the genus Cynodon Rich

Abstract

Eleusininae is the largest subtribe of the Poaceae family with about 238 species in 31 genera. Within subtribe Eleusininae there is the genus Cynodon, with 15 species accepted, some species with forage potential. In both taxa the taxonomic circumscription, it is not well elucidated. Species belonging to Eleusininae are diploid and/or polyploid cytological forms. Cynodon is a genus with a wide variation in levels ploidy from diploid (2n = 2x = 18) to hexaploid (2n = 6x = 54). Understanding the events that caused natural polyploidization in the subtribe Eleusininae and Cynodon, allow selecting the species with potential forage that can be used in genetic breeding. Besides, answering gaps on the evolution of the group. Many taxonomic, morphological, and cytogenetic questions which are not yet well elucidated can be evaluated with a robust cytotaxonomic study. Thus, the present study aims to reconstruct ancestral state of the chromosome number in Eleusininae, in order to elucidate the evolutionary history of the group. This work has a focus in Cynodon genus, due to its wide geographical distribution and forage potential. Based on cytomolecular and morphological analyzes we compared Cynodon species/accessions, aiming to understand the genomic and chromosomal organization of the genus and generate information for taxonomic, evolutionary and genetic breeding studies of the group. In both taxa, speciation events occurred due to high influence of polyploidization events. The chromosome number ancestral of Eleusininae is p = 6 and Cynodon is p = 10. However, the basic number for Cynodon is x = 9. The common ancestor of the species, C. dactylon, C. nlemfuensis, C. incompletus, and C. transvaalensis, has two 5S and 35S rDNA sites, two CMA + bands, all chromosomes have DAPI + terminal bands on the long arm, five chromosomes have five DAPI + bands on the short arm and three chromosomes with DAPI + bands on the centromeric region. The karyotypic diversity of Cynodon is influenced by losses and gains of DAPI + bands and the mobility of ribosomal genes.