Cytogenetic and genomic aspects of wild species of the lolium-festuca complex

Abstract

The genera Lolium L. and Festuca Tourn. ex L. compose a complex of closely related species and aggregate grasses of high forage interest. However, both genera have a diversity of wild species that have been poorly studied and that may characterize important reservoirs of resistance genes for genetic improvement programs. The main objective of the first study was to characterize and compare the karyotypes of five wild species of Lolium using chromosomal markers rDNA 35S and rDNA 5S via fluorescent in situ hybridization (FISH). All species presented 2n = 2x = 14, symmetrical karyotypes composed of metacentric and submetacentric chromosomes. Regarding the mapping of ribosomal genes, the autogamous species L. temulentum, L. persicum, and L. remotum were uniform with four 35S rDNA sites. On the other hand, L. subulatum and the allogamous species L. rigidum were more divergent, presenting nine and six 35S rDNA sites, respectively. All species presented two 5S rDNA sites in synteny with one 35S rDNA site. However, the autogamous species present these sites in a contiguous position, while in L. rigidum (allogamous) they were in opposite arms. In a second approach, we investigate the genomic relationship between the native species F. ulochaeta and F. fimbriata and compare them to the cultivated species of the Lolium-Festuca complex, using the genomic in situ hybridization (GISH) technique and flow cytometry. The species F. fimbriata and F. ulochaeta showed high genomic homology with probable species-specific sequences in the (sub)telomeric, centromeric and 18S rDNA regions, but this portion of repetitive sequences was not sufficient to discriminate the genomes. In addition, they showed a variation of 0.37pg in nuclear DNA content. Regarding the Eurasian species, F. fimbriata showed an affinity with the genomes of L. multiflorum (LmLm), F. pratensis (FpFp), and also with all genomes that set up F. arundinacea (FpFpFgFgFg'Fg'). On the other hand, the affinity between F. ulochaeta and F. arundinacea seems to be restricted to the Fg/Fg' genomes. GISH data reveal high genomic homology between Festuca species native to different centers of diversification and may provide new insights into the evolution of the Festuca genus.