Distribution patterns of rDNA loci in the Schedonorus-Lolium complex (Poaceae)

Abstract

The Schedonorus-Lolium complex of the subtribe Loliinae (Poaceae) includes several economically important forage and turf grasses. This complex encompasses Lolium Linnaeus, 1753, Festuca Linnaeus, 1753 subgenus Schedonorus (P. Beauvois, 1824) Petermann, 1849 and Micropyropsis Romero Zarco et Cabezudo, 1983. New FISH results of 5S and 18S–26S rDNA sequences are presented for three species and the results are interpreted in a review of distribution patterns of 5S and 18S–26S rDNA sequences among other species in the complex. Micropyropsis tuberosa Romero Zarco et Cabezudo, 1983 (2n = 2x = 14) displayed a distribution pattern of rDNA sequences identical to that of F. pratensis Hudson, 1762, supporting a close phylogenetic relationship at the bottom of the phylogenetic tree. “Lolium multiflorum” Lamarck, 1779 accessions sourced from Morocco showed a different pattern from European L. multiflorum and could be a unique and previously uncharacterised taxon. North African Festuca simensis Hochstetter ex A. Richard, 1851 had a marker pattern consistent with allotetraploidy and uniparental loss of one 18S–26S rDNA locus. This allotetraploid has previously been suggested to have originated from a hybrid with Festuca glaucescens (Festuca arundinacea var. glaucescens Boissier, 1844). However, the distribution patterns of the two rDNA sequences in this allotetraploid do not align with F. glaucescens, suggesting that its origin from this species is unlikely. Furthermore, comparisons with other higher alloploids in the complex indicate that F. simensis was a potential donor of two sub-genomes of allohexaploid Festuca gigantea (Linnaeus) Villars, 1787. In the overall complex, the proximal locations of both rDNA markers were conserved among the diploid species. Two types of synteny of the two markers could, to a considerable extent, distinguish allo- and autogamous Lolium species. The ancestral parentage of the three Festuca allotetraploids has not yet been determined, but all three appear to have been sub-genome donors to the higher allopolypoids of sub-genus Schedonorus. Terminal locations of both the markers were absent from the diploids but were very frequently observed in the polyploids.