Evolutionary Relationships between Rhynchosporium lolii sp. nov. and Other Rhynchosporium Species on Grasses

Abstract

The fungal genus Rhynchosporium (causative agent of leaf blotch) contains several host-specialised species, including R. commune (colonising barley and brome-grass), R. agropyri (couch-grass), R. secalis (rye and triticale) and the more distantly related R. orthosporum (cocksfoot). This study used molecular fingerprinting, multilocus DNA sequence data, conidial morphology, host range tests and scanning electron microscopy to investigate the relationship between Rhynchosporium species on ryegrasses, both economically important forage grasses and common wild grasses in many cereal growing areas, and other plant species. Two different types of Rhynchosporium were found on ryegrasses in the UK. Firstly, there were isolates of R. commune that were pathogenic to both barley and Italian ryegrass. Secondly, there were isolates of a new species, here named R. lolii, that were pathogenic only to ryegrass species. R. lolii was most closely related to R. orthosporum, but exhibited clear molecular, morphological and host range differences. The species was estimated to have diverged from R. orthosporum ca. 5735 years before the present. The colonisation strategy of all of the different Rhynchosporium species involved extensive hyphal growth in the sub-cuticular regions of the leaves. Finally, new species-specific PCR diagnostic tests were developed that could distinguish between these five closely related Rhynchosporium species.

Comparative genomics to explore phylogenetic relationship, cryptic sexual potential and host specificity of Rhynchosporium species on grasses

“…The genes of R. commune and R. secalis are highly similar lacking any introns, whereas an intron is present in the 28S gene of R. agropyri . The CCG species R. orthosporum and the recently described R. lolii [16] carry two introns of the same size in the 18S gene and single introns differing in length by one nucleotide in the 28S gene. The latter are homologous to the 28S intron of R. agropyri and located at the same site, but their sequences are 99 bp and 87 bp shorter at the 5′ and the 3′ side, respectively.…”

“…Agropyron repens ). Finally, fungal isolates from perennial ryegrass ( Lolium perenne ) were found to represent yet another species, R. lolii [16]. The cylindrical shape of the spores as well as phylogenetic analysis based on nucleic acid sequences position the latter species closer to R. orthosporum (cylindrical conidia group, CCG) than to the other three species (beaked conidia group, BCG).…”

“…Phylogenetic concordance analyses based on the sequences of four housekeeping genes (ITS1-5.8S-rRNA-ITS2, EF1-α, α-tubulin, β-tubulin) and neutral RFLP loci using several hundred fungal isolates suggested that the CCG and the BCG branches separated 14,000–35,000 years ago, hence long before the advent of agriculture, with R. lolii diverging from R. orthoporum 4300–7200 years ago [16]. In contrast, R. commune , R. secalis and R. agropyri originated from a common ancestor only 1200–3600 years ago [8, 9, 16].…”

“…In contrast, R. commune , R. secalis and R. agropyri originated from a common ancestor only 1200–3600 years ago [8, 9, 16]. Furthermore, reconstructions of demographic growth indicate that populations of the three BCG species evolved in parallel.…”

Diagnosis of Ramularia collo-cygni and Rhynchosporium spp. in Barley

“…The barley-infecting pathogen has been renamed Rhynchosporium commune . Recent taxonomic studies have shown that Rhynchosporium commune is a complex of four closely related Rhynchosporium species [ 9 ]. The assay has not yet been tested against the other Rhynchosporium species on other hosts.…”