Phylogenetic analyses of Septoria species based on the ITS and LSU-D2 regions of nuclear ribosomal DNA

摘要

The phylogenetic relationships of 17 selected Septoria spp. (eight with a known Mycosphaerella teleomorph), Phloeospora ulmi (teleomorph M. ulmi) and 18 additional taxa (10 with a Mycosphaerella teleomorph) were inferred from ITS and D2-LSU nrDNA sequences. In total, 10 anamorph genera associated with Mycosphaerella were represented. Intraspecific variation in ITS was limited in Septoria, with the exception of three strains that all were identified as S. rubi but originated from different Rubus spp. and probably belong to different species of Septoria. The results of D2 region sequencing confirmed Mycosphaerella sense lato (including Davidiella and Eruptio) as monophyletic. The cereal pathogen Septoria tritici, which is closely related to S. passerinii as found in ITS analysis, clusters with Ramularia spp. in the D2 analyses, distant from the other Septoria spp. The pathogens S. apiicola, S. linicola, and S. populicola cluster in a major clade containing Phl. ulmi, and other Septoria spp. and Cercospora. spp. Short branch lengths in this clade suggest a very recent evolution. Septoria castaneicola and S. pyricola also might represent relatively distant lineages. Both analyses of the regions indicated that Septoria is not monophyletic within Mycosphaerella and that conidiomatal structure (acervulus, pycnidium) has little value for predicting phylogenetic relatedness. As a consequence, the separation between the acervular Phloeospora and pycnidial Septoria is untenable. The loss of the teleomorph most likely has occurred several times in the evolutionary history of Mycosphaerella.