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Phylogenetic studies of Pleospora species with Stemphylium anamorphs based on four loci: lack of separation of Pleospora herbarum and five new lineages

     ¹ Plant Pathology, University of California Davis, One Shields Avenue, 354 Hutchison Hall, Davis, CA, 95616, United States of America
² IAPAR, Caixa Postal 481,, Londrina, CEP 8600-970, PR, Brazil
³ University of British Columbia, Vancouver, B.C.

Stemphylium is a genus of plant pathogens and saprobes in the Pleosporaceae (Pleosporales, Dothideomycetes, Ascomycetes). The teleomorphs of Stemphylium, where known, are in Pleospora, with Pleospora herbarum as the type. The goal of this study was to present a rigorous phylogenetic analysis of the relationships among Stemphylium isolates with particular emphasis on species delimitation in the P. herbarum clade, on possible new species and on the relationship of clades to cultures from type specimens. Our taxon sampling comprised 110 Stemphylium strains collected worldwide from various hosts and DNA sequences from four loci, from the ITS, the protein encoding GPD and EF-1 alpha genes, and the intergenic spacer between vmaA and vpsA. A large EF-1 alpha intron delimited by non-canonical splice sites and encoding putative proteins was present in three unrelated isolates and was excluded from analyses. Isolates used comprised 23 representatives derived from type strains, compared to type strains or otherwise connected to type material, 40 unnamed strains morphologically similar to the type P. herbarum, four strains from an outbreak of Stemphylium leaf blight of cotton in Brazil, and eight strains collected in British Columbia mainly from non-agricultural hosts. Our results provided strong support for the main groupings of Stemphylium obtained earlier but also revealed six possible new species. Other variation within morphological species may point to additional cryptic species. On the other hand, even with four loci, cultures ex-type of five species including P. herbarum were inseparable. We speculate that being self-fertile, the clade including P. herbarum might represent a group of highly inbred, morphologically distinct lineages that have yet to accumulate detectable species-specific sequence variation. The lack of variation in P. herbarum clade contrasts with many other a priori defined morphological species where multigene phylogenetic analyses revealed new cryptic species.

Key words: Ascomycota, Fungi, genealogical concordance phylogenetic species recognition, morphological species concept, phylogenetic species concept, species delimitation

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