Taxonomic re-examination of several Japanese Stemphylium strains based on morphological and molecular phylogenetic analyses

Abstract

Most of the many Stemphylium species on record as plant pathogens in Japan have been identified by morphology. Using molecular phylogenetic analysis of four loci (rDNA-ITS, EF-1α, GPD, and vmaA-vpsA) combined, we re-examined the taxonomy of 31 Stemphylium strains that had been identified morphologically before or after their deposit in the NIAS Genebank, Japan. In the present study, these Japanese strains were separated into three groups (Groups A, C, and E). Sixteen Japanese strains formed a new subgroup (designated Subgroup C2) that contained no type or ex-type strains of existing species. Four of the strains had been identified correctly, whereas the other 27 strains appear to have been misidentified based on our phylogenetic analysis. We examined the conidial morphology of four representative misidentified strains selected from each clade. While the morphological characteristics of a strain isolated from Welsh onion resembles those of the S. vesicarium type, this strain belongs to Subgroup C2 rather than Subgroup C1 and, therefore, could not be identified at the species level. Conversely, three pathogenic strains isolated from aster, asparagus, and Chinese chive were re-identified based on our combined morphological and phylogenetic data. We propose the scientific names of the aster leaf spot pathogen as S. lycopersici, and the asparagus Stemphylium leaf spot and Chinese chive brown leaf blight pathogens as S. herbarum.