ITS rDNA phylogeny of selected Mycosphaerella species and their anamorphs occurring on Myrtaceae

Species of Mycosphaerella and their anamorphs are commonly found on the lea ves of Myrtaceae, many of which are defoliated by these pathogens. The taxo nomy of these fungi has been based on minute morphological differences, and virtually nothing is known regarding their relatedness to each other. In t his study, we present a phylogeny of 30 species of Mycosphaerella or their anamorphs from myrtaceous hosts, based on sequence data from the ITS region s of the ribosomal RNA operon. Fifteen of the species were also analysed fo r the 5' end of the large subunit (28S), which produced a phylogeny similar to that obtained for the ITS data set. The Mycosphaerella species included in this analysis are all regarded as representatives of section Plaga, and appear to represent a monophyletic assemblage. Mycosphaerella lateralis wa s the only species shown to have a wide host range. In general, species clu stered together based on their anamorph genera. Species with Colletogloeops is and Stenella anamorphs always grouped in two respective clusters. Howeve r, species with Mycovellosiella. Phaeophleospora. Pseudocercospora and Uweb raumia anamorphs occurred separately, suggesting that they have evolved mor e than once within Mycosphaerella. Based on the ITS data set, all morphospe cies were also shown to be phylogenetic species, although too few isolates were available to address questions relating to intraspecies variation. Nev ertheless, ITS sequence data proved sufficient to distinguish morphological ly similar taxa that have hitherto only been distinguished based on ascospo re germination patterns and anamorph characteristics. Sequence data present ed in this study should facilitate the identification of Mycosphaerella spe cies occurring on Myrtaceae in the future.