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Oomycete species occupy many different environments and many ecological niches. The genera Phytophthora and Pythium for example, contain many plant pathogens which cause enormous damage to a wide range of plant species. Proper identification to the species level is a critical first step in any investigation of oomycetes, whether it is research driven or compelled by the need for rapid and accurate diagnostics during a pathogen outbreak. The use of DNA for oomycete species identification is well established, but DNA barcoding with cytochrome c oxidase subunit I (COI) is a relatively new approach that has yet to be assessed over a significant sample of oomycete genera. In this study we have sequenced COI, from 1205 isolates representing 23 genera. A comparison to internal transcribed spacer (ITS) sequences from the same isolates showed that COI identification is a practical option; complementary because it uses the mitochondrial genome instead of nuclear DNA. In some cases COI was more discriminative than ITS at the species level. This is in contrast to the large ribosomal subunit, which showed poor species resolution when sequenced from a subset of the isolates used in this study. The results described in this paper indicate that COI sequencing and the dataset generated are a valuable addition to the currently available oomycete taxonomy resources, and that both COI, the default DNA barcode supported by GenBank, and ITS, the de facto barcode accepted by the oomycete and mycology community, are acceptable and complementary DNA barcodes to be used for identification of oomycetes.

Inappropriate taxon definitions may have severe consequences in many areas. For instance, biologically sensible species delimitation of plant pathogens is crucial for measures such as plant protection or biological control and for comparative studies involving model organisms. However, delimiting species is challenging in the case of organisms for which often only molecular data are available, such as prokaryotes, fungi, and many unicellular eukaryotes. Even in the case of organisms with well-established morphological characteristics, molecular taxonomy is often necessary to emend current taxonomic concepts and to analyze DNA sequences directly sampled from the environment. Typically, for this purpose clustering approaches to delineate molecular operational taxonomic units have been applied using arbitrary choices regarding the distance threshold values, and the clustering algorithms. Here, we report on a clustering optimization method to establish a molecular taxonomy of Peronospora based on ITS nrDNA sequences. Peronospora is the largest genus within the downy mildews, which are obligate parasites of higher plants, and includes various economically important pathogens. The method determines the distance function and clustering setting that result in an optimal agreement with selected reference data. Optimization was based on both taxonomy-based and host-based reference information, yielding the same outcome. Resampling and permutation methods indicate that the method is robust regarding taxon sampling and errors in the reference data. Tests with newly obtained ITS sequences demonstrate the use of the re-classified dataset in molecular identification of downy mildews. A corrected taxonomy is provided for all Peronospora ITS sequences contained in public databases. Clustering optimization appears to be broadly applicable in automated, sequence-based taxonomy. The method connects traditional and modern taxonomic disciplines by specifically addressing the issue of how to optimally account for both traditional species concepts and genetic divergence.

The first large-scale survey of sexual and asexual Trichoderma morphs collected from plant and fungal materials conducted in Southern Europe and Macaronesia including a few collections from French islands east of Africa yielded more than 650 specimens identified to the species level. Routine sequencing of tef1 revealed a genetic variation among these isolates that exceeds previous experience and ca. 90 species were recognized, of which 74 are named and 17 species newly described. Aphysiostroma stercorarium is combined in Trichoderma. For the first time a sexual morph is described for T. hamatum. The hitherto most complete phylogenetic tree is presented for the entire genus Trichoderma, based on rpb2 sequences. For the first time also a genus-wide phylogenetic tree based on acl1 sequences is shown. Detailed phylogenetic analyses using tef1 sequences are presented in four separate trees representing major clades of Trichoderma. Discussions involve species composition of clades and ecological and biogeographic considerations including distribution of species.

In advancing to one name for fungi, this paper treats generic names competing for use in the order Diaporthales (Ascomycota, Sordariomycetes) and makes a recommendation for the use or protection of one generic name among synonymous names that may be either sexually or asexually typified. A table is presented that summarizes these recommendations. Among the genera most commonly encountered in this order, Cytospora is recommended over Valsa and Diaporthe over Phomopsis. New combinations are introduced for the oldest epithet of important species in the recommended genus. These include Amphiporthe tiliae, Coryneum lanciforme, Cytospora brevispora, C. ceratosperma, C. cinereostroma, C. eugeniae, C. fallax, C. myrtagena, Diaporthe amaranthophila, D. annonacearum, D. bougainvilleicola, D. caricae-papayae, D. cocoina, D. cucurbitae, D. juniperivora, D. leptostromiformis, D. pterophila, D. theae, D. vitimegaspora, Mastigosporella georgiana, Pilidiella angustispora, P. calamicola, P. pseudogranati, P. stromatica, and P. terminaliae.