Progress and challenges in systematics of downy mildews and white blister rusts: new insights from genes and morphology

Recent advances in the classification of downy mildews and white blister rusts are presented from ordinal to species level. Using molecular data (mainly LSU of nuclear ribosomal DNA and ITS rDNA data, but also cox2, beta-tubulin and NADH genes), ordinal, family and generic circumscriptions have been reconsidered and changed during the last years; species circumscription and concepts are also changing. These rearrangements also lead to a reevaluation of the traditional morphological characters used for classification. The recent changes have various implications for applied sciences (phytopathology, molecular biology) mainly at the species level; besides name changes for some taxa, revised species circumscriptions and improved species identification using genetic markers have important consequences on host ranges, source inocula and risk assessment of phytopathologically important taxa. However, there are also some substantial unresolved problems which need to be addressed in the future with new data and methods. These include the systematic position of some rarely sampled taxa, the phylogenetic relationships of the main downy mildew lineages to each other, more detailed molecular studies on speciation processes to develop appropriate sound species concepts and circumscriptions, and the development of a molecular bar coding system for downy mildews enabling reliable species identification. Applying molecular methods has the potential to greatly enhance our knowledge on the overall biodiversity of downy mildews.