First record of Basidiophora simplex causing downy mildew on Symphiotrichum novae-angliae in Switzerland and Europe.
The New England aster, Symphyotrichum novae-angliae, is a perennial plant native to North America. Cultivars of the species are very popular ornamental plants. In October 2019, and again in August and September 2020, Basidiophora simplex was found causing downy mildew on leaves of S. novae-angliae in public parks and private gardens in Basel, Bern, Rafz, St. Gallen, Winterthur and Zurich, Switzerland. Yellow to brownish red, angular leaf spots limited by veins, with a white lawn of sporangiophores on the abaxial leaf surface are the typical symptoms. Based on the morphological characteristics and molecular data (sequence analysis of the mitochondrial cytochrome oxidase subunit II (cox2) gene region), the causal pathogen corresponds to B. simplex. test. This is thought to be the first report of B. simplex causing downy mildew on S. novae-angliae in Switzerland and Europe.