First report of Coleosporium montanum on Symphyotrichum in Austria and Europe.
North American species of the genus Symphyotrichum ('asters' or 'Michaelmas daisies') are popular, widely cultivated ornamentals, some of which have become invasive and widely naturalised in Europe, posing threats to natural ecosystems. In October 2017, a rust fungus was collected on naturalised S. lanceolatum in Baumgarten an der March, Lower Austria, and in October 2020 on S. novae-angliae in a garden in St. Willibald, Upper Austria. Infected plants displayed chlorotic spots on the upper leaf surfaces and uredinia with powdery urediniospores on the lower leaf surfaces and stems. The causal pathogen was isolated and identified as Coleosporium montanum based on morphological characteristics and molecular data (sequence analysis of the ITS2-LSU region and phylogenetics). This is thought to be the first report of C. montanum on Symphyotrichum in Austria and Europe.