First report of Puccinia gibberosa on blue oatgrass (Helictotrichon sempervirens) in Canada, with taxonomic revision of the rust species

Helictotrichon sempervirens (blue oatgrass) is a perennial grass widely grown for ornamental use in Canada. Rusted blue oatgrass plants with diseased leaves covered with uredinia were collected from two locations at metropolitan Vancouver, British Columbia (BC), in summer 2022. The rust fungus was identified as Puccinia gibberosa (= P. coronata var. gibberosa) based on combined results of morphological characteristics and molecular analyses. The internal transcribed spacer two (ITS2) and partial large subunit ribosomal DNA were amplified and sequenced. The sequence obtained for the rust fungus showed 99.9% identity with the previously reported P. coronata var. gibberosa from USA. This is the first report of rust caused by P. gibberosa on blue oatgrass in Canada. Evidence from phylogenetic analyses supports the recognition of this rust at the species level. A revised description for P. gibberosa is provided, including synonyms, host range and distribution across the globe, and incorporating comprehensive molecular and morphological results for several North American and European specimens. In addition, a lectotype and an epitype are designated here for the rust species.