Puccinia coronata var. coronata, a crown rust pathogen of two highly invasive species, is detected across the Midwest and Northeastern United States

Puccinia coronata var. coronata (Pcc) causes crown rust disease of glossy buckthorn (Frangula alnus) and reed canarygrass (Phalaris arundinacea), two highly invasive plant species in North America. Pcc is closely related to major pathogens of cereals, turfgrasses, and forage grasses. It occurs throughout Europe but was first recorded in North America in 2013. Where its hosts co-occur, such as in wetlands in the Twin Cities metro area in Minnesota, we have observed Pcc causing significant infection that results in defoliation and fruit loss in glossy buckthorns and premature leaf senescence in reed canarygrass. In this research, we mapped the distribution of this likely recently introduced rust fungus and provide a description of disease signs and symptoms and pathogen morphology. Samples were acquired by two primary means: by surveys in Minnesota and by correspondence with users of iNaturalist.org, a social network for nature enthusiasts and community scientists. With an Oxford Nanopore MinION, we sequenced two to four loci from twenty-two samples across thirteen states and identified samples by phylogenetic analysis and sequence similarity. Notably, four pure isolates appear to have intragenomic variation of the ITS region. We find that Pcc is present throughout the range of glossy buckthorn in the eastern United States. In Minnesota, Pcc is not common outside the range of glossy buckthorn, however, despite the presence of susceptible grass hosts.