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

Authors: GREATENS, NICHOLAS - University Of Minnesota; KELJESKI, NICK - University Of Minnesota; Szabo, Les; Jin, Yue; OLIVERA, PABLO - University Of Minnesota

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2022
Publication Date: 6/26/2023
Citation: Greatens, N.J., Keljeski, N., Szabo, L.J., Jin, Y., Olivera, P.D. 2023. Puccinia coronata var. coronata, a crown rust pathogen of two highly invasive species, is detected across the Midwestand Northeastern United States. Plant Disease. 107(7):2009-2016. https://doi.org/10.1094/pdis-07-22-1711-re.
DOI: https://doi.org/10.1094/pdis-07-22-1711-re

Interpretive Summary: The fungus 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. The disease occurs throughout Europe but was first recorded in the United States in 2016. In wetlands around St. Paul, Minnesota where its telial and aecial hosts co-occur, the rust can cause severe infection that results in defoliation and fruit loss on the aecial host glossy buckthorns and premature leaf senescence on telial host reed canarygrass. Samples were acquired by surveys in Minnesota and correspondence with users of iNaturalist.org, a social network for nature enthusiasts and community scientists. Twenty samples across eleven states were analyzed through sequencing to confirm the pathogen identity. These results and the reports in iNaturalist.org indicated that the rust pathogen is present throughout the range of glossy buckthorn in the eastern United States. In Minnesota, the rust was not common on reed canarygrass outside the range of glossy buckthorn. Intragenomic variation within the ITS region was detected. In this report, we presented a map of the distribution of this likely recently introduced rust fungus associated its telial and aecial hosts and provided further descriptions of the disease and pathogen morphology. This research will be useful for plant pathologists, ecologists and land managers who work with invasive plant species.

Technical Abstract: 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 the United States in 2016. In wetlands around St. Paul, Minnesota where its hosts co-occur, Pcc causes significant infection that results in defoliation and fruit loss in glossy buckthorns and premature leaf senescence in reed canarygrass. Here we map the distribution of this likely recently introduced rust fungus and provide an updated description of disease symptoms and signs and pathogen morphology. Samples were acquired by two primary means: by surveys in Minnesota and 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 samples across eleven states. Samples were identified by phylogenetic analysis and sequence similarity. Notably, four pure isolates appear to have intragenomic variation within the ITS region, a phenomenon not uncommon in fungi, but scarcely examined in rust fungi. 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.