Aecial and telial host specificity of Puccinia coronata var. coronata, a Eurasian crown rust fungus of two highly invasive wetland species in North America

Authors: GREATENS, NICHOLAS - University Of Minnesota; Jin, Yue; OLIVERA, PABLO - University Of Minnesota

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2023
Publication Date: 1/24/2024
Citation: Greatens, N.J., Jin, Y., Olivera, P.D. 2024. Aecial and telial host specificity of Puccinia coronata var. coronata, a Eurasian crown rust fungus of two highly invasive wetland species in North America. Plant Disease. 108:175-181. https://doi.org/10.1094/PDIS-04-23-0776-RE.
DOI: https://doi.org/10.1094/PDIS-04-23-0776-RE

Interpretive Summary: Puccinia coronata var. coronata, or Pcc, is a crown rust fungus that causes disease in two highly invasive wetland plants in North America, glossy buckthorn (Frangula alnus) and reed canarygrass (Phalaris arundinacea). It is a close relative of major pathogens of oat and barley. Pcc was likely recently introduced from Europe, but it is now widespread across the Midwest and Northeast United States. It is important to investigate the host specificity of introduced pathogens—that is which plants can host the pathogens—in order to assess risk to plants of value, such as cereal crop species, turfgrasses, and native plant species. The previous knowledge regarding the host specificity was specific to Europe and difficult to interpret given recent changes in the classification of crown rust fungi. We found that all cereal crop species and turfgrasses were highly resistant to Pcc. Some other grass and buckthorn species, however, were susceptible, in addition to the two invasive hosts. In total, 13 grass species and four buckthorn species were found to be susceptible, and 35 other diverse grass species were able to host the rust weakly. Notably, some lines of oat, barley, rye, and a model organism, Brachypodium distachyon, were weakly infected by Pcc, raising the possibility of its use in studies of disease resistance. While we expect Pcc to offer some benefit to native ecosystems through causing disease of invasive plants, some other affected species are of concern, and these species should be monitored for disease development. This research will be useful for plant pathologists, ecologists and land managers who work with invasive plant species and land managements.

Technical Abstract: The Eurasian crown rust fungus Puccinia coronata var. coronata (Pcc) was recently reported in North America and is widespread across the Midwest and Northeast United States. Pcc is a close relative of major pathogens of oats, barley, and turfgrasses. It infects two highly invasive wetland plants, glossy buckthorn (Frangula alnus) and reed canarygrass (Phalaris arundinacea) and could be useful as an augmentative biological control agent. We conducted large greenhouse trials to assess the host specificity of Pcc and determine any threat to cultivated cereals, turfgrasses, or native North American species. A total of 1,830 accessions of cereal crop species and 783 accessions of 110 other gramineous species were evaluated. Young plants were first inoculated with diverse uredinial inoculum derived from aecia. Accessions showing sporulation were further tested with pure rust isolates. Sixteen potential aecial hosts in the families Rhamnaceae and Elaeagnaceae were tested for susceptibility through inoculation with germinating teliospores. Thirteen grass species within five genera in the tribe Poeae, Apera, Calamagrostis, Lamarckia, Phalaris, and Puccinellia, and four species in Rhamnaceae, F. californica, F. caroliniana, and Rhamnus lanceolata, were found to be susceptible to Pcc, including some species native to North America. All assessed crop species and turfgrasses were resistant. Limited sporulation was observed on some other accessions within Poeae and four other tribes, Brachypodieae, Bromeae, Meliceae, and Triticeae. Among these species are oats, barley, and Brachypodium distachyon, suggesting the possible use of Pcc in studies of non-host resistance.