Detection and host specificity of Puccinia digitaticoronata, a new crown rust fungus of Kentucky bluegrass in North America.

In North America, crown rust has emerged as a disease of Kentucky bluegrass (Poa pratensis) and may cause significant damage. After observing crown rust on Poa spp. in Minnesota and on three East Asian buckthorns (Rhamnus crenata, R. davurica, and R. japonica) in North Dakota, we sequenced one to four loci of nine samples for identification and to determine their placement within Puccinia series Coronata. Earlier studies had shown that the P. coronata var. avenae f. sp. avenae clade caused crown rust of Kentucky bluegrass in North America, but phylogenetic analysis identified our samples as a second species, Puccinia digitaticoronata, a crown rust fungus described in 2022 in northeast China and not previously reported in North America. To assess the pathogenicity on potential grass hosts, 787 accessions of 98 species were evaluated with two inocula: one field collection and one pure isolate. Eleven species in Rhamnaceae and Elaeagnaceae were evaluated as potential aecial hosts by inoculation with germinating teliospores. Cereal crops and turfgrasses other than Poa were highly resistant. Twenty-two of the tested gramineous species were susceptible, including twelve Poa spp., and several other native and introduced species in North America. In addition to the three East Asian buckthorn species, the native R. lanceolata and the widespread invasive common buckthorn (R. cathartica) are susceptible and may serve as hosts. Continued observation of Puccinia digitaticornata, a pathogen of the economically significant turfgrass Kentucky bluegrass, will be important to determine the potential impacts of this newly reported rust disease in North America.