Rosa multiflora Thunb. is a perennial shrub native to eastern Asia. It is commonly found on habitat margins, such as forest edges, streams, and roadsides (CABI n.d.). Due to its aromatic flowers, its usefulness in erosion control, and as a living livestock fence, R. multiflora was introduced to North America as an ornamental in the early 1800's (Hindal and Wong 1988). However, R. multifora, grows rapidly and frequently outcompetes native species, and is therefore considered invasive in North America (Hindal and Wong 1988). In May 2020 Phragmidium rosae-multiflorae Dietel, or rose rust, was collected from R. multiflora in Patton Woods Park, a small residential park in Patton Township, Centre Co., PA, USA (40° 47' 28.40" N; 77° 55' 33.37" W). P. rosae-multiflorae is an autoecious macrocyclic rust fungus known to occur on R. multiflora in the plant's native range. To our knowledge, there are no previously published records of P. rosae-multiflorae in North America. The host exhibited conspicuous aecia on the stems and petioles. Aecia were caeoma form, orange, irregular, erumpant, and pulverulent. Aeciospores were one-celled, verrucose, hyaline to pale yellow, variable in shape, ranging from ellipsoidal to globose (Fig.1), measuring 22.5 ± 3 × 15.5 ± 5 μm (n = 30). Disease symptomology and aecia are consistent with P. rosae-multiflorae Dietel (Wei 1988; Liu et. al 2020). Fungal DNA was extracted from infected petioles. Polymerase chain reaction and sequencing of the 28S region of the nuclear ribosomal DNA repeat was conducted with primers Rust2inv and LR6 following protocols in Aime (2006). The sequence shares 98.77% identity (900 / 487 bp) with P. Rosae-multiflorae from China (MN264739). A voucher specimen has been preserved in the Arthur Fungarium at Purdue University (PUR N23123) with corresponding 28S sequence (GenBank accession #MZ323415). The recorded occurrence of P. rosae-multiflorae on R. multiflora in North America is significant, given the ecological impact of the host plant as an invasive species and need for biocontrol. While no formally published records of this fungus in North America exist, there are putative occurrences across the northeastern United States reported on Global Biodiversity Information Facility (GBIF) and the Maryland Biodiversity Project websites.
Keywords: biocontrol; fungus; invasive; pathogen; rust.