First report of <i>Phragmidium rubi‐oldhami</i> causing rust disease on <i>Rubus pungens</i> in Korea

Rubus pungens (‘Korean creeping raspberry’; Rosaceae) is a deciduous, broad-leaved tree native to East Asia. Its edible fruit consumed fresh or used as medicinal ingredient for diabetes and asthma (Moon, 1991). In May 2021, symptoms of rust disease were observed on in the Korea National Arboretum, Pocheon, Korea, with incidence 50% amongst 30 plants surveyed. Bright yellow-orange pustules uredinial stages found both sides infected leaves. The often erumpent 1 3 mm diameter (Figure 1). leaves examined under light microscope. Uredinia 2; n = 20) erumpent, round, yellow pale yellow, mostly scattered, rarely grouped 200–536 µm 2). Urediniospores (= 50) hyaline, globose sub-globose (16.0–)18.4–21.2(–23.6) × (12.6–)15.3–18.5(–19.7) (mean 19.8 16.9 µm), an echinulate wall 1.0 thick (Figures 3, 4). Paraphyses (n 30) oblong curved, 56.2–11.1 µm, thin 0.5–1.0 occasionally slightly thickened at apex, 1.2–2.5 5). telial stage was not found. Based morphological characteristics, fungus identified Phragmidium rubi-oldhami Togashi & Y. Maki (Hiratsuka, 1934). To confirm identification rust, genomic DNA extracted from representative specimen (KSNUH1322). Two ribosomal regions amplified, internal transcribed spacer (ITS) primers ITS5u ITS4rust (Pfunder Schürch, 2001) large subunit (LSU) LRust1R LRust3 (Beenken et al., 2012). resulting sequences deposited GenBank (Accession Nos. ON180674 ITS ON170371 LSU). A BLASTn search revealed that Korean isolate had 99.43% identity LSU region only P. sequence Genbank, which obtained China (MG669116). Close identities other species when analysing sequences, however, there no reference rubi-oldhami. maximum likelihood phylogenetic analysis using 6) 7) formed distinct branch among tree. originally described oldhami Japan (Togashi Maki, 1934) has since been recorded R. amabilis, R, thibetanus (Farr Rossman, 2022; Liu 2018; Zhuang Wei, 2009). our knowledge, this first report Korea. Given urediniospores can easily disperse long distances by wind, pose potential risk This work supported Arboretum grant (KNA3-1-10, 21–4) Forest Service,