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First Report of Rust Caused by Tranzschelia discolor on Peach (Prunus persica) in Korea

Shin, H. D., Lee, S. H., Jeon, C. H., Choi, W. I.
Plant disease 2019 v.103 no.4 pp. 764
Prunus persica, Tranzschelia discolor, cinnamon, defoliation, genes, herbaria, host plants, internal transcribed spacers, leaves, oligodeoxyribonucleotides, ornamental trees, parks, peaches, plant pathogenic fungi, polymerase chain reaction, ribosomal DNA, ribosomal RNA, rust diseases, sequence analysis, type collections, urediniospores, Korean Peninsula
Peach (Prunus persica [L.] Batsch) is grown as an economically important fruit tree and also planted as an ornamental in parks in Korea. In October 2017, peach trees of unknown variety grown for ornamental purposes in a private garden in Jeju (33°30′01″N, 126°30′40″E) in Korea were found to be infected with a rust fungus. All three trees exhibited disease symptoms. The lower surfaces of the infected leaves were dotted with cinnamon brown pustules, exhibiting pale greenish to yellowish angular spots on the corresponding upper surface. Severe infection often resulted in early defoliation and poor growth. Two representative voucher specimens were deposited in the Korea University herbarium (accession nos. KUS-F30251 and F30409). Uredinia were hypophyllous, scattered or partly gregarious, cinnamon brown, erumpent, and 120 to 300 μm in diameter. Urediniospores were ellipsoid to obovoid but somewhat irregular in shape, pale brown, verrucose or echinulate in the lower half and less ornamented in the upper half, 28 to 42 μm long with 3 to 7 μm thick-walled at apex and 14 to 22 μm wide including 1 to 2 μm thick-walled at lateral side, and accompanied with colorless capitate paraphyses more or less thickened at the apex. No telia were detected from infected leaves collected in October and December 2017 and March 2018. This species is known to overwinter in its uredinial rust stage in Korea. Based on the morphological characteristics, the rust was identified as Tranzschelia discolor (Fuckel) Tranzschel & Litv., as described by Hiratsuka et al. (1992). To confirm the morphological identification, genomic DNA was extracted from urediniospores of a dried herbarium specimen, KUS-F30251 (Korea, Jeju, 25 Oct 2017, leg. H.D. Shin). The internal transcribed spacer (5.8S-ITS2) and the partial 28S large subunit (LSU) region of rRNA gene were polymerase chain reaction (PCR) amplified using specific primer pairs Rust2inv/ITS4rust (Aime et al. 2006; Beenken et al. 2012) and universal primers LR0R/LR6 (Vilgalys and Hester 1990), respectively. The PCR product was sequenced and submitted to GenBank (accession nos. MH599069 and MH591760). A BLAST analysis revealed that ITS-28S sequences had 100% homology with the ITS and the LSU sequence of T. discolor on Prunus spp. (DQ995341, DQ354542, and KY764179). T. discolor, T. pruni-spinosae, and T. pruni-persicae (now, Leucotelium pruni-persicae) have been recorded on P. persica (Farr and Rossman 2018). Although Prunus japonica var. nakaii has been recorded in Korea as a host plant of T. discolor, P. persica has never been associated with any rust fungi. To our knowledge, this is the first report of P. persica as a host of T. discolor in Korea. Occurrence of peach rust in Korea poses a potential threat to the production of peach fruits and their use as ornamental trees.