First Report of Rust Caused by Puccinia oxalidis on Oxalis debilis var. corymbosa in Korea

Abstract

Pink woodsorrel, Oxalis debilis var. corymbosa (DC.) Lourteig (syn. O. corymbosa DC.), is native to South America and, given its showy flowers, is a popular plant within the horticultural trade worldwide. In Korea, this plant has been naturalized in the southern part of the Korean peninsula including Jeju Island and is also valued as an ornamental garden plant. In May 2012, we observed several hundred severely rust-infected pink woodsorrel (100% disease incidence) in a public garden located within the city of Seogwipo on Jeju Island, Korea (33°14′20″N, 126°32′40″E). Similar signs with typical rust pustules on this plant species have been frequently found at many localities on Jeju Island as well as mainland South Korea in the city of Mokpo (34°47′51″N, 126°22′30″E). The abaxial surfaces of the infected leaves were covered with powdery golden yellow to orange yellow pustules, markedly detracting from the aesthetic value of the plants and suppressing the plant growth. Severely infected leaves soon withered and died. Twelve voucher specimens were deposited in the Korea University herbarium (KUS), Seoul, Korea. Two representative specimens, KUS-F27920 (Korea, Jeju Island, Seogwipo, 17 July 2014, leg. H. D. Shin) and KUS-F28585 (Korea, Jeju Island, Jeju, 9 December 2014, leg. H.D. Shin) were used for microscopy and molecular analysis. Uredinia (n = 20) were hypophyllous, occasionally cauligenous, orange-yellow, erumpent, and 200 to 350 μm in diameter. About 10 to 30 uredinia were clustered to form a colony of 2 to 5 or up to 8 mm in diameter. Urediniospores (n = 20) were subglobose to ellipsoid but somewhat irregular and variable in shape, yellow-orange, finely echinulate, and 16 to 24 × 14 to 20 μm including 2 μm in wall thickness. The telial stage was not found at sites examined throughout the course of this study, May 2012 to April 2018. Based on morphology, the rust fungus was identified to be Puccinia oxalidis Dietel & Ellis (Hiratsuka et al. 1992). To confirm the morphological identification, genomic DNA was extracted from urediniospores taken from two dried herbarium specimens, and the complete internal transcribed spacer 2 (ITS2) and partial 28S were polymerase chain reaction (PCR) amplified using Rust2inv (Aime et al. 2006) and LR6 primers (Vilgalys and Hester 1990). PCR products were sequenced and deposited in GenBank (MH325473 and MH325474). A BLASTn search revealed that the ITS2-28S sequences resulted in 99 to 100% nucleotide similarity with 28S sequences of P. oxalidis obtained from O. latifolia (KY798348) and an Oxalis sp. (EU851130). P. oxalidis historically has been reported to occur on woodsorrels throughout countries of the western hemisphere and, more recently, has been found in Australia, China, India, Japan, and New Zealand (Farr and Rossman 2018). However, to the best of our knowledge, this is the first report of P. oxalidis infecting an Oxalis (O. debilis var. corymbosa) in Korea. This rust fungus reportedly host-alternates to and produces aecia on Mahonia repens (Lindl.) G. Don (Berberidaceae) in the southwestern United States and northern Mexico (Long and Harsch 1918). Because the alternate host M. repens is outside East Asia, this rust fungus is supposed to survive in the uredinial state in Korea.