First Report of False Rust Caused by Synchytrium minutum on Kudzu in Korea

Kudzu (Pueraria montana var. lobata (Willd.) Maesen & S. Almeida) is a weedy, fabaceous vine that is native to and widely distributed in Asia where it is used for various medicinal purposes such as treating convulsions and fever (2). In the United States, especially the southeastern states, kudzu has become a problematic invasive species that overgrows nearly every substrate on which it occurs. Thus, biological control strategies for controlling this vine are of great interest (4). From October to November 2004, a disease of kudzu was observed in Gwangju and Pyeongtaek in Gyeonggi Province, Korea. The disease appeared on leaves and stems as numerous, discrete, small galls, which enlarged, becoming yellowish orange and eventually erupting into orange, pulverulent sori. Galls were scattered or gregarious, amphigenous, predominately hypophyllous, and sometimes formed along veins as well as on petioles and stems. Sori that formed from galls were solitary but sometimes became confluent, 0.1 to 1 mm in diameter, globose to subglobose, and orange to dark orange; walls were hyaline and thin. Sporangia were copious in sori, typically polyhedral due to compression or globose, 16 to 32 μm in diameter, with smooth, hyaline walls and orange contents. Zoospores were not observed during several failed attempts to germinate sporangia. On the basis of morphological descriptions and keys (3), the fungus was identified as Synchytrium minutum (Pat.) Gäum. (Chytridiomycota), the only species of Synchytrium known to occur on Pueraria (1,3). Comparison with specimens from China and New Guinea (BPI 794733 and BPI 1109528) confirmed this identification. Portions of the nLSU and nSSU rDNA from one of the two Korean specimens deposited as voucher material in the U.S. National Fungus Collections (BPI 880898 and BPI 880899) were sequenced (GenBank Accession Nos. HQ324138 and HQ324139), and a subsequent BLAST search against GenBank confirmed placement in the genus Synchytrium with 95% similarity to S. decipiens. S. minutum is widespread in Asia and Oceania and also has been reported from California (1,3). To our knowledge, this is the first report of S. minutum in Korea (1) and is noteworthy to those interested in biological control of kudzu because S. minutum may have potential in this regard. References: (1) D. F. Farr and A. Y. Rossman. Fungal Databases. Systematic Mycology and Microbiology Laboratory, Retrieved from http://nt.ars-grin.gov/fungaldatabases/ , September, 2010. (2) H. S. Jung. M.S. thesis. Seoul National University, Seoul, Korea, 1997. (3) J. S. Karling. Synchytrium. Academic Press Inc., New York, NY, 1964. (4) M. A. Weaver et al. Biol. Control 50:150, 2009.