Viburnum sargentii Koehne belongs to the family Caprifoliaceae. It is a deciduous shrub that grows in wet mountainous area in Korea, Japan, and China. On July 2011, rust symptoms were observed on V. sargentii Koehne in Balwang mountain, Gangwon Province, Korea, at an altitude of 1,450 meters. The specimen was coded as DUCC506 and used to study in detail. Rust symptoms were present on leaves, floral axes, and petioles. The infected lesions slightly swelled and leaflets and leaves were distorted. These caused sharp bends in the petioles and wart-like galls on twigs. Defoliation and deflowering could result when infection was severe. The first symptom was small and pale yellow spots on the upper surfaces of the leaves. As the spots increased in size, they turned brown and tanned. Bright orange or yellow powdery masses of spores were produced in tiny cup-like structures that appeared on the undersurfaces of leaves and the surface of floral axes and petioles. Aecia were gregarious, cupulate, yellowish, and erumpent with a peridium having a lacerate, somewhat recurved margin. Peridial cells were hyaline to whitish, rhomboidal, 18 to 25 (avg. 21.5) × 15 to 20 (avg. 18) μm, smooth to finely verrucose, and not observed in aecial stage on floral axes and petioles. Aeciospores were globose to ellipsoid, 14 to 16 (avg. 15.4) × 15 to 16.5 (avg. 16) μm, hyaline to yellowish, with many verrucose surface and hyaline walls. These morphological properties correspond to the aecial stage of Uromyces acuminatus (1,4). From extracted genomic DNA, the D1 and D2 region of 28S ribosomal DNA was amplified with LROR (5′- ACCCGCTGAACTTAAGC-3′) and LR4 (5′-ACCAGAGTTTCCTCTGG- 3′) primer set. The 28S rDNA sequence of DUCC506 was deposited in GenBank DNA database under accession number KC570451. A nucleotide sequence similarity search through BLAST in the GenBank database revealed that the DUCC506's 28S rDNA shared 98% (607/622) similarity with that of U. acuminatus LD1005 (GU058004). Aecidium magnatum Arthur is the anamorph of U. acuminatus (2). Aecial and telial hosts of U. acuminatus belong to several families of Angiosperms and Spartina spp., respectively. No telial host was found near the infected aecial host V. sargentii. These morphological and molecular results support the morphological data to identify DUCC506 specimen is A. magnatum. To our knowledge, this is the first report of rust caused by A. magnatum on V. sargentii in Korea or elsewhere in the world. Rust caused by A. viburni was reported on V. sargentii in Korea without any morphological description (3). Peoples in Asia are interested in this host plant as it is used for ornamental and medicinal purpose. Therefore, our report would be useful information for the management of V. sargentii.
References: (1) G. B. Cummins. The Rust Fungi of Cereals, Grasses and Bamboos. Springer-Verlag, New York, 1971. (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. Page 1009. American Phytopathological Society Press, St. Paul, MN, 1989. (3) C. J. Kim. Kor. J. Micorbiol. 1:51, 1963. (4) H. Y. Yun et al. Plant Dis. 94:279, 2010.