In September 2011, we observed a rust disease affecting about 90% of the leaves of several Rubus fruticosus L. plants at Andong (36°32′12.4″ N, 128°47′20.1″ E), Korea. Pustule formation occurred on cane surfaces and on the undersurfaces of leaves, with yellowing, reddening, and necrosis on the corresponding upper leaf surface. Leaf distortion and senescence also occurred. For light and scanning electron microscopy, uredinia were detached from leaf lesions using a razor blade and then mounted in water without staining. Leaves with lesions were prepared by gold sputtering and then observed by SEM (Hitachi S-2500C microscope, Japan). We observed the development of uredinial colonies with abundant sporulation. The echinulate urediniospores, which were 16.3 to 19.8 × 17.5 to 25.3 μm, were yellowish or occasionally pale brown, with a globose or subglobose shape (2). Telia were a floccose and pale yellowish-buff or almost white. Teliospores were four- to seven-celled. Cells were trapezoid-cylindric, 15 to 40 × 14 to 24 μm, with hyaline walls. Cell wall surface was smooth but often bearing coronate projections or bumps at the top (in apical cells) or upper rim (in intercalary cells). Cell wall thickness was about 0.5 μm at the sides and 2 to 4 μm at the apex; apical pores occurred on short cell-wall projections. Teliospore pedicels were short (0.17 to 1.34 × 0.78 to 1.45 μm), hyaline, and fragile (3). The pathogen was identified as Kuehneola uredinis L. on the basis of morphology (3), and this identification was confirmed by internal transcribed spacer (ITS) analysis. ITS rDNA of the fungus was amplified using the ITS1 and ITS4 primer set (ITS1: 5′-TCCGTAGGTGAACCTGCGG-3′, ITS4: 5′-TCCTCCGCTTATTGATATGC-3′). BLAST analysis of the PCR product showed that the sequence shared 99% identity with the published nucleotide sequences for K. uredinis (Accession No. EU14069). The D1/D2 domain of 28S rDNA was amplified by PCR using the primer pair 5′-ACCCGCTGAAYTTAAGCATAT-3′ and 5′-CTTCCTTGGTCCGTGTTTCAAGACGG-3′ (1). Phylogenetic analysis using 28S rDNA sequences identified the causal fungus as K. uredinis. The identity of the fungus was confirmed as K. uredinis by DNA sequencing; the sequence was 99% similar to that of other K. uredinis (AF426218, AY745696, DQ354551, and GU058013). To the best of our knowledge, this is the first report of an outbreak of cane and leaf rust on Rubus fruticosus Linné caused by K. uredinis in Korea.
References: (1) V. der Auwera et al. FEBS Microbiol. Lett. 338:133, 1994. (2) D. E. Gardner. Plant Dis. 67:963, 1983. (3) G. F. Laundon and A. F. Rainbow. CMI Descriptions of Pathogenic Fungi and Bacteria 202:1, 1969.
