Kalanchoe blossfeldiana Poelln., belonging to the Crassulaceae, is a common ornamental houseplant with many cultivars. In May 2010, powdery mildew was observed on about 50% of 3,000 potted kalanchoe ‘Rose Queen’ plants in plastic greenhouses located in Yongin city of central Korea. Farmers producing potted kalanchoes in Yongin region stated that powdery mildew on kalanchoes was mild without causing problems for the last several years. The disease became severe from April 2010 and caused economic losses. The economic and esthetic value was reduced by the unsightly appearance of infected plants with most being unmarketable. Damage due to powdery mildew infections on kalanchoes appeared every year. A representative specimen was deposited in the Korea University herbarium (Accession No. KUS-F24911). Mycelial colonies were white, conspicuous and epiphytic on leaves and stems. Hyphae were septate, branched, and 3 to 6 μm wide. Appressoria on the hyphae were well developed, lobed, and mostly positioned in pairs. Conidiophores were cylindrical, 70 to 145 × 7 to 11.5 μm, and composed of three to four cells. Foot-cells of conidiophores were straight, cylindrical, and 28 to 48 μm long. Conidia produced singly were variable in shape, oval to cylindrical, oval or oblong-elliptical, 30 to 55 × 14 to 24 μm, lacked distinct fibrosin bodies, and showed angular/rectangular wrinkling of outer walls. Germ tubes were produced on the perihilar position of conidia. No chasmothecia were found. The morphological characteristics were consistent with descriptions of Erysiphe sedi U. Braun (1). To confirm the identity of the causal fungus, the complete ITS region of rDNA from KUS-F24911 was amplified with primers ITS5 and P3 as described by Takamatsu et al. (4) and directly sequenced. The resulting sequence was deposited in GenBank (Accession No. JX173288). A GenBank BLAST search using the present data revealed that the ITS sequence shares 100% (552/552 bp) similarity with those of E. sedi on Sedum spp. (Accession Nos. JX173289, JX173290). Pathogenicity was confirmed through inoculation by gently pressing diseased leaves onto leaves of five healthy potted kalanchoe plants. Five non-inoculated plants served as controls. Plants were maintained in a greenhouse at 22 ± 2°C. Inoculated plants developed signs and symptoms after 7 days, whereas the control plants remained symptomless. The fungus present on the inoculated plants was morphologically identical to that originally observed on diseased plants, fulfilling Koch's postulates. E. sedi is also known to infect Kalanchoe pinnata (Lam.) Pers. (= Bryophyllum calycinum Salisb.) in Romania (1,2) and other crassulaceous plants including Sedum spectabile in North America (3). To our knowledge, this is the first report of E. sedi infections of K. blossfeldiana in Korea. This disease seems to be a serious threat to the commercial production of kalanchoe plants which are cultivated under plastic greenhouses of poor ventilation and low light levels in Korea.
References: (1) U. Braun and R. T. A. Cook. Taxonomic Manual of the Erysiphales (Powdery Mildews), CBS Biodiversity Series No. 11. CBS, Utrecht, 2012. (2) D. F. Farr and A. Y. Rossman. Fungal Databases, Systematic Mycology & Microbiology Laboratory, ARS, USDA. Retrieved from http://nt.ars-grin.gov/fungaldatabases/, June 13, 2012. (3) L. Kiss and M. L. Daughtrey. Plant Dis. 85:1207, 2001. (4) S. Takamatsu et al. Mycol. Res. 113:117, 2009.
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