Gypsophila paniculata L. (baby's breath, family Caryophyllaceae), native to Central and Eastern Europe, is commonly cultivated as a commercial cut flower crop in greenhouses in Korea. Since 2011, baby's breath cv. Cassiopeia has been observed affected by a powdery mildew with nearly 100% disease incidence at the stage of harvesting in Iksan City. Powdery mildew colonies first appeared as thin white patches on stems and both sides of the leaves. As disease progressed, plants were covered with dense masses of spores, followed by senescence and reduction of quality of cut flowers. A voucher specimen was deposited in the Korea University Herbarium (Accession KUS-F27313). Appressoria were well-developed, multilobed or moderately lobed, and single or opposite in pairs. Conidiophores were straight, 95 to 150 × 7 to 10 μm, and composed of 3 to 4 cells. Foot-cells were cylindric or slightly sinuous at the base and 37 to 53 μm long. Singly produced conidia were cylindrical to oblong-elliptical, 35 to 56 × 12.5 to 18 μm with a length/width ratio of 2.1 to 3.6, devoid of fibrosin bodies, and with angular/rectangular wrinkling of outer walls. Germ tubes were in the perihilar position on conidia, and ended with lobed appressoria. No chasmothecia were found. These structures are typical of the Pseudoidium anamorph of the genus Erysiphe. Specific measurements and host range were consistent with those of E. buhrii U. Braun (2). To confirm identification, the complete internal transcribed spacer (ITS) region of rDNA of isolate KUS-F27313 was amplified with primers ITS1/ITS4, and sequenced directly. The resulting 725-bp sequence was deposited in GenBank (KJ530705). A GenBank BLAST search of the Korean isolate showed 99% similarity with E. buhrii on Acanthophyllum sp. (Caryophyllaceae) from Iran (AB128924). Pathogenicity was confirmed through inoculation by gently dusting conidia onto leaves of five healthy, potted baby's breath cv. Cassiopeia. Five non-inoculated plants served as controls. Inoculated plants were isolated from non-inoculated plants in separate rooms in a greenhouse at 25 ± 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 identical morphologically to that originally observed on diseased plants. Pathogenicity test was repeated twice. The powdery mildew disease caused by E. buhrii on baby's breath has been recorded in the former Soviet Union (Armenia, Kazakhstan, Ukraine), Romania, Turkey, Iran, Mongolia, and Argentina (1,3). Also, a fungus occurring on baby's breath was recorded as Oidium sp. from Japan (4). To our knowledge, this is the first report of powdery mildew caused by E. buhrii on baby's breath in Korea. Powdery mildew infections pose a serious threat to production of this cut flower crop.
References: (1) K. Amano. Host Range and Geographical Distribution of the Powdery Mildew Fungi. Japan Scientific Societies Press, Tokyo, 1986. (2) U. Braun and R. T. A. Cook. Taxonomic Manual of the Erysiphales (Powdery Mildews), CBS Biodiversity Series No. 11. CBS, Utrecht, 2012. (3) D. F. Farr and A. Y. Rossman. Fungal Databases. Syst. Mycol. Microbiol. Lab., Online publication, ARS, USDA, Retrieved February 18, 2014. (4) M. Satou et al. Ann. Phytopathol. Soc. Jpn. 62:541, 1996.