Platycodon grandiflorum (balloon flower), a perennial plant belonging to the Campanulaceae family, is widely grown as a bedding plant in temperate gardens. This species is characterized by the ability to bloom profusely throughout the summer into early fall and for its white to blue and pink flowers. In September 2008, symptoms of a previously unknown blight were observed in six gardens located in the Biella Province of northern Italy. When the disease developed, temperatures ranged between 15 and 22°C with frequent rains (149.8 mm of rainfall registered in September 2008 by the meteorological station of Oropa, located in the same area in which the disease appeared). Initially, leaves and petioles appeared chlorotic. Subsequently, lesions developed on the stems and flowers were sometimes affected. In each garden examined, approximately 50% of the plants were affected by the disease. A soft, gray mycelium was observed on symptomatic tissues, especially the stems. Severely infected leaves and stems eventually became completely rotted and later desiccated. Diseased tissue was excised from affected leaves, immersed in a solution containing 1% sodium hypochlorite for 10 s, and then cultured on potato dextrose agar (PDA) medium. A fungus developed that produced abundant mycelium on PDA medium when incubated under constant fluorescent light at 22 ± 1°C. Numerous sclerotia were produced on PDA plates incubated for 20 days at 8 ± 1°C. Sclerotia were dark, irregular, and measured 1 to 3.5 × 0.9 to 2.5 (average 2.1 × 1.5) mm. Conidia were smooth, ash colored, unicellular, ovoid, and measured 11 to 19 × 7 to 13 (average 15 × 11) μm. These morphological features were typical of those described for Botrytis cinerea (2). The internal transcribed spacer (ITS) region of rDNA was amplified using primers ITS4/ITS6 and sequenced. BLAST analysis (1) of the 539-bp segment showed 100% similarity with the sequence of Botryotinia fuckeliana (perfect stage of B. cinerea). The nucleotide sequence has been assigned the GenBank Accession No. GQ149480. Pathogenicity tests were performed by placing 1-cm2 fragments removed from PDA cultures of B. cinerea isolated from balloon flower on leaves of healthy potted P. grandiflorum plants (4-month-old). Five fragments were placed on each plant. Plants inoculated with PDA alone served as controls. Ten plants per treatment were used. Plants were covered with plastic bags for 5 days after inoculation and maintained in a greenhouse at temperatures between 18 and 23°C. The first foliar lesions developed on leaves 3 days after inoculation, and after 5 days, 80% of the leaves were severely infected. As the infection progressed after the inoculation, the stems also became infected. Control plants remained healthy. B. cinerea was consistently reisolated from leaf and stem lesions. The pathogenicity test was completed twice. To our knowledge, this is the first report of the presence of B. cinerea on P. grandiflorum in Italy, as well as in Europe. Blight on balloon flower attributed to Botrytis spp. was previously reported in the United States (3).
References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) M. B. Ellis. Dematiaceous Hyphomycetes. Commonwealth Mycological Institute, Kew, England, 1971. (3) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN, 1989.
