Catharanthus roseus (periwinkle), a perennial plant belonging to the Apocynaceae family, is grown as a warm-season bedding plant in temperate gardens. This species is characterized by a long flowering period and prized for its white-to-dark pink flowers. In October of 2008, 15% of C. roseus plants in a public garden located in Torino (northern Italy) showed symptoms of a previously unknown blight. When the disease developed, temperatures ranged between 10 and 24°C (average 17.3°C) and plants were being watered through sprinkle irrigation. Necrosis developed on the stems first, eventually spreading to leaf stalks, and the the entire leaf. Subsequently, the pathogen developed a scant, delicate, gray mycelium on affected tissues, particularly diffused on the stems. Severely infected leaves and stems eventually became completely rotted and desiccated. Tissues were excised from diseased leaves, immersed in a solution containing 1% sodium hypochlorite for 10 s, and cultured on potato dextrose agar (PDA) medium. The fungus 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 and irregular, measuring 0.5 to 2.8 × 0.5 to 2.2 (average 1.4 × 1.1) mm. Conidia were smooth, ash colored, ovoid, measuring 8 to 16 × 6 to 10 (average 10 × 7) μm, and similar to those described for Botrytis cinerea (2). The internal transcribed spacer (ITS) region of rDNA was amplified with primers ITS4/ITS6 and sequenced. BLAST analysis (1) of the 780-bp segment showed a 100% homology with the sequence of Botryotinia fuckeliana (perfect stage of B. cinerea). The nucleotide sequence has been assigned GenBank Accession No. FJ486271. Pathogenicity tests were performed by placing numerous fragments of PDA cultures on leaves of healthy, potted, 8-month-old C. roseus plants. Plants inoculated with PDA alone served as controls. Three plants per treatment were used. Plants were covered with plastic bags for 5 days after inoculation and maintained in a greenhouse at temperatures ranging between 18 and 25°C. The first foliar lesions developed on leaves 5 days after inoculation, whereas control plants remained healthy. B. cinerea was consistently reisolated from these lesions. The pathogenicity test was completed twice. To our knowledge, this is the first report of the presence of B. cinerea on C. roseus in Italy. The same disease was previously reported in many countries including the United States (3) and Taiwan (4).
References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) H. L. Barnett and B. B. Hunter. Illustrated Genera of Imperfect Fungi. Burgess Publishing Company, Minneapolis, MN, 1972. (3) M. L. Daughtrey et al. Compendium of Flowering Potted Plant Diseases. The American Phytopathological Society, St Paul, MN, 1995. (4) W. Ou-Yang and W. S. Wu. Plant Pathol. Bull. 7:147, 1998.
