Rudbeckia fulgida (orange coneflower), a flowering plant belonging to the Asteraceae, is increasingly used as a border in parks and gardens. In September 2007, severe outbreaks of a previously unknown powdery mildew were observed on plants in a public park in Torino (northern Italy). More than 90% of the plants were affected by the disease. Both surfaces of leaves of affected plants were covered with white mycelia and conidia. As the disease progressed, infected leaves turned yellow and wilted. Mycelia and conidia also were observed on stems and flower calyxes. Conidia were hyaline, ellipsoid, borne in chains (as many as three to four conidia per chain) and measured 34 × 23 (30 to 39 × 21 to 25) μm. Conidiophores measured 129 × 12 (89 to 181 × 11 to 13) μm and showed a foot cell measuring 88 × 12 (48 to 129 × 11 to 13) μm followed by two shorter cells. Fibrosin bodies were absent. Chasmothecia were not observed in the collected samples. The internal transcribed spacer (ITS) region of rDNA was amplified using the primers ITS4/ITS6 and sequenced. BLASTn analysis (1) of the 619 bp showed a 100% homology with the sequence of Golovinomyces cichoracearum (3). The nucleotide sequence has been assigned GenBank Accession No. EU 233820. Pathogenicity was confirmed through inoculations by gently pressing diseased leaves onto leaves of healthy R. fulgida plants. Twenty plants were inoculated. Fifteen noninoculated plants served as the control. Plants were maintained in a greenhouse at temperatures ranging from 18 to 22°C. Eight days after inoculation, typical symptoms of powdery mildew developed on inoculated plants. The fungus observed on inoculated plants was morphologically identical to that originally observed. Noninoculated plants did not show symptoms. The pathogenicity test was carried out twice. To our knowledge, this is the first report of powdery mildew on R. fulgida in Italy. Powdery mildew on Rudbeckia spp. was previously reported in the United States (4), Poland, and more recently, India and Switzerland. Particularly, in Switzerland the disease has been observed on R. laciniata and R. nitida (2). The economic importance of this disease is currently limited. Voucher specimens are available at the AGROINNOVA Collection, University of Torino.
References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) A. Bolay. Cryptogam. Helv. 20:1, 2005. (3) U. Braun and S. Takamatsu. Schlechtendalia 4:1, 2000. (4) D. F. Farr et al. Page 82 in: Fungi on Plants and Plants Products in the United States. The American Phytopathological Society, St Paul, MN, 1989.
