FIRST REPORT OF A LEAF SPOT CAUSED BY ALTERNARIA SP ON RUDBECKIA FULGIDA IN ITALY
A. Garibaldi, D. Bertetti, G. Gilardi, S. Franco Ortega, M.L. Gullino
In summer 2014, symptoms of a previously unknown leaf spot were observed on about 100 plants of Rudbeckia fulgida (family Asteraceae) growing in a garden located near Biella (northern Italy). Extensive necrosis was observed on the leaves, starting from the basal ones, then on flowers and, as the time went on, on the stems. Eventually leaves and stems wilted and the plant, in full blooming, died. A fungus with a soft, greenish mycelium was consistently isolated on potato dextrose agar (PDA). DNA was extracted using the Nucleospin Plant kit (Macherey Nagel, Germany) and PCR was carried out using ITS1/ITS4 primers. A 473 bp PCR product was sequenced (GenBank accession No. KP941053) and a BLASTn search (Altschul et al., 1997) assigned the sequence to Alternaria sp. In pathogenicity tests, leaves of three healthy plants of R. fulgida were inoculated by spraying a spore and mycelium suspension, 1×105 CFU/ml, of the fungus grown on PDA. Plants treated only with sterile water served as control. Plants were covered with plastic bags for 5 days and maintained at 20 -25°C. About five days post inoculation, the first lesions developed only on inoculated leaves from which an Alternaria sp. was consistently reisolated. This is the first report of Alternaria sp. on R. fulgida in Italy as well as in the world.