First Report of Leaf Spot Caused by Phoma multirostrata on Fuchsia × hybrida in Italy.

Abstract

Fuchsia × hybrida (Onagraceae) is widely used in gardens and very much appreciated as a potted plant. During the summer of 2008, a severe foliar disease was observed on 1- to 2-year-old plants in several gardens located near Biella (northern Italy). Small necrotic spots were observed on the upper and lower sides of infected leaves. Spots enlarged to form round areas of 2 to 12 mm in diameter and were well defined by a brown-purple margin at temperatures between 15 and 25°C. Severely infected leaves wilted and abscised as disease progressed. The disease occurred on 100% of the plants and at least 30% of the leaf surface was affected. Stems and flowers were not affected by the disease. A fungus was consistently isolated from infected leaves on potato dextrose agar amended with 25 mg/liter of streptomycin. The fungus was grown on leaf extract agar, including 30 g of autoclaved fuchsia leaves per liter, and maintained at 22°C (12-h light, 12-h dark). After 30 days, black pycnidia 150 to 450 μm in diameter developed, releasing abundant hyaline, elliptical, nonseptate conidia measuring 5.6 to 14.3 (10.3) × 1.9 to 5.6 (3.5) μm. On the basis of these morphological characteristics, the fungus was identified as a Phoma sp. (2). The internal transcribed spacer (ITS) region of rDNA of the isolate coded FuHy1 was amplified using primers ITS4/ITS6 (3) and sequenced. BLAST analysis (1) of the 488-bp segment obtained showed an E-value of 0.0 with Phoma multirostrata. The nucleotide sequence has been assigned GenBank Accession No. GU220539. Pathogenicity tests were performed by spraying leaves of healthy 6-month-old potted Fuchsia × hybrida plants with a spore and mycelial suspension (1 × 106 spores or mycelial fragments per milliliter). Noninoculated plants sprayed with water served as controls. Five plants were used for each treatment. Plants were covered with plastic bags for 5 days after inoculation and kept under greenhouse conditions at 20 to 24°C. Symptoms previously described developed on leaves 12 days after inoculation, whereas control plants remained healthy. The fungus was consistently reisolated from the lesions of the inoculated plants. The pathogenicity test was carried out twice. To our knowledge, this is the first report of the presence of P. multirostrata on fuchsia in Italy as well as worldwide. The importance of the disease is still limited in Italy.