First Report of Sclerotium rolfsii on Sunflower in Italy

During June 1996, 1-month-old sunflower plants (Helianthus annuus. L.) of the cvs. Blue Mix and Romsun × 590, grown at the experimental farm of the Istituto Sperimentale per la Nutrizione delle Piante (Montelibretti, Rome), showed symptoms of wilting, and then gradually dried out. Discolored areas were observed on the crown, where whitish, fan-shaped mycelia were occasionally present. A fungus was isolated on potato dextrose agar from surface-disinfested, diseased stem fragments. It also developed from diseased stem segments incubated in moist chambers. In both cases, round sclerotia developed after 9 days at room temperature. The fungus was identified as Sclerotium rolfsii Sacc. The fungus has been deposited in the ISPaVe collection (no. ER 883). To test pathogenicity, 20-day-old sunflower seedlings of the cvs. Blue Mix and Romsun × 590 were grown singly in an autoclaved peat/soil mixture in 20-cm-diameter plastic pots in a greenhouse at 30 ± 3°C. Plants were inoculated by placing five sclerotia of isolate ER 883 near the crown of each plant about 5 mm below the soil surface. For each cultivar, 10 plants were inoculated and 10 were left uninoculated. Wilting symptoms and stem discoloration appeared after 12 days. Sclerotia were produced at the stem base of some inoculated plants. All inoculated plants died after 20 days. S. rolfsii was consistently reisolated from all the inoculated plants, while no symptoms or signs were observed on the uninoculated plants. This is the first report of S. rolfsii on sunflower in Italy and has important implications for the use of sunflower in crop rotation. An unusual rainy period delayed planting of sunflowers by 1 month in 1996 and this could have favored the disease.