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Blight of English Ivy (Hedera helix) Caused by Sclerotium rolfsii in Sicily

English ivy, Hedera helix L. (Araliaceae), an evergreen climbing vine is widely cultivated as an ornamental and foliage plant. In the summer of 2005, a severe blight of ivy plants trained as topiaries and grown in an open field was observed in a nursery near Giarre (eastern Sicily). Foliage of infected plants appeared lighter green and progressively turned bronze and withered. Eventually, the entire plant collapsed. Foliar symptoms were associated with basal stem and root rot. White, cottony mycelium and numerous sclerotia developed externally on the lower stem and on the soil around the affected plants. The disease was randomly distributed, affecting approximately 5% of plants in a stock of 1,500 English ivy plants. Sclerotium rolfsii Sacc. (teleomorph Athelia rolfsii (Curzi) Tu & Kimbrough) was consistently isolated from symptomatic basal stem tissues by disinfecting in 1% NaOCl and plating on potato dextrose agar (PDA) amended with 100 mg/liter of streptomycin sulfate. The isolated fungus was identified on the basis of morphological and cultural characteristics (2). On PDA, it produced a densely, floccose, white mycelium. Mycelium was septate with clamp connections at hyphal septa. Optimum growth temperature was 30 ± 2°C. Numerous small (0.5 to 1.9 mm in diameter) sclerotia developed on the colony surface; they were spherical, occasionally slightly ellipsoidal, quite uniform in size (modal value of the diameter 1.4 mm), with a smooth surface. The surface color of the sclerotia was initially white, turned to pinkish buff, then to olive-brown, and eventually to clove brown as sclerotia matured. Sclerotia were most numerous in the center as well as close to the edge of petri dishes. Pathogenicity of one isolate obtained from infected plants was confirmed by inoculating 10 1-year-old potted English ivy plants by placing mycelium-infested wheat kernels and sclerotia on the soil surface around the collar of each plant. Ten noninoculated plants served as control. Plants were held in a dew chamber for 48 h at 28°C and subsequently placed in a greenhouse where the temperature ranged between 25 and 31°C. Plants showed wilting within 3 weeks after inoculation. Fans of white mycelium and numerous sclerotia were produced on the basal stem of inoculated test plants. Noninoculated controls remained healthy. S. rolfsii was reisolated from infected plants to fulfill Koch's postulates. English ivy has been already reported as a host of S. rolfsii, the causative agent of southern blight in nurseries of ornamentals (1). However, to our knowledge, this is the first report of southern blight on English ivy in Italy. The disease may have been favored by warm summer temperatures and overwatering with a drip irrigation system.

References: (1) A. R. Chase. Compendium of Ornamental Foliage Plant Diseases. The American Phytopathological Society, St. Paul, MN, 1992. (2) J. E. M. Mordue. Corticium rolfsii. No. 410 in: Description of Pathogenic Fungi and Bacteria. CMI. Kew, Surrey, UK, 1974.