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First Report of Southern Blight on Firewheel Tree, Bay Laurel, Bird of Paradise, Mediterranean Fan Palm, and Liverwort Caused by Sclerotium rolfsii in Italy

During the summer of 2006, a widespread blight was observed on 6-month-old potted plants of firewheel tree (Stenocarpus sinuatus Endl.) and 3-month-old potted plants of bay laurel (Laurus nobilis L.) growing in a nursery in eastern Sicily, Italy. On both species, symptomatic plants initially had sunken, tan lesions at ground level where white mycelia and small (1 to 2 mm in diameter), brown, spherical sclerotia typical of Sclerotium rolfsii Sacc. were formed. As the disease progressed, the mycelia extended up the stem and entire plants collapsed. A sudden wilting affecting 4-month-old potted seedlings of bird of paradise (Strelitzia reginae Aiton) and 5-month-old potted seedlings of Mediterranean fan palm (Chamaerops humilis L.) was occasionally detected in other greenhouses of the same nursery. Liverwort (Marchantia polymorpha L.) was abundantly present on the surfaces of the containers where these plants were grown. Circular and crescent-shaped patches as much as 100 cm in diameter were observed on the massed liverwort plants. In these patches, the liverwort died and sclerotia typical of S. rolfsii were dispersed on white mycelial strands. Symptomatic tissues of the ornamental plants and liverwort were surface disinfested in 1% NaOCl for 1 min, rinsed in sterile water, and plated on potato dextrose agar. Tissues consistently yielded S. rolfsii (teleomorph Athelia rolfsii (Curzi) Tu & Kimbrough) and typical sclerotia with internally differentiated rind, cortex, and medulla were produced within 6 or 7 days (3). Pathogenicity tests were performed by placing 30 sclerotia obtained from 10-day-old cultures in the soil below the crown portion on each of 2-month-old healthy seedlings of Stenocarpus sinuatus, L. nobilis, Strelitzia reginae, and C. humilis (20 seedlings per host). In addition, liverwort growing in 10 pots (7 cm in diameter) was inoculated with 30 sclerotia per pot. For each species, the same number of plants or pots served as control. All ornamental plants and liverwort were maintained in a growth chamber at 25 ± 1°C and enclosed for 7 days in polyethylene bags and then moved to a greenhouse where temperatures ranged from 24 to 28°C. The inoculation trial was repeated once. Symptoms of southern blight developed after 5 to 20 days on all inoculated plants of Stenocarpus sinuatus and sporadically (two to five plants) after 20 days on L. nobilis, Strelitzia reginae, and C. humilis. After 5 days, liverwort in all inoculated pots was colonized and plants died within 12 days. Control plants of all species remained symptomless. S. rolfsii was reisolated from symptomatic plants. S. rolfsii was reported for the first time in Sicily in 2004 on ornamental plants (2). Strelitzia reginae was previously reported as a host of Corticium rolfsii (synonym S. rolfsii) in Portugal (1). To our knowledge, this is the first report of S. rolfsii on Stenocarpus sinuatus, L. nobilis, and C. humilis. In addition, this is the first report of the susceptibility of M. polimorpha to S. rolfsii. Liverwort could provide a food source for the fungus in container-grown nursery plants.

References: (1) M. R. de Sousa Dias and M. T. Lusas. Bol. Soc. Brot. 53:469, 1980. (2) G. Polizzi et al. Plant Dis. 88:310, 2004. (3) Z. K. Punja and A. Damiani. Mycologia 88:694, 1996.