European hackberry (Celtis australis L.; Ulmaceae), a semideciduous tree or shrub that produces small edible berries was originally grown in Italy to produce charcoal and timber and was particularly suitable for making whipstocks, carriage wheel spokes, and hoe handles. European hackberry is currently used for reforestation and as shade trees in parks and roadside plantings. Recently, a foliar disease caused by the dematiaceous hyphomycetous fungus Sirosporium celtidis (Biv.-Bern. ex Sprengel) M.B. Ellis on hackberry saplings in a nursery was observed in the Piedmont Region (northern Italy) by Giannetti et al. (2), who referred to it as a rare disease. However, during a survey in the nature reserve of the Anapo River Valley, in the Sicily Region (southern Italy), where European hackberry and a closely related species (C. tournefortii Lam.) grow naturally, most hackberry plants were found to be infected by S. celtidis, with variable intensity. During autumn, symptoms appeared on lower leaf surfaces as reddish brown to dark black-brown subcircular velvety spots (up to 10 to 15 mm wide) surrounded by narrow paler margins that were evenly distributed over the leaf surface and later confluent. Nonspecific symptoms on upper leaf surfaces were visible only in advanced stages and consisted of necrotic areas, usually apical or marginal, that were at first red-brown and later turned gray. A few trees were prematurely defoliated. Usually, however, severely affected leaves were necrotic, withered, and curled but remained attached. Spots on lower leaf surfaces were covered by mycelium, conidiophores, and conidia that corresponded to the description of S. celtidis published by Ellis (1). Conidia were straight, flexuous, occasionally markedly curved or coiled, cylindrical or obclavate, smooth, wrinkled or verrucose, subhyaline to golden or reddish brown, typically multicellular with 1 to 32 transverse septa, and occasionally had longitudinal or oblique septa that were often constricted, more than 100 μm long and up to 5 to 8 μm thick, with an inconspicuous scar at the base. From 1997 to 1999, infection by S. celtidis in the Anapo River Valley occurred each year, probably favored by the moist environment. S. celtidis, first described in Sicily as early as 1815 (1), has been recorded on various hackberry species in many countries, including the United States (3). Apparently this pathogen is of little economic and ecological significance in natural ecosystems; however, the fungus could become a serious problem in nurseries (2).
References: (1) M. B. Ellis. 1963. Mycological Papers, No. 87. Commonw. Mycol. Inst. Kew, England. (2) G. Giannetti et al. Inform. Fitopatol. 49:39, 1999. (3) D. H. Linder. Ann. Mo. Bot. Garden 18:31, 1931.
