Cornus sericea (synonym C. stolonifera), family Cornaceae, is becoming widely used in Italy as ground cover in parks and gardens. In spring 2001, severe outbreaks of a previously unknown disease were observed in several gardens located in northern Italy (Biella Province). Infected leaves displayed small, circular, angular, or irregular necrotic lesions measuring 1 to 3 mm in diameter. Lesions were olivaceous to dark brown with a distinct reddish-to-black margin and surrounded by a chlorotic halo. Lesions eventually coalesced. Under favorable conditions, infected leaves become heavily spotted, dulling their appearance; severe infections resulted in premature defoliation. Pycnidia occurred on diseased leaves, and a fungus identified as Septoria cornicola (1) was consistently isolated on potato dextrose agar (PDA). Dark mycelium grew slowly on PDA and produced abundant pycnidia and conidia. Conidia were holoblastic, hyaline, 2 to 6 septate, 22 to 48 µm (average 35) × 2.2 to 3.6 µm (average 2.5). Pathogenicity tests were performed by inoculating leaves of healthy plants of C. sericea (cv. Flaviramea) with a conidial suspension (1 × 106 CFU/ml). Noninoculated plants served as controls. Plants were covered for 72 h with plastic bags and maintained in a growth chamber at 20°C. The first lesions developed on leaves of inoculated plants after 15 days. From such lesions, S. cornicola was consistently reisolated. No symptoms occurred on control plants. The presence of S. cornicola on C. sericea cv. Flaviramea has been reported in the United States (2) and was observed in 1905 in northeastern Italy on Cornus sanguinea (1), but to our knowledge, this is the first report of septoria leaf spot on C. sericea in Italy.
References: (1) D. F. Farr. Mycologia, 83:611, 1991. (2) D. Neely and D. S. Nolte. J. Arboric. 15:263, 1989.
