A Twig Canker on English Hawthorn Caused by Coniothyrium sporulosum in Italy

Large, open, irregularly shaped cankers on trunks and twigs of 4- to 12-year-old Crataegus monogyna Jacq. in a mixed oak forest in northern Italy were observed in 2001. Radial sections through the cankers, which often occurred at sites of hail damage from the previous year, showed a brown discoloration in the xylem. Foliage distal to the cankers became chlorotic, wilted, and finally died. When the disease was severe, the entire top of the plant died, and epicormic shoots developed below the cankers. Fruiting bodies were not present on the canker surface, and symptoms were not observed on root collars or roots. Microscopic examination of cankers showed that vessels frequently contained mycelium. Five symptomatic plants were selected, and from each of these plants isolations were made from one canker. Two chips, 3 mm wide, were cut from the necrotic margin of each canker, superficially sterilized with sodium hypochlorite, rinsed, plated on potato dextrose agar (PDA), and incubated at 20 ± 1°C for 8 days in the dark. Among a variety of microorganisms isolated from the necrotic tissues, Fusarium solani (Mart) Sacc. and Coniothyrium sporulosum (Gams & Domsch) van der Aa (1,2) were isolated from 70 and 100% of the chips, respectively. Artificial inoculations were made on 3-year-old, container-grown Crataegus monogyna seedlings obtained from the same seed stock using two isolates each of the two fungi. Where the stems measured 5 mm in diameter, the bark was surface sterilized with sodium hypochlorite, rinsed, wounded with a 2-mm-diameter cork borer, inoculated with a PDA disk containing mycelium and spores, and the wound sealed with Parafilm. Controls were treated the same but using sterile discs of PDA. Each treatment was replicated on five seedlings, incubated in the greenhouse (20 ± 2°C, 80% relative humidity, and 12-h natural light per day) for 60 days. After 20 days, the 10 plants treated with C. sporulosum showed small necrotic lesions, which developed into small patches of dead bark that cracked and formed spindle-shaped cankers. Radial sections through the stem at the canker site from four of the inoculated plants showed the presence of mycelium in the vessels, and C. sporulosum was reisolated from the infected tissue. After 60 days, the cankers measured as much as 22 mm, and the microscopic observations on the remaining six plants confirmed the presence of the fungus. No disease symptoms or mycelium in the inner tissues were observed for control plants, or plants inoculated with Fusarium spp. The present work adds the genus Crataegus to the wide list of hosts (e.g., Rubus, Malus, Quercus, Picea, Taxus, Juniperus, Chamaecyparis, Cupressocyparis, and Mahonia) susceptible to C. sporulosum, which may act as an important pathogen under forest conditions, in orchards, and in breeding programs. References: 1) W. Gams and K. H. Domsch. Nova Hedwigia, 18:1, 1969. 2) I. Vegh and A. Le Berre. Pepinieristes Hort. Maraich. Rev. Hortic. 331:11, 1992.