Damping-Off of Beech Seedlings Caused by Fusarium avenaceum in Italy

During May of 2004, damping-off of an estimated 70% of beech (Fagus sylvatica L.) seedlings was observed in a bare-root forest nursery located in northern Italy. Twenty-eight days after sowing, cotyledonary leaves were chlorotic, wilted, and occasionally desiccated; stem and collars appeared stunted and discolored with yellowish gray-to-brownish longitudinal streaks arising from the foot region, and rootlets were partially to completely rotten. No fruiting bodies were present on or near the damaged regions. Seedling establishment was poor within the disease foci that gradually increased in size. Longitudinal sections through the damaged stems showed dark brown streaks in the vascular tissue, and microscopic examination revealed that vessels frequently contained mycelium. Ten symptomatic plants were selected, and isolations were made from the necrotic margins of stems previously surface sterilized with 1% sodium hypochlorite and thoroughly rinsed, longitudinally cut into two parts 5-mm long, placed on potato dextrose agar (PDA), and incubated at 22 ± 1°C for 5 days in the dark. Although a variety of microorganisms were isolated, Fusarium avenaceum (Fr.:Fr.) Sacc. (1) was always recovered. Artificial inoculations with the fungus were made on 20-day-old, container-grown beech seedlings. The epidermis surrounding the collar was surface sterilized with 1% sodium hypochlorite, rinsed, and gently scraped with a sterile scalpel. After masking the rest of the plant with a plastic sheet, the wound was sprayed with a conidial suspension containing 10³ macroconidia per cm³ in water and sealed with Parafilm. Controls were treated the same way but with sterile water. Each treatment was applied to 10 seedlings and incubated in the greenhouse (20 ± 2°C, 80% relative humidity, and 12 h of natural light per day). After 20 days, wounds treated with F. avenaceum showed necrotic lesions that developed into small patches of dead epidermis. Radial sections through the stem 2 cm above the inoculation site from five plants showed the presence of mycelium in the vessels, from which the fungus was reisolated. Thirty days postinoculation, the remaining five plants showed the same symptoms observed in the nursery, and microscopic observations confirmed the presence of the fungus. No disease symptoms or mycelium were observed in the inner tissues of control plants. The pathogenicity test was repeated twice with the same results. The fungus was not detected by culturing 100 surface-sterilized seeds from the same stock that had been sown in the nursery. F. avenaceum has a broad host range including angiosperms and gymnosperms, and the described symptoms are fairly typical (2). To our knowledge, this is the first report of this disease in Italy. Further research on fungal survivability in nursery soil and plant debris is in progress. The isolate is preserved in the Centraalbureau voor Schimmelcultures (NL) collection as no. 115957. References: (1) C. Booth. Fusarium. Commonwealth Mycological Institute, Kew, UK, 1977. (2) H. Butin. Tree Diseases and Disorders. Oxford University Press, New York, 1995.