In April 2006, damping-off of common oak (Quercus robur L.) plantlets as much as 3-years-old was observed in a typically declining Q. robur L. forest located in northeastern Italy (Cessalto, VE). Cotyledons on seedlings were chlorotic and wilted and occasionally desiccated. Stems were stunted and discolored with yellowish brown longitudinal streaks starting from the collar. Rootlets were partly rotten and their apices frequently dead (approximately 65%). There were no fruiting bodies on or near the damaged areas. Longitudinal stem sections showed dark brown streaks in the vascular tissue, and microscopic examination revealed that vessels frequently contained mycelium. Twenty plants with these symptoms were selected, and from each of them, isolations were made from surface-sterilized (1% sodium hypochlorite) necrotic margins of stems. Lesions were cut lengthwise into two parts approximately 5 mm long, placed on potato dextrose agar, and incubated at 22 ± 1°C for 5 days in the dark. Among a variety of microorganisms, Cylindrocladiella parva (P.J. Anderson) Boesewinkel was isolated from 12 plants. The epidermis on the collars of 21-day-old, container-grown Q. robur asymptomatic seedlings was surface sterilized with 1% sodium hypochlorite, rinsed in water, and gently scraped (wounded) with a sterile scalpel. After masking the remainder of the plant with a plastic sheet, the wounds were sprayed with a conidial suspension in water (103 conidia/ml) and sealed with Parafilm. Controls were treated the same way but sprayed only with sterile water. Each treatment was replicated on 10 seedlings and incubated in the greenhouse (20 ± 2°C, 80% relative humidity, and 12 h of natural light per day). After 21 days, wounds treated with C. parva developed necrotic lesions that turned into small patches of dead epidermis forming discolored streaks. Radial sections through the stem 15 mm above the inoculation site from five plants showed the presence of mycelium in the vessels from which the fungus was reisolated. Thirty-five days after inoculation, the remaining five plants showed the same symptoms as those observed in the forest and microscopic observations confirmed the presence of the fungus. No disease symptoms or mycelium in the xylem tissue were observed in the control plants. The pathogenicity test was repeated twice with the same results. C. parva is the known causal agent of seedling blight, damping-off, and root rots on a broad host range of monocots and dicots. Detailed information on taxonomic and epidemiological features is available (1). To our knowledge, this is the first report of the disease in Italy where common oak decline is widespread (2). The isolate is preserved in the Centraalbureau voor Schimmelcultures (Baarn, the Netherlands) collection (No. 114857).
References: (1) P. W. Crous and M. J. Wingfield. IMI Descriptions of Fungi and Bacteria. 116:1160, 1993. (2) A. Ragazzi and I. Dellavalle, eds. Decline of Oak Species in Italy. Problems and Perspectives. Accademia Scienze Forestali, Firenze, Italy, 2000.
