A Twig Canker on Russian Olive Caused by Phomopsis arnoldiae in Italy
Authors: Montecchio L. , Causin R. , Buresti E. 
Published: May 2007

In June 2002, open, irregularly shaped cankers on stems and twigs of Russian olive (Eleagnus angustifolia L.) were observed in central Italy in two neighboring experimental walnut timber plantations (i.e., Juglans regia L. or J. nigra L. grown with Alnus glutinosa L. and E. angustifolia as nitrogen-fixing plants). Foliage distal to the cankers appeared chlorotic and wilted and occasionally desiccated. No fungal, fruiting bodies were present on or near the canker surface, nor were symptoms were observed on root collars or roots. Radial sections through the cankers revealed dark brown discoloration of xylem, and microscopic examination showed that vessels frequently contained tyloses and mycelium. Four symptomatic plants were selected, and from each of these plants, isolations were made from one canker. From the necrotic margin of each canker previously surface-sterilized with 2% sodium hypochlorite and rinsed, two chips, 3-mm-wide, were placed on potato dextrose agar (PDA) and incubated at 20 ± 1°C for 8 days in the dark. Among a variety of microorganisms isolated were Coniothyrium fuckelii Sacc., Penicillium spp., and Phomopsis arnoldiae B. Sutton (3). Artificial inoculations were made on 3-year-old, container-grown E. angustifolia seedlings using two isolates each of the three fungi. Where the stems measured 5 mm in diameter, the bark was surface sterilized with 2% sodium hypochlorite, rinsed, wounded with a 3-mm-diameter cork borer, inoculated with a PDA disk containing mycelium and spores, and the wound sealed with Parafilm. Controls were treated the same way but with sterile disks of PDA. Each treatment was replicated with 10 seedlings and incubated in the greenhouse (20 ± 2°C, 80% relative humidity, and 12 h of natural light per day) for 60 days. After 30 days, wounds treated with P. arnoldiae showed necrotic lesions that developed into small patches of dead bark that cracked forming cankers. Radial sections through the stem at the canker site from 10 plants (five per isolate) showed the presence of mycelium in the vessels, from which P. arnoldiae was reisolated. After 60 days, the cankers on the remaining 10 plants measured 8 to 14 mm long, and microscopic observations confirmed the presence of the fungus. No disease symptoms or mycelium in the inner tissues were observed in the control plants or in the plants inoculated with the other fungi. The pathogenicity test was repeated twice with the same results. Detailed descriptions of both fungal features in vitro (1,3) and symptoms on larger plants are available (2). To our knowledge, this is the first report of this disease in Italy. Further research is in progress since Russian olive in Italy is frequently grown in the nursery for agronomic purposes because of its nitrogen-fixing ability. Cultures of our isolates of P. arnoldiae, the identification of which was confirmed by the Centraal Bureau voor Schimmelcultures (Utrecht, the Netherlands), are preserved in the herbarium L. Montecchio (LMPa1 and LMPa2) in Padova.

References: (1) R. H. Arnold and J. C. Carter. Mycologia 66:191, 1974. (2) W. A. Sinclair et al. Diseases of Trees and Shrubs. Cornell University Press, Ithaca, NY, 1987. (3) B. C. Sutton. The Coelomycetes. Commonwealth Mycological Institute, Kew, UK, 1980.