First Report of Sclerotium rolfsii on Juglans in Europe. A. Belisario, Istituto Sperimentale per la Patologia Vegetale, Via C. G. Bertero 22, 00156 Roma, Italy . L. Corazza, Istituto Sperimentale per la Patologia Vegetale, Via C. G. Bertero 22, 00156 Roma, Italy. Plant Dis. 80:824. Accepted for publication 14 May 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0824A.
In the summer of 1995, a rapid dieback of 1-year-old black (Juglans nigra L.) and English walnut (Juglans regia L.) seedlings was observed in central Italy. Diseased seedlings occurred among those raised in an open-field nursery, in a seedbed, and in pots. In the nursery, seedlings of the Northern California black walnut (Juglans hindsii (Jeps.) Jeps. ex R. E. Smith) were also found to be diseased. Dying plants were observed starting from the first half of June. The leaves showed chlorosis and necrosis in quick succession but remained attached. The diseased seedlings often had collar and root rot. In some cases the entire root system was destroyed. Thick, whitish mycelial strands, with scattered brown to blackish sclerotia averaging 1.5 mm in diameter were present. Isolations onto potato dextrose agar (PDA) developed sclerotia within 7 days at 25 ± 2°C in the dark. The fungus was identified as Sclerotium rolfsii Sacc, (anamorph of Athelia rolfsii (Curzi) Tu & Kimbrough) and compared with S. delphinii Welch., a well-known European crown-rot pathogen of iris and other ornamental plants. One-year-old black and English walnut seedlings in 3.5-liter pots were inoculated. A 7-day-old plate of S. rolfsii per pot was mixed with the top 3 cm of soil, coaling well the root collar. Control walnuts were treated with PDA only. Seedlings were kept outside and provided with water supply every other day. Within 90 days, most of the inoculated seedlings showed disease symptoms similar to those observed with natural infection. Black walnut was more susceptible than English walnut. The pathogen was reisolated from the diseased seedlings, thus completing Koch's postulates. In the genus Juglans, the pathogen was recorded only on J. nigra in 1941 in the United Stales (1). This is the first report of S. rolfsii on J. regia and J. hindsii, and its first record on Juglans in Europe. This outbreak might have been favored by greater than normal rainfall and warmer temperatures in late spring and summerReference: (1) W. N. Ezekiel and C. Nelson. Plant Dis. Rep. 12:336, 1941.