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First Report of Verticillium Wilt of Sugar Beet, Caused by Verticillium dahliae, in Greece

Wilting sugar beet plants (Beta vulgaris L.) were observed in fields in the Larissa area of central Greece during the summers of 1997 and 1998. Diseased plants, showing general yellowing and epinasty, were sporadically distributed in the fields. As symptoms progressed, the outer leaves wilted and became desiccated. Inner leaves showed marginal and interveinal yellowing. These areas later turned brown and became necrotic. Longitudinal sections of the roots of diseased plants displayed browning of vascular tissues. Fungal isolates obtained from discolored vascular tissues on potato dextrose agar (PDA) medium were identified as Verticillium dahliae based on morphological features (1). Cultures grew moderately fast on PDA at 23°C. Mycelia were hyaline and white to cream colored, becoming black with formation of microsclerotia. Conidiophores were hyaline and verticillately branched, with three to four phialides at each node. Conidia borne on phialides were ellipsoidal to short and cylindrical and mainly one-celled (2.5 to 8 × 1.4 to 3.2 µm). Microsclerotia began to form in 6- to 7-day-old cultures and were dark brown to black and varied in shape and size (25 × 50 to 100 µm diameter). Pathogenicity tests were carried out using the root-dip technique. Two-week-old seedlings (cv. Rizor) were inoculated by dipping roots in an aqueous suspension of 10⁸ conidia per ml for 1 min. Inocula were obtained from 2-week-old cultures grown on PDA at 21°C by adding sterile water to the petri dish, gently shaking to detach conidia from the conidiophores, and filtering through a doublelayer of sterile cheesecloth. Roots of control plants were dipped in distilled water, and seedlings were transplanted to pots and placed in a growth chamber at 23°C with a 12-h photoperiod. Inoculated plants exhibited wilted leaves with interveinal yellowing ≈30 days after inoculation; symptoms were not observed on control plants. V. dahliae was reisolated from artificially inoculated plants. Measurements of yield parameters in healthy and diseased plants showed that the sugar content of diseased roots was significantly reduced, whereas root weight was not affected. Such results agree with a previous report on the effects of the disease on yield parameters (2). However, the disease is of minor importance in Greece mainly because of the low number of infected plants in the fields. This is the first report of Verticillium wilt of sugar beet in Greece.

References: (1) Anonymous. 1971. Verticillium dahliae. No 256: Descriptions of Plant Pathogenic Fungi and Bacteria. Common w. Mycol. Inst., Kew, England. (2) J. O. Gaskill and W. A. Krentzer. Phytopathology 30:769, 1940.