First Report of Anthracnose of Salsola tragus Caused by Colletotrichum gloeosporioides in Greece

Abstract

In early October of 2005, dying Salsola tragus L. (Russian thistle, tumbleweed), family Chenopodiaceae, plants were found along the Aegean Sea at Kryopigi Beach, Greece (40°02′29″N, 23°29′02″E, elevation 0 m). All of the 30 to 40 plants in the area were diseased and approximately 80% were dead or dying. All plants were relatively large (approximately 1 m tall × 0.5 m diameter), and living portions of diseased plants were flowering. Dying plants had irregular, necrotic lesions extending the length of the stems. Leaves of these plants were also necrotic. Lesions on stems and leaves were dark brown and usually coalesced. Diseased stem pieces were taken to the European Biological Control Laboratory, USDA, ARS at the American Farm School in Thessaloniki, Greece. There, diseased stem pieces were surface disinfested for 15 min with 0.5% NaOCl and placed on moist filter paper in petri dishes. Numerous, waxy subepidermal acervuli with black setae were observed in all lesions after 2 to 3 days. Conidiophores were simple, short, and erect. Conidia were one-celled, hyaline, ovoid to oblong, falcate to straight, 12.9 to 18.0 × 2.8 to 5.5 μm (mode 16.1 × 4.5 μm). These characters conformed to the description of Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. in Penz. (2). Conidia were placed on modified potato carrot agar and axenic cultures from these isolations were sent to the quarantine facility of the Foreign Disease-Weed Science Research Unit, USDA, ARS, Fort Detrick, MD for testing. On the basis of DNA sequences, two variants within S. tragus have been described in California and named “Type A” and “Type B” (1). Conidia were harvested from 14-day-old cultures grown on 20% V8 juice agar, and healthy stems and leaves of 18 30-day-old plants of S. tragus Type A and 10 Type B plants were spray inoculated with an aqueous conidial suspension (1.0 × 106 conidia/ml plus 0.1% non-ionic surfactant). Three control plants of each type were sprayed with water and surfactant only. Plants were placed in an environmental chamber (18 h of dew in darkness at 25°C). After 1 day, all plants were transferred to a greenhouse (20 to 25°C, 30 to 50% relative humidity, and natural light augmented with 12-h light periods with 500-W sodium vapor lights). Lesions developed on stems of inoculated Type A plants after 5 days. After 14 days, all inoculated Type A plants were dead. Lesions on Type B plants were small and localized; all plants were diseased but no plants died. No symptoms occurred on control plants. C. gloeosporioides was reisolated 14 to 21 days after inoculation from stem pieces of all inoculated plants of both types of S. tragus. This isolate of C. gloeosporioides is a destructive pathogen on S. tragus Type A and is a potential candidate for biological control of this weed in the United States. To our knowledge, this is the first report of anthracnose caused by C. gloeosporioides on S. tragus in Greece. A voucher specimen has been deposited with the U.S. National Fungus Collections, Beltsville, MD (BPI 871126). Nucleotide sequences for the internal transcribed spacers (ITS 1 and 2) were deposited in GenBank (Accession No. DQ344621) and exactly matched sequences of the teleomorph, Glomerella cingulata. References: (1) F. Ryan and D. Ayres. Can. J. Bot. 78:59, 2000. (2) B. C. Sutton. Page 15 in: Colletotrichum Biology, Pathology and Control. J. A. Bailey and M. J. Jeger, eds. CAB International Mycological Institute, Wallingford, UK, 1992.