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Title: FIRST REPORT OF ANTHRACNOSE OF SALSOLA TRAGUS CAUSED BY COLLETOTRICHUM GLOEOSPORIOIDES IN GREECE

Author
item Berner, Dana
item Cavin, Craig
item McMahon, Michael - Mike
item LOUMBOURDIS, IEROTHEOS - AMERICAN FARM SCHOOL

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2006
Publication Date: 6/22/2006
Citation: Berner, D.K., Cavin, C.A., Mcmahon, M.B., Loumbourdis, I. 2006. First report of anthracnose of salsola tragus caused by colletotrichum gloeosporioides in greece. Plant Disease. 90:971.

Interpretive Summary: Russian thistle or tumbleweed is a problematic invasive weed in the western United States and a target of biological control. In early October 2005, dying tumbleweed plants were found along the Aegean Sea at Kryopigi Beach, Greece. All plants in the area were diseased and about 80% were dead or dying. Diseased stem pieces were taken to the European Biological Control Laboratory, USDA, ARS, at American Farm School in Thessaloniki, Greece. There, a fungus with characters conforming to the description of Colletotrichum gloeosporioides was isolated from the diseased stems. Pure 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. This isolate of C. gloeosporioides is a potential candidate for biological control of this weed in the U.S. To our knowledge, this is the first report of this disease caused by C. gloeosporioides on tumbleweed in Greece.

Technical Abstract: Salsola tragus L. (Russian thistle, tumbleweed), family Chenopodiaceae, is a problematic invasive weed in the western United States and a target of biological control. In early October 2005, dying S. tragus plants were found along the Aegean Sea at Kryopigi Beach, Greece. All 30-40 plants in the area were diseased and about 80% of these were dead or dying. Diseased stem pieces were taken to the European Biological Control Laboratory, USDA, ARS, at American Farm School in Thessaloniki, Greece. There, diseased stem pieces were surface disinfested and placed on moist filter paper in petri dishes. Numerous waxy subepidermal acervuli with black setae were observed in all of the disease lesions after 2-3 days. Conidiophores were simple, short, and erect. Conidia were one-celled, hyaline, ovoid to oblong, falcate to straight, 12.9-18.0 × 2.8-5.5 um (mode 16.1 × 4.5 um). These characters conformed to the description of Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. in Penz. 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 sympatric variants within S. tragus have been described in California and named "Type A" and "Type B." Conidia were harvested from 14-day-old cultures grown on 20% V-8 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 × 10**6 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 dew in darkness at 25 deg C). After one day, all plants were transferred to a greenhouse (20-25 deg C, 30-50% relative humidity, and natural light, augmented with 12-hour light periods with 500 watt sodium vapor lights). Lesions developed on stems of inoculated Type A plants after five 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, 14-21 days after inoculation, from stem pieces of each inoculated plant 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 U.S. 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) have been deposited in GenBank (DQ344621).