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First Report of Leaf Spot Caused by Colletotrichum cf. linicola on Field Bindweed in Turkey

Field bindweed (Convolvulus arvensis L., Convolvulaceae) is one of the most problematic weeds in the world (1) and a target of biological control efforts (2). In the summer of 2006, dying field bindweed plants were found in a wheat field near Bafra, Turkey (41°21.197′N, 36°12.524′E). Plants had water-soaked lesions that developed into necrotic leaf spots on most of the leaves, particularly along the leaf margins, and on some stems. In most cases, the leaf spots coalesced, causing the leaves and later plants to wilt and die. Diseased leaves and stems were taken to the Phytopathology Laboratory of the Faculty of Agriculture, Ondokuz Mayis University, Samsun, Turkey. Diseased tissue was surface disinfested and placed on moist filter paper in petri dishes. Numerous acervuli with setae and conidia typical of a Colletotrichum sp. were observed after 2 to 5 days. A fungus, designated 06-01, was isolated from the diseased leaves. Stems and leaves of seven 12-week-old plants were spray inoculated in the laboratory with an aqueous suspension of conidia (10⁶ spores per ml; 10 ml per plant) harvested from 6- to 8-day-old cultures grown on malt extract agar. The plants and two noninoculated checks were placed in a dew chamber at 22°C in darkness and continuous dew. After 48 h, plants from the dew chamber were moved to a greenhouse bench. All plants were watered twice daily. Symptoms were observed 5 days after inoculation. No symptoms were observed on noninoculated plants. Isolate 06-01 was reisolated from all inoculated plants. In the field, 20 inoculated plants became diseased after 20 days with approximately 36% diseased leaf tissue from which 06-01 was consistently reisolated. Diseased tissue and cultures of the fungus were sent to the Foreign Disease-Weed Science Research Unit, USDA/ARS, Fort Detrick, MD. The fungus conformed to the description of Colletotrichum linicola Pethybr. & Laff., which was noted as distinct from C. lini (3). The original description is also different than the description of C. lini (Westerdijk) Tochinai by Sutton (4). Acervuli were sparse, subepidermal, and erumpent. Conidia were hyaline, oblong or cylindrical or somewhat spindle-shaped with dull-pointed ends, guttulate, and 14 to 19 × 4 to 5 μm (mean 17 × 4 μm). Conidiophores were short, simple, hyaline, and emerged from subepidermal stroma. Setae were simple, erect, 3-septate, and dark with hyaline tips. DNA sequences were obtained for the internal transcribed spacer regions (GenBank Accession No. EU000060) and compared with other sequences in GenBank. Sequences from 06-01 matched 100% with one isolate of C. linicola and 99% with two other isolates of C. linicola. These isolates formed a unique clade. However, 06-01 was also 99% identical to other species of Colletotrichum. Thus, species identification is inconclusive. Isolate 06-01 is a destructive pathogen on field bindweed, and severe disease can be produced by inoculation of foliage with an aqueous suspension of conidia. To our knowledge, this is the first report of Colletotrichum on field bindweed. A voucher specimen has been deposited with the U.S. National Fungus Collections (BPI 878174).

References: (1) L. Holm et al. The World's Worst Weeds. University Hawaii Press, Honolulu, Hawaii, 1977. (2) G. Defago et al. BioControl 46:157, 2001. (3) G. H. Pethybridge and H. A. Lafferty. Sci. Proc. R. Dublin Soc. 15:359, 1918. (4) B. C. Sutton. The Coelomycetes. Commonw. Mycol. Inst., Kew, England, 1980.