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First Report of Cylindrocarpon macrodidymum Associated with Black Foot Diseases of Grapevine in Turkey

Grape (Vitis vinifera) is widely planted and is an economically important crop in Turkey for domestic consumption and export. Black foot disease, caused by Cylindrocarpon macrodidymum Halleen, Schroers & Crous, is a recently identified but worsening problem in vineyards worldwide (3,4). Symptomatic grapevines show reduced vigor, shortened internodes, small leaves with interveinal chlorosis, and necrosis frequently leading to the death of the plants (1). Roots of symptomatic grapevines exhibit black, sunken, necrotic lesions with a reduction in root biomass. Pith of affected vines is discolored (4). During the summers of 2009 and 2010, a survey was carried out in 63 vineyards (4 to 15 years old) in six locations of Ankara Province. We collected 44 samples from roots and crowns of grapevines exhibiting black foot symptoms. In cross section, extensive necrosis at the base of the trunk and brown-black spots in xylem vessels were observed, resembling those previously reported for black foot disease (2,4). Isolations were made from roots, vascular elements, and pith tissue. In this study, 26 isolates were identified as C. macrodidymum on the basis of morphological characteristics. Isolates identified as C. macrodidymum had a dark orange-brown colony color and abundant aerial mycelia when grown on potato dextrose agar. Isolates produced ellipsoid or ovoid microconidia. The macroconidia were one to three septate, straight, and cylindrical. One-septate macroconidia were 24 to 32 × 5 to 7 μm; three-septate macroconidia were 26 to 40 × 5 to 6 μm. Chlamydospores developed in short, intercalary chains. Conidiophores were simple or complex and sporodochial. Isolate identities were confirmed by sequence analysis of the ribosomal DNA internal transcribed spacer (GenBank Accession No. HM245331) with primers ITS1 and ITS4 (4). Isolates had 99% genetic identity with other isolates of C. macrodidymum present in GenBank. In pathogenicity tests, one representative isolate was used to inoculate five grapevine plants. Tests were completed by drench inoculation onto 3-month-old rooted cuttings of cv. Sultana with 25 ml of a conidia suspension (10⁶ conidia ml^–1). Controls were inoculated with an equal volume of sterile distilled water. Plants were incubated for 4 months in a controlled environment facility at 25°C. After 3 to 4 months, inoculations resulted in reduction of root mass, and C. macrodidymum was reisolated from regions of brown streaking in wood and discolored vascular tissue in all inoculated plants, fulfilling Koch's postulates. Control plants were asymptomatic and C. macrodidymum was not recovered from control plants. To our knowledge, this is the first report of the presence of C. macrodidymum causing black foot disease on grapevine in Turkey.

References: (1) S. Alaniz et al. Plant Dis. 93:821, 2009. (2) F. Hallen et al. Stud. Mycol. 50:431, 2004. (3) F. Halleen et al. Phytopathol. Mediterr. 45:S55, 2006. (4) E. Petit and W. D. Gubler. Plant Dis. 89:1051, 2005.