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Etiology

Etiology of Rhizoctonia cerealis in Sharp Eyespot of Wheat. P. E. Lipps, Assistant professor, Department of Plant Pathology, Ohio Agricultural Research and Development Center, Wooster 44691; L. J. Herr, professor, Department of Plant Pathology, Ohio Agricultural Research and Development Center, Wooster 44691. Phytopathology 72:1574-1577. Accepted for publication 9 June 1982. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-1574.

Isolates of a Rhizoctonia sp. with binucleate hyphal cells were obtained from sharp eyespot lesions on wheat culms in Ohio. These isolates were compared to known isolates of Rhizoctonia cerealis with reference to cultural morphology, growth rate, hyphal anastomosis, and pathogenicity on wheat. The wheat isolates were similar in cultural morphology and anastomosed with the Ceratobasidium-anastomosis-group 1 (CAG 1) tester isolate of R. cerealis. Growth rates at 23 C on freshly prepared potato-dextrose agar ranged 10.5–11.7 mm/24 hr for the wheat isolates and 7.2–11.0 mm/24 hr for the known isolates of R. cerealis. Inoculated plants developed sharp eyespot lesions on culms and white head symptoms typical of the disease. Virulence ratings for the wheat isolates on inoculated wheat seedlings ranged 2.0–4.4 on a scale of 0 = no symptoms and 5 = dead plants. The rating for the CAG 1 tester isolate (R. cerealis) was 4.0. Representative isolates from CAG 2 through 7 were nonpathogenic (0.0–0.2 ratings). None of the wheat isolates tested caused root rot on wheat seedlings. Based on these results, the pathogenic binucleate isolates from wheat were assigned to R. cerealis.