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Ecology and Epidemiology

Variation in Virulence in Isolates of Septoria nodorum. Rebeca C. Rufty, Former graduate student, Department of Crop Science, North Carolina State University, Raleigh 27650, Present address of senior author: Department of Plant Pathology, North Carolina State University; T. T. Hebert(2), and C. F. Murphy(3). (2)(3)Professor, Department of Plant Pathology; and professor, Department of Crop Science, North Carolina State University, Raleigh 27650. Phytopathology 71:593-596. Accepted for publication 6 November 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-593.

Nine isolates of S. nodorum differed significantly in pathogenicity on four wheat cultivars. Seven isolates were more virulent on Blueboy than on Coker 68-15 and two isolates were more virulent on Coker 68-15 than on Blueboy. The cultivars Anderson and Hadden were intermediate in reaction to the nine isolates. A significant cultivar × isolate interaction indicated the presence of specific resistance. Passage of an isolate of S. nodorum from wheat through three cycles of inoculation and reisolation on barley decreased the disease (percent leaf area covered by lesions) from 75 to 35% on wheat and increased the disease on barley from 5 to 50%. Similarly, passage of a barley isolate through three cycles on wheat decreased the disease on barley from 75 to 25% and increased the disease on wheat from 5 to 60%. Both isolates infected species of Agropyron, Elymus, Festuca, Hordeum, Hystrix, Lolium, and Poa. Neither isolate infected oats.