Variation in Virulence in Isolates ofSeptoria nodorum

Abstract

Nine isolates of S. nodorum differed significantly in pathogenicity on 4 wheat [Triticum aestivum] cultivars. Seven isolates were more virulent on ''Blueboy'' than on ''Coker 68-15'' and 2 isolates were more virulent on ''Coker 68-15'' than on ''Blueboy''. The cultivars ''Anderson'' and ''Hadden'' were intermediate in reaction to the 9 isolates. A significant cultivar .times. isolate interaction indicated the presence of specific resistance. Passage of an isolate of S. nodorum from wheat through 3 cycles of inoculation and reisolation on barley decreased the disease (percent leaf area covered by lesions) from 75-35% on wheat and increased the disease on barley from 5-50%. Similarly, passage of a barley isolate through 3 cycles on wheat decreased the disease on barley from 75-25% 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.