Gene-for-gene relationship for resistance in wheat to isolates of Karnal bunt, Neovossia indica

Reactions to eight isolates of Karnal bunt, Neovossia indica, collected fro m seven different locations in northern India were studied on 13 host lines , including cultivars and breeding lines of Triticum aestivum, Triticum dur um and Triticosecale in all possible combinations. The incidence of Karnal bunt varied from zero in PBW 34 and PBW 248 with isolates Ni8 and Ni2, resp ectively, to as high as 66.8% in a highly susceptible cultivar WL 711 with isolate Ni5. The differences in disease incidence among cultivars and isola tes were highly significant. All the isolates could be distinguished on the basis of differential reactions on one or more of the host lines. Even the most resistant lines of durum (PDW 215), triticale (TL 1210) and wheat (HD 29) could be distinguished by the differential disease reaction with one o r more of the eight isolates. The cultivar-isolate interaction for disease score was highly significant, indicating the probable existence of a gene-f or-gene relationship in this host-pathogen system.