Physiologic Differentiation of Wheat Stem Rust on Rye

Abstract

Five self-fertile lines of Secale cereale possessing single genes conferring resistance to stem rust were successfully used to differentiate between strains of Puccinia graminis tritici. In an earlier study four of these lines were shown to differentiate between Australian cultures of P. graminis secalis. Gene H transferred from Wrens-5 rye to one of the five lines appears to be identical with gene Sr27 in Acosta's wheat-Imperial rye translocation stock WRT 238.5.Since, in the past, the genes for resistance in the rye lines have not been closely associated with P. graminis tritici and thus could not have exerted a selection pressure on the fungus, the present results imply that differentiation of a pathogen on host genotypes is, in the first instance, not due to specialization but is an intrinsic phenomenon of host-pathogen relationships. The results further suggest that fungal virulence per se is not associated with reduced fitness.