Identification of a new race in Pyrenophora tritici-repentis: Implications for the current pathotype classification system

Pyrenophora tritici-repentis induces necrosis and chlorosis in its wheat host. Isolates of the fungus have been grouped into four pathotypes based on their ability to cause necrosis and chlorosis in differential hexaploid wheat genotypes. Virulence tests on 39 isolates recovered from samples collected in eastern Algeria indicated that these isolates had a virulence pattern different from those reported to date. All of the isolates from the Algerian collection were similar to those of pathotype 3, as they caused chlorosis but not necrosis in differential hexaploid wheats; however, the Algerian isolates induced chlorosis in cv. Katepwa but not in line 6B365, which is used to differentiate isolates of pathotype 3 (virulent on 6B365) from those of pathotye 2 (avirulent on 6B365). A race designation is proposed to describe isolates of P. tritici-repentis on the basis of their virulence on differential wheat lines, and not only on the necrosis-chlorosis symptoms they induce in Glenlea and 6B365, a system which allows a theoretical limit of only four pathotypes. Isolates originally ascribed to pathotypes 1, 2, 3, and 4 now represent races 1,2,3, and 4, respectively. The isolates from eastern Algeria described in this study represent race 5. Isolates of race 5 produced the Ptr-necrosis toxin in culture. A wheat accession (line 6B662), previously known to be resistant to isolates from all pathotypes, developed chlorosis to race 5, suggesting the potential of this pathogen to overcome resistance of its host.