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 whe at host. Isolates of the fungus have been grouped into four pathotypes based on their ability to cause necrosis and chlorosis in differentia l hexaploid wheat genotypes. Virulence tests on 39 isolates recovered from samples collected in eastern Algeria indicated that these isolate s had a virulence pattern different from those reported to date. All o f the isolates from the Algerian collection were similar to those of p athotype 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 isol ates of pathotype 3 (virulent on 6B365) from those of pathotye 2 (avir ulent on 6B365). A race designation is proposed to describe isolates o f P. tritici-repentis on the basis of their virulence on differential wheat lines, and not only on the necrosis-chlorosis symptoms they indu ce 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. Isolat es of race 5 produced the Ptr-necrosis toxin in culture. A wheat acces sion (line 6B662), previously known to be resistant to isolates from a ll pathotypes, developed chlorosis to race 5, suggesting the potential of this pathogen to overcome resistance of its host.