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Host Range of Pyrenophora teres f. teres Isolates from California. Matthew P. Brown, Former Graduate Research Assistant, Department of Plant Pathology, University of California, Davis 95616. Brian J. Steffenson, and Robert K. Webster. Assistant Professor, Department of Plant Pathology, North Dakota State University, Fargo 58105; and Professor, Department of Plant Pathology, University of California, Davis, 95616. Plant Dis. 77:942-947. Accepted for publication 14 June 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0942.

The host range of Pyrenophora teres f. teres (net blotch pathogen of barley) isolates from California was studied in the growth chamber and in the field. In the growth chamber, 28 of 43 gramineous species tested were infected by at least one of six P. t. teres isolates originating from Hordeum vulgare or H. murinum subsp. leporinum. Sixty-five of 95 species evaluated in the field also were infected, and 38 new host species were identified. On a generic basis, 15 of the 16 genera tested had susceptible species; this list included four genera (Cynodon, Deschampsia, Hordelymus, and Stipa) never reported to contain hosts for P. t. teres. Among the wild grasses tested, only H. m. leporinum consistently exhibited the netted lesions characteristic of infection by virulent isolates of P. t. teres on susceptible genotypes of H. vulgare. However, an isolate of the pathogen collected from H. m. leporinum exhibited reduced virulence on barley cultivars and may represent pathogenic specialization to the wild host. The net blotch fungus was reisolated from all species infected in the field trial, and these isolates retained their pathogenicity on barley after a single passage through alternative hosts. The broad host range of P. t. teres under field conditions indicates the potential of alternative hosts as sources of primary inoculum; however, their role in actually initiating epidemics of net blotch in California is still unresolved.