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Resistance

Criteria for Identifying Pathogenic Races of Phytophthora fragariae on Selected Strawberry Genotypes. R. D. Milholland, Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616; W. O. Cline, and M. E. Daykin. Research and extension specialist, and Research technician, respectively, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Phytopathology 79:535-538. Accepted for publication 26 October 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-535.

The pathogenicity of 12 isolates of Phytophthora fragariae was evaluated on 13 strawberry genotypes and then separated into seven distinct pathogenic races by their ability to infect and produce oospores in the roots of a set of differential strawberry hosts. The cultivars Aberdeen, Climax, Stelemaster, Surecrop, and Tennessee Beauty, MD683 selection, and the Fragaria chiloensis clone Del Norte are proposed as a new set of differential genotypes for identifying races of Phytophthora fragariae. A disease severity index based on the number of oospores in the root stele and the percentage of roots infected with P. fragariae is used to determine genotype susceptibility.