Physiologic Races of Cercospora oryzae in the Philippines. B. A. Estrada, Senior Research Assistant, Department of Plant Pathology, International Rice Research Institute, Los Baños, Laguna, Philippines. L. M. Sanchez, Research Aide, F. L. Nuque, Assistant Plant Pathologist, and J. P. Crill, Plant Pathologist and Head, Department of Plant Pathology, International Rice Research Institute, Los Baños, Laguna, Philippines. Plant Dis. 65:793-795. Accepted for publication 17 February 1981. Copyright 1981 American Phytopathological Society. DOI: 10.1094/PD-65-793.

Because narrow brown leaf spot of rice has become economically important in the Philippines, the reactions of 437 cultivars and breeding lines inoculated with the pathogen Cercospora oryzae were evaluated in the field during the 1978 dry season. From the 3,024 naturally infected cultivars and lines evaluated in 1976 and 1977, 49 were selected and inoculated with C. oryzae in the greenhouse. Eight of these (IR8, Zenith, IR20, Delitus, IR26, Southern Red Rice, IR9129-159-3-2-3-3, and MI 273) were used to differentiate the physiologic races of C. oryzae. The differential varieties were inoculated with isolates of C. oryzae 21 days after seeding and were evaluated 3 wk later. Nineteen races in six race groups were differentiated among 60 cultures. The most important physiologic races were predominantly in newly designated C. oryzae groups A and C (CA and CC). In these two groups, 20 and 18% of the isolates exhibited pathogenicity patterns typical of races CA-95 and CC-31, respectively. The remaining isolates belonged to other races.