Physiological Races of Cercospora oryzae in the Southern United States. D. N. Sah, Graduate Research Assistant, Department of Plant Pathology, Louisiana Agricultural Experiment Station, Louisiana State University Agriculture Center, Baton Rouge 70803. M. C. Rush, Professor, Department of Plant Pathology, Louisiana Agricultural Experiment Station, Louisiana State University Agriculture Center, Baton Rouge 70803. Plant Dis. 72:262-264. Accepted for publication 10 October 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0262.

Single-conidiospore isolates of Cercospora oryzae were obtained from leaf and sheath samples of rice (Oryzae sativa) collected from rice-growing regions of Louisiana and Arkansas, and one isolate was obtained from Texas. Eight differential cultivars (Nira, Mars, Kamrose, Rexoro, Shoemed, Zenith, Bluerose, and Fortuna) were inoculated with conidial suspensions from each isolate 4 wk after planting, then evaluated for disease reaction 3 wk later. Forty-three races in six physiologic race groups were identified among 76 isolates. The recently released cultivar Mars, which has vertical resistance to C. oryzae, was found to be susceptible to 18 of the 43 races. The weed form of rice known as Louisiana red rice was resistant to all 76 isolates tested.