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Apparent Infection Rates of Pyricularia oryzae on Different Rice Cultivars. R. L. Villareal, Graduate student, Department of Plant Pathology, The Pennsylvania State University, University Park 16802, Current address of senior author: International Rice Research Institute, P. O. Box 933, Manila, Philippines; D. R. MacKenzie(2), R. R. Nelson(3), and W. R. Coffman(4). (2)(3)Associate professor, and Evan Pugh professor, respectively, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; (4)Plant breeder, International Rice Research Institute, P.O. Box 933, Manila, Philippines. Phytopathology 70:1224-1226. Accepted for publication 26 June 1980. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-1224.

Sixteen rice cultivars, reported in the Ivory Coast to exhibit low apparent infection rates (r) or slow lesion development of rice blast, were evaluated at the International Rice Research Institute for their r-values and disease severity ratings. When inoculated with a highly virulent and stable isolate of Pyricularia oryzae, nine of the 16 cultivars showed slow-blasting tendencies as evidenced by reduced r-values (.02–.12) compared to three susceptible check cultivars (r = 0.20–0.23) and terminal disease severities (1.4–16.1% for slow-blasting cultivars vs 88% for the susceptible checks). The five cultivars exhibiting the lowest r-values were re-evaluated in two additional field experiments with similar results. The prospects for developing slow-blasting rice cultivars seem more promising than previously thought.