Physiologic Specialization of Pyricularia oryzae in the Philippines. J. M. Bonman, Associate Plant Pathologist, Department of Plant Pathology, International Rice Research Institute, P.O. Box 933, Manila, Philippines. T. I. Vergel De Dios, Research Assistant, and M. M. Khin, Research Scholar, Department of Plant Pathology, International Rice Research Institute, P.O. Box 933, Manila, Philippines. Plant Dis. 70:767-769. Accepted for publication 19 November 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-767.

The rice blast pathogen, Pyricularia oryzae, was collected from various regions in the Philippines and tested on widely grown Philippine cultivars and the International, Japanese, and Korean differential cultivar sets. Isolates with virulence to Philippine IR cultivars were common in samples from lowland areas, where such cultivars are widely grown, but virulence was rare among isolates from Zamboanga del Sur, where upland rice is cultivated. Virulence to C22 was most frequent among Zamboanga del Sur isolates. Virulence to IR56, UPLRi3, and UPLRi5 was rare. Virulence to the newly released cultivars IR58, IR60, and IR62 was present in the fungus population. IR60 and IR62 showed a higher frequency of intermediate reaction types than other IR cultivars. None of the three differential sets could adequately differentiate agriculturally important isolates. Differential sets using established cultivars grown within a geographic region are recommended for practical use in describing the virulence of a blast pathogen population.