Physiologic Specialization ofPyricularia oryzaein the Philippines

equivalent for the purposes of this study. Bonman, J. M., Vergel de Dios, T. I., and Khin, M. M. 1986. Physiologic specialization of All cultures were maintained initially Pyricularia oryzae in the Philippines. Plant Disease 70:767-769. in prune agar slants. For long-term The rice blast pathogen, Pyricularia oryzae, was collected from various regions in the Philippines storage, sorghum grains were used as a and tested on widely grown Philippine cultivars and the International, Japanese, and Korean substrate. The grains were steeped, differential cultivar sets. Isolates with virulence to Philippine IR cultivars were common in samples boiled, and autoclaved on two consecutive from lowland areas, where such cultivars are widely grown, but virulence was rare among isolates days. The grains were seeded with the from Zamboanga del Sur, where upland rice is cultivated. Virulence to C22 was most frequent fungus and incubated at 25-28 C until all among Zamboanga del Sur isolates. Virulence to IR56, UPLRi3, and UPLRi5 was rare. Virulence grains were colonized. The colonized to the newly released cultivars IR58, IR60, and IR62 was present in the fungus population. IR60 grains were dried at 40 C for 24 hr, and IR62 showed a higher frequency of intermediate reaction types than other IR cultivars. None transferred to a vial of silica gel, and of the three differential sets could adequately differentiate agriculturally important isolates. stored at 4 C. These colonized grains Differential sets using established cultivars grown within a geographic region are recommended for were used as stock cultures for all retested practical use in describing the virulence of a blast pathogen population. isolates.