Technical Abstract: The Pi-ta gene in rice prevents the infection of the fungal pathogen Magnaporthe oryzae races containing the corresponding avirulence gene AVR-Pita. The Pi-ta gene encodes a putative cytoplasmic protein with a centrally localized nucleotide binding site and a leucine rich domain. AVR-Pita is a metalloprotease that is predicted to interact with the product of the Pi-ta gene inside plant cells triggering an active defense response. The US rice cultivar, Katy, containing the Pi-ta gene, was treated with ethyl methyl sulfate, fast neutrons and gamma irradiations to create mutations in the components of Pi-ta-mediated resistance. Forty-two blast susceptible mutants were collected from a total of 15,000 M1 random panicles. The disease susceptibility was verified in 5 M6 mutants that were confirmed to be from Katy using simple sequence repeat markers. To identify natural Pi-ta mutants, 181 rice accessions were identified to contain the Pi-ta gene from a core collection of rice germplasm using a Pi-ta single nucleotide length polymorphism marker. Subsequent inoculations with M. oryzae isolates containing AVR-Pita identified 4 susceptible mutants. Progress on molecular genetic analysis of the Pi-ta-mediated signaling components in these induced and natural mutants will be presented.