The AVR-Pita1 gene,from the Chinese isolate O-137 of Magnaporthe oryzae,is an effector that determines the efficacy of the Pi-ta rice blast resistance gene.In the present study,the avirulence function of AVR-Pita1 was induced by transformation of field isolates(TM2,ZN19,B2 and B8)that originally were collected from the U.S.and are virulent on Pi-ta-carrying rice cultivars.The presence of AVR-Pita1 from O-137 in independent transformants was detected by PCR using AVR-Pita1 specific primers and verified by DNA sequencing and Southern blot analysis using the AVR-Pita1 coding region as a probe.The results of pathogenicity assays showed that the AVR-Pita1-transformed isolates were not able to infect rice cultivars Katy and Drew carrying Pi-ta.Control isolates that were transformed with inserts lacking the AVR-Pita1gene remained virulent.Our findings demonstrate that AVR-Pita1 can be used to induce novel gene-specific blast resistance in nature. The AVR-Pita1 gene, from the Chinese isolate O-137 of Magnaporthe oryzae, is an effector that determines the efficacy of the Pi-ta rice blast resistance gene. In the present study, the avirulence function of AVR-Pita1 was induced by transformation of field isolates (TM2, ZN19, B2 and B8) that originally were collected from the US and are virulent on Pi-ta-carrying rice cultivars. The presence of AVR-Pita1 from O-137 in independent transformants was detected by PCR using AVR -Pita1 specific primers and verified by DNA sequencing and Southern blot analysis using the AVR-Pita1 coding region as a probe. The results of pathogenicity assays showed that the AVR-Pita1-transformed isolates were not able to infect rice cultivars Katy and Drew carrying Pi -ta.Control isolates that were transformed with inserts lacking the AVR-Pita1gene remained virulent. Our findings demonstrate that AVR-Pita1 can be used to induce novel gene-specific blast resistance in nature.