ABSTRACT A genetic cross was performed between a Setaria isolate (pathogenic on foxtail millet) and a Triticum isolate (pathogenic on wheat) of Magnaporthe grisea to elucidate genetic mechanisms of its specific parasitism toward wheat. A total of 80 F(1) progenies were obtained from 10 mature asci containing 8 ascospores. Lesions on wheat leaves produced by the F(1) progenies were classified into four types, which segregated in a 1:1:1:1 ratio. This result suggested that the pathogenicity of the F(1) population on wheat was controlled by two genes located at different loci. This idea was supported by backcross analyses. We designated these loci as Pwt1 and Pwt2. Cytological analyses revealed that Pwt1 and Pwt2 were mainly associated with the hypersensitive reaction and papilla formation, respectively.