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Analysis of Host Species Specificity of Magnaporthe grisea Toward Wheat Using a Genetic Cross Between Isolates from Wheat and Foxtail Millet

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 F₁ progenies were obtained from 10 mature asci containing 8 ascospores. Lesions on wheat leaves produced by the F₁ progenies were classified into four types, which segregated in a 1:1:1:1 ratio. This result suggested that the pathogenicity of the F₁ 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.