Genetical and Physiological Studies on the Species-Specific Parasitism of Magnaporthe Grisea in Gramineous Plants with a Special Reference to a Cross Between the Triticum Isolate and the Setaria Isolate

Pyricularia grisea, the blast fungus of many gramineous plants, includes several host-specific subgroups, A phenogram constructed from rDNA-RFLP data showed that subgroups pathogenic on crops (i.e., rice, foxtail millet, common millet; finger millet, and wheal) and the subgroup pathogenic on crabgrass were classified into different clusters and that this fungeal species has a high diversity. The distribution of MAGGY on the phenogram suggested that this retrotransposon was acquired by a common ancestor of four rDNA types including Oryza isolates (pathogenic oil rice) and Setaria isolates (pathogenic on foxtail millet). To elucidate mechanisms of the species-specific parasitism in gramineous crops classified as a subgroup; we crossed a Setaria isolate with a Triticum isolate (pathogenic on wheat and with no MAGGY), and produced an F-1 population which (i) showed segregation in pathogenicity, phytotoxic compounds, and MAGGY copies, (ii) included mutants in mycelial color: appressorium formation, pathogenicity, and phytotoxic compounds. and (iii) contained many transposed copies of MAGGY. The usefulness of this population for analyses of the species-specific parasitism was discussed.