Analyses of The pathogenic race mutation In Magnaporthe grisea

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We characterized Japanese rice blast fungus by means of DNA fingerprinting and electrophoretic karyotyping in order to know their genetic backgrounds. Seven Japanese differential strains and 24 field isolates were clustered into 5 clonal lineages, in the DNA fingerprinting analyses using MGR586 and pMG60I5. In JBLA-K04, one of the lineages, all field isolates from various pathogenic races were included, In these field isolates, a relationship between karyotypes and pathogenic races Further analyses using 142 strains, revealed that two major clonal lineages, JBLA-K04 and JBLB-K33. These results suggested that the variation of pathogenicity among Japanese rice blast fungus were derived from mutations including chromosomal rearrangements.We also analyzed a karyotypic mutation in Magnaporthe grisea strain Ina168. This karyotypic mutation generates one additional chromosomal band in the pulsed field separated karyotype. This mutation was characterized to occur at a high rate of 12.5% sponta … More neously, in uni-direction to generate the extra band, by deleting app. 1Mb DNA from a chromosomal band IIIb which comigrates with band IIIa in the wild type strain. rDNA, the gene encodes rRNA which reported to be causes of chromosomal rearrangement in yeasts, were cloned from the strain and analyzed. The gene located on band IIIb, and unit size of the cluster was revealed to be app. 8kb. The size of the rDNA cluster was app. 400kb in both mutant and wild type. We concluded that rDNA cluster was not the cause of the karyotypic mutation. The rDNA was used for detecting chromosomal size variation among field isolates belong to JBLA-K04. We could not detect major size variation, indicating that the cluster would not be responsible for the chromosomal rearrangement in field isolates.A cross-system utilizing Japanese strain was constructed for genetic analyses of avirulrence genes. A genetic analysis of avirulence toward rice variety K59 was performed, and revealed segregation of avirulence : virulence =21 : 8. Less