Abstract
Aggressiveness of a mutant for virulence of rice blast fungus was investigated using isogenic lines of rice which were selected from japonica×indica crosses for incorporating a gene for blast resistance Pi-zt. The mutant fungus strain acquired a specific virulence to Pi-zt, which is resistant to a blast fungus strain Ken 53-33. The mutant blast strain was found to be weaker in aggressiveness on the resistant isolines than on the susceptible ones.
Aggressiveness of three mutant strains isolated from different fungus strains was compared with that of the original strains on five susceptible rice varieties. One of the mutants, Ken 53-33-zt+, was less aggressive than the original strain, but the other two mutants were as much aggressive as their parental strains.
These results were discussed in reference to the gene-for-gene theory for hostpathogen interaction.
