Abstract
In order to know whether or not a simple method in which a formula Ra/Sa×Sv/Rv can be employed for calculation of the mutation frequency for virulence in blast fungus strains, the mixture inoculation effect between original (avirulent) and its mutant (virulent) strains was compared among several fungus strains.
The existence of the mixture inoculation effect including the concentration effect was found in all four fungus strains tested. This leads to the conclusion that the mutation frequency obtained by such a method is slightly over estimated as compared with the actual rate of mutant spores in the spore suspension. Therefore, the mutation frequency calculated by the formula, Ra/Sa×Sv/Rv' must be corrected on the basis of the mixture inoculation effect.
Significant differences among strains were observed in the infectivity on susceptible varieties and in the mutation frequencies from Av-k (avirulent) to Av-k+ (virulent), but not in the mixture inoculation effect. The differences in the infectivity between each original and its virulent mutant were not observed on Av-k allele in the strains used.
