Fukunishiki and its parental cultivar Zenith were confirmed to have the same major resistance gene Pi-z in common, but the former was less resistant to the blast disease than the latter. In addition to Pi-z, Fukunishiki has one recessive gene, and Zenith one modifier Rb₆, respectively, to control resistance to Ken 53-33. Responses of these two cultivars varied with inoculation methods and with growth conditions, and these two genes sometimes gave segregation ratios different from those that could be expected on the basis of dominancy of Pi-z. These phenomena were explained by the linkage relationships of Pi-z-ws, Pi-z-C and Rb₆-la, of which recombination values were estimated to be 9.0%, 30.4% and 10.5%, respectively. A linear order of these three genes was proposed to be C-ws-Pi-z.
The data of the sheath inoculation suggested that Rb₆ plays an important part, and Pi-z a minor part, respectively, in the resistance of Zenith to isolates of IB-Group. Fukunishiki was significantly more susceptible to IB-Group than Zenith, but seemed to be slightly more resistant than the testers with Pi-z⁺.