Identification and isolation of blast resistance genes in three Indica-type rice [Oryza sativa] varieties

Two methods were used to identify blast resistance genes in indica -type varieties and isolate the genes found: one was an inoculation of F3 Iines between indica -type and japonica varieties (Suweon 262 x Reimei) with a common fungus strain (Ken 54-20) and a fungus strain having many virulence genes (AO 14-20) and selection of F3 Iines showing different reactions to the two fungus strains, and the other was selection of F3 Iines showing a 3 : I segregation ratio in the hybrid (Norin 29 x Hokuriku 129 and Norin 22 x sifeng 43) for Ken 54-20. The former method was used to identify and to select the resistance gene brokendown by Ao 14-20 having several number of virulence genes. The latter was to identify and isolate all major genes included in the resistant variety. It was demon-strated that Suweon 262 had Pi-i and an unidentified major gene and at least a minor one, and Hokuriku 129 had two major genes, Pi-i and Pi-b : Sifeng 43 had one major gene Pi-b and at least one minor gene. Minor genes dis-turbed the isolation of major genes in cross combinations of Suweon 262 x Reimei and Norin 29 x Hokuriku 129. It was considered that Hokuriku 129 is heterogeneous at least for Pi-i and Pi-b.