Genetic and breeding analysis of blast resistance in elite indica-type rice (Oryza sativa L.) bred in International Rice Research Institute

Using a new differential system which is based on the gene-for-gene relationship between rice resistance genes and blast races, at least seven kinds of genes, Pi20, Pita, Pik(dagger) (one of the Pik allele genes except for Pik-s), Pik-s, Pib, Piz-t, and PH or Pi3, were estimated.in 42 International Rice Research Institute (IRRI)-bred rice (Oryza sativa L.) varieties using 14 blast isolates from the Philippines. Moreover, genetic analyses based on the segregation of BC1F2 populations derived from the crosses between IRRI varieties and susceptible rice, CO39, as recurrent parents, and allelism tests with differential varieties, were performed to identify and confirm these estimated genes using 10 varieties among them. A total of 7 genes, Pi20, Pita, Pik(dagger), Pia, Pib, Pik-s, and Piz-t, were identified. In some varieties, the four genes Pia, Pib, Pik-s, and Piz-t that were not estimated by reaction patterns in the previous analysis, were identified by these genetic analyses. Among the genes identified, Pib and Pik alleles (Pik-s or Pik(dagger)) were considered widely distributed.