Identification of Blast Resistance Genes in Elite Indica-Type Varieties of Rice (Oryza Sativa L.)

Abstract

Eight blast (Magnaporthe grisea) resistance genes - Pia, Pib, Pik-s, Pik-h, Pita, Piz-t, Pi20, and one of three (Pii, Pi3, or Pi5 (t)) were identified in 42 IRRI-bred rice cultivars following a differential system using Philippine blast isolates. Among these genes, 2 genes Pib and one of Pik alleles (Pik-s or Pik-h), were found in almost all IRRI cultivars. The number of resistance genes in each cultivar varied from 2 to 5, and the kinds of gene combination were also limited. This limitation might be due to the gene sources such that IR8, IR24, IR36, or their hybrid progenies were often included in the breeding of these varieties. Using the gene-for-gene theory, this study was carried out in three steps: (1) estimation of genes following the reaction patterns of monogenic lines to blast isolates, (2) genetic analysis using BC1F2 populations with a susceptible variety as recurrent parent, and (3) allelism test with Japanese differential varieties. Through genetic analysis, each investigation's ability to identify resistance genes was demonstrated.