Characterization of resistance genes to rice blast fungus Magnaporthe oryzae in a Green Revolution rice variety

The indica rice variety Dee Geo Woo Gen (DGWG) was the source of the semidwarf gene (SD1) which played an important role in the Green Revolution. In the present study, resistance (R) genes to the US race (isolate) IB54 of Magnaporthe oryzae, causal agent of rice blast disease, was investigated. Two recombinant inbred line mapping populations, consisting of 175 and 224 individuals derived from crosses of DGWG with the straw hull weedy rice type PI653435 (AR-2001-1135; S population) and the black hull type PI653419 (MS-1996-9; B population), respectively, were used for mapping blast R genes and quantitative trait loci (QTLs). Two high-resolution linkage maps with 6,513 (S population) and 14,382 (B population) single nucleotide polymorphic markers derived from genotypingby-sequencing data were used to map R genes. Two partial resistance QTLs, qBR1.1 and qBR6.1, and one major resistance QTL, qBR11.1, were identified in the B population. One partial resistance QTL, qBR6.1, and one major resistance QTL, qBR11.1, were confirmed with the S population. The total phenotypic variation of three resistance QTLs was 51 %, ranging from 1.12 to 47.62 %, in the B population. All three resistance QTLs were localized to relatively small genomic regions. The major resistance QTL, qBR11.1, was mapped to a 129-kb region on chromosome 11 near nine known blast R genes. Within this 129-kb region, three genes encoding putative nucleotide-binding site and leucine-rich repeat (LRR) disease resistance proteins and three genes encoding WRKY transcription factors WRKY61, WRKY63, and WRKY41 were identified as candidate genes of qBR11.1 and tentatively designated as Pi66(t). Identification of blast R genes in DGWG should help continued deployment of useful genes for improving crop productivity and resistance to rice blast disease.