Mapping Blast Resistance Genes in Rice Varieties 'Minghui 63' and 'M-202'

Rice blast caused by the fungus Magnaporthe oryzae (syn. Magnaporthe grisea) is one of the most lethal diseases for sustainable rice production worldwide. Blast resistance mediated by major resistance genes is often broken down after a short period of deployment, while minor blast resistance genes, each providing a small effect on disease reactions, are more durable. In the present study, we first evaluated disease reactions of two rice breeding parents 'Minghui 63' and 'M-202' with 11 blast races, IA45, IB1, IB45, IB49, IB54, IC1, IC17, ID1, IE1, IG1, and IH1, commonly present in the United States, under greenhouse conditions using a category disease rating resembling infection types under field conditions. 'Minghui 63' exhibited differential resistance responses in comparison with those of 'M-202' to the tested blast races. A recombinant inbred line (RIL) population of 275 lines from a cross between 'Minghui 63' and 'M-202' was also evaluated with the above-mentioned blast races. The population was genotyped with 156 simple sequence repeat (SSR) and insertion and deletion (Indel) markers. A linkage map with a genetic distance of 1,022.84 cM was constructed using inclusive composite interval mapping (ICIM) software. A total of 10 resistance QTLs, eight from 'Minghui 63' and two from 'M-202', were identified. One major QTL, qBLAST2 on chromosome 2, was identified by seven races/isolates. The remaining nine minor resistance QTLs were mapped on chromosomes 1, 3, 6, 9, 10, 11, and 12. These findings provide useful genetic markers and resources to tag minor blast resistance genes for marker-assisted selection in rice breeding program and for further studies of underlying genes.