State Key Laboratory of Crop Genetics & Germplasm Enhancement, Nanjing Agricultural University, Nanjing 210095, China. Y. Wu and Y. Bao contributed equally to this work.
One Japonica rice landrace, Heikezijing, from the Taihu Lake region of China, exhibits broad-spectrum resistance to rice blast. As characterized in our previous research, a main-effect resistance (R) gene, Pi-hk1, in Heikezijing against five isolates (GD10-279a, JS2004-141-1, JS2004-185, JS90-78, and Hoku1) was roughly mapped on the long arm of chromosome 11. To fine map Pi-hk1, one recombinant inbred line (RIL), RIL72 (F2:8), from the cross between Heikezijing and blast-susceptible variety Suyunuo, was further crossed and backcrossed with Suyunuo to produce a BC1F2 population of 477 individuals. Inoculation experiments with the representative isolate Hoku 1 indicated that RIL72 carries a single dominant R gene for blast resistance. With the help of advanced BC1F3 (915 plants), BC1F4 (4,459 plants), and BC1F5 (2,000 plants) mapping populations, Pi-hk1 was finally mapped to a 107-kb region between molecular markers P3586 and ILP3, and co-segregated with the markers P4098, RM7654, and P4099. By sequence analysis of Heikezijing bacterial artificial chromosome clones covering Pi-hk1 region, 16 predicted genes were identified within this region, including three nucleotide-binding site leucine-rich repeat candidate genes. These results provide essential information for cloning of Pi-hk1 and its application in rice breeding for broad-spectrum blast resistance by marker-assisted selection.