Fine mapping of a new race-specific blast resistance gene Pi-hk2 in Japonica Heikezijing from Taihu region of China.

Heikezijing, a japonica rice landrace from Taihu region of China, exhibited broad-spectrum resistance to more than 300 isolates of the blast (Magnaporthe oryzae). In our previous research, we fine mapped a broad-spectrum resistance gene Pi-hk1 in chromosome 11. In this research, 2010-9(G1), one of the predominant race of the blast in Taihu Lake region of China, was inoculated into 162 recombinant inbred lines (RILs) and two parents Heikezijing and Suyunuo for mapping the resistance-blast quantitative trait loci (QTLs). Three QTLs Lsqtl4-1, Lsqtl9-1 and Lsqtl11-1 associated with lesion scores were detected on chromosomes 4, 9, and 11 and two QTLs, Lnqtl1-1 and Lnqtl9-1 associated with average lesion number on chromosomes 1 and 9. The QTL Lsqtl9-1 conferring race-specific resistance to 2010-9(G1) at seedling stages showed the logarithm of the odds (LOD) scores of 9.10 and phenotypic variance of 46.19% and might be a major QTL, named as Pi-hk2. The line RIL84 with Pi-hk2 derived from a cross between Heikezijing and Suyunuo was selected as Pi-hk2 gene donor for developing fine mapping populations. According to the resistance evaluation of recombinants of three generations (BC1F2, BC1F3 and BC1F4), Pi-hk2 was finally mapped to 143 kb region between ILP-19 and RM24048, and 18 candidate genes were predicted, including two pleiotropic drug resistance protein 4, one WRKY74, one cytochrome b5-like Heme/Steroid binding domain containing protein, one protein kinase and one ankyrin repeat family protein. These results provide essential information for cloning of Pi-hk2 and its potential utility in breeding resistant rice cultivars by marker-assisted selection.