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 the Taihu region of China, exhibited broad-spectrum resistance to more than 300 isolates of the blast pathogen (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 races of blast in the Taihu Lake region of China, was inoculated into 162 recombinant inbred lines (RIL) and two parents, Heikezijing and Suyunuo, for mapping the resistance-blast quantitative trait loci (QTL). Three QTL (Lsqtl4-1, Lsqtl9-1, and Lsqtl11-1) associated with lesion scores were detected on chromosomes 4, 9, and 11 and two QTL (Lnqtl1-1 and Lnqtl9-1) associated with average lesion numbers were detected on chromosomes 1 and 9. The QTL Lsqtl9-1 conferring race-specific resistance to 2010-9(G1) at seedling stages showed logarithm of the odds scores of 9.10 and phenotypic variance of 46.19% and might be a major QTL, named 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 (BC1 F2 , BC1 F3 , and BC1 F4 ), Pi-hk2 was finally mapped to a 143-kb region between ILP-19 and RM24048, and 18 candidate genes were predicted, including genes that encode pleiotropic drug resistance protein 4 (n = 2), WRKY74 (n = 1), cytochrome b5-like heme/steroid-binding domain containing protein (n = 1), protein kinase (n = 1), and ankyrin repeat family protein (n = 1). These results provide essential information for cloning of Pi-hk2 and its potential utility in breeding resistant rice cultivars by marker-assisted selection.