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 (BC1F2, BC1F3, and BC1F4), 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.

Fine mapping of a panicle blast resistance gene Pb-bd1 in Japonica landrace Bodao and its application in rice breeding.

BACKGROUND: Rice blast caused by Magnaporthe oryzae is the most devastating disease in rice production. Compared with seedling blast, panicle blast is considered to be more destructive, which can occur without being preceded by severe seedling blast. However, panicle blast resistance research is rarely reported. RESULTS: Bodao, a japonica landrace from Taihu Lake region, showed a high level of panicle blast resistance. In this study, a mapping population of 212 recombination inbreeding lines (RILs) was developed from a cross of Bodao and the susceptible cultivar Suyunuo, and the RILs were evaluated for panicle blast resistance in three trials. Two quantitative trait loci (QTLs) qPb11-1 and qPb6-1 for panicle-blast resistance were identified, including a major QTL qPb11-1 (Pb-bd1) on chromosome 11 of Bodao explaining from 55.31% to 71.68% of the phenotype variance, and a minor QTL qPb6-1 on chromosome 6 of Suyunuo explaining from 3.54% to 6.98% of the phenotype variance. With the various segregation populations, Pb-bd1 was fine mapped in a 40.6 Kb region flanked by markers BS83 and BS98, and six candidate genes were identified within this region, including one gene encoding NAC domain-containing protein, one gene encoding unknown expression proteins, two genes encoding nucleotide binding site-leucine rich repeat (NBS-LRR) type disease resistance proteins, and two genes encoding von Willebrand factor type A (VWA) domain containing proteins. For application in rice breeding, three introgression lines of Pb-bd1with significantly enhanced panicle blast resistance were developed by using molecular assisted method (MAS) from the commercial variety Nanjing46 (NJ46). CONCLUSION: Two QTLs, qPb11-1(Pb-bd1) and qPb6-1 conferring panicle blast resistance, were identified from japonica landrace Bodao and Suyunuo.qPb11-1(Pb-bd1) was fine mapped in a 40.6 Kb region flanked by marker BS83 and BS98. Three introgression lines of Pb-bd1with significantly enhanced panicle blast resistance were developed by MAS method from the commercial variety NJ46. It indicated that Pb-bd1 would be useful gene source in panicle blast resistance breeding.

Characterization and Fine Mapping of a Blast Resistant Gene Pi-jnw1 from the japonica Rice Landrace Jiangnanwan.

Rice blast is a destructive disease caused by Magnaporthe oryzae, and it has a large impact on rice production worldwide. Compared with leaf blast resistance, our understanding of panicle blast resistance is limited. The japonica landrace Jiangnanwan from Taihu Lake region in China shows highly resistance to panicle and leaf blast. In this study, three generations (F2:5, F2:6, F2:7) consisting of 221 RILs (recombination inbreeding lines), developed from the cross of Jiangnanwan and Suyunuo, a susceptible-blast japonica variety, were evaluated for panicle blast resistance in the fields and leaf blast resistance in greenhouse in Nanjing in 2013, 2014 and 2015. A blast resistance gene Pi-jnw1 referring to panicle blast resistance and leaf blast resistance was identified in the three generations and located in the region of RM27273 and RM27381 in chromosome 11. The RIL18 line harboring Pi-jnw1 was selected to be backcrossed with Suyunuo to develop BC2F2 populations. According to the genotyping of 1,150 BC2F2 individuals and panicle blast and leaf blast resistance evaluation of 47 recombinants between RM27150 and RM27381, Pi-jnw1 was finally mapped to the 282 kb region between markers W28 and BS39. This study revealed that Jiangnanwan harboring a panicle blast and leaf blast resistance gene Pi-jnw1 could be a genetic source for breeding new rice cultivars with panicle blast resistance.