Identification and molecular mapping of the rice bacterial blight resistance gene allelic to Xa7 from an elite restorer line Zhenhui 084

Rice bacterial blight (BB), caused by Xanthomonas oryzae pv. Oryzae (Xoo) , is a serious disease in rice production worldwide. Rice cv. Zhenhui 084, a newly developed strong indica restorer line, exhibits high resistance to most of the Philippine races of BB and has been widely used in rice hybrids in China; however, the resistance gene has not yet been cloned. Here, we show that the resistance of Zhenhui 084 to Xoo strains is similar to that of IRBB7 containing Xa7 , a durable and broad resistance dominant gene for BB. To map the resistance gene in Zhenhui 084, a F 2 population with 331 highly susceptible individuals derived from a cross between Chenghui 448 and Zhenhui 084 was built. We finely mapped the target R gene to a region between two proximal markers RM20576 and MY4 in rice chromosome 6. A marker-based physical map of chromosome six was used to construct the contig covering the genomic region between two markers RM20576 and MY4. The target gene was assumed to be in an interval of approximate 200 kb, in which 16 candidate genes were predicted. Our findings will greatly facilitate the isolation and characterisation of the target R gene allelic to Xa7 . Additionally, two PCR-based markers, tightly linked to the target R gene locus, will be a useful tool for the marker-assisted selection of the target R gene allelic to Xa7 in breeding programmes.