Molecular mapping of the Pi2/9 allelic gene Pi2-2 conferring broad-spectrum resistance to Magnaporthe oryzae in the rice cultivar Jefferson
1 Hunan Provincial Key Laboratory of Crop Germplasm Innovation and Utilization, College of Agronomy, College of Bio-Safety Science and Technology, Hunan Agricultural University, Changsha 410128, China
2 State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China
3 State Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan 430070, China
4 Department of Plant Pathology, Ohio State University, Columbus, Ohio 43210, USA
Rice 2012, 5:29 doi:10.1186/1939-8433-5-29Published: 3 October 2012
Utilization of broad-spectrum resistance (R) genes is an effective and economical strategy to control the fungal pathogen Magnaporthe oryzae, the causal agent of the rice blast disease. Among the cloned blast resistance genes, Pi9, Pi2 and Piz-t confer broad-spectrum resistance to diverse M. oryzae isolates and were isolated from the Pi2/9 locus on chromosome 6. Identification and isolation of additional R genes with different resistance spectra from this locus will provide novel genetic resources for better control of this important rice disease.
In this study, we identified a dominant R gene, Pi2-2, at the Pi2/9 locus from Jefferson, an elite U.S. rice cultivar, through genetic and physical mapping. Inoculation tests showed that Jefferson has different resistant specificities to M. oryzae isolates compared rice lines with the Pi9, Pi2 and Piz-t genes. Fine mapping delimited Pi2-2 to a 270-kb interval between the markers AP5659-3 and RM19817, and this interval contains three nucleotide-binding site-leucine-rich repeat (NBS-LRR) genes in the Nipponbare genome. Five bacterial artificial chromosome (BAC) clones spanning the region were identified, and a BAC contig covering the Pi2-2 locus was constructed.
We identified a new allelic gene at the Pi2/9 locus and fine-mapped the gene within a 270-kb region. Our results provide essential information for the isolation of the Pi2-2 gene and tightly linked DNA markers for rice blast resistance breeding.