Identification And Molecular Mapping Of A Novel Blast Resistance Gene In Rice

Rice blast, caused by Magnaporthe grisea （Hebert） Barr, is one of the most serious and widespread diseases of rice worldwide. The exploitation and utilization of broad-spectrum or durable resistance genes is considered to be a very important and effective way for rice blast control.YNG, a japonica landrice from Yunnan province of China, showed high-level resistance to at least 140 Magnaporthe grisea isolates and had a broader resistance-spectrum than the well-known broad-spectrum resistance genes Pi9, Pi1, Pi2, etc.. In this study, we conducted the genetic analysis of YNG for its blast resistance by inoculating F₂ and F₃ populations derived from a cross LTH x YNG with four differential isolates 99-20-2 （437.5）, 98095 （007.2）, Sichuan 26 （217.3） and 97-3-2 （077.5）, which showed broad-spectrum virulence to 31 monogenic lines jointly developed by IRRI and Japan. The result indicated that the resistance of YNG to isolates 99-20-2 and 98095 could be controlled by one same dominant resistance gene; and that to isolates 97-3-2 and Sichuan 26 by two and three dominant resistance genes, respectively. Therefore, it could be concluded that the resistance donor YNG had at least three resistance genes effective to Magnaporthe grisea isolates.We developed two mapping populations consisting of 876 F₂ plants susceptible to isolate 99-20-2 and 732 F₂ plants susceptible to isolate 98095 respectively, and mapped the gene effective to isolates 99-20-2 and 98095 within a 2.6 cM interval flanked by two SSR markers RM16368 （1.8cM） and RM6770 （0.85cM） on chromosome 4 in both of the two populations by using BSA-RCA （bulked-segregate analysis and recessive-class analysis） strategy and SSR markers, confirming that the resistance of YNG to the two isolates is indeed controlled by one same gene, tentatively named Pi-ym（t） herein. We enlarged the mapping population to 2817 susceptible F₂ plants, and finally fine-mapped the gene within a 65kb interval flanked by two marker ID2736 and CAPs2810. Due to no blast resistance genes located on the short arm of chromosome 4, we deduced the gene Pi-ym（t） is a novel gene. Based on the DNA sequence of Nipponbare, we predicted two candidate genes of Pi-ym（t） by using several gene prediction programs, which lays good foundation for cloning of this gene.