Genetic Analysis And Mapping Of A Broad-spectrum Resistance Gene To Rice Blast (Magnaporthe Grisea)

Rice blast, caused by the fungus Magnaporthe grisea, is one of the most serious and widespread diseases of rice (Oryza sativa L.) all over the world. In China, rice blast is considered as one of the most harmful diseases. To identify and use the broad-spectrum or durable resistance gene(s) is consided very important and effective way to control rice blast disease. Gu-mei 4 (GM4), a native variety from Sichuan, China, was identified in different disease nurseries for more than 20 years, and was characterized of broad-spectrum and durable resistance to blast. GM4 was inoculated with 30 blast isolates collected from different rice regions of China, Thailand and French. The results showed that GM4 could resist 29 of 30 isolates tested. Also the resistance spectrum of GM4 is broader than that of gene Pi-1, Pi-2, Pi-3.The F1, F2, BC1, BC1F2 from the crosses between GM4 and susceptible verieties Cpslo17, Maratellu Suyunuo were obtained. Both parents and partial populations were sprayed by 7 isolates CH109, CH199, CH63, CH174, CH13K 101/1/1, 101/4/8, respectively. The inoculation results showed that blast resistance of GM4 was controlled by a single dominant gene tentively named Pi-gm(t). The F2 segregation of GM4/Cpslol7 populations inoculated with CHI09 isolate was inoculated by injecting CHI74 and CHI31 isolates at tillering stage. The result was the same to CHI09. This indicate that the Pi-gm(t) is a broad-spectrum resistance gene that controlled the resistance to 3 blast isolates.We constructed the mapping population of Pi-gm(t) and conducted mapping study with 105 SSR makers using DNA extracted from different resistance/susceptible pools inoculated with the isolates CHI09. The gene Pi-gm(t) was preliminary mapped onto chromosome 6 near marker SRF5,and then we further designed some SSR and CAPS marker, mapping Pi-gm(t) in the region approximately 5.1cM between CAPS marker C26348 and C15959 , The CAPS marker C26348 amplified in different pools produced the same pattern to CH109,this result show that resistance to different isolates in GM4 is controlled by Pi-gm(t) gene, which is broad-spectrum gene or gene cluster.The gene Pi-gm(l) is near to Pi-2 ^ Pi-9 and Pi-25 on chromosome 6. But the isolates CHI09 is virulence to Pi-2 presented in the rice line C101A51,also the resistance spectrum of Pi-gm(t)is broader than that of Pi-2, Pi-gm(t) should not be the same gene as Pi-2.The relation between Pi-gmft)and Pi-2, Pi-9 will be identified by allelic test.Yet the relation between Pi-gm(t) and Pi-25 was not beidentified for different inoculating isolates.