Establishing Near Isogenic Lines Of Major Rice Blast Resistance Genes And Evaluation On Its Application In Breeding

Rice blast is one of the three most severe diseases, caused by Magnaporthe grisea, and threatened seriously to the stability of rice yield and quality. The most efficient and economical strategy to control this disease is to breed resistant varieties. But Magnaporthe grisea has a high degree of variability of physiological race and serious differentiation of pathogenicity, which led to loss of variety resistance only about3-5years after being application. Recent researches showed that there were large differences in race specificity and resistance spectrum (RS) of different multi-alleles even on the same gene site, while the genetic basis of durable resistance to rice blast is the combination of broad-spectrum qualitative resistance controlled by multiple major genes and quantitative resistance controlled by minor genes. Broad-spectrum resistance genes own resist to more races and different genes resistant to blast possess certain complementarity on RS. Pyramiding of major and broad-spectrum resistance genes can enhance durable resistance of rice cultivars. Therefore, it is the important way to dig out and get together different broad-spectrum resistance genes in breeding resistant to rice blast.In this research, Magnaporthe grisea strains were collected and isolated from different ecological regions to analyze race’s composition and distribution and infection characteristics. Meanwhile, a set of near-isogenic lines (NILs) with different major resistance genes was constructed by marker-assisted selection (MAS). Artificial inoculation on seedling and booting stage and natural induction in disease nursery were conducted in order to research RSs of the resistance genes. The results are providing a scientific basis for establishing reasonable strategy to utilize these genes resistant to rice blast. The main research results are as follows:1. Two hundred and four single-spore isolates were obtained from diseased panicles, which were collected from five ecological regions, including Guangdong, Jiangsu, Hainan, Hubei and Zhejiang. Using7Chinese differential materials of rice, these isolates were inoculated in seedling stage. Among all of the isolates, the dominant group is ZB and dominant race was ZB15in Guangdong, ZD, ZG, ZD1and ZG1in Jiangsu, ZB, ZG, ZB1and ZG1in Hainan, ZB, ZG, ZB15and ZG1in Hubei, ZB and ZB15in Zhejiang, respectively. On the whole, the distributions of races were relatively abundant and involved A to F groups. Of them, ZB15predominated in distribution and virulence. ZB group was the main in southern indica rice region, while ZG group was the main in northern japonica rice region.2. Twenty seven rice materials, which included Tsunematru mono-resistance gene lines from Japan (TM GLs), NILs of different single resistance genes with Lijiangxintuanheigu background from Chinese Academy of Agricultural Sciences (LTH NILs), NILs with Co39background from International Rice Research Institute (Co39NILs), and Gumei4and IR64with known resistance gene(s), were selected to inoculate with above identified representitive races. The results showed that resistance spectrums of Pi-1, Pi-2, Pi-33, Pi-gm and Pi-kh were all wider under different backgrounds than other genes, with89.7%,92.7%,80.0%,91.9%and88.5%of the respective resistance frequency, respectively.3. Under the genetic backgrounds of rice cultivars, Guangzhan63S,97S, R609and R084, NILs with Pi-1, Pi-2, Pi-gm and Pi-33were being established, respectively. By MAS, pure lines from BC4F3populations of above backcrosses were obtained. The lines were inoculated on seedling stage with104representitive races from different regions. The results showed that RS of monogenic rice lines with Pi-33was narrower than with Pi-1, Pi-2and Pi-gm. The results also revealed that, as multi-alleles on Pi-z locus, Pi-gm and Pi-2were significantly different in aspect of RS and resistance frequency of Pi-gm was around10%lower than of Pi-2, but their RS complementarity was higher, with about63.29-74.68%of RS overlapping degrees. Moreover, there was obvious higher RS complementarity among Pi-1, Pi-2and Pi-gm, with RS overlapping degree of50-60%. The results of pyramiding resistance genes showed that the RSs of Pi-1/Pi-2and Pi-1/Pi-gm were90%-95%and87%-92%, respectively, higher than monogenic lines. The genetic backgrounds and main agronomic characters of most NILs have restored the aspects of their recurrent parents, which held important breeding value.4. To study systematically RSs and interaction effect of Pi-1, Pi-kh, Pi-33and7multi-alleles on Pi-z loci involving Pi-z, Pi-zt, Pi-2, Pi-9, Pi-26, Pi-40and Pi-gm, NILs of above10genes have been establishing by marker-assisted selection, under the backgrounds of two excerlent cultivars, Yangdao6(indica) and07GY31(japonica), respectively. We have obtained homozygous individual plants or lines in generations of BC3F2, It would lay a good foundation for subsequent work.