Breeding New Indica Rice Lines With Blast Resistance By Molecular Marker-assisted Selection Of The Pi9 Gene And Pigm Gene

Rice is the main staple food for more than 50% population in the world. Rice blast, caused by the fungus pathogen of Magnaporthe oryzae, is the main destructive disease in rice production and distributes almost all regions where rice grows. To improve the blast disease resistance of the main indica rice cultivars in South China, two resistant donor variety 75-1-127 and Gumei4, harboring the broad-spectrum blast disease resistance gene Pi9 and Pigm respectively, and 35 indica rice acceptor lines were used through backcross breeding by molecular marker-assisted selection (MAS) method in this study. The main results are shown as follows:1. A functional DNA marker Clon2-1 for Pi9 gene were designed based on the sequence variations of Pi9 allele in different rice lines. Clon2-1 is a co-dominant molecular marker and showed 97.1% polymorphism rate between Pi9 donor line 75-1-127 and 35 tested acceptor lines.2. A co-dominant DNA marker T9E3 was developed based on the finely mapping result of the broad-spectrum blast resistance gene Pigm, and the genotypic analysis showed that polymorphism rate was 100% between Pigm donor line Gumei4 and the 35 acceptor lines.3. The evaluation of blast resistance level in field disease nurse revealed that 35 indica acceptor lines show a susceptible phenotype, comparing with the resistance donor lines 75-1-17 and Gumei4. After inoculated with 17 Magnaporthe oryzae isolates from different countries or regions in greenhouse, the results showed that the resistance frequency of 25 tested acceptor lines varied from 16.7% to 82.3%, while the donor lines 75-1-127 and Gumei4 express a high level and broad-spectrum resistance to 88.2% and 94.1% isolates respectively.4. The selection efficiency of molecular markers Clon2-1 and T9E3 were both up to 100%, after checking the genotype and phenotype by randomly sampling in the backcross populations.5. By backcross selection assisted with MAS,48 backcross inbreed homozygous lines from 11 acceptor lines with Pi9 genes(locus) were developed,and four F1 hybrids were produced with these homozygous lines and three sterility rice lines for further hybrids blast disease evaluation and heterosis analysis. BC6F1 populations of 10 indica acceptors with Pigm gene(locus) were also obtained. Our current work provides an important fundamental step for further breeding elite rice varieties with blast resistance.