Mapping Of Broad-spectrum And Durable Blast Resistance Genes In Rice Cultivar Xiangzi3150

Rice blast, caused by the fungal pathogen Magnaporthe oryzae, is one of the most devastating diseases in rice production. Xiangzi 3150, a local rice cultivar from Hunan province, confers high-level resistance to many blast isolates in China. To identify the resistance (R) genes controlling the broad-spectrum resistance from the cultivar, a recombinant inbred line (RIL) population has been generated from a cross between Xiangzi 3150 and the highly susceptible cultivar CO39 (C/X) using single seed descent. The main results are summarized as follows:1. The resistance spectrum of Xiangzi 3150 was identified using 303 blast isolates collected from different regions of Hunan province. The results showed that it was resistant to 95.38% of the tested isolates,100% to 30 races including ZG1 and ZB13, two predominant races in Hunan province.2. To survey the genomic polymorphism between Xiangzi3150 and CO39, a total of 914 markers were selcected. Among them,220(200 SSR and 20 SFP polymorphic markers were identified, which counted 24.10% of the tested markers.3. A ratio of 3 (R) to 1 (S) in the 286 RI lines was observed when inoculated with isolate 193-1-1, indicating that there are two major R genes in Xiangzi 3150 conferring resistance to isolate 193-1-1 (ZC11)4. To construct a linkage map, about 150 pairs polymorphic molecular markers were used for the genotype analysis of the 286 F10 RI lines of the C/X population and the program Mapmaker/Exp3.0 was utilized.The total map distance was 2097.1cM and the average distance betweem markers was 15.42 cM.5. Using the composite interval mapping (CIM) method, two major R genes were mapped on chromosome 11, named Pi47(t), with a LOD score of 14.62, and on chromosome 12, named Pi48(t), with a LOD score of 17.95. The Pi47(t) gene accounts for 23.81% of the phenotypic variance, and is flanked by two SSR markers RM206 and RM224 within a 33.0 cM span. The Pi48(t) gene accounts for 23.39% of the phenotypic variance, and is mapped between the flanking SSR marker RM5364 and RM7102 within a 4.2 cM span.6. To further fine mapping the two genes,12 and 28 RI lines containing single Pi47(t) and Pi48(t), respectively, were selected to backcross with CO39.