Screening And Application Of An SSR Marker Closely Linked To Pi-2(t), A Gene Resistant To Rice Blast

Rice blast disease, caused by fungal pathogen Magnaporthe grisea (Hebert) Ban, is one of the most serious disease of rice worldwide. Pi-2(t) is a wide-spectrum and dominant rice blast resistant gene. The objective of this study was to find new SSR markers more tightly linked to Pi-2(t) on the basis of others' researches, and to introgress Pi-2(t) gene from a donor parent 5173, an indica rice variety, into Zhenshan 97A(B), the most widely used CMS line in China, by marker-assisted selection.BAC/PAC clones between a RAPD marker P125 and a SSR marker AP22, which are the most tightly linked to Pi-2(t) at present and located at the two sides of Pi-2(t), were searched from rice genome database on internet, and a contig of this region was constructed Based on the contig, SSRs were searched and 5 pairs of SSR primers were designed. After screening, a pair of primers SRM24 showing polymorphism between the receptor parent Zhenshan 97 and donor parent 5173 was found. Genetic linkage analysis was performed based on the BC3F2 population, suggesting that SRM24 is 3.0cM distant from Pi-2(t).The new marker can facilitate the positional cloning and marker-assisted breeding of Pi-2(t).With a combination of molecular marker testing and resistance identification, Pi-2(t) was introgressed into the receptor parent Zhenshan 97B(A) via three backcrossing and one selfing, resulting in 53 and 46 isogenic plant of Zhenshan 97B and Zhenshan 97A carrying Pi-2(t) respectively. The genetic backgrounds of 10 isogenic plants of Zhenshan 97B were analyzed with 64 SSR markers evenly distributed on rice chromosomes. Results showed that the percentage of recurrent patent's background recovered ranged from 89.6%~96.7%, with an average of 92.94%.