Breeding of R8012, a Rice Restorer Line Resistant to Blast and Bacterial Blight Through Marker-Assisted Selection

Genetic improvement is one of the most effective strategies to prevent rice from blast and bacterial blight (BB) diseases, the two most prevalent diseases jeopardizing rice production. Rice hybrids with dural resistance to blast and BB are needed for sustainable production of food. An incomplete diallele design resulted in 25 crosses between five blast and five BB resistant germplasm accessions. Only one pair of parents, DH146 x TM487, showed polymorphism for all the markers to identify one blast resistance gene Pi25 and three BB resistance genes, Xa21, xa13 and xa5, thus it was used in the marker-assisted selection (MAS). F-2 individuals of DH146 x TM487 were genotyped using flanking markers of RM3330 and sequence tagged site (STS) marker SA7 for Pi25. The resistant F-2 plants with Pi25 were used for pyramiding BB resistance genes Xa21, xa13 and xa5 identified by the markers pTA248, RM264 and RM153, respectively in subsequent generations. Finally, after selection for agronomic traits and restoration ability among 12 pyramided lines, we acquired an elite restorer line, R8012 including all four target genes (Pi25+ Xa21+ xa13+ xa5). Hybrid Zhong 9A/ R8012 derived from the selected line showed stronger resistance to blast and BB, and higher grain yield than the commercial checks uniformally in experimental plots, 2007 state-wide yield trial and 2008 nation-wide yield trial. This study provides a paradigmatic example to show that MAS is a practically feasible tool in effectively pyramiding multiple resistance genes. The resultant restoring line and its hybrid would play an important role in securing rice production in China.