Improving of Rice Blast Resistances in Japonica by Pyramiding Major R Genes

Rice blast, caused by the fungal pathogen Magnaporthe oryzae, is a major constraint to rice production worldwide. In this study, we developed monogenic near-isogenic lines (NILs) NIL Pi9, NIL Pizt , and NIL Pi54 carrying genes Pi9, Pizt, and Pi54, respectively, by marker assisted backcross breeding using 07GY31 as the japonica genetic background with good agronomic traits. Polygene pyramid lines (PPLs) PPL Pi9+Pi54 combining Pi9 with Pi54, and PPL Pizt+Pi54 combining Pizt with Pi54 were then developed using corresponding NILs with genetic background recovery rates of more than 97%. Compared to 07GY31, the above NILs and PPLs exhibited significantly enhanced resistance frequencies (RFs) for both leaf and panicle blasts. RFs of both PPLs for leaf blast were somewhat higher than those of their own parental NILs, respectively, and PPL Pizt+Pi54 exhibited higher RF for panicle blast than NIL Pizt and NIL Pi54 (P < 0.001), hinting an additive effect on the resistance. However, PPL Pi9+Pi54 exhibited lower RF for panicle blast than NIL Pi9 (P < 0.001), failing to realize an additive effect. PPL Pizt+Pi54 showed higher resistant level for panicle blast and better additive effects on the resistance than PPL Pi9+Pi54. It was suggested that major R genes interacted with each other in a way more complex than additive effect in determining panicle blast resistance levels. Genotyping by sequencing analysis and extreme-phenotype genome-wide association study further confirmed the above results. Moreover, data showed that pyramiding multiple resistance genes did not affect the performance of basic agronomic traits. So the way to enhance levels of leaf and panicle blast resistances for rice breeding in this study is effective and may serve as a reference for breeders. Key Message: Resistant levels of rice blast is resulted from different combinations of major R genes, PPL Pizt+Pi54 showed higher resistant level and better additive effects on the panicle blast resistance than PPL Pi9+Pi54.