Challenges and Insights into Pyramided R Genes for Durable Rice Blast Resistance in Southwest China

Rice blast, caused by Magnaporthe oryzae , threatens global rice productivity through severe yield losses. Developing cultivars with durable resistance via strategic pyramiding of resistance (R) genes is essential for sustainable disease management. This study aimed to develop elite rice germplasm harboring effective R-gene compositions and evaluate their resistance stability across geographically distinct blast hotspots in Southwest China. From disease nursery screenings in Wanzhou and Enshi, 136 resistant lines were selected from crosses of elite parents. Subsequent multilocation evaluations identified 20 lines demonstrating stable resistance in Meitan, a region with distinct M. oryzae pathogenic populations, highlighting significant geographical variation in pathogen virulence. These results emphasize the necessity of multilocation testing for breeding durably resistant varieties. Allele-specific marker analysis of 14 major R genes revealed genetic compositions across resistant lines. Over 50% of lines carried Pi5 , Pi54 , Pita , or Pia , with most genotypes pyramiding 3-5 genes, reflecting the widespread adoption of R-gene pyramiding in rice breeding programs, with elite parental lines harboring diverse resistance gene combinations. Notably, lines demonstrating blast resistance in Meitan shared identical R-gene profiles with susceptible materials, suggesting the involvement of uncharacterized major-effect genes in conferring resistance. This finding underscores the prioritization of functional major-effect genes over quantitative gene stacking in resistance breeding. Our study establishes a regionally optimized framework for blast resistance evaluation and provides validated genetic resources for developing adapted rice cultivars in Southwest China.