Resistance architecture and breeding implications of blast and bacterial blight resistance genes in core WDR parents

BACKGROUND: Water-saving and drought-resistance rice (WDR) is crucial for sustainable cultivation under water scarcity, yet its productivity is increasingly compromised by rice blast and bacterial blight (BB). A systematic assessment of resistance gene deployment in elite WDR parents is urgently needed to guide resistance breeding. RESULTS: We dissected the resistance architecture of 47 core WDR parental lines by genotyping 11 blast and 4 BB resistance genes. For blast, Ptr was nearly fixed (97.9%), whereas loci previously reported to confer broad-spectrum blast resistance, such as Pigm (0%) and Pi9 (19.1%), were scarce. Blast resistance scores correlated negatively with gene number (ρ = -0.330, P = 0.023). For BB, resistance genes were only detected in 34.0% of lines, mainly restorers, with Xa23 (21.3%) and Xa7 (23.4%) being most frequent. The recessive gene xa5 was absent, and Xa21 (8.5%) was rare. BB resistance exhibited a strong negative correlation with gene count (ρ = -0.771, P < 0.001). CONCLUSIONS: Resistance-associated loci were unevenly distributed in the WDR breeding panel, with apparent gaps in loci previously associated with durable or broad-spectrum resistance. These findings provide a preliminary basis for genotype-guided parental selection and marker-assisted pyramiding strategies in WDR breeding. Previous resistance-oriented improvement of elite restorers further suggests the potential value of integrating resistance-locus profiling with breeding design.