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

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.

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).

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.