Gene pyramiding for enhancing resistance to blast and bacterial blight disease in rice through maker assisted selection.

Diseases are a global threat to rice production. Among them, rice blast and bacterial blight (BB) are most significant. To enhance targeted disease resistance, the marker-assisted backcross breeding (MABB) approach was employed to pyramid two blast (Pi9 and Pb1) and three BB resistant (R) genes (Xa4, xa13, and Xa21) into a high-quality rice cultivar BRRI dhan100. The donor parents Pi9-US2 (Pi9), Pb1-US2 (Pb1), and IRBB58 (Xa4, xa13, and Xa21) contributed these five genes. We followed a triple-cross breeding strategy, followed by backcrossing, selfing, and foreground selection to produce BC₃F₅ progenies. Chi-square analysis of 420 BC₃F₂ individuals confirmed the inheritance patterns of blast and BB resistance were controlled by a simple Mendelian fashion. Finally, we selected 38 advanced lines (ALs), and among them, twelve lines possessed all 5 candidate R genes, while fifteen consisted of 4 genes in different combinations. The disease rating scale of these ALs varied from 0 to 3 for both blast and BB diseases, while BRRI dhan100 ranging from 7 to 9. The G23, G13, G5, G10, G15, and G29 ALs exhibited higher yields ranging from 7.22-7.34 ton ha^-1 compared to the check, BRRI dhan100. Marker-trait association analysis displayed molecular markers negatively associated with disease susceptibility. Therefore, gene introgression by MABB could effectively identify and functionally validate the candidate R genes with high accuracy to develop a resistant variety to multiple diseases in rice breeding programs.