Blast and bacterial blight (BB) pose a significant threat to rice production. To enhance resistance to blast and BB, we employed marker-assisted backcross breeding to introgress the resistance genes into the genetic background of BRRI dhan48. The resistant (R) genes Pi9, Pb1, Xa4, xa13, and Xa21 were introgressed from Pi9-US2, Pb1-US2, and IRBB58, respectively. The Pb1 gene strengthens blast resistance in rice by interacting with WRKY45 transcription factor to modulate salicylic acid and phytoalexin pathways, while the Pi9 gene triggers a signaling cascade involving reactive oxygen species (ROS) production and hormones like jasmonic acid and ethylene activation to enhance defense responses. Xa4 strengthens the cell wall via WAK (cell wall-associated kinase) protein, hindering pathogen invasion, xa13 disrupts SWEET (Sugar Will Eventually be Exported Transporter) protein function to limit sugar availability for Xanthomonas oryzae pv. oryzae (Xoo). Xa21 triggers mitogen-activated protein kinases (MAPKs)-mediated signaling cascades, leading to the activation of WRKY transcription factors that suppress bacterial proliferation. For that, triple cross was made, followed by repeated backcrosses, self-pollinations, and marker-assisted selection to generate BC3F5 progeny. Chi-square analysis of 380 BC3F2 individuals confirmed a monogenic inheritance pattern for blast and BB resistance traits. Finally, we selected 32 advanced lines, and among them nineteen lines possessed all these 5 R genes, i.e., Pi9, Pb1, Xa4, xa13, and Xa21, while eight lines consisted of 4 R genes in different combinations. The disease rating of the advanced lines varied from 0 to 5 for both blast and BB diseases, while BRRI dhan48 had a disease rating ranging from 7 to 9. The lines G10, G25, G16, G31, G9, G2, and G20 demonstrated significantly higher grain yield (7.73, 7.72, 7.70, 7.65, 7.64, 7.59, and 7.58 t ha−1, respectively) than the parent (7.00 t ha−1). Investigation of marker trait association showed that molecular markers were negatively linked with blast and BB diseases. So, gene introgression by marker-assisted backcrossing (MABB) offers a robust and efficient way to identify and validate candidate genes with high precision for the development of durable, resistant rice breeding lines. These multiple disease resistant advanced lines may use as a potential genetic stock or incorporate with other desired genes for ensuring sustainable rice production under changing climatic conditions.
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