Development of multiple disease resistant rice variety through marker assisted selection

The increasing reliance on pesticides to manage major rice diseases has raised concerns about resistance development. To address this, the present study aimed to genetically improve the widely cultivated mega variety BRRI dhan29, which already carries the tungro resistance gene tsv1, by pyramiding multiple disease resistance genes. Unlike previous pyramiding studies, this work integrates resistance to three major rice diseases blast, bacterial blight, and tungro into a single mega-variety under Bangladesh-specific agro-ecological conditions. The blast resistance genes Pi9 and Pb1 and bacterial blight resistance gene Xa21 were introgressed into BRRI dhan29 using BR(Path)13800-BC₂-224 and IRBB58 as donor parents, while the endogenous Xa4 and tsv1 alleles were monitored and retained during marker-assisted backcrossing. Importantly, tsv1 an endogenous homozygous-recessive resistance allele in BRRI dhan29 rather than a newly introgressed gene; therefore, it was monitored during backcrossing and re-fixed in homozygous form during subsequent selfing generations. Marker-assisted selection was conducted using gene specific-functional markers for all target genes. Following two backcross generations, selected BC₂F₁ plants were self-pollinated and advanced from BC₂F₂ to BC₂F₇ under marker-assisted foreground selection and phenotypic selection. The recessive tsv1 gene was carefully tracked and fixed through marker-assisted selection across segregating generations to ensure stable tungro resistance. Seven lines (G14, G5, G10, G17, G19, G22, and G4) recorded higher yields (8.67-8.75 t ha^-1) than BRRI dhan29 (7.09 t ha^-1) and showed low disease scores (0-3) against three diseases. These lines demonstrate durable, broad-spectrum resistance to three major pathogens alongside numerically superior yield and potential agronomic performance, highlighting them as promising candidates for multi-location and multi-season evaluation prior to varietal release consideration.