Molecular mapping and transfer of sheath blight resistance QTLs from PAU-shb8  to cultivated rice PR-121

Sheath blight, caused by Rhizoctonia solani, severely affects rice, causing 20-69% yield losses in tropical and temperate regions. Key challenges include the pathogen's broad host range, persistent sclerotia, climate change, and the reliance on semi-dwarf varieties. The disease's complex inheritance and lack of highly resistant cultivars hinder management, making resistant variety breeding a sustainable solution. This study mapped sheath blight resistance Quantitative trait locus (QTLs) from PAU-shb8, a moderately resistant rice line. This line exhibited moderate resistance with a disease score of 3 (RLH < 20%), whereas susceptible rice cultivar PR121 scored 9 (RLH > 60%). Screening of 1160 plants from BC₁F₅ and BC₁F₆ populations revealed 50.34% as moderately resistant, 37.76% moderately susceptible, and 11.88% susceptible. (QTL) mapping using 4622 SNP markers identified 20 QTLs across eight traits, with significant loci on chromosomes 2, 4, 6, 8, 9, 10, 11, and 12. Chromosome 12 harbored a cluster of QTLs associated with multiple traits, including RLH, lesion height, and disease score, while chromosome 8 exhibited a major QTL for RLH with a LOD score of 9.8 and 9.2% phenotypic variance. Genomic analysis pinpointed candidate genes related to resistance, such as leucine-rich repeat proteins and calcium/calmodulin-dependent protein kinases. Promising genotypes 7168, 7183, and 7152 demonstrated moderate resistance, combining key QTLs for RLH, disease severity, and lesion height with favorable agronomic traits. These backcross inbred lines are pivotal for breeding sheath blight-resistant rice varieties and for the expansion of resistance gene pool of sheath blight.