Fine mapping and candidate gene analysis of qSB12YSB, a gene conferring major quantitative resistance to rice sheath blight.

Key message: qSB12^YSB, a major quantitative sheath blight resistance gene originated from rice variety YSBR1 with good breeding potential, was mapped to a 289-Kb region on chromosome 12. Sheath blight (ShB), caused by Rhizoctonia solani kühn, is one of the most serious global rice diseases. Rice resistance to ShB is a typical of quantitative trait controlled by multiple quantitative trait loci (QTLs). Many QTLs for ShB resistance have been reported while only few of them were fine-mapped. In this study, we identified a QTL on chromosome 12, in which the qSB12^YSB resistant allele shows significant ShB resistance, by using 150 BC₄ backcross inbred lines employing the resistant rice variety YSBR1 as the donor and the susceptible variety Lemont (LE) as the recurrent parent. We further fine-mapped qSB12^YSB to a 289-kb region by generating 34 chromosomal segment substitution lines and identified a total of 18 annotated genes as the most likely candidates for qSB12^YSB after analyzing resequencing and transcriptomic data. KEGG analysis suggested that qSB12^YSB might activate secondary metabolites biosynthesis and ROS scavenging system to improve ShB resistance. qSB12^YSB conferred significantly stable resistance in three commercial rice cultivars (NJ9108, NJ5055 and NJ44) in field trials when introduced through marker assisted selection. Under severe ShB disease conditions, qSB12^YSB significantly reduced yield losses by up to 13.5% in the LE background, indicating its great breeding potential. Our results will accelerate the isolation of qSB12^YSB and its utilization in rice breeding programs against ShB.