Molecular mapping and transfer of sheath blight resistance QTLs from wild rice Oryza nivara to cultivated rice (Oryza sativa L.)

Abstract Background Sheath blight (ShB) is the most serious disease of rice ( Oryza sativa L.), caused by a soil-borne fungus Rhizoctonia solani Kühn ( R. solani ). It limits global rice productivity by causing ~50% yield loss every year. Broad host range, rapid resurgence of new pathogen races, and the lack of highly resistant germplasm are the major caveat to managing this disease. Therefore, continuous scouting of new germplasm resources resistance to R. solani is urgently required. Results In this report, we identified a very promising resistance source O. nivara accession IRGC81941A which displays partial resistance across the five years of screening against R. solani . Quantitative trait loci (QTL) mapping was performed in F 2 populations that identified a total of 29 QTLs with the total phenotypic variance explained (PVE) ranged from 4.70 to 48.05%. A cluster of four QTL qRLH1.1, qRLH1.2, qRLH1.5, and qRLH1.8 stably detected which showed consistent resistant response against R. solani. The size of these QTL ranging from 0.096-420.1 Kb, based on the rice reference genome harboring several important disease resistant genes such as Ser/Thr protein kinase, auxin-responsive protein, Protease inhibitor/seed storage/LTP family protein, MLO domain-containing protein, disease responsive protein, Thaumatin-like protein, Avr9/Cf9 eliciting protein, and many transcription factors. A simple sequence repeat (SSR) marker RM212 co-segregates with this QTL cluster. Conclusion Our finding suggests that a highly stable QTL cluster confers resistance to sheath blight disease. Effective transferring of this cluster as a single unit through backcross breeding marked the identification of three agronomically superior resistant lines. These promising germplasms could be an important pre-breeding material for varietal development. PCR-based SSR marker linked to these QTLs could facilitate efficient transfer of the QTLs into rice cultivars through marker-assisted selection programs.