Confirming QTLs and finding additional loci conditioning sheath blight resistance in rice using recombinant inbred lines

One method for confirming the existence of quantitative trait loci (QTLs) is to identify loci of similar location and effect in multiple populations and/or environments. The literature contains two prior publications reporting the location of QTLs affecting resistance to sheath blight (SB) disease in rice (Oryza sativa L.), but lack of agreement between QTLs in the studies left all 12 unconfirmed, limiting the potential of marker-assisted selection of this trait with worldwide importance. The earlier linkage analyses were imprecise due to heterozygosity, segregation, and limited plot size and replication. We evaluated a replicated set of pure-breeding recombinant inbred lines (RILs) to increase reliability of the quantitative disease data and in turn improve accuracy of the QTL mapping. The RILs were F-2:10 descendants from an early-generation 'Lemont' X 'Teqing' population wherein SB resistance QTLs (SB-QTLs) were first identified. The present study confirmed the location and effect of six SB-QTLs, confirmed the existence but not the specific location of another, and identified eight new loci. Three of the confirmed QTLs were also found to be independent from undesirable plant height and maturity effects. This research demonstrated the importance of using replicated phenotypic data for reliably establishing the identity and effect of putative QTLs for complex traits such as SB resistance. Further marker development to facilitate marker-assisted selection of these three SB-QTLs is warranted.