Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2004
Publication Date: 1/31/2005
Citation: Pinson, S.R., Capdevielle, F.M., Oard, J.H. 2005. Confirming QTLs and finding additional loci conditioning sheath blight resistance in rice (Oryza sativa L.) using recombinant inbred lines. Crop Science. 45:503-510. Interpretive Summary: Genes with small individual effect are very difficult for breeders to select for because they are overshadowed by the larger trait variations caused by uncontrolled environmental effects. These genes can be used by breeders, however, and efficiently incorporated into new varieties, if they are tagged with linked molecular markers. At the initiation of this study, two publications reported a total of 12 genes affecting resistance to sheath blight disease in rice. There was only weak agreement on QTLs located by the two studies, however. As "tentative genes", breeders and geneticists have been reluctant to pursue the costly marker development required to produce the necessary molecular tags. By identifying six of these same genes in a second, independent study conducted with different genetics and environments, this study confirms the presence of six QTLs for sheath blight resistance genes. Three of these genes, however, are also associated with tall plant height and/or late flowering time, which are not desired in modern US rice varieties for other agronomic reasons. Marker development for the other three confirmed resistance genes is warranted, and will be the basis for further research in this area.
Technical Abstract: One method for confirming the existence of 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 the 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) in order to increase the reliability of the quantitative disease data, and in turn improve the accuracy of the QTL mapping. The RILs were in fact F2:10 descendants from the early-generation 'Lemont' x 'Teqing' population wherein SB-QTLs were first identified. The present study confirmed the location and effect of six SB-QTLs, and newly identified nine. Three of the confirmed QTLs were also confirmed as independent from undesirable plant height and maturity effects. The confirmed SB-QTL locations reported herein will be used to direct efforts to further develop economical molecular tags suitable for marker-assisted selection of the confirmed SB-QTLs within US rice breeding populations.