Abstract
Genetic background and environmental effects of QTL for sheath blight resistance to the isolate RH-9(Rhizoctonia solani Kuhn) were revealed using the reciprocal introgression line populations derived from the cross of Lemont/Teqing.Lemont is highly susceptible while Teqing resistant to RH-9.The relative lesion height(a ratio of lesion height to plant height,RLH) of TQ-ILs was normally distributed whereas that of LT-ILs was apparently inclined to the susceptible parent,Lemont.Total 10 main-effect QTLs and 13 epistatic QTLs affecting sheath blight resistance were mapped under different years and genetic back-grounds.Among them,six main-effect QTLs detected in 2006 were all verified in 2007,suggesting these QTLs had reliable per-formance across years.QSh4 was the only one QTL expressed under the reciprocal backgrounds and Teqing allele at this locus decreased RLH,suggesting the improvement of resistance level.QSh10a detected in the TQ-ILs and located in the region ofRM216–RM311 on the chromosome 10 and QSh10b detected in the LT-ILs in the neighboring region of RM222–RM216 were not the same gene but existed tight linkage as regards to different gene directions in different backgrounds.Most QTLs identified in TQ-ILs were not expressed in LT-ILs,indicating there was evident genetic background effect.By comparative mapping,8 QTLs detected in this study were located in the same or near regions that associated with sheath blight resistance identified in the previ-ous studies,suggesting these main-effect QTLs could be applied in rice breeding for sheath blight resistance by marker-assisted selection.As indicated in this study,it is an effective way to further improve sheath blight resistance by selecting the QTL stably expressed in different backgrounds or pyramiding different main-effect QTLs.
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