[Mapping QTLs for horizontal resistance to sheath blight in an elite rice restorer line, Minghui 63]

This study was conducted with a recombinant inbred line (RILs) population consisting of 240 recombination lines, derived from an elite combination, Zhenshan 97B x Minghui 63. The RILs and their parents were grown in a randomized complete design with two replications in the years of 1999 and 2000. Sheath blight response ratings for the population and their parents were identified by an improved method of inoculation, which was carried out with short woody toothpicks incubated with a Rhizoctonia solani strain, RH-9, and inserted the third sheath in the late tillering/green ring stage of growth. A linkage map was constructed from the RILs. The QTL mapping of sheath blight resistance was carried out by the method of interval QTL mapping. Two QTLs for sheath blight resistance were detected in each year, and were located on chromosome 5 and chromosome 9, respectively. The QTL for sheath blight resistance on chromosome 5 was flanked by markers C624 and C246 on the basis of 1999 data, and by markers C246 and RM26 using 2000 data. The 1-LOD-confidence intervals of QTLs for sheath blight resistance on chromosome 5 detected in two years greatly overlapped with each other, and the peak of the 1-LOD-confidence intervals were approximately the same site. This suggested that the QTL for resistance on chromosome 5 detected in 1999 was probably the same as the QTL detected in 2000. The QTL for sheath blight resistance on chromosome 9 was located on the marker interval of C472-R2638 in term of 1999 data, and on the interval of RM257-RM242 based on 2000 data, and the two intervals were 9.7 cM away from each other. Based on the effect analysis of QTLs for resistance, the genotype of MH63 had negative additive effects or reduced sheath blight rating.