Genetic mapping of a QTL controlling leaf width and grain number in rice

Large panicle and leaf sizes are distinctive characteristics of heavy panicle type (HPT) rice (Oryza sativa L.) cultivated under deficient solar radiation and humid conditions in southwestern China. However, the genetic determinants of these traits remain unknown. An HPT restorer line, HP, which is derived from multiple hybridizations between indica and japonica rice cultivars, was used in this study. Two major quantitative trait loci (QTLs), qGNPP1-1 and qFLW1-1, which control grain number per panicle and flag leaf width, respectively, were detected by QTL analysis on the same interval of chromosome 1 between markers RM3521 and RM8111 using an F-2 population derived from the cross HP x Nipponbare. Thus, a single QTL, designated qLG1 (Leaf width and grain number 1), was presumed to control both traits. The locus qLG1 showed segregation as a single locus in the BC5F2 line, which was obtained by backcrossing, molecular marker-assisted selection, and confirmation with the BCnF2 population. Location of the locus was narrowed down to the 1,137-kb region between the markers InDel13 and InDel18. It is hypothesized that qLG1 is a non-cloned locus, on the basis of published QTLs, located in the interval between InDel13 and InDel18. The locus qLG1 provides novel genetic material suitable for use in molecular-assisted breeding of HPT rice and may be useful to elucidate the molecular basis of high yield in HPT hybrid rice and in future research on crosstalk among genes involved in panicle development.