Confirmation and Identification of Additional QTLs for Grain Traits Using an Advanced Backcross Line from a Cross between Oryza sativa and O. grandiglumis

An advanced backcross line, HG101, was produced from a single plant from BC5F3 families from a cross between Oryza grandiglumis (2n=48, CCDD, Acc. No. 101154) and O. sativa subsp. japonica cv. Hwaseongbyeo. HG101 showed differences from Hwaseongbyeo in several traits, including days to heading due to the O. grandiglumis introgressions. To characterize the effects of alien genes introgressed into HG101, an F2:3 population (150 lines) from the cross Hwaseongbyeo/HG101 was developed and evaluated for agronomic traits. A number of QTLs controlling traits of agronomic importance were identified and novel alleles from O. grandiglumis were detected for days to heading, spikelets per panicle, and grain traits. Eleven QTLs identified in the F2:3 population were further confirmed based on the test of F3:4 progenies derived from the single F3 line. Additional eight QTLs were further detected in the F3:4 progeny test. The result that the majority of the QTLs occurred in the same locations in the F2:3 and F3:4 generations implies that primary QTL observations based on F2:3 lines derived from a cross between isogenic lines are reliable and also demonstrated that transgressive segregants could be identified in subsequent generation. Several genomic regions were associated with more than one trait, indicating linkage and/or pleiotropic effects. The O. grandiglumis allele at the locus RM290 on chromosome 2 increased the grain weight, grain width, grain thickness, and grain yield, and also decreased panicle length. Also, the O. grandiglumis allele at the locus RM144 on chromosome 11 was associated with decrease in grain weight, grain width, and grain thickness and increase in panicle number. Epistatic effects for grain weight and grain width were highly significant between these two QTLs at chromosomes 2 and 11. To better understand the characteristics of these loci, development of further generations of near-isogenic lines (NILs) containing the fine-mapped QTLs is underway.