Quantitative trait loci associated with grain-filling ability in rice ( <i>Oryza sativa</i> L.)

Grain filling of rice is affected mainly by the source – sink ratio, but the ratio does not explain some cultivar differences. The high-yielding cultivar Momiroman generally has poorer grain filling than the high-yielding Takanari at a similar source – sink ratio. Previous analysis using an F3 population derived from Momiroman × Takanari identified a quantitative trait locus (QTL) for grain filling percentage (GFP) on chromosome 10. The objective here was to validate the effect of the QTL and to clarify whether it is associated with source – sink ratio, using two near-isogenic lines (NILs) with Takanari segments on the long arm of chromosome 10 at regions dubbed A and B (namely NIL10A and NIL10B) and a NIL with a Momiroman segments covering both of the regions (NIL10M). In field experiments using these three NILs in 2023 and 2024, we determined dry matter content, N content, grain yield, and yield components. NIL10A and NIL10B had higher GFP than NIL10M, verifying QTLs for grain filling in regions A (qGF10A) and B (qGF10B). A higher GFP in NIL10A and NIL10B than in NIL10M at the same source – sink ratio suggests that these QTLs are associated with grain-filling ability. A QTL for the ability of N accumulation in grain or N remobilization from vegetative parts appears to be unrelated to qGF10B but to be located in region A. The association between qGF10 and N partitioning should be further explored.