Foliar ornithine application at panicle initiation improves rice yield and grain quality in japonica rice

The panicle initiation stage is critical for determining rice yield potential and grain quality formation. In a two-year field study, foliar application of ornithine to the japonica rice cultivar Ningxiangjing 9 increased grain yield by 8.54% and 3.95% in 2024 and 2025, respectively, compared with the control. The yield improvement was mainly associated with enhanced sink capacity, reflected by more grains on secondary branches and a higher 1000-grain weight. Ornithine treatment also improved grain quality by increasing brown rice, milled rice, and head milled rice rates, while reducing chalky rice rate and chalkiness degree. In addition, ornithine maintained higher SPAD values and promoted dry matter and non-structural carbohydrate accumulation during grain filling. Leaf transcriptomic analysis indicated upregulation of genes related to nitrogen assimilation, sugar transport, and panicle development. Metabolomic profiling of young panicles showed enrichment of flavonoid- and phenylpropanoid-related pathways, accompanied by the accumulation of naringenin, naringenin chalcone, pinobanksin, and chlorogenic acid. These findings provide field evidence for the potential use of foliar ornithine during reproductive development, although its underlying regulatory mechanisms require further functional validation.