Application of ornithine-induced regulation in yield formation, grain quality and aroma of fragrant rice

Ornithine is one of the precursors of 2-acetyl-1-pyrroline, the key compound of fragrant rice aroma, in fragrant rice. However, the application of ornithine in fragrant rice production has never been reported. The present study was conducted with a 2-year field experiment in order to study the effects of foliar application of ornithine on fragrant rice yield formation, quality characters and aroma. At the heading stage, ornithine solutions at three concentrations (0.5, 1.0, 2.0 g L−1) were foliar applied to fragrant rice plants in paddy field and treatment applied with distilled water was taken as control. Our results showed that foliar application of ornithine significantly improved fragrant rice grain yield as well as the seed-setting rate and 1000-grain weight. Higher contents of photosynthetic pigments (chlorophyll a, chlorophyll b and carotenoid) and stronger net photosynthetic net were recorded in ornithine treatments compared with control. Foliar application of ornithine also increased grain protein content and reduced the grain amylose content, chalky rice rate, chalk area ratio and chalkiness. Moreover, we observed higher grain 2-AP concentrations were recorded in ornithine treatments and the ornithine treatments significantly reduced the transcript level of BADH2 which is the key gene controlling the 2-AP biosynthesis in fragrant rice. Overall, 1.0 g L−1 was considered as the optimal amendment for foliar application of ornithine in fragrant rice production.