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The aim of this study was to investigate the optimum time for γ-aminobutyric acid (GABA) application to improve the yield and quality in fragrant rice. Pot and field experiments were conducted during 2016–17 with two fragrant rice cultivars (for pot experiment), and five fragrant rice cultivars (for field experiment) which were applied with five GABA levels i.e. no GABA application (CK), application of GABA at 250 mg l−1 with 25 ml pot−1 at tillering stage (S1), panicle initiation stage (S2), heading stage (S3), and at tillering, panicle initiation and heading stages (S4) in the pot experiment. Similarly, the same treatments with 100 ml m−2 were applied to all rice cultivars in the field experiment. The S3 treatment significantly increased the 2-acetyl-1-pyrroline (2AP) contents in Meixiangzhan2 (14.76%) and Yuxiangyouzhan (20.19%) in pot experiment, Meixiangzhan2 (27.27%), Yuxiangyouzhan (40.24%), Basmati (43.07%) and Yungengyou14 (13.66%) in field experiment owing to regulations in the contents of proline, Δ1-pyrroline-5-carboxylic acid (P5C), GABA and the activities of enzymes involved in 2AP formation. The GABA treatments improved yield and modulated the antioxidant enzyme activities. This study provides a reference for the GABA application to improve yield and quality in fragrant rice. [ABSTRACT FROM AUTHOR]

The 2‐acetyl‐1‐pyrroline (2AP) is a key aroma compound in fragrant rice. The present study assessed the γ‐aminobutyric acid (GABA) and nitrogen (N) application induced regulations in the biochemical basis of rice aroma formation. Four N levels, that is, 0, 0.87, 1.75, and 2.61 g/pot, and two GABA treatments, that is, 0 mg/L (GABA0) and 250 mg/L (GABA250), were applied to three fragrant rice cultivars, that is, Yuxiangyouzhan, Yungengyou 14, and Basmati‐385. Results showed that GABA250 increased 2AP, Na, Mn, Zn, and Fe contents by 8.44%, 10.95%, 25.70%, 11.14%, and 43.30%, respectively, under N treatments across cultivars. The GABA250 further enhanced the activities of proline dehydrogenase (PDH), ornithine aminotransferase (OAT) (both at 15 days after heading (d AH), and diamine oxidase (DAO) (at maturity) by 20.36%, 11.24%, and 17.71%, respectively. Significant interaction between GABA and N for Mn, Zn, and Fe contents in grains, proline content in leaves, GABA content in leaves at 15 d AH and maturity stage (MS), Δ1‐pyrroline‐5‐carboxylic acid (P5C) contents in leaves at 15 d AH, and Δ1‐pyrroline‐5‐carboxylate synthase (P5CS), PDH, and OAT activities in leaves at MS was noted. Moreover, the 2AP contents in grains at MS showed a significant and positive correlation with the proline contents in the leaves at 15d AH. In conclusion, GABA250 enhanced the 2AP, Na, Mn, Zn, and Fe contents, as well as the enzyme activities involved in 2AP biosynthesis. Exogenous GABA and N application improved the 2AP contents and nutrient uptake in fragrant rice. [ABSTRACT FROM AUTHOR]