Enhancement of Yield, Grain Quality Characters, 2-Acetyl-1-Pyrroline Content, and Photosynthesis of Fragrant Rice Cultivars by Foliar Application of Paclobutrazol

Paclobutrazol is a well-known plant growth regulator. However, the application of paclobutrazol in fragrant rice production has not been reported. The present study conducted a field experiment with two cropping seasons and three fragrant rice cultivars to investigate the effects of paclobutrazol application on yield formation, grain quality, 2-acetyl-1-pyrroline (2-AP, key component of fragrant rice aroma) biosynthesis, and photosynthesis of fragrant rice. At the initial heading stage, paclobutrazol solutions at 0 (control), 30, 60, 100, and 120 mg L-1 were foliar applied to fragrant rice plants, respectively. Compared with control, paclobutrazol treatments significantly (P < 0.05) increased grain yield and seed-setting rate of fragrant rice cultivars by 6.77-22.82% and 5.09-25.66%, respectively. Increased contents of photosynthetic pigments (chlorophyll a, chlorophyll b, and carotenoid) and the improved net photosynthetic rate at the grain-filling stage were observed due to paclobutrazol treatments. The paclobutrazol application increased head rice rate and grain 2-AP content by 3.94-8.94% and 6.47-18.80%, respectively. Lower chalky rice rate and chalkiness were recorded in paclobutrazol treatment than in control. Moreover, foliar application of paclobutrazol increased proline and Delta 1-pyrroline contents in fragrant rice by 7.90-32.12% and 13.21-34.90%. Overall, foliar application of paclobutrazol could enhance productivity, improve grain quality, and increase the 2-AP content of fragrant rice, and 100-120 mg L-1 was considered the suggested concentration of paclobutrazol application in fragrant rice production.