Foliar-Applied Silicon and Nano-Silicon Alter the Product Quality and Defense System in Ginger Mint (Mentha gracilis R.Br.) Under Drought Stress by Inducing Essential Oil Accumulation and Antioxidant Activity

This study was conducted to evaluate the effects of foliar-applied nano-silicon (Nano-Si, 0-50 mg/L) and silicon (Si, 25 mg/L) on growth and physiological characteristics of ginger mint (Mentha gracilis R.Br.) under different levels of drought stress (DS: 100%, 75%, 55%, and 35% FC). The traits examined included plant height, biomass, antioxidant enxymes (SOD, GPX, APX) activities, protein levels, MDA, proline, H2O2, essential oil production, and chlorophyll fluorescence indices (CFI: F0, Fv, Fm, Fv/F0, and Fv/Fm) using high-performance chlorophyll fluorometer. The esults showed that exposure to Si/Nano-Si alleviated the negative effects of drought stress in ginger mint. Application of Si/Nano-Si increased plant height, biomass, proline, APX, SOD, CFIs and essential oil, and decreased H2O2, and MDA in exposed plants under DS. By applying of 25 mg/L of Si, plant height, biomass, essential oil, APX, SOD, Fm and Fv increased up to 22.0%, 3.5%, 18.0%, 37.0%, 38.0%, 27.0% and 98.0%, and H2O2, and MDA decreased by 8.5% and 32.0%, respectively under 35%FC. Overall, foliar application of 25 mg/L of Si or 50 mg/L of nano-Si alleviated the effects of drought stress and improved the physiological and morphological characteristics of ginger mint, especially under severe drought stress conditions. Application of Nano-Si/Si can be beneficial as a strengthening substance for growth parameters under drought stress conditions by stimulating photosynthesis and inducing essential oil accumulation and antioxidant activity.