Seed Priming Mellissa officinalis L. with Potassium Nitrate and Inoculation with Plant Growth Promoting Rhizobacteria at Different Times

Abstract

Seed priming and seedling inoculation with bioelicitors can enhance growth and phytochemical constituents in medicinal plants. This study was conducted to investigate seed priming with potassium nitrate (at concentrations of 0, 0.25, 0.5, 0.75, and 1%) for various durations, in combination with the inoculation of seedlings derived from seeds primed with rhizobacteria strains (Pseudomonas fluorescens and P. putida). The treatments were assumed to affect the physiological and metabolic attributes of Melissa officinalis L. The findings revealed that the interaction of these treatments had a significant impact on morphological, physiological, photosynthetic pigments, and metabolic traits, including the percentage and composition of essential oils. The most pronounced effects were observed at the 0.25% concentration of potassium nitrate with 72 hours of priming followed by inoculation with P. putida. The phenolic content increased to 56.30 mg g-1 of gallic acid per mL of extract in seedlings inoculated with P. putida and P. fluorescens strains. Maximum antioxidant activity (50.05 mg mL-1) was recorded in seedlings inoculated with P. fluorescens, following 12 hours of priming. A notable increase occurred in essential oils (20%) and related compounds, such as carvacrol, thymol, and isomenthone. In conclusion, seed priming and seedling inoculation with Pseudomonas strains had a crucial role in enhancing the primary and secondary metabolites of lemon balm (Melissa officinalis) plants.