Peppermint hydrosol as a novel bio-stimulant promotes growth and antioxidant activity of Solanum lycopersicum L.

The genus Mentha has promising antifungal, antiviral, antibacterial, antioxidant and plant growth promoting activities. Mint hydrosols is a product of hydro-distillation of mint plants and is obtained during the extraction process of essential oils. The present study attempts to investigate the role of mint hydrosol in promoting growth of tomato plants. Seedlings of uniform size raised from healthy seeds were planted in pots under open field conditions. The well-established tomato plants were treated with different concentrations (0, 25, 50 and 100%) of freshly prepared mint hydrosol as foliar spray twice a week. The hydrosol was applied for six weeks. At the time of completion of the experiment, data for different vegetative growth parameters such as shoot length (cm), number of leaves, root length (cm) and stem diameter (cm) were noted. A suitable scale was used to measure the length of shoot and root. Increased root and shoot length (58.05 and 23.46 cm from 40.99 to 16.45 cm, respectively), fresh and dry weight of shoots and roots (28.0 and 3.43 g) were observed at 100% hydrosol treatment. There was a significant increase in number of flowers (5.41), leaves, and fruits (3.79) after 6 weeks at 100% hydrosol treatment. Fruit size and weight (3.79 cm, and 31.12 g, respectively) was also higher in tomato plants treated with 100% mint hydrosol. Activities of antioxidant enzymes were also significantly enhanced, e.g., superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) (41.0 U. mg^- 1 of protein, 5.1 U. mL^- 1 of enzyme and 5.28 U. mL^- 1 of enzyme from 23.09 U. mg^- 1 of protein, 3.01 U. mL^- 1 of enzyme and 3.12 U. mL^- 1 of enzyme, respectively) by treatment with 100% hydrosol. Relative water content, total chlorophyll content, total phenols, polyphenols oxidase and uptake of various ions (Na^+ 1, K^+ 1, Mg^+ 2, and Zn^+ 2) also increased significantly (45.1 mg. L^- 1, 34.67 mg. L^- 1, 1.59 mg. L^- 1, 1.03 mg. L^- 1, respectively) in hydrosol treated plants. It can, therefore, be concluded that application of peppermint hydrosol enhances the growth, antioxidant activity and mineral uptake in tomato.