Foliar application of plant growth regulators increases the production of biomass, content, yield and chemical constituents of Origanum vulgare L. essential oil

Origanum vulgare is used in the prevention of neurodegenerative diseases; for feeding poultry, fish, and cattle; and in the food industry. The objective of this study was to evaluate the influence of foliar application of plant growth regulators (PGRs) on biomass, secondary metabolites and antioxidant enzymatic activity. The experiment had a double-factorial design with a control, 3 types of regulators and 3 doses. After 90 days, the dry weight, essential oil content and photosynthetic pigments were measured. The effects of PGRs on the antioxidative system and the activities of several antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), were investigated. With the use of PGRs, the increase in branch length was greater than that in the control. Compared with the control, the application of 25 mg/L GA3 increased the leaf, stem, root, shoot and total dry weights. The highest chlorophyll a content was observed with the KIN25 dose. The oil content gains from the KIN25 and IBA25 doses were 30.9 and 29.6%, respectively, compared to the control. The highest thymol content was observed in the plants that received the GA350 dose (24.80%), which was 12.14% greater than that in the control. The lowest mean hydrogen peroxide (H2O2) and malondialdehyde (MDA) levels were observed in the presence of the PGRs. The PGRs stimulated enzymatic antioxidant activity, decreasing oxidative stress signaling. These findings suggest that foliar application of PGRs at low doses may contribute to increased biomass and active ingredient levels.