Evaluation of the Effect of a Hormonal Combination with Amino Acids on the Chemical Content and Antioxidant Activity in the Rosemary Plant

Abstract

During the spring season of 2023-2024, a factorial experiment was carried out at the research station unit of the College of Agricultural Engineering Sciences/ University of Baghdad - Jadriyah, using a complete randomized block design (RCBD), inside an open field (site A), with the aim of evaluating the effect of a combination of growth regulators with amino acids on the growth, yield, chemical content, and antioxidant activity of the local variety of rosemary (Rosmarinus officinalis L.). The experiment included two factors, each with three levels and all interactions, with three replications, and the experimental unit contained 16 plants, totaling 432 plants. Homogeneous saplings with a height of 8–10 cm were used, planted in 8-liter plastic pots filled with gypsum soil, and the plants were acclimatized prior to treatment application. The first factor included growth regulators (control, Kin, BA) at a rate of 50 mg L⁻¹, while the second factor included amino acids (control, Glutamic acid, Aspartic acid) at the same concentration, and the treatments were sprayed three times during different growth stages. Statistical analysis of the means revealed significant differences between most of the traits. Kinetin treatment was superior in chemical and qualitative traits, especially with regard to percentage yield of essential oil, leaf carbohydrate content, total flavonoid contents and improvement the composition of some volatile components and physical characteristics. The Benzyladenine treatment gave the highest total phenolic content and free radical scavenging activity, along with improved oil traits. Glutamic acid significantly increased essential oil percentage and the corresponding yield, carbohydrate content, phenolics, flavonoids and antioxidant activity whereas aspartic acid was more effective in improving essential oil percentage, some volatile oil constituents and physical properties of the oils. The interaction between growth regulators and amino acids had a prominent synergetic effect which was evident in yield, chemical composition, and antioxidants activity. These results verified that co-application of growth regulators and amino acids is a successful approach to promote the yield as well as oil quality of rosemary.