Investigating the Changes of Some Agronomic and Biochemical Characteristics of Thymus vulgaris L. with Application of Mycorrhizal Species and Foliar Spraying Humic Acid

IntroductionGarden thyme (Thymus vulgaris L.), is a small perennial plant native to the Mediterranean region that is now found worldwide. It is commonly used as a culinary herb and for medicinal purposes as well (Silva et al., 2021). Thymol is one of the main and active chemical compounds of thyme. It has been shown to have antibacterial, antifungal and antiviral properties and is often used as a natural preservative in food and cosmetic products (Hammoudi et al., 2022). Golubkina et al. (2020) reported that the use of mycorrhizal fungi as a technology that is compatible with the environment and by increasing plant access to nutrients and increasing resistance to stresses as well as improving water absorption, can lead to improved plant growth. Today, the use of organic compounds such as humic acid can affect many morphological, physiological and biochemical processes of plants and lead to improvement in plant growth (Mousavi et al., 2022).Materials and MethodsIn order to investigate the effects of foliar application of humic acid fertilization and mycorrhizal fungi symbiosis on Thymus vulgaris L., a factorial layout has been applied, based on a randomized complete block design with three replications at the field of the research farm of Islamic Azad University, Takestan Branch during 2020-2021 and 2021-2022 growing seasons. Experimental factors included three species of mycorrhiza fungi (control, Glomus mosseae, G.etunicatum and G.intradices) and humic acid fertilizer levels included (control, 150 and 300 mg.L-1). Important traits such as plant height, herbal fresh weight, essential oil percentage, and yield, flavonoid content, root colonization percentage, thymol and carvacrol percentage were measured and analyzed.Results and DiscussionThe results showed that the effects of the treatments were significant at the 1% level for all investigated traits. For the characteristics of essential oil percentage and essential oil yield, the interaction effect was also significant at 1%, with an observed increase of over 200%. The application of 300 mg/liter humic acid resulted in a 14% increase in root colonization and a 16% increase in flavonoid percentage. Similarly, the application of mycorrhiza increased these traits by 23% and 30%, respectively. Thymol and carvacrol were the most abundant essential oil compounds. It can be concluded that the quality of thyme essential oil improved under the treatments. Among the mycorrhizae used in this research, G. mosseae mycorrhizae were more effective than the other two types. The results suggest that the application of mycorrhiza has a more significant impact on improving the examined traits compared to humic acid.ConclusionBased on the results of this study, application of mycorrhiza due to creating a symbiotic relationship with the roots of the garden thyme plant and humic acid spraying could increase the quantity and quality of the produced product. mycorrhiza was better than the use of humic acid in most treatments.