Effects of inoculation with Piriformospora indica on some vegetative, physiological, and biochemical parameters and essential oil content of Origanum vulgare L. ssp. vulgare

Piriformospora indica is one of the growth-promoting microorganisms that can stimulate growth and increase plant tolerance in adverse environmental conditions. To evaluate the effects of P. indica inoculation on some vegetative, physiological, biochemical, and nutrient acquisition parameters and essential oil content of Origanum vulgare L. ssp. vulgare, a pot experiment was conducted in a completely randomized design with three replications. Treatments included control (without inoculation) and inoculation with P. indica. The results showed that inoculation with P. indica increased growth parameters, chlorophyll index, total phenols and total flavonoids content, essential oil content, and nutrients uptake of iron, potassium, and phosphorus singnificantly. The highest and lowest amounts for aerial parts fresh yield (3.92 and 3.06 g plant-1), aerial parts dry yield (1.12 and 0.78 g plant-1), chlorophyll index (47 and 42.23), total phenol (4.88 and 2.96 mg GAE g-1 FW), total flavonoids (0.52 and 0.23 mg QE g-1 FW), essential oil content (1.43 and 1.01%), phosphorus (0.41 and 0.35%), potassium (3.8 and 2.6%), and iron (219 and 180 mg kg-1) were obtained in the plants inoculated with fungus and non-inoculated plants, respectively. Inoculation with P. indica decreased the amount of major essential oil compounds such as carvacrol and thymol and increased the amount of ρ-cymene, carvacrol methyl ether, and γ-terpinene compared to the control. Overall, the findings of this study showed that inoculation with growth-promoting microorganisms can improve the morphological and phytochemical traits of oregano by improving nutrients uptake.