Abstract

Marjoram with its scientific name (Origanum majorana L.) is considered one of the most important and best-selling medicinal and spice plants in Iran and the world. Environmental stresses are one of the important factors in reducing the production of agricultural products in the world. Under natural and agricultural conditions, plants are constantly exposed to various stresses, which is one of the obstacles to the potential production of water deficit, which has a negative effect on the growth and physiological traits of plants. Therefore, one of the possible ways to increase tolerance to drought stress is inoculation with useful microorganisms. These organisms form a colony in the rhizosphere of the plant and increase the growth of the plant through direct and indirect mechanisms. Arbuscular mycorrhizal fungi increase host plant drought tolerance through physiological mechanisms of nutrient uptake and biochemical mechanisms related to hormone synthesis, osmotic regulation, and antioxidant systems. Salicylic acid is a phenolic compound and an essential plant hormone that plays an important role in stress defense and growth regulation. Several studies have investigated the effect of using salicylic acid in plants and have come to the conclusion that salicylic acid causes resistance to a variety of non-biological stresses. The increase in salicylic acid production, along with the decrease in auxin biosynthesis, coordinates plant defense responses, reduces the adverse effects of drought and salinity stress by improving physiological parameters, membrane integrity, and photosynthetic efficiency. For this purpose, an experiment was conducted with the aim of investigating the growth and physiological response of marjoram to the application of mycorrhiza and salicylic acid under drought stress conditions.

Materials and Methods

This experiment was carried out as a split-factorial design in the form of a basic randomized complete block design with three replications. The experimental factors include the main plot of different levels of drought stress (35, 70 and 90% of the field capacity) and the secondary plot with two factors, the first factor including mycorrhizal fungus with two levels (without inoculation and inoculation with Glomus hoi species) and the second factor of concentrations Salicylic acid was different at three levels (zero, 100 and 300 mg/L). One month after planting, salicylic acid treatment was done as foliar spraying. The foliar spraying was repeated twice on the aerial parts of marjoram plants before flowering. The control treatment was considered without foliar spraying and with distilled water.

Results and Discussion

Based on the results of the present research, the medicinal plant marjoram showed a different response to different levels of drought stress. With the increase of drought stress and irrigation at 35% of the field capacity, the lowest measured parameters were observed. Also, the physiological characteristics of marjoram showed a significant difference in the conditions of application of mycorrhizal fungus and salicylic acid foliar spray compared to the absence of application. In irrigation conditions at 70% of field capacity, the use of mycorrhizal fungi can compensate for the damage caused by drought stress and increase plant performance up to the irrigation level of 90% of field capacity. Also, the results proved that with irrigation at 35% of the field capacity, a severe decrease in growth traits was observed, but in irrigation at 70% of the field capacity, the use of mycorrhizal fungi led to an increase in growth and physiological traits compared to the absence of mycorrhizal use. Therefore, the efficiency of mycorrhizal fungus was also evident at this stress level.

Conclusion

According to the results of the present research, Marjoram medicinal plant showed a different response to different levels of drought stress. In drought stress conditions and in irrigated conditions at 70% of field capacity, the use of mycorrhizal fungi and salicylic acid foliar spraying could partially compensate the effects of drought stress.