1.Introduction: Drought stress can limit the growth and yield of plants like peppermint. One way to increase yield and product quality is by using growth stimulants that can increase resistance to stress and accelerate plant development. The role of growth stimulants is to increase resistance to stress and accelerate plant development and growth, especially of roots and leaves. Kitoplus is a growth stimulant that contains chitosan and has been used to reduce the effects of drought stress. Iron also reduces the effects of drought stress by improving gas exchange, stomatal conductance, water use efficiency, and reducing transpiration. The use of nano-fertilizers for plant nutrition is a new application of nanotechnology in agriculture. Iron oxide nanoparticles with chitosan coating can provide the necessary elements for plants. This study examined the effect of chitosan-coated iron oxide nanoparticles on mitigating drought stress in peppermint.
2.Materials and Methods: To assess the impact of Kitoplus growth stimulant and chitosan-coated iron oxide nanoparticles on peppermint yield, morphology, and essential oil under drought stress, a factorial split-plot experiment was conducted. The experiment had three replications and treatments included three levels of water stress (irrigation in soil moisture depletion of 30, 60, and 90% of field capacity moisture), three concentrations of Kitoplus growth stimulant (0, 0.5, and 1%), and three concentrations of chitosan-coated iron oxide nanoparticles (0, 5 and 10 µM)). Peppermint rhizomes planted in small pots and keeping them in a greenhouse for 20 days before planting in the experimental field. Drought stress and foliar spraying began 20 days after transferring the plants to the field. Soil moisture was measured using hygrometer sensors and irrigation was done when the desired level of soil moisture was reached (90, 60 and 30% soil FC moisture) with an equal volume (400 liters) for each plot separately. Foliar application was performed three times with a 15-day interval. One week after the last spraying, characteristics such as stem diameter, number of nodes, inter-node distance, flower cluster weight, fresh and dry weight of aerial parts, and essential oil percentage were evaluated.
3.Results and Discussion: The study found that foliar spraying with Kitoplus growth stimulant and chitosan-coated iron oxide nanoparticles had a positive impact on peppermint yield and quality, especially under drought stress. Drought stress significantly affected the fresh and dry weight and morphology of peppermint. Increasing irrigation, Kitoplus growth stimulant concentration, and chitosan-coated iron oxide nanoparticle concentration improved these attributes. However, high concentrations of Kitoplus growth stimulant and chitosan-coated iron oxide nanoparticles caused a sharp decrease. The ratio of dry to fresh weight was higher in treated plants than in untreated plants under irrigation conditions. The highest ratio of dry to fresh weight (36.08%) was observed in plants treated with 1% Kitoplus growth stimulant and 5 µM chitosan-coated iron oxide nanoparticles under 30% field capacity irrigation conditions. The highest essential oil yield was observed in plants under 90% field capacity irrigation conditions combined with 1% Kitoplus growth stimulant foliar application (1.056 ml per 30 gr of dry tissue).
4.Conclusion: The study concluded that combined foliar application of 0.5% Kitoplus growth stimulant and 10 μM chitosan-coated iron oxide nanoparticles had a greater impact on peppermint yield and quality, especially under drought stress. This treatment compensated for the negative effects of drought stress. In general, agricultural techniques can increase peppermint yield and essential oil percentage.