A new method in mitigation of drought stress by chitosan-coated iron oxide nanoparticles and growth stimulant in peppermint

Damage to the plant's photosynthetic system is known as the main symptoms of sensitivity to environmental stresses. Little is known about beneficial role of new chitosan compounds such as Kitoplus®, and chitosan-coated nanomaterials on alleviation of adveres effects of drought stress in plants. In the present study, a factorial experiment was conducted in a split-plot manner based on a randomized complete block design (RCBD) with three replications to evaluate the effects of Kitoplus® growth stimulant and Chitosan-Coated Iron Oxide Nanoparticles (Fe-CTs NPS) on peppermint growth, chlorophyll fluorescence and essential oil biosynthesis under drought stress conditions. Treatments included three levels of drought stress (irrigation at soil moisture levels of 30%, 60%, and 90%), three concentrations of Kitoplus®(control without Kitoplus®, 0.5% and 1%), and three concentrations of Fe-CTs NPs (control without Fe-CTs NPs, 5 and 10 µM). Drought stress, growth stimulation treatment with Kitoplus®, and Fe-CTs NPs had significant dual and triple effects on the studied physiological traits. According to the results, chlorophyll index and stomatal conductance were significantly lower in control plants than in those undergoing drought stress. Under 60% field capacity moisture conditions, the chlorophyll index was increased with 1% Kitoplus® treatment. The maximum fluorescence (Fm) and variable fluorescence (Fv) raised as the drought stress intensity increased. The highest Fm and Fv were observed in plants treated with 1% Kitoplus® and 10 µM Fe-CTs NPS under 30% soil moisture stress. Results also showed that the highest value of menthone (33.31%) was obtained in plants treated with Kitoplus® at 1% and Fe-CTs NPs at 10 μM under drought stress of 60% field capacity. In addition, the highest amount of menthol (26.5%) was observed in plants treated with 0.5% Kitoplus® under drought stress of 30% field capacity. The overall importance of the study lies in devising the simultaneous application of biostimulants and nanomaterials in enhancing essential oils production in the mint plant under drought stress challenges.