Evaluation of changes in morpho-physiological traits and essential oil of peppermint (Mentha piperita L.) under different irrigation managements

The current limitations in water resources necessitate the adoption of strategies to increase water use efficiency (WUE) and improve the active ingredients of medicinal plants, which requires increasing WUE to produce more crops per unit of consumed water. A method to increase WUE is to apply deficit irrigation (DI) management based on the identification of stress consequences. The effect of different DI methods on the growth and physiological properties of peppermint was investigated in a completely randomized experimental design based on potted planting with three replications in the research greenhouse of Ferdowsi University in 2017-2018. DI treatments were Full Irrigation (FI), DI 50%, Fixed Partial Rootzone Drying (FPRD), and Alternate Partial Rootzone Drying (APRD). The results indicated that the highest (173) and the lowest (140) numbers of leaves belonged to FI and (DI 50%) treatments, respectively. DI 50% and FI treatments presented the highest (39.3 mmol/m2/s) and the lowest (31.3 mmol/m2/s) values of stomatal conductance. The highest values of greenness index (GI, 53.7), electrolyte leakage (48.27%), relative water content (RWC, 55.3%), essential oil (1.58%), and proline content (2.50 mg/l) were obtained in the FPRD treatment. The lowest corresponding values ​​of GI (41.5), electrolyte leakage (35.72%), essential oil (1.14%), and proline content (1.23 mg/l) were recorded in the FI treatment. Essential oil yield was uppermost in the FI treatment and no significant difference was detected in the other treatments. Altogether, given the water crisis in Iran and the reduced yield of the active ingredients of the plant, the APRD treatment is recommended for the irrigation of this plant in greenhouse conditions.