Physiological responses of peppermint (Mentha piperita L.) to plant growth regulators and salinity stress

Salinity of soil is a major abiotic stress limiting the crop production and growth of peppermint. The aim of study was assessment the plant growth regulators efficacy (salicylic acid (SA), jasmonic acid (JA), brassinosteroids (BRs), and non-application of hormone as control) on physiological traits of peppermint under salinity stress (0, 30, and 60 mM). The experiment was conducted using the completely randomized design (CRD) with three replications at a greenhouse in Varamin city, Iran. Results indicated that the salinity stress caused an increase in malondialdehyde and proline contents, activity of superoxide dismutase and catalase enzymes, and essential oil content while decreased total chlorophyll content and menthol percentage. In 60 mM salinity, we observed 20.10% decreases of total chlorophyll compared to the control treatment (free salinity). In the interaction effects of salinity and spraying, the highest MDA content was related to the non-application of plant growth regulators under 60 mM salinity (13.8 mol/g FW) and the lowest was the foliar application of SA under free salinity conditions (5.35 mol/g FW). The highest proline content was observed in the non-application of plant growth regulators under high level of salinity (60 mM) by 7.68 µmol/g FW, which had an increase of 73.5% compared to the control treatment. Finally, the application of growth regulators under salinity stress moderated the negative effects of salinity stress by increasing the synthesis of malondialdehyde, proline, and antioxidant enzymes.