Foliar melatonin application enhances strawberry tolerance to combined salinity and drought stress: Insights into physiological and biochemical mechanisms

Abstract

Background

Drought and salinity are major abiotic constraints in strawberry production, adversely affecting plant growth, photosynthesis, and cellular stability. Melatonin has emerged as a promising biostimulant due to its role in regulating stress responses and antioxidant defense mechanisms in plants.

Objective

This study aimed to assess the effectiveness of foliar melatonin application in mitigating the effects of individual and combined drought and salinity stress in strawberry (Fragaria × ananassa Duch. cv. ‘Albion’).

Method

The experiment was conducted in a completely randomized design. Strawberry plants were exposed to salinity stress (35 mM NaCl), drought stress (40% reduced irrigation), or their combination. Melatonin was applied foliarly at 50 µM under stress conditions. Growth parameters, chlorophyll content, membrane permeability, oxidative stress indicators, proline content, and antioxidant enzyme activities were evaluated.

Results

Under drought stress, melatonin-treated plants exhibited significant improvements in leaf number (5.7%), fresh weight (4.2%), and chlorophyll content (11.2% SPAD increase) compared to untreated plants. Melatonin significantly reduced malondialdehyde (MDA) accumulation by 24.4% under drought (9.31 vs. 12.31 nmol g⁻¹ FW) and by 18.6% under salinity stress (8.49 vs. 10.43 nmol g⁻¹ FW). Furthermore, melatonin enhanced antioxidant defense, with superoxide dismutase (SOD) and peroxidase (POD) activities increasing by 28.1% and 12.7%, respectively, under drought stress compared to non-melatonin drought-stressed plants. In contrast, under combined drought and salinity stress, melatonin showed limited effectiveness; although it supported survival, the plants displayed reduced growth performance and a significant increase in membrane permeability (reaching 21.13%), suggesting a physiological threshold under multifaceted stress.

Conclusions

Foliar melatonin application effectively improves strawberry tolerance to individual drought or salinity stress by enhancing growth performance and antioxidant capacity, whereas its protective effect is markedly reduced under combined stress conditions. These findings suggest that while melatonin is a sustainable strategy for single-stress mitigation, its efficacy is constrained under the synergistic pressure of the abiotic stress matrix.