Melatonin-mediated alleviation of salinity stress in diverse mango (Mangifera indica L.) rootstock genotypes

Mango (Mangifera indica L.), a tropical fruit crop with significant commercial value, is particularly vulnerable to salt stress. Salinity exposure causes severe physiological disruptions, including leaf burning, chlorosis, and stunted growth, especially in the early phases of plant development, and can be mitigated by salt tolerance. The current study evaluated the effectiveness of exogenous melatonin in mitigating salinity stress at 60 mM NaCl. The findings showed that applying melatonin at an optimal level of 150 μM improved photosynthetic efficiency, relative water content, and membrane stability index, thereby enhancing plant performance. Furthermore, melatonin treatment significantly reduced the build-up of malondialdehyde, a marker of membrane lipid peroxidation, while maintaining increased levels of phenol, proline, and total sugars. Increased activity of superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase enzymes, which together reduced oxidative stress, indicated a stronger antioxidant defense system, strongly linked to enhanced tolerance. Correlation analysis further revealed strong positive relationships among physiological and biochemical parameters, whereas malondialdehyde exhibited negative correlations with all other traits. Also, principal component analysis of six rootstock genotypes under salinity showed that melatonin enhanced stress tolerance in Kurukkan, K 106, and Olour by boosting antioxidant enzymes and preserving photosynthetic pigments. Overall, our findings demonstrate that melatonin increases mango rootstock resilience in saline environments by preserving cellular stability and regulating redox equilibrium.