Methyl Jasmonate Modulates Morphophysiological, Photochemical, and Nutritional Responses to Alleviate Salt Stress in Safflower

Abstract

This study aimed to evaluate whether foliar application of methyl jasmonate (MeJa) at different concentrations could mitigate salt stress and its effects on the growth, physiology, water relations, osmotic adjustment, and mineral nutrition of safflower ( Carthamus tinctorius L.). Plants were subjected to three levels of electrical conductivity of irrigation water (0.5, 3.5, and 6.5 dS m⁻¹) and three foliar MeJa concentrations: 0, 250, and 500 µM. Increasing salinity reduced plant growth, biomass accumulation, gas exchange, chlorophyll indices, photochemical performance, relative water content, leaf mass per area, starch content, and leaf P and K concentrations, while increasing electrolyte leakage, leaf succulence, proline, and total soluble sugars. MeJa alleviated selected salt-induced limitations in a concentration- and stress-dependent manner. At 3.5 dS m⁻¹, 250 µM MeJa produced the most consistent responses across several traits, whereas at 6.5 dS m⁻¹, 500 µM MeJa improved multiple growth, gas-exchange, photochemical, and water-relation variables. MeJa did not reduce electrolyte leakage. Foliar MeJa can partially improve safflower performance during early growth under saline irrigation, but the most effective concentration depends on salinity level and the trait evaluated. Under controlled conditions, 250 µM was the more consistent treatment at moderate salinity, whereas 500 µM benefited several traits at high salinity. Full-cycle field studies using mixed-salt waters are required before agronomic recommendations can be made.