Salinity stress is a major limiting factor for the growth and productivity of both field and ornamental crops, causing reductions in morphological growth and photosynthesis, ionic imbalances, and increased oxidative stress. This study investigated the effects of foliar-applied gibberellic acid (GA₃) on the morphological, physiological, and biochemical responses of African marigold (Tagetes erecta L.) under different salinity levels. The experiment was conducted during 2025–2026 in the greenhouse of Ilam University, with daytime and nighttime temperatures of 28-30 °C and 18-20 °C, respectively, and relative humidity of 60-75%. In this study, a factorial experiment was designed and implemented in a completely randomized design with three replications. The experimental factors included three concentrations of GA₃ (0, 100, and 200 μM( and four salinity levels (0, 50, 100, and 150 mM NaCl). Our results showed that increasing salinity to 150 mM significantly reduced various traits. These traits included reduced plant height, stem diameter, root length and volume, leaf area, and fresh and dry biomass of shoots and roots, as well as reduced photosynthesis rate, transpiration, and relative water content. Phytochemical compounds such as chlorophyll, carotenoids, lutein, and zeaxanthin were reduced under salinity stress; however, GA₃ treatments increased lutein and zeaxanthin content in petals compared to untreated controls, although their levels declined at higher salinity intensities. Salinity also led to increased ion leakage, hydrogen peroxide (H₂O₂), lipid peroxidation (MDA), proline accumulation, and activities of polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL). The content of γ-aminobutyric acid (GABA) and activities of its biosynthetic enzymes, glutamate decarboxylase (GAD) and GABA transaminase (GABA-T), increased in response to salinity, with the highest elevations observed at higher salinity levels. Foliar application of GA₃, particularly at 200 μM, improved morphological and physiological traits. At the highest salinity level (150 mM), plant height, stem diameter, root length and volume, and fresh and dry shoot biomass significantly increased compared to untreated controls. GA₃ enhanced photosynthesis and relative water content while reducing excessive transpiration, improved ionic balance (increased K⁺, decreased Na⁺, and higher K⁺/Na⁺ ratio), and enhanced antioxidant enzyme activities (SOD, CAT, POD) and protective compounds (soluble proteins and phenolics), thereby strengthening plant defense against salinity. GA₃ also increased GABA levels and boosted GAD and GABA-T activities. This indicates that this treatment effectively activated signaling and metabolic pathways in response to salt stress. In this experiment, the greatest increase in proline, GABA, GAD and GABA-T induced by GA₃ occurred at moderate salinity (100 mM), and the application of GA₃, especially at a concentration of 200 μM, improved salinity tolerance in African marigold. It improves growth, photosynthesis, water status, ionic balance, antioxidant activity, and GABA pathways. This helps the plant defend itself against salt stress.
