Methyl jasmonate and ascorbic acid enhance salinity tolerance in pot marigold (Calendula officinalis L.) through improved morphophysiological and biochemical traits.

Salinity stress severely limits the growth and floral quality of ornamental plants in arid regions. This study evaluated the combined effects of foliar-applied methyl jasmonate (MeJA) and ascorbic acid (AA) on salinity tolerance in pot marigold (Calendula officinalis L.) under 8.64 dS m⁻¹ salinity stress. A factorial greenhouse experiment tested three MeJA concentrations (0, 100, 200 µM) and three AA concentrations (0, 100, 200 mg L⁻¹), with three replicates of six plants per treatment (18 plants total per treatment). The combined 200 µM MeJA and 200 mg L⁻¹ AA treatment significantly enhanced flower number (80%), diameter (37%), and longevity (33%), as well as shoot biomass (up to 50%) and root biomass (up to fourfold) compared to controls. It also reduced electrolyte leakage by 53% and increased relative water content (21%), photosynthetic efficiency (400%), and photosystem II performance (71.8%) relative to controls. Furthermore, antioxidant enzyme activities (catalase: 38.3%; peroxidase: 50%), proline accumulation (188.6%), and protein content (159.5%) increased compared to controls, reflecting enhanced osmotic regulation and cellular protection. These findings demonstrate that MeJA and AA synergistically improve salinity tolerance, boosting physiological resilience and floral quality under salt stress. Further field trials are needed to validate and optimize this approach for broader application.