Modulation of Physiological Responses in Damask Rose to Combined Salinity and Botrytis cinerea Stress by Chitosan and Nano‐Chelated Copper

Salinity exacerbates Botrytis cinerea damage, posing a major constraint to Rosa × damascena greenhouse cultivation. This study investigated the physio‐biochemical responses of R. × damascena to individual and combined salinity (50 and 100 mM NaCl/CaCl 2 ) and B. cinerea stress, evaluating the mitigating potential of foliar‐applied chitosan (0.4% w/v) and nano‐chelated copper (NCC; 1000 and 2000 mg L −1 ). Using a four‐way factorial design (36 treatments; N = 108), we assessed morphological traits, photosynthetic pigments, proline content, antioxidant enzyme activities (superoxide dismutase, peroxidase, catalase), and membrane integrity via electrolyte leakage (EC). Combined stress resulted in nonadditive physiological deterioration, characterized by significantly elevated EC and disease indices alongside suppressed antioxidant capacity and pigment retention compared to individual stressors. While salinity alone induced dose‐dependent osmotic adjustments, its combination with B. cinerea overwhelmed host defense mechanisms, leading to severe membrane destabilization. Both chitosan and NCC applications partially restored physiological homeostasis by enhancing superoxide dismutase and peroxidase activities, reducing electrolyte leakage, and preserving chlorophyll and carotenoid levels. The co‐application of chitosan and NCC demonstrated superior efficacy, particularly under moderate combined stress, by synergistically improving membrane stability and reducing leaf and flower disease severity. However, antioxidant responses were context‐dependent, with catalase activity remaining largely unaffected, suggesting a partial rather than complete restoration of redox balance. These findings indicate that while chitosan and NCC offer promising mitigation strategies against compounded abiotic–biotic stress, their efficacy is limited by stress intensity. Future work must validate environmental safety, ion dynamics, and field efficacy to ensure sustainable rose production.