Background: Drought stress remains a primary abiotic constraint limiting crop productivity globally, with yield losses in semi-arid agricultural zones remaining substantial due to oxidative damage, stomatal closure, and disrupted photosynthetic machinery.¹² Biostimulant applications, particularly chitosan oligosaccharides (COS), have been proposed as a scalable, eco-friendly strategy for enhancing drought resilience in resource-constrained farming systems ^[3].

Objective: This study evaluated the effectiveness of a 12-week COS foliar application protocol, comprising pre-stress priming and post-stress recovery treatments, on photosynthetic efficiency, antioxidant enzyme activity, and biomass accumulation in tomato (Solanum lycopersicum L.) under simulated drought conditions.

Method: A two-arm, parallel-group design compared COS-treated plants against water-sprayed controls under polyethylene glycol (PEG)-induced drought stress. **This study uses a simulated dataset created for academic training purposes;** all physiological measurements, growth parameters, and enzymatic activity data were generated to reflect plausible patterns consistent with published plant biostimulant literature and do not represent data collected from real experiments or actual greenhouse trials. One hundred plants (n = 50 per treatment) were monitored over 12 weeks, with physiological parameters measured at baseline and every three weeks.

Key Results: Mean net photosynthetic rate declined from 18.4 to 6.2 μmol CO₂ m⁻² s⁻¹ in control plants over 12 weeks of drought, compared with a decline from 18.6 to 13.8 μmol CO₂ m⁻² s⁻¹ in the COS-treated arm. Relative water content at 12-week follow-up was higher in the COS arm across all developmental stages, with the largest absolute difference observed during the flowering stage (72.4% versus 58.9%). Membrane lipid peroxidation (MDA content) was the most severely affected parameter in untreated controls at peak stress (3.8-fold increase over baseline).

Conclusion: The COS foliar intervention was associated with substantially greater maintenance of photosynthetic function and membrane integrity than untreated controls, suggesting that COS-based biostimulants represent a promising, scalable model for drought mitigation in semi-arid tomato production, pending confirmation with data from an actual implemented greenhouse or field program.