Elevated Atmospheric CO₂ Concentrations Reduce Tomato Mosaic Virus Severity in Tomato Plants

Tomato mosaic disease, caused by tomato mosaic virus (ToMV), was studied under naturally elevated [CO₂] concentrations to simulate the potential impacts of future climate scenarios on the ToMV–tomato pathosystem. Tomato plants infected with ToMV were cultivated under two distinct [CO₂] environments: elevated [CO₂] (naturally enriched to approximately 1000 μmol mol⁻¹) and ambient [CO₂] (ambient atmospheric [CO₂] of 420 μmol mol⁻¹). Key parameters, including phytopathological (disease index, ToMV gene expression), growth-related (plant height, leaf area), and physiological traits (chlorophyll content, flavonoid levels, nitrogen balance index), were monitored to assess the effects of elevated [CO₂]. Elevated [CO₂] significantly reduced the disease index from 2.4 under ambient [CO₂] to 1.7 under elevated [CO₂]. Additionally, viral RNA expression was notably lower in plants grown at elevated [CO₂] compared to those under ambient [CO₂]. While ToMV infection led to reductions in the chlorophyll content and nitrogen balance index and an increase in the flavonoid levels under ambient [CO₂], these physiological effects were largely mitigated under elevated [CO₂]. Infected plants grown at elevated [CO₂] showed values for these parameters that approached those of healthy plants grown under ambient [CO₂]. These findings demonstrate that elevated [CO₂] helps to mitigate the effects of tomato mosaic disease and contribute to understanding how future climate scenarios may influence the tomato–ToMV interaction and other plant–pathogen interactions.