Red Emissive Carbon Dots Photosensitizers for Plant Protection: Highly Effective and Plant-Safe Photodynamic Inactivation of Botrytis cinerea

Gray mold caused by Botrytis cinerea severely threatens many crops and is increasingly difficult to control due to fungicide resistance and residue concerns. Here, we evaluate red-emissive, positively charged carbon dots (PCDs) as photosensitizers for plant photodynamic protection. PCDs, prepared hydrothermally, showed broad visible absorption and strong singlet oxygen generation. Under visible light, PCDs markedly inhibited B. cinerea mycelial growth in vitro, achieving ≈99.9% inhibition at 200 mg L–1. Microscopy and biochemical assays revealed severe cell wall and membrane damage, with lipid peroxidation and leakage of intracellular contents. Transcriptomic analysis showed global reprogramming, with activation of ROS-detoxification pathways and suppression of growth- and virulence-related genes. In greenhouse tomato assays, PCDs-mediated photodynamic treatment afforded up to 93.2% disease control, comparable to carbendazim, without detectable effects on chlorophyll status or biomass. These results identify PCDs as a promising, plant-safe, and green alternative for managing gray mold.