Zhi-Jing Ni, Ruo-Tong Yang, Run-Hui Ma, Wei Wang, Kiran Thakur, Zhao-Jun Wei
Alternaria alternata, a major postharvest pathogen of grapes and goji berries, causes black spot disease and produces Alternaria toxins that threaten food safety and human health. Carbon quantum dots (CQDs) are emerging promising nanophotosensitizers for photodynamic antimicrobial therapy (PDT), yet their efficacy against A. alternata remains unclear. This study systematically investigated the antifungal effect of CDs-PDT against A. alternata and revealed the possible mechanisms at cellular and physiological-biochemical levels. The inhibitory effect of CDs-PDT against A. alternata exhibited a clear concentration-dependent characteristic, achieving a 100% inhibition rate at 48 h; meanwhile, mycelial dry and fresh weights were reduced by 98.4% and 94.7%, respectively. The possible inhibitory mechanism of CDs-PDT against A. alternata was revealed that it damages cell wall and membrane integrity, evidenced by scanning electron microscope (SEM) observation, propidium iodide (PI) staining, increased malondialdehyde (MDA) content, and altered lactate dehydrogenase (LDH) and alkaline phosphatase (AKP) activities. Intracellular reactive oxygen species (ROS) accumulation was confirmed via 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA), 3,3'-diaminobenzidine (DAB), and nitroblue tetrazolium (NBT) staining, accompanied by initial upregulation followed by collapse of antioxidant defenses, such as superoxide dismutase (SOD), glutathione peroxidase (GPX), catalase (CAT), glutathione (GSH). CDs-PDT further impaired energy metabolism, reflected by decreased adenosine triphosphate (ATP) and acetyl-CoA content. Additionally, CDs-PDT can also increase A. alternata's sensitivity to exogenous stress. These results indicate that CDs-PDT is an effective strategy for controlling A. alternata diseases and provide mechanistic insights into future nanophotosensitizer-based antifungal research in postharvest grape and goji berries management.