Cell‐Free Supernatant of <em>Bacillus subtilis</em> Suppresses the Mycelial Growth of <em>Penicillium expansum</em> by Destroyed the Cell Membrane Integrity and Provoke Cell Death

Penicillium expansum inflicts significant economic damage in the fruit and vegetable industry due to its wide distribution and ability to infect a diverse range of hosts. Therefore, developing safe and environmentally sustainable strategies to suppress the growth of this pathogen is of critical importance. Bacillus subtilis, recognized for its broad antimicrobial activity and widespread occurrence, has been widely utilized in the biological management of plant diseases. This research seeks to assess the inhibitory potential of B. subtilis against P. expansum. The cell-free supernatant (CFS) derived from B. subtilis significantly suppresses the germination spores, germ tube extension, and hyphal development of P. expansum. It also reduces disease incidence in grapes and citrus and suppresses the expansion of lesions. Further investigate had shown that it can induced mycelium reactive oxygen species (ROS) accumulation, destroyed the cell membrane integrity, led to leakage of cytoplasmic contents and induced membrane lipid peroxidation. Moreover, exposure to high concentrations of CFS results in mycelial contraction and morphological abnormalities, triggering the disintegration of intracellular organelles and markedly upregulating the expression of apoptosis-associated genes. The self-protective response elicited by 5% CFS is insufficient to counteract the extent of cellular damage, ultimately driving cells toward a dynamic, multistage, and disintegrative form of cell death. The findings of this study offer a theoretical foundation for managing P. expansum after harvest.