The ester derivatives of ferulic acid exhibit strong inhibitory effect on the growth of Alternaria alternata in vitro and in vivo

Alternaria alternata is the principal pathogenic fungus causing postharvest black spot disease of Korla pear, leading to enormous economic losses. This study aimed to explore the antifungal activity of ferulic acid (FA) and its two simple esterified derivatives, methyl ferulate (MF) and ethyl ferulate (EF), against A. alternata in vitro and in vivo, and to reveal the underlying inhibitory mechanisms. The results showed that MF and EF exhibited stronger inhibitory effects than FA on mycelial growth, spore germination and germ tube elongation of A. alternata in vitro, and on reducing the development of black spot disease in Korla pear fruit. Scanning electron microscopy images indicated that the surface morphology of A. alternata hyphae treated with FA, MF, and EF presented irreversible deformation, and transmission electron microscopy observation further demonstrated that MF and EF caused more serious damage to the cell membranes, cytoplasm, and organelles of A. alternata than FA, which impeded the normal growth of A. alternata. Notably, EF was slightly better than MF in inhibiting spore germination and damaging cell ultrastructure of A. alternata. In addition, propidium iodide staining suggested that FA, MF, and EF treatments damaged the plasma membrane integrity of A. alternata spores. At the same conditions, MF and EF treatments induced more leakage of intercellular electrolytes, nucleic acids and proteins of A. alternata than FA, indicating the increase of cell membrane permeability. Taken together, all these results evidenced that MF and EF exerted stronger antifungal activity than FA against A. alternata in vitro and in vivo through membrane damage mechanism, therefore they can be used as promising green substitutes to control postharvest black spot disease on Korla pear fruit.