Antifungal activity and mechanism of action of tannic acid against Penicillium digitatum

Penicillium digitatum is a destructive post-harvest pathogen of citrus fruit during storage and marketing. The aim of this study is to evaluate the activity of the natural polyphenolic compounds, tannins, on P. digitatum. Tannins acted against P. digitatum by inhibiting its mycelial growth and spore germination. In vivo tests showed that tannins significantly (P < 0.05) decrease the disease symptoms of P. digitatum in artificially inoculated citrus fruit. Storage tests also showed that tannins reduce the disease severity of green mold on citrus fruit by 70%. To determine the antifungal mechanism of tannins on P. digitatum, we evaluated the integrity of the cell wall and the permeability of the membrane. The disruption of cell wall and the plasma membrane caused leakage of the intracellular contents, such as sugars. These findings suggest that the cell wall of P. digitatum is the target for tannins and that they can potentially be used as an alternative to control citrus green mold.