Antifungal Effects of ε-Poly-L-lysine on Lasiodiplodia theobromae Causing Fruit Rot of Passiflora caerulea L. and Its Mechanism

To investigate the inhibitory effects and mechanism of ε-poly-L-lysine (ε-PL) against the Lasiodiplodia theobromae causing fruit rot on postharvest passions, the changes of L. theobromae mycelial growth, conductivity, malonaldehyde content, intracellular materials leakage, contents of cell membrane and cell wall components, adenosine triphosphatase activity, propidium iodide staining, and Fourier transform infrared spectroscopy were determined after being treated with ε-PL, and the inhibition effects of ε-PL on L. theobromae-induced fruit rot of harvested passion fruits were studied. In vitro assay showed that ε-PL inhibited the mycelial growth of L. theobromae, and the inhibitory effects increased with increasing ε-PL concentration. The optimal inhibitory concentration of ε-PL was 100 mg/L. Additionally, ε-PL might increase the conductivity and malondialdehyde content, promote the leakage of intercellular nucleic acid and protein, decrease the contents of ergosterol, total lipids and chitin, reduce the activity of adenosine triphosphate. Moreover, ε-PL also changed the mycelial morphology of L. theobromae, resulting in the mycelial distortion, and lowered the number of methylene, methyl, hydroxyl and carbon-oxygen bonds in mycelium of L. theobromae. Furthermore, ε-PL could suppress the L. theobromae-induced fruit rot development of harvested passion fruits. Therefore, ε-PL could display the antifungal activity on L. theobromae through destroying the structure of cell membrane and cell wall, promoting the leakage of intracellular materials, disordering the energy metabolism, and destroying the structure of biological macromolecules.