Abstract:

In order to prevent citrus fruit decay caused by Penicillium italicum and P. digitatum in postharvest，a self-screened strain of Lysobacter enzymogenes LE16 applied to test，and the inhibitory effects of self-digestive fermentation liquid and volatile organic compounds（VOCs）of LE16 on the mycelium growth and spore germination of P. italicum and P. digitatum were studied. In addition，the antibacterial components of self-digestive fermentation liquid were analyzed by liquid chromatography-mass spectrometry（LC-MS）. Furthermore，the control effect of strain LE16 on P. italicum and P. digitatum was determined by the fruit trauma inoculation and commercial simulation storage. Results from the pure culture experiment showed that both self-digestive fermentation liquid and volatile organic compounds significantly inhibited the mycelium growth of P. digitatum and P. italicum by 100% and 77.52%-91.11%，respectively. The self-digestive fermentation liquid also reduced the spore germination rate by > 96%，and resulted in the mycelial vacuolation and distortion. No significantly differences on the mycelium growth of P. digitatum and P. italicum were observed for the inhibition effect of self-digestive fermentation liquid that was treated under 80，90 and 100 ℃ for 30 minutes. The result of self-digestive fermentation liquid through LC-MS analysis showed that LE16 produced a number of secondary metabolites including cinnamaldehyde，cinnamic acid，dodecanoic acid and γ-butyrolactone and other antibacterial chemicals. In the fruit trauma inoculation test with P. italicum，the activities of superoxide dismutase and catalase in citrus peel were increased，but the content of malondialdehyde and cell membrane permeability was decreased. Significant decreases in the disease incidence and disease index of citrus fruit were ranked as the control > LE16 > prochloraz > 50% LE16 + 50% prochloraz，while the control efficacy showed an opposite trend. There were no significant changes in the quality of citrus fruits under the self-digestive fermentation liquid treatment during the commercial simulation storage. The control effects were 50.00% under LE16，83.33% under prochloraz and 75.93% under 50% LE16 + 50% prochloraz after 15 days storage，respectively. The results demonstrate that self-digestive fermentation liquid of LE16 as a promising biological preservative for the postharvest fruit preservation，can decrease the mycelium growth of P. digitatum and P. italicum and related fruit disease incidence，and the self-digestive fermentation liquid application will partly reduce the use of chemical fungicides without changes in the quality of citrus fruits.

Key words: citrus, postharvest, biological control, Lysobacter enzymogenes, Penicillium digitatum, Penicillium italicum, secondary metabolite