Antifungal Activity And Mechanism Of Natamycin Against Colletotrichum G Oeosporioides

Mango(Magnifera indica L.)is an important tropical economic fruit with its desirable flavor,rich nutrition and high marketing value.However,as a typical climacteric fruit,mango is very susceptible to various pathogens during its after-ripening stage,and leading to postharvest diseases which often cause fruit decay and severe economic losses.Anthracnose caused by Colletotrichum gloeosporioides(Penz.)is one of the major aggressive posthairvest diseases in mango fruit,and its control has become the focus of research at home and abroad.Natamycin is a common biological preservation in food industry and having several advantages such as high effectiveness at low concentration,a broad range of activity against spoilage fungi and no resistance to human.In this study,the inhibitory effects of natamycin against Colletotrichum gloeosporioides and anthracnose were investigated,and its possible antifungal mechanism was revealed from cell biology,physiology and biochemistry level.The results are as follows:(1)Natamycin has effective antifungal activity against colony growth of C.gloeosporioides and in a dose-dependent.The virulence regression equation was y=2.6339 x+3.9567,R2=0.985,and half-inhibition concentration was 2.20 mg L-1.Natamycin can also significantly inhibit spore germination and germ tube elongation at 2 mg L-1.In vivo experiment results showed that Natamycin could suppress the incidence of anthracnose and the expansion of anthracnose lesions on mango fruit inoculated with C.gloeosporioides,thus indicating that natamycin had significant control effect on the anthracnose of mango fruit.(2)The morphology of hyphae and conidia of C.gloeosporioides were observed after treatment with 2 mg L-1 natamycin.The mycelia at the edge of the colony grew densely,and branches decreased.The conidia became swollen and distorted,the germ tube grew abnormally.Scanning electron microscopy(SEM)clearly showed the mycelia with deformed,sagged and shrunk,even be damaged and fractured.Transmission electron microscopy showed the mitochondria decreased and vacuoles increased after treatment with natamycin for 6 h.and cell membranes shrunk,plasmolysis was serious,mitochondria decreased significantly,conidia were damaged seriously with some organelles deformed and distributed disorderly after 10 h.(3)After natamycin treatment,the relative permeability,the leakage of nucleic acid and reducing sugar and the content of soluble protein of gloeosporioides increased.In addition,natamycin reduced the ergosterol content in the cell membrane and membrane integrity of C.gloeosporioides,and meanwhile promoting the accumulation of malondialdehyde and reactive oxygen species,resulting in the loss of cell membrane integrity and mitochondrial degradation.(4)The hardness and the contents of titratable acid and vitamin C of mango fruits soaked with natamycin were higher than those of the control during storage at room temperature.The increase of soluble solids content was delayed,and the emergence of respiratory peak was delayed to some extent.