Efficacy Of Yarrowia Lipolytica In The Biocontrol Of Green Mold And Blue Mold In Citrus Reticulata And The Mechanisms Involved

Blue mold and green mold are two main fungal diseases of Citrus reticulata Blanco(mandarin orange)worldwide.Traditionally,chemical fungicide is the most effective way to control postharvest diseases of mandarins,but long-term use of chemical fungicides can cause serious problems.In recent years,some achievements have been achieved through biological control methods,but few of antagonistic yeasts can inhibit the invitation of Penicillium spp.fungi of mandarins for their strong invasiveness,and mechanisms which antagonistic yeasts control diseases are complex.Thence,it is a pressing task to find an antagonistic yeast that can inhibit both blue mold and green mold of mandarins.In this study,Yarrowia lipolytica was used against blue mold and green mold of mandarins,and relative disease-resistant mechanisms were investigated in many aspects.Results of this study were as follows:1.Y.lipolytica inhibited the occurrence of blue mold and green mold of mandarins in a dose-dependent way,and the colony diameter of P.digitatum and P.italicum were negatively correlated with Y.lipolytica concentration.Furthermore,Y.lipolytica significantly reduced the natural decay incidence of mandarins and had no side effects on their quality paraments after 40 days storage.2.On the one hand,Y.lipolytica inhibited spore germination and germ tube length of P.digitatum and P.italicum directly.Y.lipolytica can get more nutrients and space than pathogens for its better environmental adaptability,and this yeast can adsorb in the hyphae of P.italicum and P.digitatum which inhibited pathogens to get nutrients and had bad effects on their normal metabolism.On the other hand,Y.lipolytica improved content of disease-resistant metabolites and enzyme activity which can enhance disease-resistant ability of mandarins.This yeast induced higher activity of antioxidantrelated enzymes which can avoid the threat of reactive oxygen species(ROS).And peroxidation of membrane was weakened after treating by Y.lipolytica,it can reduce the damage of membrane and organelle of mandarins.3.The transcriptomics technique was used to investigate the molecular mechanisms of disease-resistance in mandarins after Y.lipolytica induction,and the results showed:(1)Y.lipolytica activated some genes important for phenylpropanoid biosynthesis and stilbenoid,diarylheptanoid and gingerol biosynthesis in mandarin peel tissue which promoted the biosynthesis of phytoalexins.(2)Many genes related to starch and sucrose metabolism were significantly repressed by Y.lipolytica treatment which was beneficial to the accumulation of pectin,and large amounts of up-regulated genes related to synthesis of lignin and sterol strengthened the cell wall and cell membrane.(3)Y.lipolytica induced some genes up-regulated in the pathway of plantpathogen interaction.These genes could make the stomatal closure of mandarin peel,trigger the hypersensitivity response,strengthen the cell wall and activate the expression of defense-related genes.(4)After Y.lipolytica treatment,up-regulation of glutathione metabolism and numerous genes related to remove ROS could reduce the oxidative stress on mandarins.(5)Y.lipolytica induced the expression of genes related to JA,SA and ET synthesis and signal transduction in mandarins,thereby activating downstream defense-related genes and triggering a series of immune responses.4.The metabolomic analysis and comparison of mandarins in response to Y.lipolytica was analyzed,and the results showed:(1)Y.lipolytica treatment increased the content of phenylpropanoid,flavonoid,citric acid,succinic acid,4-hydroxybenzoic acid,riboflavin,citrine and protocatechuic acid which could inhibit the growth of fungi and enhance the ability of removing ROS.(2)The accumulation of betaine maintained intracellular osmotic pressure and protect the biological activity of macromolecules in mandarins.(3)The increase of purine ensured the normal operation of basic life activities in cells.(4)The increase of 4-hydroxysphingosine stabilized cell membrane structure and act as an important signal molecule in response to stress.(5)The decrease of leucine could delay the aging of mandarins.