Biocontrol Efficacy Of Wickerhamomyces Anomalus Against Blue Mold Decay Of Apples And The Mechanisms Involved

China is the leading producer of apples globally.Apples are highly favored fruit worldwide because of their high nutritional value.However,they are highly susceptible to various pathogenic fungal infections during harvest,packaging,storage,and transportation.Blue mold decay is one of the most important postharvest diseases of apples caused by Penicillium expansum.At present,the use of chemical reagents is still the main method in controlling postharvest diseases of apples.Yet,chemical additives utilization produces negative impacts such as pollute the environment,endanger human health,and develop pathogen resistance to the antagonists.In recent years,numerous studies have been conducted to find alternative methods to replace the use of chemical reagents.It is reported that the use of biological control such as antagonistic yeasts in controlling postharvest diseases of fruits and vegetables has been gradually discovered to have a better control effect against postharvest penicillium of apples.Therefore,selecting a yeast strain with a high biocontrol effect to inhibit blue mold decay and expounding its mechanism can promote the commercial application of antagonistic yeast in China in the future.In this study,Wickerhamomyces anomalus was taken to explore its biocontrol effects on postharvest blue mold decay of apples.Furthermore,the mechanism of W.anomalus in controlling postharvest blue mold decay of apples was expounded from the point of view of physiological mechanism and molecular mechanism.The main research contents of this study are as follows:1.W.anomalus could significantly reduce the blue mold decay of apples,in which the maximum inhibition was obtained when the concentration of W.anomalus was 1×10~8 cells/m L.Furthermore,after 35 days of storage,W.anomalus significantly reduced the fruit decay under ambient conditions,without generating any change in fruit quality.2.The physiological mechanisms of W.anomalus to control postharvest diseases of apples mainly include:W.anomalus could inhibit the germination rate and tube length of P.expansum;W.anomalus could inhibit the growth of P.expansum;W.anomalus could quickly colonize and grow steadily on the wounds or surfaces of apples;W.anomalus could induce the activity of apple-related resistance enzymes(PPO,POD,CAT,PAL,APX,CHI)and the content of resistance-related substances,including total phenols and flavonoids.3.Transcriptomics was performed to investigate the molecular mechanisms of disease resistance in apples after W.anomalus induction.The results showed that there were 2215 differentially expressed genes in apples after W.anomalus induction,of which 630 were up-regulated and 1585 were down-regulated.The differentially expressed genes are mainly concentrated in improving resistance-related genes,resistance-related substance synthesis genes,plant signal transduction pathway genes,enhancing plant cell wall strength genes,antioxidant stress-related genes,and maintaining normal metabolism-related genes.4.The effect of W.anomalus treatment on apple metabolites was explored through metabolomics.The results showed that:among the 141 differential metabolites produced by W.anomalus treatment in positive ion mode,80 were up-regulated and 61down-regulated,while 24 differential metabolites were detected in negative ion mode,consisting of 22 up-regulated and 2 down-regulated.Through functional analysis of differential metabolites,it could be known that W.anomalus induces lipids and lipid molecules,phenylpropanes and polyketides,benzoates,amino acids,purines,organic acids and their derivatives in apples.Changes in the content of these substances could improve the disease resistance of apples,improve the ability of apples to scavenge ROS free radicals,maintain the normal metabolism of apples,and enhance the strength of cell walls.