Biocontrol Efficacy Of Kluyveromyces Marxianus XZ1 Against Blue Mold Decay Of Postharvest Apples And The Mechanisms Involved

Output and consumption of apple in China rank first in the world.However,the postharvest decay caused by Penicillium expansum generate negative effects on the well development of apple industry.Patulin(PAT),the secondary metabolite produced by P.expansum,is highly toxic to bacteria,plants and animals,which seriously threatens ecological balance and consumer health.The application of traditional chemical fungicide can effectively control the contamination of P.expansum and PAT in postharvest apple,but causes problems such as pesticide residues and drug-resistant strains.It is meaningful to develop economic,green and efficient biological strategies to control P.expansum and PAT in postharvest apple for apple industry development and consumer health.Some studies have shown that the antagonistic yeast can effectively reduce mold decay in apple during storage and shown the potential to replace traditional chemical fungicides.Therefore,this paper intends to screen the antagonistic yeast strains with control effect on P.expansum and PAT contamination and to reveal the mechanism of actions of antagonistic yeast against the P.expansum.The antagonistic yeast XZ1 with the best effect on controlling blue mold disease caused by P.expansum in apple was acquired from 5 yeast strains stored in our laboratory.The XZ1 was identified as Kluyveromyces marxianus,based on single colony morphological observation,sequencing the conserved sequences of the internally transcribed space(ITS)and analysis of the evolutionary tree,and was named K.marxianus XZ1 and preserved in China typical culture preservation center with the preservation number CCTCC NO:M 2022014.On potato dextrose agar(PDA)medium,the colony diameter of P.expansum ZL treated with K.marxianus XZ1(1×108 ce1ls/mL)was significantly reduced(2.57 cm)compared with the control group(4.38 cm).K.marxianus XZ1 could significantly reduce the disease incidence and lesion diameter of apple caused by P.expansum,and effectively control PAT accumulation in Potato Dextrose Broth(PDB)medium and apple.K.marxianus XZ1 sprayed on the surface of apple in natural storage can significantly reduce the natural disease incidence of apple,and is conducive to the maintenance of physical and chemical quality of apple during storage.Researches on the mechanism of K.marxianus XZ1 on controlling P.expansum showed that K.marxianus XZ1 completely inhibited the spore germination and mycelium growth of P.expansum ZL in PDB medium within 18 h.The results of scanning electron microscope(SEM)observation and wound growth dynamics of K.marxianus XZ1 showed that K.marxianus XZ1 could colonize the wound quickly and establish niche advantage of competing nutrition and space.It was also observed that K.marxianus XZ1 destroyed P.expansum ZL mycelia through parasitism.The antibacterial substances in the metabolites of K.marxianus XZ1 can inhibit the growth of P.expansum ZL.The induction effect of K.marxianus XZ1 on the resistance of apple was further studied.The results showed that K.marxianus XZ1 could significantly activate the activity of catalase(CAT)(1,4 days)and ceroxidase(POD)(1,2,5,7 days),Polyphenol Oxidase(PPO)(2,5 days)at different time.The results showed that K.marxianus XZ1 controlled the infection of P.expansum on apple through the mechanism of competition for nutrient and space,secretion of antibacterial substances,parasitism,induction of resistance related enzyme activities in apple,etc.The molecular mechanism of defense response to the infection of P.expansum in apple induced by K.marxianus XZ1 was studied based on transcriptomic analysis.There are 35,3197 and 1193 genes were significantly expressed on day 1,2,and 3 in apple after treatment with K.marxianus XZ1 compared with the apple untreatment,respectively.Kyoto Encyclopedia of Genes and Genomes(KEGG)analysis on the up regulated genes indicated that the pathway related to plant resistance to pathogens,including plant-pathogen interaction pathway,plant hormone signal transduction pathway,mitogen activated protein kinase(MAPK)signal pathway,phenylpropanoid metabolic pathway,α-linolenic acid metabolic pathway,were activated.In addition,K.marxianus XZ1 treatment significantly upregulated the expression levels of some genes related to plant resistance in apple,such as POD,CAT and PPO genes and pathogenesis-related gene PR1,PR4,thereby inducing the improvement of apple’s defense ability and participating in defense the infection of P.expansum.In conclusion,this paper initially revealed the biological control effect and mechanism of K.marxianus XZ1 on blue mold disease caused by P.expansum in apple,which provide theoretical support for the application of K.marxianus XZ1 in controlling blue mold disease of apple.