Study On The Antagonism Of Pichia Scaptomyzae Against Penicillium Expansum Infecting Apples

In the process of postharvest storage,transportation and sale,apples are vulnerable to mechanical damage and fungal infection,resulting in decay,deterioration and economic losses.Penicillium expansum exists in many kinds of fruits and is one of the most important pathogens in the process of apple decay.At present,there are mainly chemical and physical methods for the prevention and control blue mold in apples.However,there are some problems,such as chemical ways are not conducive to human health and ecological environment,physical ways are costly and can not be universally applicable.So far,with the breakthrough of biocontrol,chemical fungicides and physical sterilization ways have been gradually replaced.The antagonistic strain led by yeast has the strong points in surrounding fridendliness,and has a remarkable effect in the biological control of blue mold.In this study,X26(Pichia scaptomyzae)isolated and preserved in our laboratory was used as antagonistic yeast,and Penicillium expansum of P.exp and LPH10 was used as pathogen.To explore the antagonistic effect of different concentrations of P.scaptomyze cell suspension against P.expansum in vitro and on apples;to further analyze the possible molecular mechanism of P.scaptomyze antagonism against P.expansum by transcriptology;to explore the early detection method of apple infection by HS-GC-IMS based on the detection of volatile substances in P.scaptomyzae antagonistic group and control group using GC-IMS.In vitro antibacterial test results showed that P.scaptomyzae had the largest inhibition zone(45.7 mm)at 10~8 CFU/m L;The spore germination rate and germ tube length of 10~8 CFU/m L P.scaptomyzae antagonistic group were decreased by 64%and 31.05?m compared with the control group after incubation 12 h.The effect of P.scaptomyzae on the biomass of P.expansum was measured in PDB.The dry weight of mycelium in 10~8 CFU/m L and P.scaptomyzae antagonistic group decreased by 0.398 g,respectively,compared with the control group.The inhibitory effect of P.scaptomyzae against P.expansum increased significantly with the increase of concentration.Among them,10~8 CFU/m L P.scaptomyzae had the most significant inhibitory effect on spore germination and biomass accumulation of P.expansum.The transcriptome analysis of PS?exp antagonist group and exp control group showed that 1127genes were up-regulated and 587 genes were down-regulated in the differentially expressed genes(DEG).GO functions focus on oxidation-reduction process and transmembrane transport.KEGG pathway is mainly enriched in ABC transporters,amino acid metabolism,peroxidase,fatty acid elongation,etc.It is speculated that the molecular mechanism of P.scaptomyzae against P.expansum may be as follows:P.scaptomyzae interacts with P.expansum,and takes the space and nutrients needed for the growth and reproduction of the pathogen,such as iron,so that P.expansum cells are in the state of iron imbalance and oxidative stress.It induces the overexpression of genes related to the hydrolysis of cell wall and iron metabolism,and anti-oxidative stress-related proteins,which leads to the cell wall cracking of the pathogen and inhibits the spore germination and mycelial biomass accumulation of P.expansum.These possible antagonistic molecular mechanisms need further experimental verification.P.expansum was inoculation into P.scaptomyzae and apples treated with sterile water,respectively,The decay incidence and lesion diameter were determined.The decay incidence of apple in P.scaptomyzae antagonistic group was(10.55%)for 10 d,which was much lower than that in control group(92.2%),and the lesion diameter was 9.77 mm lower than that in the control group,which significantly inhibited the production of blue mold in apples.The results of HS-GC-IMS showed that a total of 38 volatile components were identified,mainly esters,aldehyde and alcohols.The contents of styrene,6-methyl-5-hepten-2-one,ethyl propanoate and 3-methylbutanoic acid in control group were much higher than those in P.scaptomyzae antagonistic group.These compounds can be used as volatile markers of blue mold in apples.