Effect Of Several Kinds Of Aromatic Substances In Citrus Postharvest Main Pathogenic Fungus

In this paper,the main pathogens of citrus were taken as the research object,and the effects of limonene,myrcene,citronellal on the the mycelial growth and spores' germination of Penicillium digitatum,P.italicum,and Geotrichum citri-aurantii were explored.Among them,limonene and myrcene stimulated the pathogen mycelial growth and spores' germination,while citronellal was just the opposite.The main results were as follows:(1)For mycelium,limonene showed stimulating effect to P.digitatum,P.italicum,and G.citri-aurantii in low concentrations of 0.2-0.8,0.2-1.6 and 0.2-3.2?L/m L,respectively.Stimulating effect of the concentration of myrcene were 0.2-6.4(for P.digitatum),0.2-1.6(for P.italicum),0.2-6.4(for G.citri-aurantii)?L/mL,respectively.Inhibiting effect of limonene and myrcene on these fungi was not obvious.Citronellal also stimulated these fungi in low concentrations.When its concentration was less than 0.2,0.2 and 0.8 ?L/m L,respectively,citronellal showed the promoting effects to P.digitatum,P.italicum and G.citri-aurantii.High concentrations of citronellal significantly inhibited the mycelial growth of P.digitatum,P.italicum,and G.citri-aurantii,the minimum inhibitory concentration(MIC)were all 1.6 ?L/mL,and the minimum fungicidal concentration(MFC)were3.2,1.6 and 1.6 ?L/mL,respectively.(2)For spores,limonene showed stimulating effect to P.digitatum,P.italicum,and G.citri-aurantii at low concentrations of 0.1-0.4,0.4 and 0.4-1.6 ?L/mL,respectively.Myrcene have been showed high stimulating effect when the concentration was 3.2 ?L/mL or less.Citronellal showed stimulating effect to P.digitatum,P.italicum,and G.citri-aurantii in low concentrations of 0.05,0.1 and0.05-0.2 ?L/mL,respectively.(3)Limonene showed stimulating effect to P.digitatum spores' germination in low concentrations.Through transcriptomics and proteomics association analysis,19 differentially expressed genes and proteins were found.Quantitative PCR was used to verify the 19 differentially expressed genes,founding that 11 genes were up-regulated and 8 genes were down-regulated.A large number of related up-regulated genes were on the cell membrane.We found 35 species of differences metabolites associated with48 kinds of metabolic pathways in metabonomics.This is related to the ABC transport pathway,conducting on the cell membrane,which is the response of P.digitatum to the limonene signal.In conclusion,limonene might be act as a signal molecule ininducing the spores' germination of P.digitatum,and that receptor in the cytoplasmic membrane would be the site.(4)Myrcene showed stimulating effect to P.digitatum spores' germination even in high concentrations.GC-MS and GC quantitative analysis the concentration of myrcene in the spores' germination process of P.digitatum,found that myrcene is decreasing constantly.Associated metabonomics analysis,found that the myrcene can be converted to pyruvic acid.With myrcene treated,pyruvic acid content has risen sharply.Pyruvic acid is converted in TCA circle to produce ATP.Under the action of myrcene,the content of ATP,ADP,AMP has risen sharply.In conclusion,myrcene might be act as nutrients in inducing the spores' germination of P.digitatum.Myrcene can be converted into pyruvate to provide energy for spores' germination.(5)The mycelial growth and spores' germination of P.digitatum were inhibited by citronellal in a dose-dependent manner.MIC and MFC were determined to be 1.60?L/mL and 3.20 ?L/mL,respectively.It was found that the plasma membrane of citronellal-treated P.digitatum spores was obviously damaged.As convinced by the propidium iodide stain results,as well as a higher extracellular conductivity and a higher release of cell constituents in citronellal-treated samples than in control samples,the cell membrane permeability was destroyed.Moreover,in vivo test results demonstrated that wax+citronellal(WC;10×MFC)treatment could effectively reduce the incidence of green mold after 5 d of storage at 25±2 ?.These findings suggested that the plasma damage mechanism contributes to the antifungal activity of citronellal against P.digitatum,and that citronellal is a potential alternative as fungicidal agents in controlling green mold of citrus fruit.