Inhibition Of Ammonium Carbonate Against Penicillium Italicum On Citrus

Citrus is one of the important cash crops and plays an important role in agricultural economy,the taste is suitable and rich in nutritious,people like it very much.However,citrus is susceptible to pathogen infection postharvest,especially Penicillium italicum,Penicillium digitatum and Geotrichum citri-aurantii,which are the main diseases postharvest.Seeking a new preservative that can control its main diseases is crucial,while ammonium carbonate,as a generally recognized as safe substance,has strong antifungal ability and can be used as an alternative to other chemical fungicides at present.bicarbonates to the main pathogen of citrus postharvest,we found that ammonium carbonate has remarkable bacteriostatic activity.We applied it to the preservation of citrus fruit in vivo,explored the possible mechanism of ammonium carbonate on Penicillium italicum.The results were as follows:?1?Hyphae growth rate method was used to evaluate the inhibition ability of six carbonates and bicarbonates on the main pathogen in citrus postharvest and to calculate their MIC value to the pathogen.Among them,the antifungal ability of carbonates are stronger than that of bicarbonates,and ammonium carbonate is the strongest.The effect of ammonium carbonate on fungal significantly decrease spore activity and germ tube elongation,show concentration-effect relationship.The results of spore germination method showed that ammonium carbonate concentrations of 0.25 g/L,0.40 g/L,0.80 g/L can completely inhibit spore germination of P.digitatum,P.italicum,and G.citri-aurantii;For inhibiting the growth of mycelium,the MICs of ammonium carbonate on P.digitatum,P.italicum,and G.citri-aurantii were 0.4417 g/L,0.8090 g/L,and 0.8000 g/L,respectively.Under the conditions of liquid culture,ammonium carbonate treatment also had a significant inhibitory effect on the mycelial growth of pathogen.The challenge inoculation in vivo test showed that 20 g/L ammonium carbonate treatment could significantly delay the expansion of the diameter of Xia Cheng lesions.?2?Taking P.italicum as the research object to analy the action mode of ammonium carbonate,inhibit the growth of pathogen to some extent.The plate-to-buckle test showed that the ammonia volatilized by ammonium carbonate could inhibit the growth of pathogen,and when the concentration was 1.6 g/L,the volatilized ammonia gas could completely inhibit the growth of P.italicum,suggesting that volatile ammonia was the main reason to inhibit the growth of pathogen on solid medium.The effect of carbonate ions on antifungal was investigated under liquid culture,which indicated that the stress of carbonate ions was also an important reason for ammonium carbonate to inhibit pathogen growth.The effects of ammonium carbonate on spores and hyphae of P.italicum were investigated by spore germination and hyphae transfer,which indicated that ammonium carbonate would not kill spores,but only prolong their germination time,causing irreparable damage to mycelium.?3?Further exploration of the mechanism of ammonium carbonate's antifungal action:ammonium carbonate could change the surface morphology of mycelium of P.italicum and make mycelium fold.TEM observation showed that mycelium cell morphology changed and the wall of mycelium was thickened.In terms of its effect on the cell wall of P.italicum,the permeability of the mycelium cell wall after ammonium carbonate action was changed,the AKP enzyme was released extracellular.The chitin content and glucanase activity were significantly higher than that of the control group,destroyed the structure and function of the cell wall.By measuring the p H of the cell membrane,the release of cell components,and the conductivity of the membrane,it was found that ammonium carbonate could affect the acid excretion ability,destroy the integrity of the cell membrane and promote leakage of nucleic acids and proteins.The content of total lipid and ergosterol in cell membrane showed that ammonium carbonate could decrease the content of cell membrane lipid but had no effect on ergosterol.After24 h of ammonium carbonate treatment,the content of reducing sugar in mycelium was only 22%of the control,and the content of reducing sugar and protein in mycelium was6.94 times and 6.45 times of the control,respectively,indicating that ammonium carbonate treatment had a significant effect on the mycelium using external proteins and sugar to complete its own metabolism.Ammonium carbonate treatment inhibited mycelial respiration,led to disorder mitochondrial membrane potential and cytochrome C oxidase inactivation,and accumulated H₂O₂.?4?By the natural storage test of citrus fruit,it was found that 4g/L of ammonium carbonate soaking could significantly reduce the incidence of citrus during storage,and the incidence rate could be reduced from 47.78%to 23.33%.Whether before or after storage,the treatment of ammonium carbonate would not adversely affect the appearance quality of citrus,soluble solids,vitamin C and other nutritional qualities.Ammonium carbonate treatment could significantly increase the polyphenol content,decrease the reactive oxygen species content and decrease the polyphenol oxidase activity in citrus fruit,indicating that ammonium carbonate treatment could reduce the incidence of citrus during storage by improving the antioxidant ability of citrus fruit,delaying its aging process.In summary,ammonium carbonate has a good control effect on the main diseases of citrus postharvest.The mechanism of action of ammonium carbonate on fungal is that it can form volatile ammonia.Ammonium carbonate has different effects on mycelium morphology,cell wall,cell membrane,respiration,and reactive oxygen species of P.italicum,among which the effects on cell membrane and respiration are more serious.It is suggested that ammonium carbonate can cause serious damage to cell membranes and affect mycelium respiration,which interferes with its energy metabolism and causes mycelium death.