Study On Regulation Of Citral On The Growth Of Fusarium Graminearum And Mildew Control In Wheat

Fusarium graminearum and its mycotoxins seriously affect the quality of food and the health of humans and animals.Citral,a natural compound found in essential oils of lemon,has been shown to possess antifungal activity against various pathogens.As a permitted food additive,it has been applied in food,toothpaste,cosmetics and so on.In order to develop an efficient and safe natural antibacterial agent to ensure the safety of wheat,the effects of citral on the growth and toxin production of F.graminearum were analyzed,as well as its anti-mildew effect in grain storage.The main results are as follows:The effects of citral on the growth and toxin production of F.graminearum were studied.The results showed that citral could inhibit the growth of mycelium,and the minimum inhibitory concentrations in CM solid medium and liquid medium were 0.04%and 0.02%,respectively.Citral can inhibit the formation and germination of spores and destroy the morphology of spores:0.01%citral can completely inhibit the formation of conidia,0.02%citral can completely inhibit the germination of spores,and the surface of spores is concave or even broken.In wheat with a moisture content of 40%,the level of DON produced by F.graminearum was significantly correlated with the concentration of citral added to wheat.When the concentration of citral was 0.3%,the DON content after 21 days of storage was only 12.62μg/kg,which was 99.55%lower than that of the control group,indicating that citral could significantly inhibit the formation of DON toxin.The effect of citral on the cell membrane of F.graminearum was was analyzed.The results showed that 0.02%citral treatment significantly increased the conductivity and absorbance at A₂₆₀ nm of F.graminearum culture solution.After PI staining of the mycelium treated with citral,the fluorescence intensity of the mycelium was enhanced;the malondialdehyde content in the culture medium and the ergosterol content of the mycelium were detected.The results showed that the malondialdehyde content in the culture medium treated with citral increased and the ergosterol content decreased.The results showed that citral treatment could damage the cell membrane structure and function of F.graminearum,increase the permeability of cell membrane and leak intracellular substances,which significantly affected the growth of bacteria.The effects of citral on the oxidative system and energy metabolism of F.graminearum were examined.The results showed that compared with the control,a large amount of ROS,hydrogen peroxide and superoxide anion were accumulated in the mycelium cells after citral treatment.Compared with the control group,the hydrogen peroxide content increased by18.56%,38.41%and 45.57%,and the superoxide anion increased by 18.19%,69.65%and21.07%,respectively.The activities of antioxidant enzymes such as superoxide dismutase（SOD）,peroxidase（POD）and catalase（CAT）were significantly decreased.The mitochondrial membrane potential（MMP）related to cell energy metabolism was significantly decreased,and the activities of mitochondrial ATPase,mitochondrial dehydrogenase and succinate dehydrogenase were significantly decreased.The results showed that citral caused oxidative stress reaction,induced the accumulation of intracellular reactive oxygen species and the disorder of antioxidant enzyme activity in F.graminearum.Citral also destroyed the function of mitochondria,affected energy metabolism,and ultimately led to cell damage and cell death.The differentially expressed genes of mycelium transcriptome before and after citral treatment were analyzed.The results showed that there were 1642 differentially expressed genes after citral treatment,of which 720 genes were up-regulated and 922 genes were down-regulated.The significant differential genes of GO enrichment were mainly related to biological processes such as organic acid metabolism,plasma membrane components,and oxidoreductase activity.KEGG enrichment pathways were mainly peroxisome,glucose metabolism,pyruvate metabolism and other pathways.The differentially expressed genes regulating growth were identified by comprehensive analysis.Functional analysis of the significantly down-regulated aldehyde dehydrogenase gene FGSG＿00979 showed that the gene deletion mutant played an important role in regulating spore formation,DON synthesis and oxidative stress.The antifungal effect of citral in stored wheat was studied.The results showed that compared with activated carbon,zeolite and vermiculite,perlite had better adsorption performance for citral,and 1 g perlite could effectively adsorb 1.5 m L pure citral.Citral adsorbed on the carrier for uniform grain mixing treatment,0.2%citral can make 16%moisture wheat storage 15 d without mildew,0.3%can completely inhibit the activity of mold.Under the forced circulation fumigation treatment mode,the 16%moisture wheat stored at 30°C was treated with a single circulation of 60 min per day for 9 days without mildew,and the wheat with 18%moisture content could be maintained for 3 days without mildew.The circulation treatment twice a day could keep the wheat with water content of16%and 18%from mildew for 15 days and 6 days,and the latter significantly improved the effect of citral on wheat mildew prevention.These findings suggest that citral has potential as a natural antifungal agent for the control of wheat scab and toxin contamination of wheat.