Study On The Antibacterial Mechanism Of Carvacrol Against Mango Anthracnose Pathogens Resistant To And Susceptible To Carbendazi

Mangos（Mangifera indica L.）are metabolically active during post-harvest storage and transport and are susceptible to pathogenic bacteria,which cause rapid fruit decay and affect commercial sales,causing huge economic losses to the mango industry.Anthracnose caused by Colletotrichum gloeosporioides species complex is one of the most important post-harvest diseases of mangoes,and polymyxin-resistant mango anthracnose is already widespread in mango production areas.Therefore,it is important to screen for efficient and safe agents and to study their mechanism of action against the pathogenic bacteria for the control of mango anthracnose.The main findings of the study are as follows:1.Combining morphological characteristics and molecular biological identification,both the polymyxin-resistant and susceptible anthrax strains SY12and SY04 were Colletotrichum asianum in the Colletotrichum complex,and the EC₇₅value of carvacrol for the two strains was determined to be 0.12μL/mL.The indoor virulence of carbendazim was determined for the strains（52 strains）kept in the laboratory,and the strains SY12 and SY04 were identified for this test..The inhibition activity of carvacrol against the two strains was measured at eight concentrations of 0.02,0.04,0.06,0.08,0.10,0.12,0.14 and 0.16μL/mL with increasing EC75 values of 0.12μL/mL.The mycelial growth rate,dry weight of mycelium,spore production,and spore weight of 0.12μL/mL of carvacrol against the two strains were determined.The inhibition of mycelial growth rate,mycelial dry weight,spore production and spore germination of both strains was significant;the ultrastructural observation showed that the mycelium of both strains showed irregular shrinkage and wrinkling,the cell structure was destroyed,the cytoplasmic membrane was blurred and the cytoplasmic structure was changed.2.Transcript levels of genes related to cell membrane,ion transport inside and outside the membrane and energy metabolism were altered in the resistant strain SY12 after treatment with 0.12μL/mL of carvacrol for 1 h.Compared with the control group,the transcriptome of the resistant strain SY12was sequenced after 1 h treatment with 0.12μL/mL carvacrol,and 2388 differentially expressed genes were analyzed,of which 1501 genes were up-regulated and 887genes were down-regulated（Padj<0.001,|log 2 Foldchange|≥1.0）;by GO annotation and KEGG It was found that the differential genes were mainly expressed in the cell membrane,membrane transport and energy metabolism pathways.It was hypothesized that carvacrol could alter the transcriptional levels of genes related to cell membrane,ion transport inside and outside the membrane and energy metabolism in the resistant strain SY12,thus playing a suppressive role.3.0.12μL/mL of carvacrol significantly affected the changes in electrical conductivity,malondialdehyde（MDA）content,soluble efflux protein content,soluble reducing sugar content and tributylase activity of Polymyxin-resistant and Polymyxin-susceptible anthracnose fungi SY12 and SY04 with increasing time.Compared with the control,the changes in conductivity and MDA content of the resistant and susceptible strains SY12 and SY04 treated with 0.12μL/mL carvacrol showed a positive relationship with time,and showed an increasing trend with the extension of time;the soluble protein excretion content of the resistant and susceptible strains showed an overall trend of increasing,then decreasing and finally leveling off with the extension of time;the soluble reducing sugar content of the resistant and susceptible strains The changes of CHI enzyme activity of both resistant and susceptible strains showed a positive relationship with time,and showed an increasing trend as the time was extended.Thus,carvacrol could destroy the integrity of the cell membrane of strains SY12 and SY04,accelerate the membrane lipid peroxidation and cell membrane deformation damage,resulting in the difference in electrical potential between inside and outside the cell and the leakage of mycelium contents,affecting the normal growth of mycelium.4.0.12μL/mL of carvacrol significantly affected the changes in ATP content,ATPase activity,succinate dehydrogenase（SDH）activity and malate dehydrogenase（MDH）activityofPolymyxin-resistantand Polymyxin-susceptible anthracnose fungus SY12 and SY04,and the overall trend of change showed a continuous decrease with time.Compared with the control,the changes of ATP content,ATPase activity,SDH enzyme activity and MDH enzyme activity in the mycelia of the resistant and susceptible strains SY12 and SY04 were measured after treatment with 0.12μL/mL of carvacrol,and the changes of ATP content,ATPase activity,SDH enzyme activity and MDH enzyme activity in the mycelia of the resistant and susceptible strains showed a continuous decrease with time.This shows that carvacrol can effectively inhibit energy metabolism-related enzymes and tricarboxylic acid cycle（TCA）-related enzymes,leading to cell inactivation.5.0.12μL/mL of carvacrol was used to treat post-harvest mangoes and to determine the sensory and intrinsic qualities and physiological properties of the fruit.It was found that carvacrol was effective in maintaining the freshness of mangoes during post-harvest storage.The treatment of mangoes with 0.12μL/mL and 0.60μL/mL of carvacrol effectively inhibited the decrease in organic acid content of the flesh and fruit weight loss,maintained changes in fruit hardness,flesh soluble solids（TSS）content,vitamin C（Vc）content,soluble protein and soluble reducing sugar content;increased the content of total phenols and flavonoids in mangoes;had an inhibitory effect on antioxidant-related enzyme activity and The effect of carvacrol on the activity of antioxidant-related enzymes and disease-resistance-related enzymes has been shown to be effective in slowing down the rate of aging and quality deterioration of mangoes after harvest,thus prolonging the freshness of mangoes during post-harvest storage.