Study On The Anti-pathogenic Fungal Activity Of Chemical Constituents In Potato Endophytic Fungus Gongronella Sp.

Potato fungal disease is the main factor affecting potato yield and quality,which seriously restricts the development of potato industry.At present,the main control means is chemical control by spraying pesticides,but chemical pesticides are extremely harmful to the ecological environment and human and animal health,so it is urgent to develop high-efficiency and low-toxicity biogenic natural bactericide.Endophytes（including endophytic fungi and endophytic bacteria）and their metabolites are important sources of antimicrobials.Previous studies by our research group have shown that the potato endophytic fungus Gongronella sp.It has certain inhibitory activity against pathogenic bacteria.Seventeen compounds were isolated from the fermentation broth of the endophytic fungus Gongronella sp.In order to explore the inhibitory effect and mechanism of secondary metabolites of endophytic fungus Gongronella sp.On three potato pathogens,this study selected 17compounds isolated earlier as experimental objects and screened their antifungal activity.The antibacterial mechanism was studied from five aspects:cell wall,cell membrane,intracellular DNA content change,intracellular reactive oxygen species（ROS）level and cell growth cycle.The findings are as follows:1、Preliminary screening of compounds 1-17 against pathogenic fungi in potato.The mycelial growth inhibition and spore germination inhibition experiments of 17 compounds were carried out by filter paper method and concave glass slide method.It was found that compound 2,5-dihydroxytoluene had a good inhibitory effect on the mycelial growth of Fusarium oxysporum,and the inhibition rate was 65.71%when the concentration was40mg/m L.2,5-dihydroxytoluene and 1-methyl-9H-pyridine and[3,4-b]indole had certain inhibitory effects on the germination of Fusarium oxysporum spores,and the inhibitory rates were 19.12%and 12.14%,respectively.2、Effects of compound 2,5-dihydroxytoluene on mycelial morphology of Fusarium oxysporum.In the primary screening,2,5-dihydroxytoluene had the ability to weaken the regeneration of the inhibited mycelium.After treatment,the inhibited mycelium showed the distortion phenomena such as rounded top,enlarged,thickened,deformed,twisted and folded.With the increase of the concentration of 2,5-dihydroxytoluene treatment group,the mycelium increased from local thickening,mutual twisting and winding to dissolution.Under 8MIC treatment,the cell wall of thellunae was wrinkled and curled,with obvious dissolution and overflow of contents.The minimum inhibitory concentration（MIC）of 2,5-dihydroxytoluene on the growth of Fusarium oxysporum was 3.125 mg/m L.3、Effects of compound 2,5-dihydroxytoluene on cellular contents of Fusarium oxysporum.The concentration of 2,5-dihydroxytoluene was positively correlated with the intracellular ROS content of Fusarium oxysporum after treatment.With the extension of treatment time,the degree of cell destruction also increased,resulting in the increase of intracellular soluble protein content.In addition,the DNA damage of Fusarium oxysporum was related to the concentration of compound 2,5-dihydroxytoluene and the treatment time.The higher the concentration and the longer the treatment time,the more serious the DNA damage was,so as to achieve the effect of inhibiting the growth of mycelium.4、Effect of compound 2,5-dihydroxytoluene on the cell cycle of Fusarium oxysporum.After using different concentrations of 2,5-dihydroxytoluene,a large number of Fusarium oxysporum cells were arrested in G₁phase of cell cycle,thus inhibiting the growth of Fusarium oxysporum.In this study,17 secondary metabolites from potato endophytic fungus Gongronella sp.Were screened for antimicrobial activity,and it was found that compound2,5-dihydroxytoluene had a good inhibitory effect on Fusarium oxysporum,with an inhibition rate of 65.71%.Further study on the antibacterial mechanism of the compound showed that it could ablation and shrinkage the cell wall of Fusarium oxysporum,lead to cell membrane damage,intracellular protein leakage,increase the content of reactive oxygen species,cause DNA damage,and make the cell cycle of Fusarium oxysporum stay in G₁phase,thus inhibiting the normal growth of Fusarium oxysporum.These studies provide theoretical basis for the development of natural inhibitors of potato fungal diseases.