Inhibition And Mechanism Of Phytic Acid On Fusarium Wilt(Fusarium Oxysporum)of Pinus Sylvestris Var. Mongolica Seedlings

With the strengthening of people’s awareness of ecological and environmental protection,the problems caused by traditional chemical pesticides have gradually attracted attention,and the research and development of efficient and environmentally friendly pesticides are imminent.In recent years,botanical pesticides have attracted widespread attention.Phytic acid（PA）is a plant-based component obtained from oilseeds,cereals,legumes,nuts,and pollen with a powerful chelating activity,which has strong chelating ability,determines its strong antioxidant activity and thus exhibits physiological activities,such as prevention of inflammation,prevention of pathological calcification,and antibacterial and antitumor activities.Pinus sylvestris var.mongolica is easily infected by Fusarium and other pathogens at seedling stage,which caused a lot of symptoms of withering and necrosis of ornamental,food,medicinal and forest crops.It is a common and high-incidence disease,which could cause many common plant diseases,such as Fusarium wilt and root rot,and is the most difficult kind of plant pathogenic fungi to control in agriculture.However,there are few reports about the inhibitory effect of PA on pathogenic fungi.In the study,the inhibitory effected of PA on the growth of four phytopathogenic fungi were screened.The inhibitory effects on mycelial growth of Fusarium oxysporum were determined and the effect of PA on conidia germination of F.oxysporum and PA on the control of Fusarium wilt of P.sylvestris var.mongolica were further determined.Finally,the effects of PA on the microscopic morphology,physiological and biochemical indicators of F.oxysporum hyphae were clarified.The main results were as follows:（1）The inhibitory effect of PA on mycelium growth and spore germination of plant pathogenic fungus F.oxysporum increased with the increase of concentration.The toxicity regression equation was Y=2.322X+0.555,R²=0.940.The EC₂₀ value was 250 mg/L,and the EC₅₀ value was 577 mg/L.When the concentration was 4000 mg/L,the inhibition rate of mycelium growth of F.oxysporum was 99.62%,and the inhibition rate of conidia germination of F.oxysporum was 31.65%.The results showed that PA could effectively inhibit the mycelium growth and conidia germination of F.oxysporum.（2）Different concentrations of PA have effects on the growth parameters and incidence rate of P.sylvestris var.mongolica seedlings.After being inoculated with F.oxysporum for 10days,the incidence rate was significantly reduced and the plant height,root length and fresh weight were increased by 1.78,2.17 and 2.75 times,respectively,by dipping root treatment with PA concentration of 8000 mg/L.It showed that PA can effectively inhibit the invasion of pathogenic fungi on the roots of P.sylvestris var.mongolica seedlings.（3）PA significantly damaged the cell structure of F.oxysporum.The conductivity,extracellular protein,and MDA content of PA to F.oxysporum were significantly higher than those of the control（P<0.05）,which indicated that PA treatment had a damaging effect on the cell membrane of F.oxysporum.That is to say,PA caused changes in cell membrane permeability,resulting in a large leakage of cell contents and aggravating the degree of cell membrane lipid peroxidation.By observing the SEM of F.oxysporum hyphae,PA treatment resulted in abnormal growth of F.oxysporum hyphae,which became slender,contracted,twisted and fractured,and the surface of hyphae was rough.（4）The antifungal mechanism of PA on F.oxysporum showed that the effect of PA on F.oxysporum was multifaceted.PA has an effect on the activity of five life activities related to F.oxysporum.The activities of antioxidase enzymes（SOD,CAT）and CWDEs enzymes（PL,PG,and EG）after PA treatment were significantly less than those in the control group（P<0.05）.PA weakened the organism ability of fungi itself,thus reduced the toxic effect on host ability.It also adversely affected the activity of pathogenic enzymes of F.oxysporum,disturbed the pathogenic ability of F.oxysporum and inhibited its growth.The results showed that PA had a certain inhibitory effect on antioxidant enzymes and degrading enzymes of F.oxysporum.（5）PA affected the gene expression of four enzymes related to the life activities of F.oxysporum.After 8000 mg/L PA treatment,the expression levels of genes related to defense enzymes（Fo SOD,Fo POD）and pathogenic enzymes（Fo PL,Fo EG）were down-regulated,with significant differences（P<0.05）.The results showed that PA had a certain inhibitory effect on the expression of genes related to defense enzymes and pathogenic enzymes of F.oxysporum.Therefore,this study confirmed that PA has great development potential in plant-derived fungicides,and the antifungal mechanism of PA on F.oxysporum could provide theoretical basis for exploring new antifungal substances.