| Fusarium oxysporum f.sp.cucumerinum(FOC)as a damaged plant pathogen is difficult to control in cucumber planting.Cucumber cultivation in the same plot for three years,the incidence rate can be as high as 70%and yield loss reaches 10%to 50%.The prevention and control of conventional chemical pesticides can easily lead to a series of problems such as pesticide residues,pesticide resistance and environmental pollution and so on,while plant essential oils(EOs)are a kind of plant secondary metabolite,which is safe and environment-friendly and most of them have proven antifungal activities;therefore,the use of plant EOs for the prevention and control of plant pathogens has important significance.This study mainly discusses the antifungal effects on nine kinds of EOs and monomer components,analyzes the composition of four EOs,combines EOs or monomer components which are with good antifungal activity,and explores the mechanisms of the antifungal activity of monomer components.Finally it is to provide experimental basis and data accumulation for the application of EOs in the field of agricultural pesticides.The main research findings of this paper are as follows:1.The chemical component from the four EOs was analyzed by gas chromatography spectrometry(GC-MS)technique.The results showed that the compositions of cinnamon essential oil were trans-cinnamaldehyde(90.81%),cinnamyl acetate(5.06%)and 2’-methoxycinnamaldehyde(4.13%).Cuminal,2,6-diisopropylphenol,phenyl-3-butenol,p-cymene were identified in cumin essential oil which were 63.93%,11.03%,8.41%and 6.87%respectively.The main component of clove essential oil was eugenol(66.14%);the main componds of essential oil from oregano were carvacrol(90.27%),linalool(3.31%),terpinenes(1.1 5%)and p-cymene(1.55%)respectively.2.The antifungal activities of nine kinds of EOs and monomer components against FOC were tested by using the inhibition zone methods,growth rate methods and fumigation methods.In the inhibition circle test,allyl isothiocyanate showed best antifungal effect and the inhibition zone diameter of FOC was 32.00±0.25mm,and its antifungal effect was significantly stronger than the positive control(p<0.05).Then followed by cinnamon essential oil,its inhibition zone diameter was 24.32±0.77mm,and the inhibition effect was comparable to that of thiram.In mycelial growth rate experiments,the antifungal effect of thymol was significantly stronger than that of thiram(p<0.05),the EC50 value was 1.189mg/mL,followed by carvacrol and oregano oil.The antifungal effects were equivalent to that of thiram and the EC50 values were 1.439μL/mL and 1.440μL/mL,respectively.In vitro fumigation experiments,allyl isothiocyanate,thymol,carvacrol,oregano essential oil,cuminal,eugenol achieved good inhibition activities at 3μL/plate,and the inhibition rate reached more than 80%.3.Based on the above tests,the primary screening of EOs and essential oil monomer components was further tested for their biological activities via using spore germination,mycelial biomass,minimal inhibitory concentration(MIC)and minimal fungicidal concentration(MFC).The results showed that allyl isothiocyanate,thymol,carvacrol,oregano essential oil,cuminal,and eugenol had strong antifungal activity in the spore germination test,and the inhibitory effect was enhanced with increasing concentrations.The biomass of the pathogenic fungi mycelial was all 0g/100mL at 1μL/mL,and the MIC and MFC of allyl isothiocyanate against FOC were both 0.049 μL/mL,which had the strongest antifungal effect.Followed by thymol,carvacrol,the MIC of FOC reached 0.195 mg/mL and 0.195μL/mL,while the MFC were 0.195mg/mL and 0.391 μL/mL respectively.Three kinds of essential oil monomer components were selected to combine detecting their inhibitory activities.The results showed that there were no synergies among allyl isothiocyanate,thymol and carvacrol.4.Through test of the observation of ordinary optical microscope,the determination of the electrical conductivity and the content of sugar and soluble protein,the antifungal mechanisms of allyl isothiocyanate and thymol were preliminarily investigated.Results showed that both inhibited the absorption and utilization of nutrients,changed the permeability of cell membranes,disrupted the cell membrane structure,and eventually caused cell contents to leak,leading to the death of FOC. |
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