Preliminary Study On The Antibacterial Mechanism Of Three Plant Extracts Against Fusarium Oxysporum F. Tomato

With the expansion of tomato cultivation area in China,tomato fusarium wilt has become one of the important factors affecting the quality and yield of tomato,and restricts the development of tomato production.In the present study,the biological activities of the extracts of Syzygium aromaticum,Stellera chamaejasme and Glycyrrhiza uralensis were investigated.The effects and the underlying mechanism of the three plant extracts on the cell wall of Fusarium oxysporum were analyzed through real-time fluorescence quantitative technique and physiological and biochemical indexes.Pot experiments were conducted to test the impacts of three plant extracts on the defense enzymes and disease-related proteins before and after treatment,and to analyze the effects of extracts on the physiological responses of tomatoes.The main findings were as follows:1.The mycelial growth rate method and suspension drop method were used to determine the inhibitory effect of extracts of S.aromaticum,S.chamaejasme and G.uralensis against F.oxysporum.The results showed that the inhibitory effects of S.aromaticum extract possessed the greatest inhibition activity against F.oxysporum at the mass concentration of 2 mg·m L^-1,and the inhibition rate reached up to 100% at 96 h,followed by S.chamaejasme and G.uralensis with the inhibition rates at 57.46% and43.61%,respectively.The EC50 values of the extracts of S.aromaticum,S.chamaejasme and G.uralensis were determined as 0.155 mg·m L^-1,1.339 mg·m L^-1 and 3.076 mg·m L^-1,respectively.When the concentration was 4 mg·m L^-1,S.chamaejasme extract displayed the best inhibitory effect on conidia germination of F.oxysporum with the inhibition rate of99%,followed by S.chamaejasme and G.uralensis extracts with the inhibition rates of 59%and 29%,respectively.At a mass concentration of 4 mg·m L^-1,S.chamaejasme extract had the best inhibitory effect on conidial germination of F.oxysporum,with a spore germination inhibition rate of 99.66%;S.aromaticum and G.uralensis extracts had the second highest inhibitory effects,and the rates are 59.79% and 29.03%,respectively.2.The effects of three plant extracts on the activities of cell wall degrading enzymes of F.oxysporum were determined by the micro method,the results indiated that the S.aromaticum extracts could activate β^-1,3-GA activity in mycelium,and enhance mycelial chitinase activity in the early stage of treatment,thereby destroying the integrity of the cell wall;S.chamaejasme extracts could enhance mycelial chitinase and SOD activity,reduce mycelial PG activity,and reduce mycelial infectivity;G.uralensis extracts could reduce mycelial POD activity and enhance the toxic effect of mycelium.3.Real time fluorescence quantitative technology was used to determine the chitin and defense related genes of three plant extracts against F.oxysporum.The results demonstrated that S.aromaticum extract promoted the process of converting inactive enzyme sources into active chitinase,increasing the content of chitinase;S.chamaejasme extracts could increase chitinase content by increasing the expression of chitinase at the transcription level;G.uralensis extracts affect the concentration of active oxygen in the hyphae by inhibiting the expression of defense-related genes at the transcriptional level and inhibiting the POD content of the hyphae,thereby inhibiting the growth of the hyphae.4.Pot experiment results showed that three plant extracts could reduce the MDA activity of tomato plants and diseased tomatoes,and reduce the impact of membrane lipid peroxidation on cells.S.aromaticum extracts could activate β^-1,3-GA activity of diseased tomatoes and enhance the POD activity of tomato plants and the SOD activity of diseased tomatoes;S.chamaejasme extracts could activate the activity of chitinase and β^-1,3-GA of diseased tomatoes,enhance the activity of POD and CAT,and inhibit the activity of PG;G.uralensis extracts activate the chitinase and CAT activities of susceptible tomatoes,thereby increasing the resistance of tomatoes to Fusarium wilt.The results indicated that all three plant extracts of S.aromaticum,S.chamaejasme and G.uralensis had good inhibition effects against F.oxysporum with different inhibition mechanism,which could improve the resistance of tomato to Fusarium wilt,and have the potential to be used as botanical pesticides to control tomato Fusarium wilt in the later plant growth stages.