Antibacterial Activity Of Brassica Juncea Extract On Watermelon Fusarium Wilt

China is a big country in the production and consumption of watermelon.Watermelon production plays an important role in the adjustment of agricultural structure and the increase of farmers'income.The occurrence of watermelon blight has brought huge economic losses and waste of resources to watermelon production.Today,when green consumption is prevalent,safe,environmentally friendly and inexpensive plant-derived bacteriostatic agents meet the needs of the country and society.Therefore,it is of great practical significance to find and screen bacteriostatic active substances which are bacteriostatic and have no harmful effects on human health and ecological environment from natural plants,especially edible plants.This experiment aims to develop and develop a plant-derived fungicide suitable for watermelon wilt to replace chemical fungicides.The results are as follows:1.The antifungal activities of Brassica juncea extracts against Fusarium oxysporum f.sp.niveum,Rhizoctonia solani,Botryosphaeria parv and Phytophthora parasitica var.nicotianae were tested by means of mycelium growth rate method.The results showed that the different organic solvent extracts from Brassica juncea had certain inhibitory effect on watermelon Fusarium wilt.The antibacterial effect of extracting with95%ethanol is the best,and the antibacterial rate of the extract can reach more than90%.Its minimum inhibitory concentration and minimum bactericidal concentration were0.5 g/mL and 1.0 g/mL.Respectively,the EC₅₀0 was determined by virulence to be 0.2212g/mL.The antibacterial activity of the other 10 plant phytopathogens showed that the ethanol extracts of Brassica juncea had strong antibacterial activity against four phytopathogens such as Rhizoctonia solani,Botryosphaeria parv,Phytophthora parasitica var.nicotianae,and Sclerotinia sclerotiorum.The EC₅₀0 was 0.0898 g/mL,0.1265 g/mL,0.1679 g/mL,and 0.1685 g/mL,respectively,and the inhibition effect against the Colletorichum gloeosporioides was the weakest,and the EC₅₀0 was 0.5833g/mL.2.Response surface methodology based on Box-Behnken design was used to explore the effects of process parameters such as ethanol concentration,temperature,ratio of material to liquid and time on the extraction of bacteriostatic substances from Brassica juncea were studied.The statistical analysis showed that the order of the effects of factors on the extraction rate of antibacterial substances was:ethanol concentration>temperature>time>liquid-to-solid ratio.The optimal process for the response surface were:ethanol concentration of 82.46%,extraction time of 2.02 hour,liquid-to-solid ratio of 15.04 mL/g and temperature of 49.79?.The predicted value of the model was98.37%and the actual average was 97.56%,the relative error between the actual value and the predicted value is only 0.82%.3.The treatment concentrations of 0,1/2 MIC,MIC and 2MIC were set to determine the morphology of mycelium.Changes in bacterial liquid conductivity,bacterial malondialdehyde content,cell wall-related hydrolase activity,respiratory metabolic pathway enzyme activity,soluble protein content and reducing sugar content.The results showed that the conductivity of the extract after the treatment of the mustard extract increased significantly,and the conductivity of the bacterial liquid at the concentration of2MIC was up to 1.45 ms/cm.When the concentration was 2MIC,the malondialdehyde content was the highest,and the chitinase and?-1,3-glucanase activities were also increased,which were 10.57 U/?g·FW?and 14.16 U/?g·FW?,cell wall degradation,impaired cell integrity;Succinate dehydrogenase and malate dehydrogenase activity decreased,the latter activity decreased from 0.53 U/mg to 0.28 U/mg;The contents of cell contents such as soluble protein,reducing sugar content were significantly reduced,respiratory energy metabolism was blocked,and cell growth was inhibited.4.Ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry?UHPLC-Q-TOF/MS?was used for qualitative and quantitative analysis of the chemical constituents of extracts from five Brssica juncea cultivars,including brussels mustard,mustard shoot,sweet mustard,mustard tuber and bamboo mustard.63major compounds were identified from 5 Brssica juncea varieties,including 27 organic acids,4 alcohols,5 glucosinolates,5 flavonoids,12 amino acids,3 carbohydrates and 7others.The relative content of glucosinolates was the highest,among which the content of3-butenyl glucoside was higher in 5 varieties,namely,brussels mustard?9.53%?,mustard shoots?3.95%?,sweet mustard?6.08%?,mustard tuber?10.98%?and bamboo mustard?14.32%?;the most organic acid compounds,5 brssica juncea varieties with higher L-malic acid content,ranging from 0.48%to 0.78%,sinapic acid content brussels mustard?0.50%?is significantly higher than mustard tuber?0.04%?;among the amino acid compounds,the higher content of edulis and mustard is 1.73%and 1.29%,respectively,while mustard tuber,sweet mustard and bamboo mustard are high.L-proline is 0.93%,0.67%and 0.56%,respectively.