| Natural plants are rich in many kinds of bioactive substances.It is one of the hot directions to search for plant-source pesticides or precursor compounds in plant active compounds to control various plant diseases and develop new plant pesticides.There are a large number of herbal medicine resources in China,which have been widely researched in the treatment of human diseases and control of plant pests and weeds,but rarely used in the prevention as plant fungi,bacterium and viral diseases in agriculture.In this thesis,the disease of Enshi Tea tree was also investigated,and 12 kinds of tea pathogen were isolated from them.In addition,colletotrichum,phomopsis,phoma,alternaria and pestalotipsis were selected as tested pathogens.10 kinds of plants such as Rattan tea,Cinnamomum camphora,Ginkgo biloba,Loquat,Pine needles,Honeysuckle,Houttuynia,Wormwood,Oleander and Eucalyptus citriodora were selected,and the active ingredients were extracted and separated by 6 kinds of methods such as constant temperature water bath extraction,water ultrasonic extraction,ethanol ultrasonic extraction,ethanol Soxhlet extraction,petroleum ether ultrasonic extraction and petroleum ether Soxhlet extraction.All the extracts were tested for antifungal activities on five tested pathogens.According to the screening results,8 kinds of the plant crude extracts which performed good inhibition were selected for the study on inhibitor activity concentration of the fungi.In order to study the time-effect of the active plant extract whether it can be used in practical application,8 kinds of plant extracts with good antifungal effect were selected.The phomosis was used as the test fungi and the antifungal effect was compared after the preparation immediately and storage of 15 d after preparation.And the ethanol ultrasonic extraction of Eucalyptus citrodora Hook.f.leaves showed good stability and excellent antifungal activity,then the structures of compound were primarily confirmed,and two bioactive ingredients were selected for testing the antifungal activity respectivelyAbout the inhibitory effects of all extracts to five tested fungi,the results are as follows:According to the bacteriostatic results of the extracts of 10 kinds of plants from Rattan tea,Cinnamomum camphora,Ginkgo biloba,Loquat,Pine needles,Honeysuckle,Houttuynia,Wormwood,Oleander and Eucalyptus citriodora,it showed that theantibacterial activity in descending order: ultrasonic extraction > Soxhlet extraction > hot water extraction,and ethanol extraction> petroleum ether extraction> water extraction.Among the ten plant extracts,the inhibitory activity of Eucalyptus citrodora Hook.f.,Ginkgo biloba and Nerium oleander were better than other plants.And all extracts showed different antibacterial activity to five tested fungi in this particle.Taking phoma as an example,,the antifungal activity of ethanol ultrasonic extraction from 10 kinds of plant was lemon eucalyptus Eucalyptus citriodora > Pine needles > Oleander >Cinnamomum camphora > Ginkgo biloba > Rattan tea > Wormwood > Honeysuckle >Houttuynia,.while the concentration of extract is 20 mg/mL.The growth inhibitory activity of ethanol ultrasonic extraction from Eucalyptus citrodora Hook.f.was 97.9% to colletotrichum,and also had the higher activities to phoma,alternaria and phomosis.The growth inhibition ratios were 97.5%,92.5% and 95.1% respectively.The crude extract of Eucalyptus citrodora ethanol Soxhlet extract A,Oleander ethanol ultrasonic extract B,Pine needles ethanol ultrasonic extract C,Cinnamomum camphora petroleum ether ultrasonic extract D,Wormwood ethanol ultrasonic extract E,Honeysuckle ethanol ultrasonic extract F,Eucalyptus citrodora ethanol ultrasonic extract G and Ginkgo biloba ethanol ultrasonic extract H were selected for exploration the relationship between concentration and antifungal activity.The experimental results showed that the EC50 of the extract A-H expect F was A > D > B > C > E > G > H,and the EC50 of G was just 0.8mg/mL Compared with the preparation immediately and storage of 15 d after preparation,it was found that there was no obvious change in the bacteriostatic activity of the crude extract G,and the antifungal activity of the other extracts decreased,and the antifungal activity of A,B and D was decreased significantly.Based on the antifungal test results of different concentration and stability of A-H,the Eucalyptus citrodora ethanol ultrasonic extract G with good antifungal activity and stability was selected as the further research study.The main components of G were identified by GC-MS.Citronellal,citrionellol,geranyl acetate and isopulegol were the major ingredients of the extraction.Citronellal and citronellol were selected for the antifungal activity study.Both of them showed good antifungal activity to some extent.And citronellal had better antifungal activity than citrionellol.Citronellal and citronellal had good fungicidal effects on the Phoma at high concentrations and showed a definite bacteriostatic activity at low concentrations.Both of them had a good fungicidal activitywhen the concentration exceeded 20 mg/L.The EC50 of Citronella is 0.275 mg/L and the EC50 of Citronella is 0.103 mg/L. |
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