| L.davidii is rich in nutrients such as sugar,protein,vitamins,mineral elements and amino acids,which has the effects of promoting gastrointestinal function,lowering blood sugar and regulating blood lipids.It is known as "vegetable ginseng" and it is mainly used to treat cardiopulmonary diseases.However,post-harvest diseases seriously restrict the healthy development of the industry of L.davidii,and the pathogen infection is one of the main causes of post-harvest diseases.Essential oils are secondary metabolites isolated and extracted from plants,with great antibacterial and antioxidant activities,and which are safe and non-toxic.In recent years,essential oils have become the research focus of postharvest antistaling agents for fruits and vegetables.Therefore,the use of essential oil and its active ingredients to control the postharvest diseases of L.davidii caused by pathogens in vivo and in vitro,which provides a theoretical basis for the biological control of the postharvest diseases of L.davidii.In this study,pathogens were isolated from L.davidii by tissue isolation and its pathogenicity was verified by koch’s postulates;all pathogens were identified by morphology,molecular biology and physiological and biochemical characteristics;the essential oils of Artemisia Annua(ALEO)were extracted by steam distillation and analyzed by Gas chromatography-mass spectrometry(GC-MS);the antibacterial activities of the essential oils and monomers were tested by fumigation and direct contact;scanning electron microscopy(SEM)was used to observe the effect of essential oils and monomers on the cell wall membrane of pathogens;water content,soluble solids,browning degree,etc.are as indicators to study the control effect of ALEO and monomers on the pathogens of postharvest diseases of L.davidii.The main results are as follows:1.The results showed that the pathogens that caused the postharvest diseases of L.davidii included 1 strain of Bacillus mojavensis(B-6)and 3 strains of pathogenic fungus Trichoderma lixii(F-2),Talaromyces tumuli(F-3)and Fusarium annulatum(F-6);2.Seven kinds of essential oils from Artemisia have good antimicrobial activity in vitro against the pathogens of postharvest diseases of L.davidii.The essential oil of Artemisia argyi has the strongest antibacterial activity,and the essential oils of Artemisia frigida Willd,Artemisia vestita and Artemisia Waldst have the stronger antifungal activity.The results of component analysis showed that the components and contents of seven kinds of Artemisia essential oils were different,and the contents of the same component in different essential oils were different.1,8-cineole is the common component of seven kinds of essential oils;3.The results of fumigation showed that when the concentration of ALEO,1,8-Cineole and Terpinen-4-ol reached 0.6 m L/L,the bactericidal rate against B-6 was over90%,the bactericidal rate of α-Terpineol against B-6 was only 76.15% with the same concentration.When the concentration of ALEO,1,8-Cineole,Terpinen-4-ol and α-Terpineol was 0.02 m L/L,the antifungal activity against pathogenic fungus was from strong to weak were Terpinen-4-ol > α-Terpineol > ALEO > 1,8-Cineole,respectively.And strain F-2 was very sensitive to Terpinen-4-ol and α-Terpineol,When the concentration was 0.02 m L/L,the fungicidal rate reached 86.67% and 54.81%,respectively.When the concentration of α-Terpineol was 0.10 m L/L,the growth of F-2was completely inhibited;4.The antimicrobial results of direct contact method showed that when the concentration of ALEO,1,8-cineole,Terpinen-4-ol and α-Terpinol was 2.5 m L/L,the bacteriostatic rate of ALEO to pathogenic bacteria B-6 was more than 99%.The fungicidal concentration of ALEO to F-2,F-3 and F-6 were 10,40 and 40 m L/L,respectively;The fungicidal concentration of 1,8-cineole against F-2,F-3 and F-6 was 20 m L/L;The fungicidal concentration of α-Terpinol to F-2,F-3 and F-6 was 10 m L/L;The fungicidal concentrations of Terpinen-4-ol to F-2,F-3 and F-6 were 5,10 and 5 m L/L,respectively;5.The results of scanning electron microscopy,intracellular and extracellular protein content showed that ALEO and 1,8-Cineole destroyed the integrity of the cell wall membrane,causing intracellular macromolecular substances to flow out,thereby inhibiting the growth and even kill pathogens;6.The optimal control concentrations of ALEO,1,8-Cineole and Terpinen-4-ol to L.davidii inoculated with pathogens were 46.15,30.77 and 15.38 μL/L,respectively.The results of physiological and biochemical indexes showed that the ALEO,1,8-Cineole and Terpinen-4-ol could inhibit the decrease of phenolics,the browning rate and the accumulation of MDA in L.davidii.In addition,the activities of defense-related enzymes in vivo were increased,which enhanced the stress resistance of L.davidii and inhibited the quality decline of L.davidii. |
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