Antifungal Activity And The Preliminary Action Mechanisms Of Three Kinds Of Natural Ptoducts

Plant disease is one of the main reasons for the reduction of crop yields,which seriously reduces the quality of agricultural products and causes huge economic losses to agricultural production.At present,the control of plant diseases is still dominated by chemical agents.However,the long-term and unreasonable use of chemical pesticides has brought serious threats to environmental protection and human-animal safety.In recent years,natural fungicides have shown environmentally friendly,easily degradable and low residues,safe and low toxicity to non-target fungi,promoting crop growth and improving crop disease resistance in controlling plant diseases.Therefore,natural fungicides have become one of the research hotspots to developing new and green pesticides.Based on the previous research,evaluated antifungal activity of isoquinoline alkaloids,flavones and pentacyclic triterpenes against common plant pathogenic fungi,such as S.sclerotiorum,M.oryzae,R.solani,F.graminearum,and B.cinerea.Then,the preliminary action mechanisms of the most-active compounds were discussed.And the research results showed that:among the twelve isoquinoline alkaloids,sanguinarine had the most antifungl activity and a broad antifungal spectrum.It had the best activity against M.oryzae with an EC₅₀ value of 6.96μg/mL,which was significantly higher than commercial fungicide azoxystrobin(EC₅₀=12.04μg/mL).Further exploration of the action mechanisms of sanguinarine revealed that it mainly destroyed the mycelium morphology of the target fungi,increase the permeability of the mycelium cell membrane and cause leakage of the contents.It also could reduce the mitochondrial membrane potential of the mycelium and cause a large accumulation of endogenous ROS to exert antifungal effect;Next,the antifungal activity of fourteen flavonoid compounds in licorice were evaluated against plant pathogens,it was found that glabridin had a good antifungal activity,especially the most active against S.sclerotiorum with an EC₅₀ value of 6.78μg/mL.The RNA-Seq was used to capture specific action mechanisms of glabridin,and the results showed glabridin mainly acted on the glycerophospholipid metabolism pathway on the mitochondrial membrane,involving the phosphatidylserine decarboxylase on the inner membrane of the mitochondria,and then affected the normal function of the mitochondria intima.And the glabridin also could act on the mycelium cell membrane,increase its permeability and accelerate mycelial cell death to effectively inhibit the growth of mycelia;Finally,the most active compound pristimerin was screened out from the eleven common pentacyclic triterpenoids,which also had a best antifungal activity against S.sclerotiorum with an EC₅₀ value of 1.36μg/mL and a good control effect against S.sclerotiorum in vivo.A preliminary study on the action mechanisms of pristimerin revealed that the ATP content and ATPase activity in mycelial mitochondria were significantly reduced（p<0.01）,Meanwhile,the activities of succinate dehydrogenase and malate dehydrogenation were decreased significantly in the TCA cycle of mitochondrial.Therefore,pristimerin could affect the energy supply of the normal life activities of the mycelium by hindering the energy production in the mitochondria,thereby inhibiting the normal growth of the mycelia.In summary,in this paper the antifungal activity of twelve isoquinoline alkaloids,fourteen flavonoids and eleven pentacyclic triterpenes was evaluated.As a result,sanguinarine,glabridin and pristimerin were screened out for the most active compounds.Then,the action mechanisms of these compounds against plant pathogens were researched from morphology,physiological and biochemical reactions and RNA level for the first time.The above research aims to provide lead compounds for the creation of natural-based agricultural fungicides and a theoretical reference for the subsequent mechanism research of these three types of compounds.