Screening And Mechanism Of Action Of Plant Extracts For Inhibiting Oryzae Oryzae

Rice blast is a highly damaging and widespread disease in rice production,threatening the yield and quality of rice.Plant-derived pesticides have good control effects and can fill the gaps of chemical fungicides,It has the advantages of environmental friendliness,low residue and easy degradation,which can fill the shortcomings of chemical pesticides such as easy to produce resistance and pollute the environment.It has good prospects for development and is conducive to the sustainable development of agricultural production.This study was carried out to screen and study the inhibition extracts against Magnaporthe oryzae,which can provide a theoretical basis for the development of plant-derived fungicides against rice blast disease.In this thesis,three plant extracts were selected from 54 plant materials using 80 %ethanol as the extraction solvent,and the mycelial growth rate method was used to determine the effect of the three extracts on the mycelial growth inhibition of Magnaporthe oryzae.The effects of the three extracts on mycelial growth and mycelial dry mass were determined by the growth rate method and the weighing method,and the effects of the three extracts on spore germination were determined by the slide germination method.The physiological indexes of mycelium were determined by conventional indoor analytical methods,and the mycelial morphology was observed by scanning electron microscopy to explore the inhibition mechanism of the three extracts against the Magnaporthe oryzae;the effect of the three extracts on the control of rice blast disease was determined by inoculation of leaves in a pot experiment,and the malondialdehyde content and polyphenol oxidase activity of rice leaves were determined by conventional indoor analytical methods to explore the induced disease resistance of the three plant extracts.The results of the study were as follows:The inhibition effect of 54 plant extracts on the mycelial growth of Magnaporthe oryzae varied,with three extracts,namely Coptis chinensis,Glycyrrhiza uralensis and Cinnamomum cassia showing stronger inhibition activity and significantly higher inhibition rate of mycelial growth than other plant extracts.At a concentration of 10mg/m L,all three extracts inhibited the mycelial growth of Magnaporthe oryzae by more than 75 %,with the inhibition rate of Coptis chinensis extract reaching 90.06 %.The extracts of Coptis chinensis,Glycyrrhiza uralensis and Cinnamomum cassia could effectively inhibit the mycelial growth of Magnaporthe oryzae.The inhibition of mycelial growth was achieved at 4.17 mg/m L,4.48 mg/m L and 5.22 mg/m L for the extracts of Coptis chinensis,Glycyrrhiza uralensis and Cinnamomum cassia,and the dry mass of mycelium was significantly lower than that of the control.The effects of the three extracts on the morphology of the mycelium were slightly different,but all of them generally caused deformation by damaging the surface of the mycelium,which eventually led to protoplasm leakage;the three extracts had certain destructive effects on the cell membrane of the mycelium of Magnaporthe oryzae,resulting in an increase in intracellular electrolyte extravasation and the content of malondialdehyde,a product of membrane peroxidation.The three extracts had a destructive effect on the cell membrane of rice fungus hyphae.The extracts of Glycyrrhiza uralensis and Cinnamomum cassia had a weak effect on the multiplication of the pathogenic fungi.The inhibition of spore germination by extracts of Coptis chinensis,Glycyrrhiza uralensis and Cinnamomum cassia was 5.04 mg/m L,41.67 mg/m L and 163.07 mg/m L in order of medium concentration.The extracts of Coptis chinensis,Glycyrrhiza uralensis and Cinnamomum cassia interfered with the synthesis and metabolism of mycelial substances of Magnaporthe oryzae.The pyruvate and soluble protein contents in the mycelium treated with the three extracts were significantly reduced compared with the control group.The extracts of Coptis chinensis,Glycyrrhiza uralensis and Cinnamomum cassia induced resistance to rice blast and activated its defence mechanism.The effect of Coptis extract was better than the other two extracts.At a mass concentration of 20mg/m L,the disease indices of Coptis chinensis,Glycyrrhiza uralensis and Cinnamomum cassia extracts were 9.49,13.41 and 14.04 respectively;the potting efficacy was52.79%,36.31% and 33.33% respectively,which could control rice blast better.The extracts of Coptis chinensis,Glycyrrhiza uralensis and Cinnamomum cassia could significantly increase the polyphenol oxidase activity of rice leaves,significantly reduce the malondialdehyde content of rice leaf cells,inhibit the spread of leaf spots,treat the leaves and slow down the disease.