Screening Of Antagonistic Trichoderma Strains For Inhibiting Soil-borne Pathogens Of Panax Quinquefolium And Their Alleviate Mechanisms Of Continuous Cropping Obstacle Factors

Soil-borne disease pathogens and phenolic acid autotoxic substances are the main obstacle factors in the continuous cropping process of American ginseng,which seriously affect the yield and quality of American ginseng.As the most widely used biocontrol fungus in crop cultivation,Trichoderma has been proven to effectively alleviate the problem of continuous cropping obstacles of various crops.In this study,the relationship between two continuous crop barrier factors of American ginseng was investigated.Trichoderma with good inhibition effect on pathogens and high degradation of phenolic acid was screened from 209 biocontrol Trichoderma strains stored in the laboratory.Finally,the effects of Trichoderma in different types of soil on various physiological indexes in the growth process of American ginseng and the effects on rhizosphere microbial community of American ginseng were investigated by pot experiment.The alleviating mechanism of Trichoderma on continuous cropping obstacles was studied from the perspective of soil microbial community.In order to provide some ideas for solving the problem of American ginseng continuous cropping obstacles.The experimental results are as follows:(1)The content changes of phenolic acids in the rhizosphere soil of American ginseng with different continuous cropping years were determined by High-Performance Liquid Chromatography(HPLC).The results showed that the total content of phydroxybenzoic acid,vanillic acid,syringic acid,p-coumaric acid,ferulic acid,and benzoic acid first decreased and then stabilized.Its content in the non-continuous cropping soil and the rhizosphere soil of American ginseng continuous cropping for 1,2,and 3 years was 29.28 μg/g,25.38 μg/g,13.31 μg/g,and 16.58 μg/g,respectively.(2)The effects of different concentrations of phenolic acids on the mycelium growth of four soil-borne disease pathogens of American ginseng were explored by exogenous addition method.The results showed that(1)Single p-coumaric acid inhibited Fusarium solani,Cylindrocarpon destructans,Fusarium oxysporum,and promote the growth of Rhizoctonia solani.Inhibition or growth promotion were significant for all pathogens at5-10 mg/L.(2)The phenolic acid mixture promoted the mycelial growth of Fusarium solani,Cylindrocarpon destructans,and Rhizoctonia solani at a concentration of 2.5-10mg/L,but inhibited the growth of Fusarium oxysporum.The growth-promoting effect was significant for Fusarium solani at 5-10 mg/L concentration.(3)The soil extract of American ginseng continuous cropping for 3 years showed a promoting effect on the mycelial growth of the four pathogens,but only had a significant effect on the mycelial growth of Fusarium solani and Cylindrocarpon destructans.(3)The results of the plate confrontation method showed that 16 Trichoderma strains showed a significant inhibitory effect on the mycelial growth of Cylindrocarpon destructans,among which the inhibition rate of 20111,LTR-2,21969,C61,and 22124 reached 100% at 4 d.20015,20045,20581,22033,22133,23315,23272 reached 100%inhibition rate at 5 d,and 20741,20225,22000 reached 100% at 6 d.18 Trichoderma strains showed a significant inhibitory effect on the mycelial growth of Fusarium solani.Among them,the inhibition rate of C61 reached 100% at 4 d,and the inhibition rate of20111 and LTR-2 reached 100% at 5 d.The inhibition rate of 23315 reached 100% at 6d.(4)Trichoderma with a good degradation effect on 6 phenolic acids was screened by bromocresol green method and High-Performance Liquid Chromatography(HPLC),and the degradation rate of each phenolic acid was calculated.The preliminary screening results showed that Trichoderma strains LTR-2,C61,23424,20111,20137,and 23455 could effectively degrade phenolic acids when cultured in the screening medium for 7days.The degradation rates were further calculated by HPLC,and the results showed that the average degradation rates of Trichoderma to the phenolic acid mixture were 95.03%,71.57%,73.08%,71.25%,53.58%,and 92.35%,respectively.Through the two indicators of phenolic acid degradation and pathogen inhibition rate,three high-efficiency Trichoderma strains were screened: C61,LTR-2,and 20111.(5)The effects of C61,LTR-2,and 20111 on the growth and physiological indexes of American ginseng were studied by pot experiment.The results showed that in 3-year continuous cropping soil(S),non-continuous cropping soil(T),and undergrowth soil(F),the three strains of Trichoderma increased the germination rate,plant height,leaf chlorophyll content,root fresh weight,and root activity of American ginseng,and reduced the incidence of root rot.(6)Through High-throughput sequencing and bioinformatics methods,the alleviating mechanism of Trichoderma on continuous cropping obstacle factors was analyzed.The results showed that for fungal communities: Fungal Chao index increased in non-continuous cropping soil(T)with Trichoderma,but decreased in 3-year continuous cropping soil(S)and undergrowth soil(F)with Trichoderma.Fungal Shannon index increased in all types of soil.In addition,the relative abundance of major pathogens such as Fusarium sp.,in rhizosphere soil of American ginseng was reduced by application of Trichoderma.The fungal community structure was significantly altered.Bacterial community: The Chao index of bacteria was increased by the application of Trichoderma in non-continuous cropping soil(T)and undergrowth soil(F).However,the Chao index of bacteria was decreased by the application of Trichoderma in 3-year continuous cropping soil(S).In addition,the bacterial community Shannon index was increased by Trichoderma in all types of soils,and the bacterial community structure became more stable.