Effect Of Endophytic Bacteria From Houttuynia Cordata Thunb. On The Growth Of Host Plants

The formation of plant disease resistance and its quality is not only related to the external environment but also closely related to the internal microbial environment.Endophytic bacteria are important microbial members in plants,which have formed unique biological characteristics in the process of long-term co-evolution with host plants.The interaction between microorganisms and plants produces complex chemical signals,which have an important impact on plants’ growth,metabolism,disease resistance,and quality formation.Therefore,finding bacteria that can promote plant growth is of great significance to the production of medicinal plants and crops.In addition,some soil-borne pathogens may cause serious plant wilt and root rot.Previous studies have shown that endophytic bacteria of plants can produce related antibacterial substances and induce plant disease resistance for a long time,so it is of great significance to find strain resources that can prevent or alleviate diseases to control the occurrence of diseases.In this paper,the endophytic bacteria from Houttuynia cordata Thunb.were used as the research object to study the effect of endophytic bacteria on the growth of H.cordata.By establishing the co-culture system of sterile tissue culture seedlings of H.cordata with endophytic bacteria.To analyze the effects of endophytic bacteria on the plant growth and secondary metabolism of H.cordata and the effects of inoculation of endophytic bacteria on the physiology and biochemistry of H.cordata were analyzed,the effects of endophytic bacteria on the content of IAA in H.cordata were determined,the antagonistic effects of endophytic bacteria on pathogenic bacteria of H.cordata were explored,as well as the effects of the secondary metabolites of H.cordata on the growth of endophytic bacteria were investigated.The main research results are as follows:1.There are 6 strains(H1～H6)of H.cordata were identified and compared by gene sequencing and molecular phylogenetic tree,and it was confirmed that these 6 strains belonged to Bacillus sp.,Pseudomonas sp.,Agrobacterium sp.,and Stenotrophomonas sp.At the same time,the ITS gene sequence of the pathogen of H.cordata was determined,which belonged to Colletotrichum sp.(HC1),Fusarium sp.(HC2),and Rhizoctonia sp.(HC5)respectively.2.Endophytic bacteria(H1～H6)were isolated from the roots of H.cordata.and co-cultured with tissue-cultured aseptic seedlings of H.cordata.to explore their growth-promoting effects on H.cordata.The results showed that strain H4 was a plant growth-promoting bacterium,which could promote plant growth and phenotypic growth.Compared with the control group,the leaves were thicker and wider,the color of the leaves was dark green,and strong stems and roots grew.The number of lateral roots,root surface area,and the number of lateral roots were significantly higher than those in the control group.The gene sequencing and phylogenetic tree comparison results showed that the sequence homology of H4 with Pseudomonas fluorescens reached 100%.3.P.fluorescens play an obvious role in promoting the accumulation of volatile secondary metabolites of Houttuynia cordata.Inoculated with P.fluorescens has shown obvious effects compared with the control group,β-Myrcene content increased by 104%,2-methyl-n-nonone increased by 91.6%,Decanal increased by 204%,β-Caryophyllene content increased by 97%,α-Pinene increased by 181%,Bornyl acetate increased by 58%,cis-3-Hexenyl-acetate increased by139%,and 3-Tetradecanone increased by 229%.The concentrations of phenolic secondary metabolites including Chlorogenic acid,Rutin,Quercitrin,and Afzelin were 184%,54%,37%,and 113% higher than the control group respectively.In addition,the activities of superoxide dismutase(SOD)and peroxidase(POD)in the seedlings of H.cordata were 137% and 29% higher than the control group,respectively,and the content of malondialdehyde(MDA)was decreased.In addition,the content of IAA in H.cordata inoculated with P.fluorescens was determined to be 2times that in the control group.4.The strains of endophytic bacteria(H1～H6)were isolated and confronted with the pathogen of Houttuynia cordata,respectively.The results showed that a single endophytic bacteria had no obvious inhibitory effect on the pathogen of Houttuynia cordata,However,the inhibitory diameter of six strains of mixed endophytic bacteria on Colletotrichum sp.was 6 mm,Fusarium was 8 mm and Rhizoctonia was 5 mm.Co-culture of pathogenic bacteria alone with aseptic seedlings of H.cordata led to seedling death.When inoculated with pathogenic bacteria,6 strains of mixed endophytic bacteria were co-cultured with H.cordata seedlings,but the seedlings did not completely die,indicating that the combined action of 6 strains of endophytic bacteria had certain antagonistic activity,which had the potential for development and application and promoted the quality of medicinal plants.5.The metabonomics and 16 S r DNA sequencing of endophytic bacteria in the roots of H.cordata inoculated with P.fluorescens were analyzed.The metabolites such as Rutin,Quercetin,and Isoquercitrin in H.cordata were significantly increased compared with those in the uninfected group.Inoculation with P.fluorescens led to the decrease of endophytic bacteria in the roots of H.cordata and the change in species composition.At the same time,with the increase of culture days,the richness of endophytic bacteria in H.cordata decreased,and the community composition also changed.Through this study,the plant growth-promoting bacteria P.fluorescens was screened out,which provided the experimental basis and bacterial source for the later development of biofertilizer.At the same time,it showed that P.fluorophores promoted plant growth because of its ability to synthesize IAA,and the combination of 6 bacteria inhibited the growth of pathogenic bacteria,which provided ideas and a theoretical basis for the establishment of more effective biological control agents by the multi-bacteria assembly.Finally,the experiment showed that the accumulation of secondary metabolism had an impact on the abundance and composition of the H.cordata community.It reasonably explains H.cordata as a crop that cannot be continuously planted and establishes a theoretical basis for establishing healthy flora induced by secondary metabolites in the future.