| Bacillus can produce a variety of extracellular active substances that can inhibit plant pathogens and promote plant growth,and it has a good application prospect in disease control and crop yield improvement.In the early stage of this project,a strain of B.amyloliquefaciens BA-26,which has strong antagonistic effect to a variety of plant pathogenic fungi such as Fusarium sambucvnmn and Rhizoctonia solani,was screened out and completed the whole genome sequencing and analysis,purification and identification of extracellular metabolites,and stability investigation of antimicrobial substances.In this study,F.sambucvnmn was used as the target to study the antibacterial mechanism of extracellular antimicrobial substances of strain BA-26.Effects of BA-26 on plant growth,disease control,soil physical and chemical properties and diversity of soil microbial community were determined by field application experiments with potato as the experimental object,which provided theoretical and experimental basis for the development of new biological agents.The main research results are as follows:1.The study on the antibacterial mechanism of F.sambucvnmn showed that the antimicrobial substance of B.amyloliticus BA-26 could significantly inhibit the spore germination of F.elderii,and had strong teratogenic effect on the spore morphology during the spore germination process.Microscope and electronic microscope observation showed that the mycelium of F.sambucvnmn treated with antimicrobial substances was abnormal in morphology.The mycelium was curved and expanded,the surface of mycelium was rough and cracked,and part of mycelium was broken.The activity of alkaline phosphatase,electrical conductivity and nucleic acid content in extracellular supernatant were significantly increased,indicating that BA-26 antibacterial substance could destroy the cell wall of mycelia and increase the permeability of cell membrane.The antimicrobial substances reduced the activities of SOD,ATP,CAT and POD enzymes in the bacteria,and damaged the normal physiological metabolic activities of cells.By staining with rhodamine 123 and DCFH-DA,it was found that the antibacterial substance could increase the membrane potential of cells,and induce the accumulation of reactive oxygen species,and induce cell apoptosis.The results of gel block experiment showed that the antibacterial substance had no obvious effect on the DNA of F.sambucvnmn.2.Research on the application of BA-26 and organic fertilizer in the field showed that,compared with chemical fertilizer and organic fertilizer,BA-26 combined with organic fertilizer could increase the plant height,stem diameter and biomass of potato and promote the growth of potato.Increase soluble sugar and protein content,improve tuber quality.The combination of BA-26 and organic fertilizer could reduce the incidence of potato fusarium wilt,and the control effect was 32.42%.Combined with organic fertilizer,BA-26 can improve soil condition,improve soil electrical conductivity,and increase the contents of organic matter,available phosphorus and rapidly available potassium in root-zone soil.The activities of soil urease and alkaline phosphatase were increased.Increase the number of bacteria and actinomycetes and decrease the number of fungi.It can be seen that BA-26 can prevent disease,promote growth and improve soil fertility.3.Illumina high-throughput sequencing showed that BA-26 combined with organic fertilizer could increase the bacterial α diversity of root-zone soil,furrow soil and geocaulosphere soil,while reduce the fungal diversity.At the soil microbial phylum level,BA-26 combined with organic fertilizer increased the relative abundance of Acidobacteria and Actinobacteria in the geocaulosphere soil.Reduce the relative abundance of Ascomycota in soil.At the genus level,the abundance of most bacteria treated with BA-26 combined with organic fertilizer was higher than that treated with chemical fertilizer and organic fertilizer,and the relative abundance of beneficial bacteria such as Sphingomonas,Lysobacter and Bacillus were significantly increased.Reduce the relative abundance of plant pathogenic bacteria such as Fusarium and Alternaria.β-diversity analysis showed that BA-26 combined with organic fertilizer could change the community structure of soil bacteria and fungi.The results of RDA show that soil electrical conductivity and available phosphorus content affect the community composition of soil bacteria and fungi. |
