| Soil-borne diseases are easy to occur in the growth process of crops,which has become one of the main reasons restricting the development of agriculture in China.The prevention and control of soil-borne diseases has always been a hot and difficult point of investigation.In recent years,due to the large-scale use of chemical fertilizers,soil fertility has decreased,soil microbial flora has become disordered,and the annual increase of crop soil-borne diseases has brought huge losses to agricultural production.Although the application of chemical agents plays an important role in the prevention and control of crop soil-borne diseases,the problems of pesticide residues,environmental pollution and drug resistance accumulation caused by the extensive use of chemical agents are not in line with the requirements for sustainable development of agricultural health.Therefore,it is imperative to find new ways to prevent and cure soil-borne diseases.Due to its low cost,environmental friendliness and drug-free residue,biological control has become a research hotspot for the prevention and control of plant-borne diseases at home and abroad.It will gradually replace traditional chemical control methods and has broad application prospects.At present,there are reports on the control of soil-borne diseases by Bacillus subtilis,but it is mostly limited to the biocontrol effect and the antibacterial mechanism.It is reported in which way to act on soil-borne bacteria and how to regulate and exert its biocontrol potential.less.Our previous research found that Bacillus subtilis M29(Gen Bank accession number KU870670)isolated from sputum manure has good control effect on various soil-borne pathogens,but its specific antagonistic effect mechanism and regulation mode.still not clear.In this study,the specific antagonistic effect was studied by an in-situ plate assay,and the regulation of how to combine the strain M29 with organic fertilizer was studied to control how to better exert the biocontrol potential of the strain.The main findings are as follows:1.The bacteriostatic effect of strain M29 was the best when the Landy medium was used as the base medium,the initial pH was 7,the culture temperature was 30℃,and the culture was 36～48 h.The antibacterial activity of the crude extract of the strain M29 bacteriostatic substance has thermal stability and enzyme stability.In addition,fenB,a regulatory gene for the synthesis of fengycin,was amplified in the genomic DNA of strain M29,and the molecular weight of Fengycin B was detected by mass spectrometry.We speculated that the lipopeptide antibiotic Fengycin B may be present in the secretion of strain M29.2.The pot experiment was conducted to study the control effect of strain M29 and its microbial organic fertilizer on the bacterial wilt of tomato growth and its promoting effect.The results showed that the antagonistic antibacterial M29 and its inoculation into the sterilized organic fertilizer could significantly reduce the number of R.solanacearum in the rhizosphere of tomato,which decreased by 64.7%and 74.3%,respectively.Antagonistic antibacterial M29 and application of organic fertilizer can enhance tomato self-resistance against R.solanacearum infection,induce the enzyme activity of POD and SOD enzymes in tomato plants to be significantly improved,and at the same time,antagonize antibacterial M29 and inoculate it into sterilized organic Fertilizer significantly reduced MDA content and total phenolic content in tomato plants.Antagonistic antibacterial M29 and its inoculation into sterilized organic fertilizer have a certain promoting effect on the growth of tomato plants,but this growth-promoting effect is unstable.The above-ground biomass of tomato plants increased by 10.8%and 21.1%respectively after application,but only the improvement trend did not reach significant difference.Both of these regulation methods significantly increased the roots of tomato,while the aboveground biomass of tomato with organic fertilizer was significantly lower than that of applied fertilizer.Strain M29 can increase soil microbial activity,nutrient content directly available in soil and related nutrient invertase activity.Antagonistic antibacterial M29 and its inoculation into sterilized organic fertilizer can increase the content of microbial carbon in soil,the content of soluble organic carbon in soil and the content of nitrate in soil.At the same time,the application of organic fertilizer is compared with that of organic fertilizer.Single application of chemical fertilizers can also significantly increase the content of soluble organic carbon in the soil.The available phosphorus content in the soil is also significantly improved under these two modes of regulation.Inoculation of antagonistic M29 could significantly enhance the activity of C and N invertase in soil,indicating that strain M29 has certain potential to promote crop growth.3.Strain M29 showed different biocontrol effects under different regulatory pathways,which mainly depended on the adaptability of strain M29 in fertilizer and soil.The colonization of strain M29 in sterilized fertilizer can reach 107～108 CFU/g dry soil,but not higher than 105 CFU/g dry soil in unsterilized fertilizer.The type of fertilizer also has a great influence on the colonization of its strain M29.In the sterilized chicken manure organic fertilizer,the amount of antagonistic bacteria in the fertilizer was maintained at 108 CFU/g dry soil,while in the sterilized cow manure organic fertilizer,the amount was maintained at 106 CFU/g dry soil.The prepared microbial organic fertilizer is applied to the soil,and the treatment which is settled in the fertilizer is more likely to exhibit a better control effect.The antagonistic effect exhibited by the inoculated strain M29 in the unsterilized organic fertilizer varies depending on the type of fertilizer.Inoculation of strain M29 in straw organic fertilizer,the number of R.solanacearum in the soil decreased,but there was no difference in cow manure organic fertilizer and straw organic fertilizer.At the same time,organic fertilizer can reduce the number of R.solanacearum in soil compared with chemical fertilizer,but this difference also varies according to the type of organic fertilizer.Inoculation of antagonistic bacteria in the sterilized organic fertilizer and application of antagonistic bacteria can reduce the amount of R.solanacearum in the soil.Therefore,the type of organic fertilizer has a certain influence on the antagonistic antibacterial effect.Therefore,the strain can improve the resistance of the plant to pathogenic bacteria and change the living environment of the pathogenic bacteria in the soil through direct antagonism,induction of plant system resistance,promotion of crop growth and improvement of soil traits. |
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