Effects Of Biological Fumigation On Soil Microbial Community In Continuous Cropping Of Tobacco And Control Effect On Bacterial Wilt

Tobacco bacterial wilt as a soil-borne disease caused by R.solanacearum,tobacco fields are prone to outbreak of tobacco bacterial wilt in the long-term continuous cropping mode,which leads to serious economic loss.Soil is the basic carrier of plant growth,and soil microbes as a key factor affecting soil health,are an important ecological factor affecting the occurrence of bacterial wilt.There are many studies have shown that biological fumigation plays a certain role in the improvement of soil physical and chemical properties,growth of main crops,control of pests and diseases,etc.,but systematically studying on the effects of biological fumigation on the microbial community structure and the control effect on tobacco bacterial wilt in continuous cropping soil have not been reported so far.In this study,pot experiment and long-term colonization experiment were conducted to investigate the effects of biological fumigation on tobacco growth,soil physical and chemical properties,and soil enzyme activities and soil microbial community composition.Futhermore,field trials were used to evaluate the control effect of biological fumigation on tobacco bacterial wilt.The purpose of the study is to explain the mechanism of biological fumigation application affecting the occurrence of tobacco bacterial wilt,and to look for a green,cyclic and efficient control model of tobacco bacterial wilt,and to provide a theoretical support for the prevention of tobacco bacterial wilt through soil microenvironment improvement and soil microecological balance regulation.1.Clarify planting biological fumigation plants and biological fumigation extracts had no effect on R.solanacearumThrough the pathogenicity test of R.solanacearum and the SMSA detection of root and stem base,it was found that ryegrass,rapeseed and Chinese milk vetch were planted as biological fumigation plants during the tobacco leisure period,which would not adversely affect the tobacco growth.Besides,growth curve method and filter paper method confirmed that the biological fumigation extracts had no effect on the growth of R.solanacearum.2.Biological fumigation could effectively improve soil physical and chemical properties,soil enzyme activity,and increase soil microbial metabolic activity.Pot experiments of dosage selection showed that ryegrass,rapeseed and Chinese milk vetch were the best in controlling tobacco bacterial wilt at 4% amount,which was expressed as ryegrass > rapeseed > Chinese milk vetch > control.Through soil physical and chemical properties and soil enzyme activity detection,the results showed that biological fumigation could increase soil total nitrogen,total potassium and available potassium content,which were 10.29%~12.04%,20.80~25.60%,52.94%~90.19%,respectively.Among different biological fumigation plants,ryegrass increased the soil organic matter,total carbon and alkali nitrogen,and increased by 13.39%,13.33% and 99.67%,respectively.The activity of soil urease and invertase were increased after biological fumigation application.The increase of soil urease activity in ryegrass and the increase of soil invertase activity in Chinese milk vetch were the highest,which were 52.53% and 71.11%,respectively.The BIOLOG ECO microplate method was used to detect the effects of biological fumigation on soil microbial metabolic activity.The results showed that the biological fumigation increased the soil microbial carbon source metabolic activity,which showed rapeseed>ryegrass> Chinese milk vetch.In addition,the ability of indigenous microbes to utilize carbohydrates,amino acids,polymers and amine carbon sources by biological fumigation application were increased,but different types of carbonaceous plants have different preferences for carbon source utilization.3.The effects of five consecutive biological fumigation on the microbial community composition of continuous cropping and conducive soil were analyzed.After analyzing the effects of biological fumigation on soil microbial metabolic activity,using 16 S rRNA and ITS sequencing techniques,the experiment examined the effects of biological fumigation on soil bacterial and fungal community composition by long-term colonization experiments.The results showed that the composition of soil bacteria and fungi had chaged greatly after long-term biological fumigation application,which reflected that the relative abundance of Proteobacteria,Actinobacteria and Firmicutes increased at the phlum level.The relative abundance of the family of Xanthobacteraceae,Xanthomonadaceae,Micrococcaceae,Bradyrhizobiaceae and Sphingomonas increased at the family level.The relative abundance of Trichosporon and Trichophyton increased at the phlum and family level of fungi.18 bacterial groups were screened by LEfSe analysis,namely Pseudarthrobacter,Arthrobacter,Janibacter,Paenarthrobacter,Microbacterium,Angustibacter,Bryobacter,Sphingomonas,Massilia,Dyella,Lactobacillus,Red Pseudomonas,Phytophthora,Achromobacter,Shortpomonas,Polycystis,Sphingopyxis and Taibaiella;and 6 fungal groups were Spirulina,Trichoderma,Plexus Red genus,Chaetomium,Cladosporium and Enterococcus can be used as potential indicators to suppress tobacco bacterial wilt.4.Biological fumigation could significantly promote tobacco growth and had significant control effects on tobacco bacterial wiltBoth the pot experiments and the field trials showed that the 4% amount of biological fumigation application had the most significant promoting effect on tobacco growth,and the biological fumigation years were positively correlated with the promotion effect.Through two consecutive years of biological fumigation,the results showed that the biological fumigation could significantly reduced the occurrence of tobacco bacterial wilt,and biological fumigation years were positively correlated with control effects.In the second year of biological fumigation,the control effects of ryegrass,rapeseed and Chinese milk vetch on tobacco bacterial wilt were 65.92%?54.07% and 41.48%,respectively.