| In the process of vegetable production,due to long-term continuous single planting,serious diseases and insect pests occur and soil productivity declines,which ultimately leads to the unsustainability of agricultural production and restricts the development of vegetable production.In this study,cabbage was used as the experimental object.By comparing and analyzing the soil microenvironment of healthy and diseased cabbage under continuous cropping conditions,the diversity of bacteria and fungi in different organs of cabbage and the differences in transcriptome,it revealed the pathogenesis of cabbage under continuous cropping conditions;and used the existing roots in the laboratory.Probiotics: Bacillus amyloliquefaciens（BA）,Azotobacter chroococcum（AC）,Fusarium culmorum（FC）,Fusarium pseudograminearum（FP）and commercially available Microbial inoculants were prepared from the inoculant "Dolivix" Pythium oligandrum oospores（PO）.Three cabbage varieties,Zhonggan 21,Manyue 56 and Ximei,were cultivated with microbial inoculants.Through field planting experiments in spring and autumn,we explored The effect of microbial control methods for continuous cropping obstacles in cabbage provides a certain theoretical basis and green environmental protection product support for the prevention and control of soil continuous cropping obstacles.The main results are as follows:1.Through comparative analysis of the differences in soil nutrients in the rhizosphere and non-rhizosphere of healthy and diseased plants under continuous cropping conditions,reveal the relationship between the occurrence of cabbage diseases and soil nutrients under continuous cropping conditions.Organic matter determination results showed that the organic matter content of cabbage rhizosphere soil was significantly higher than that of non-rhizosphere soil;there was no significant difference in soil organic matter between healthy cabbage and diseased cabbage.The non-rhizosphere soil available phosphorus content of healthy cabbage and diseased plants were 55.79 and 48.57 mg/kg,respectively.The non-rhizosphere soil available phosphorus content of diseased cabbage was significantly lower than that of healthy cabbage.There was no significant difference between healthy and diseased cabbage rhizosphere soil available phosphorus content.;Regardless of healthy or diseased cabbage,the rhizosphere soil available phosphorus content is significantly lower than the non-rhizosphere soil.There was no significant difference in total nitrogen between healthy cabbage and diseased cabbage,and no significant difference in total nitrogen content between rhizosphere and non-rhizosphere soil.The available potassium content of healthy and diseased cabbage non-rhizosphere soil is 709.29 and 726.55mg/kg,and the available potassium content of rhizosphere soil is 697.98 and 717.62mg/kg,respectively.Regardless of rhizosphere or non-rhizosphere soil,the available potassium content of healthy cabbage soil All were significantly lower than diseased cabbage,and the available potassium content of rhizosphere soil was lower than that of non-rhizosphere soil.2.By comparing the number of cultivable microorganisms in the rhizosphere and non-rhizosphere soils of healthy and diseased plants under continuous cropping conditions,sequenced analysis of the diversity of rhizosphere bacteria and fungi,revealing the relationship between the occurrence of cabbage diseases and soil microorganisms under continuous cropping conditions.The count of cultivable microorganisms showed that the number of cultivable fungi,bacteria,and ammoniating bacteria in healthy cabbage soil was higher than that in diseased cabbage,but there was no significant difference.The number of cultivable actinomycetes and nitrogen-fixing bacteria in the rhizosphere of healthy cabbage was significantly higher than that of diseased cabbage;the microbial diversity sequencing results showed that there was no significant difference in the diversity of bacteria and fungi in the rhizosphere of healthy and diseased cabbage,but there were significant differences in the community structure.3.By comparing the functional diversity of soil microbes in the rhizosphere and non-rhizosphere of healthy and diseased plants,the relationship between the occurrence of continuous cabbage cropping obstacles and soil microbial metabolism was analyzed.The results of Biolog analysis showed that the relative utilization rate of carbohydrates by the rhizosphere soil microorganisms of healthy plants was significantly higher than that of diseased plants.The rhizosphere and non-rhizosphere soil microorganisms of healthy and diseased plants had organic acids,esters,sugar alcohols,amino acids and amines.There is no significant difference in relative utilization.The average metabolic ability of microorganisms to six types of carbon sources in different soil samples showed that the AWCD values of microbes in the rhizosphere soil of healthy plants for the six types of carbon sources were esters >carbohydrates> amino acids > amines > organic acids > sugar alcohols The rhizosphere soil of diseased plants is ester >carbohydrate >sugar alcohol >amino acid >amines >sugar alcohol;the non-rhizosphere soil of healthy plants is ester>amino acid >carbohydrates >organic acid >amines >sugar alcohol;diseased plants are not roots Jitu is ester>amino acid > carbohydrate > organic acid >amine >sugar alcohol.4.Compare the bacterial community structure of the roots,stems and leaves of healthy and diseased cabbage plants through high-throughput sequencing,and analyze the changes in the bacterial community structure of the various organs of diseased cabbage.Sequencing results showed that there are certain differences in the composition and diversity of bacterial flora in different organs of cabbage.The bacterial diversity of plant leaves was significantly lower than the bacterial community diversity of roots and stems.The bacterial community composition and diversity in roots and stems are more similar,and have obvious differences compared with leaves.There are differences in bacterial diversity and microbial community structure in different organs of healthy and diseased cabbage mediated by continuous cropping.The bacterial microbial diversity of diseased cabbage is higher than that of healthy cabbage.The Shannon index of healthy and diseased cabbage leaf bacteria were 0.073 and 0.28,respectively;the Shannon index of stem bacteria were 6.198 and6.389;the Shannon index of root bacteria were 5.878 and 6.318,respectively.At the level of phyla and class classification,the relative abundance of the dominant flora in the rhizomes and leaves showed that healthy cabbage was greater than diseased cabbage.5.Through high-throughput sequencing to compare the fungal community structure of the roots,stems and leaves of healthy and diseased cabbage plants,and analyze the changes in the fungal community structure of the various organs of diseased cabbage.The sequencing results showed that there were differences in fungal diversity and microbial community structure in different organs of healthy and diseased cabbage.The Shannon index of leaf fungi in healthy and diseased cabbage were 2.939 and 2.422;the Shannon index of stem fungus were 3.307 and 2.193;the Shannon index of root fungus were 3.438 and 3.971,respectively.6.Compare the gene expression of healthy and diseased cabbage plants through transcriptome analysis,and analyze the molecular regulation mechanism of continuous cropping diseases.Transcriptome analysis results showed that 5162 differentially expressed genes（DEGs）were obtained in healthy and diseased cabbage roots.Analysis of genes related to plant defense response revealed that compared with healthy cabbage roots,29 DEGs in diseased cabbage roots are related to Jasmonic acid（JA）response,and 29 are related to salicylic acid（SA）response.Related DEGs,8 DEGs related to Ethylene（ET）response.Analysis of genes related to plant stress response revealed 296 differentially expressed genes related to abiotic stimulus response,198 differentially expressed genes related to biological stimulus response,60 differentially expressed genes related to fungal response,and 68 differentially expressed genes Differentially expressed genes related to bacterial response.10434 DEGs were obtained in healthy and diseased cabbage leaves.Analysis of genes related to plant defense response found that compared with healthy cabbage,there are60 differentially expressed genes related to JA response,69 differentially expressed genes related to SA response,and 38 differentially expressed genes related to ET response in diseased cabbage leaves.Differentially expressed genes.Analysis of genes related to plant stress response found that compared with healthy cabbage diseased cabbage leaves,there are 707 differentially expressed genes related to abiotic stimulus response,462 differentially expressed genes related to biological stimulus response,and 125 of which are related to fungal response.Among the differentially expressed genes,there are 155 differentially expressed genes related to bacterial response.7.Biological control of cabbage continuous cropping obstacles by applying exogenous beneficial microorganisms.Potted experiment results of microbial inoculant breeding on the rhizosphere seedling substrate of three cabbage varieties showed that the treatment of five microbial inoculants significantly affected the cultivable bacteria,actinomycetes,ammonifying bacteria and nitrogen-fixing bacteria in the rhizosphere soil of three cabbage varieties The number of microbial flora has no significant effect on the number of cultivable fungi;the same microbial agent has different effects on the rhizosphere microbial community structure of different cabbage varieties.8.The field transplantation experiment results of three cabbage varieties raised by five kinds of microbial inoculants showed that the disease-resistant varieties Manyue 56 and Ximei did not have continuous cropping obstacles in spring and autumn,and the susceptible variety Zhonggan 21 showed obvious problems in autumn.Continuous cropping obstacles.Microbial inoculum breeding had no significant effect on the yield of Zhonggan 21 in spring,Full Moon 56 in spring and autumn and Ximei,but it had a certain effect on the nutrient status of its rhizosphere.Microbial seedlings had a certain control effect on the continuous cropping obstacles of Zhonggan 21 in autumn.The yield of Zhonggan 21 treated with BA,AC,FC,FP and M microbial agents increased by 87.65%,86.26%,87.14%,65.61% and 97.50%,respectively.In summary,changes in the rhizosphere soil environment,including rhizosphere soil nutrients,changes in the number and structure of rhizosphere microorganisms,and the interaction between nutrients and microorganisms all affect the rhizosphere soil microenvironment.The microenvironment of the rhizosphere soil affects the microbial community structure of the various organs of cabbage,which causes the molecular response of the plant.Single planting leads to catastrophic changes in the rhizosphere micro-ecological environment,which leads to the occurrence of continuous cabbage cropping obstacles.The application of exogenous beneficial microorganisms can improve the rhizosphere microenvironment and form rhizosphere immunity to achieve biological control effects. |
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