| Other Abstract | In the process of vegetable production, due to long-term continuous single planting, serious diseases and insect pests occurred and soil productivity decreased, which eventually led to the unsustainability of agricultural production and restricted the development of vegetable production. In this study, cabbage was used as the experimental object. Through comparative analysis of 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 microbial disorder mechanism that caused continuous cropping obstacles;The rhizosphere probiotics Bacillus amyloliquefaciens (BA), Azotobacter chroococcum (AC), Fusarium culmorum (FC), Fusarium pseudograminearum (FP) and the commercially available microbial agent "Dolivix"Pythium oligandrum oospores (PO) to prepare microbial inoculants and inoculate them into the cabbage rhizosphere of Zhonggan 21, Fullyue 56 and Ximei by means of matrix seedlings. Through field planting experiments in spring and autumn, the effects of microbial control methods for continuous cropping obstacles in cabbage were explored, and a certain theoretical basis and green environmental product support were provided 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 nutrient status between the rhizosphere and non-rhizosphere soil of healthy and diseased plants under continuous cropping conditions, the relationship between the occurrence of continuous cropping obstacles in cabbage and soil nutrients was revealed. 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 726.55 mg/kg, and the available potassium content of rhizosphere soil is 697.98 and 717.62 mg/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. Through comparative analysis of the differences in the number of five cultivable microorganisms in the rhizosphere and non-rhizosphere soils of healthy and diseased plants under continuous cropping conditions, the relationship between the occurrence of continuous cropping obstacles in cabbage and soil microorganisms was revealed. The counting results showed that the number of fungi, bacteria and ammonifying bacteria in healthy cabbage soil was higher than that in diseased cabbage, but there was no significant difference. The number of actinomycetes in the rhizosphere soil of healthy cabbage was significantly higher than that in the rhizosphere of diseased cabbage, and the number of actinomycetes in the rhizosphere soil of healthy and diseased cabbage was significantly higher than that in the non-rhizosphere soil. The number of nitrogen-fixing bacteria in the rhizosphere soil of healthy cabbage was significantly higher than the number of nitrogen-fixing bacteria in the rhizosphere soil of diseased cabbage, and regardless of healthy or diseased plants, the number of nitrogen-fixing bacteria in the rhizosphere soil was significantly higher than the number of nitrogen-fixing bacteria in non-rhizosphere soil .
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: the bacterial flora of different organs in cabbage. There are certain differences in structural composition and diversity. The bacterial diversity of plant leaves is significantly lower than that of roots and stems.Diversity of bacterial community. The composition and diversity of bacterial communities in roots and stems are more similar, and have obvious differences compared with leaves.The difference. Bacterial diversity and microbial community structure in different organs of healthy and diseased cabbage mediated by continuous croppingIn the difference. The bacterial microbial diversity of diseased cabbage is higher than that of healthy cabbage. Healthy and diseased cabbage leaf bacteria Shannon indexes were 0.073 and 0.28;stem bacteria Shannon indexes were 6.198 and 6.389;root bacteria Shannon indexes 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 as a whole.
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. Sequencing results show that healthy and diseased cabbage are different organs. There are differences in the diversity of official fungi and the structure of microbial community. 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, and the Shannon index of root fungus were 3.438 and 3.971, respectively.
6. Compare gene expression of healthy and diseased cabbage plants through transcriptome analysis, and analyze the occurrence of continuous cropping diseases. The molecular regulation mechanism of health. Transcriptome analysis results show: 5162 in healthy and diseased cabbage roots. Differentially Expressed Genes (DEGs). Analysis and plant defense response phase. Related genes, found that compared with healthy cabbage roots, 29 of the diseased cabbage roots are related to jasmonic acid (Jasmonic acid, JA) response related DEGs, there are 29 DEGs related to salicylic acid (SA) response, and 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. 1043 DEGs were obtained in healthy and diseased cabbage leaves. Analysis of genes related to plant defense response found that compared with healthy cabbage, there are 60 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. Microbial inoculation. Seedlings can cultivate microorganisms in the rhizosphere seedling substrate of three cabbage varieties. The results of the pot experiment show that the five kinds of microorganisms. Agent treatment significantly affected the rhizosphere soil cultivable bacteria, actinomycetes, ammonifying bacteria and nitrogen-fixing bacteria of the three cabbage varieties. The number of microbial flora has no significant effect on the number of fungi that can be cultured;The influence of blue cultivars on rhizosphere microbial community structure is different.
8. The field transplantation experiment results of three cabbage varieties raised by five microbial inoculants showed that the disease-resistant varieties Manyue 56 and Ximei had no continuous cropping obstacles in spring and autumn, and the susceptible variety Zhonggan 21 had 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 PO 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 continuous cabbage cropping obstacles. The application of exogenous beneficial microorganisms can improve the rhizosphere microenvironment and form rhizosphere immunity to achieve biological control effects. |
