Effects of compound microbial fertilizer on the occurrence of tomato bacterial wilt and bacterial community of tomato rhizosphere soil

【Objective】 The purpose of the study was to explore the relationships between compound microbial fertilizer and the occurrence of tomato bacterial wilt，physicochemical properties of rhizosphere soil and soil bacterial communities，so as to provide theoretical basis for the the rational application of microbial fertilizer in green prevention and control of tomato bacterial wilt. 【Method】 Using plots with severe occurrence of tomato bacterial wilt in previous years as experimental plots，4 treatments were set up：clear water control（T1），compound microbial fertilizer（T2），bacterial fertilizer nutrient substrate（T3），compound microorganisms（T4）. The nutrient content in tomato rhizosphere soil，the growth of tomato plant，the carrier rate of bacterial wilt pathogen in roots，incidence of bacterial wilt，and rhizosphere soil respiration rate were measured. Using 16S rDNA sequencing technology，the differences in the bacterial community structure of the tomato rhizosphere soil after the application of compound microbial fertilizer were investigated. 【Result】 Measurement results at the tomato harvest stage showed that，the contents of organic matter，ammonium nitrogen and available phosphorus in the rhizosphere soil of tomatoes treated with compound microbial fertilizer and compound micro-organisms were higher or significantly（P<0.05）higher than those in other treatments. Compared with the clear water control，the plant height，stem circumference，leaf area，photosynthesis，chlorophyll relative content（SPAD value），yield and water-soluble sugar content treated by compound microbial fertilizer，compound microorgani-sms and microbial fertilizer nutrient substrate all increased by 6.82%-27.88%，19.59%-47.40%，2.04%-17.08%，3.88%-11.21%，1.99%-17.15%， 9.13%-22.37% and 0.45%-5.12% respectively. The carrier rate of bacterial wilt pathogens in tomato roots decreased to 11.11% with compound microbial fertilizer treatment，and the soil respiration rate increased by 54.05% compared with the clear water control. Compared with the clear water control，the ACE index and Chao1 index at the bacterial genus level in the rhizosphere soil of tomatoes treated with compound microbial fertilizer，compound microorganisms，and microbial fertilizer nutrient substrate increased by 3.12%-6.64% and 4.76%-7.18% respectively，while there was no significant differences in Simpson index and Shannon index（P>0.05）. For the compound microbial fertilizer treatment，Bacillales and Bacillus ranked among the top 10 dominant orders（8.31%）and genera（6.60%）respectively. Among the 4 treatments， the abundance of Bacillus was similar to that of Christensenellaceae_R-7_group and WCHB1 -32，and it was positively correlated with WCHB1-32，Ruminiclostridium_1，Christensenellaceae_R-7_group and uncultured_bacterium_f_Chitinophagaceae，and negatively correlated with Pseudomonas，uncultured_bacterium_f_Anaerolineaceae and Methylophilus. The compound microbial fertilizer treatment showed the most obvious increase in the abundance of functional microor‐ ganisms involved in metabolic pathways，biosynthesis of secondary metabolites，biosynthesis of antibiotic and biosynthesis of amino acid. Organic matter，available phosphorus，available potassium，Bacillus，Ralstonia and soil respiration rate were positively correlated with function of biosynthesis of antibiotic. pH，Bacillus，Ralstonia and soil respiration rate were positively correlated with function of biosynthesis of amino acid. Salinity and incidence were negatively correlated with the two functions. 【Conclusion】 Compound microbial fertili-zer can significantly improve soil nutrient ratios，modify the structure and functional characteristics of soil bacterial communities，enhance functions such as biosynthesis of antibiotic and biosynthesis of amino acid，promote the growth of tomato plant，and reduce the incidence of bacterial wilt. A 500-times dilution of compound microbial fertilizer exhibits remarkable disease prevention and growth-promoting effects on tomato bacterial wilt，indicating a promising application prospect.