Characteristics of bacterial community in bulk soil at different stages of tomato bacterial wilt under continuous monoculture system

Abstract:

[Objective] The study aimed to explore the dynamic changes of bacterial community in bulk soil at different stages of tomato bacterial wilt under a continuous monoculture system and clarify the response mechanisms of bulk soil bacteria to disease stages.[Methods] For all the bulk soil samples in the 1st,3rd,5th,and 7th crops,quantitative real-time polymerase chain reaction (qRT-PCR) was performed to measure the number of Ralstonia solanacearum at different disease stages, and high-throughput sequencing of 16S rRNA V4‒V5 region was used to study the diversity,composition,biomarkers and assembly processes of bacterial community.[Results] The number of R.solanacearum at the peak stage of disease (1.28× 10⁷ copies/g) was higher than that at the final stage of disease (1.77×10⁶ copies/g).In addition,the influence of disease stages on the diversity of bacterial community was enhanced with increasing continuous monoculture time.Alpha and beta diversities of bacterial community between different stages in the 3rd and 5th crops were significantly different.Linear discriminant analysis effect size (LEfSe) analysis showed that samples from the final and peak stages of disease during continuous monoculture comprised distinct biomarkers.Additionally,microorganisms that assisted R.solanacearum in inducing diseases gradually accumulatedwith the increasing continuous monoculture time.Microbacterium and Nitrosospira were observed with positive effect for tomato bacterial wilt at the peak stage of disease,while they were Sphingobium,norank f norank o SBR1031,and norank f Rhodothermaceae at the final stage of disease.The analysis of community assembly process revealed that bacterial community at the two stages of disease were both dominated by stochastic processes,especially the dispersal limitation,but the bacterial community at the peak stage of disease was more homogeneous than that at the final stage of disease.[Conclusion] The bacterial communities at the final and peak stages of tomato bacterial wilt were significantly different in diversity,composition and structure in 3rd and 5th crops,and these changes might be related to different community assembly mechanisms.This study facilitated the understanding of the development of tomato bacterial wilt during continuous monoculture system and provided guidance for the control of bacterial wilt.

Key words:tomato bacterial wilt;continuous monoculture;disease stage;bacterial community