番茄连作青枯病不同发病时期的非根际土壤细菌群落变化特征

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

摘要:

[目的]研究连作条件下番茄青枯病不同发病时期的非根际土壤微生物群落差异,明确土壤微生物对青枯病发病时期的响应机制。[方法]本研究对16S rRNA V4‒V5区进行实时荧光定量PCR和高通量测序,综合分析了连续种植第1、3、5和7季的发病高峰期和发病末期的番茄非根际土壤的病原菌数量、细菌群落多样性、群落组成、标志细菌类群和群落构建机制。[结果]发病高峰期的青枯菌数量(1.28×10⁷ copies/g)要高于发病末期(1.77×10⁶ copies/g)。随着连作时间的增加,发病时期对细菌群落多样性的影响逐渐增加。第3季和第5季不同发病时期之间的细菌群落alpha和beta多样性存在显著差异。LEfSe分析发现,番茄青枯病发病高峰期和发病末期的非根际土壤样品有其各自不同的标志细菌类群。此外,随连作时间的延长协助青枯菌致病的细菌逐渐累积。发病高峰期是微杆菌属(Microbacterium)和亚硝化螺菌属(Nitrosospira)协助青枯菌致病,而在发病末期,则由鞘脂菌属(Sphingobium)、norank f norank o SBR1031和norank f Rhodothermaceae协助青枯菌致病。群落构建过程分析发现不同发病时期细菌群落均以随机过程的扩散限制为主,但细菌群落在发病高峰期比发病末期的同质化作用更强。[结论]本研究发现青枯病发病高峰期和发病末期的番茄非根际土壤的细菌群落多样性、组成和结构在第3季和第5季时存在显著差异。此外,细菌群落会随着连作时间发生动态变化,而这些变化可能与细菌群落构建机制相关联。研究结果加深了对连作条件下的番茄青枯病发展过程的认识,可为防治青枯病提供参考依据。

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.