根际细菌种群丢失引起连作花生土传病害高发机制研究

Frequent occurrences of soil-borne diseases in continuous cropping significantly influenced the yield and quality of crop. Rhizosphere microorganisms play the key roles in controlling soil-borne pathogens to infect crop roots, continuous cropping could give rise to the loss of rhizosphere bacterial species in monocropping soils because of directional selection of root exudates, which would reduce the defense capability of roots to face the infection of soil-borne pathogens. The objectives of this subject therefore were to study the mechanisms of the raised soil-borne diseases in monocropping peanut induced by the lost rhizosphere bacterial species. So, monocropping soils that have been continuously cropped with peanut for different years, will be collected, and a soil without peanut planting as the control. Antimicrobial effects of rhizosphere bacterial species of peanut on soil-borne pathogens and the variation of their associated volatile organic compounds will be determined. Bacterial species that were lost in monocroping peanut, were obtained to assess their antimicrobial ability. Furthermore, the loss of bacterial species diversity and the attenuation of physiological metabolisms in monocropping peanut will be explored using the next generation sequencing combined with bioinformatics methods. As viewed from the loss of rhizosphere bacterial species that reducing the defense capability of roots, the study will elaborate the mechanisms of the raised soil-borne diseases in monocropping peanut. The results are, therefore, crucial important to further illuminate the mechanisms of rhizosphere microorganisms in controlling soil-borne diseases, and to provide new insights for developing their control techniques.

连作下土传病害高发是制约作物产量和品质的重要因素。根际微生物是控制土传病原菌侵染作物根部的重要门户，由于根系分泌物的定向选择，持续连作将会造成土壤某些细菌种群逐渐丢失，进而导致根际抑病能力下降。但连作下根际细菌种群丢失引起土传病害高发的根际微生态机制尚需揭示。对此，本项目拟选用红壤区连作花生土壤及非连作土壤，探讨连作花生根际细菌种群对土传病原菌的抑菌性能，及其抑菌挥发性物质成份的变化；分离、鉴定连作花生根际丢失的细菌种类，并检验其对病原菌的抑菌能力；进一步采用高通量测序解析连作花生根际细菌种群丢失、生理代谢功能弱化的特征；探讨根际细菌种群丢失、抑菌挥发物损失及生理代谢功能弱化与根际抑菌性能下降的关系。本研究从根际细菌种群丢失并因此降低根际抑病能力的角度，阐述连作花生土传病害上升的机理，对进一步揭示花生连作障碍发生机制有重要理论意义，为研发连作花生土传病害防控技术提供新思路和重要参考。

集约化单一种植下土传病害高发是制约植物生长发育和产量的重要障碍因素。而根际微生物是控制土传病原菌侵染作物根部的重要门户，由于根系分泌物的定向选择，单一化种植将会造成土壤某些细菌种群逐渐丢失，进而导致根际抑病能力下降。本项目选用长期连续种植花生土壤以及非连作土壤，综合温室盆栽实验、微生物离体培养和高通量测序技术等手段，系统研究了根际细菌种群丢失引起土传病害高发的根际微生态机制。通过项目4年的实施，取得主要结果如下：发现植物根际细菌对病原菌的防护在植物生长后期表现为“塌方式”失效，造成了土传病害高发。通过微生物分离、鉴定，发现连作下植物根际细菌数量增多，可能与沙雷氏菌（Serratia sp）、Glutamicibacter sp、青枯雷尔氏菌（Ralstonia sp）等在根际富集有关，而假单胞菌（Pseudomonas sp）、短波单胞菌（Brevundimonas sp）和类芽孢杆菌（Paenibacillus sp）在连作植物根际丢失。进一步利用微生物离体互作实验，发现连作植物根际细菌显著降低了对土传病原真菌的抑制作用，结合固相微萃取和气相质谱（SPME-MS）分析发现连作根际细菌产生的二甲硫醚、二甲基二硫、1,3-二甲苯等抑菌物质含量显著降低。对比分析微生物高通量测序和可培养分离鉴定的结果，得出了连作植物根际丢失的主要菌群特征。最后，通过宏基因组学和植物转录组分析，发现单一化种植主要影响根际稀有细菌类群，进而降低了根际与氮磷养分循环、植物激素和铁载体合成以及抗菌物质等微生态功能，诱导了植物体激素信号代谢途径的变化。项目研究成果在ISME J、SBB、Environ Microbial等发表了SCI论文12篇（一区TOP论文5篇），中文核心论文4篇（其中土壤学报3篇），获授权国家发明专利2项，培养研究生4名。研究成果揭示出植物根际细菌种群引起土传病害发生的微生态机制，对推动我国土传病害研究具有重要理论意义，也为攻克土传病害防控难题提供了新的依据和思路。