Tobacco bacterial wilt (TBW) caused by Ralstonia solanacearum is the most serious soil-borne disease of tobacco. However, molecular mechanism information of R. solanacearum resistance is limited to tobacco, hindering better breeding of resistant tobacco. In this study, the expression profiles of the rootstalks of Yunyan87 (susceptible cultivar) and Fandi3 (resistant cultivar) at different stages after R. solanacearum infection were compared to explore molecular mechanisms of tobacco resistance against the bacterium. Findings from gene-expression profiling indicated that the number of upregulated differentially expressed genes (DEGs) at 3 and 7 days post-inoculation (dpi) increased significantly in the resistant cultivar. WRKY6 and WRKY11 family genes in WRKY transcription factors, ERF5 and ERF15 family genes in ERFs transcription factors, and genes encoding PR5 were significantly upregulated in the resistant cultivar response to the infection. For the first time, WRKY11 and ERF15 were found to be possibly involved in disease-resistance. The Kyoto Encyclopedia of Genes and Genomes analysis demonstrated glutathione metabolism and phenylpropane pathways as primary resistance pathways to R. solanacearum infection. In the resistant cultivar, DEGs encoding CYP450, TCM, CCoAOMT, 4CL, PAL, CCR, CSE, and CADH, involved in the synthesis of plant antitoxins such as flavonoids, stilbenoids, and lignins, enriched in the phenylpropane pathway were upregulated at 3 and 7 dpi. Furthermore, a pot experiment was performed to verify the role of flavonoids in controlling TBW. This study will strongly contribute to a better understanding of molecular interactions between tobacco plants and R. solanacearum.

Bacterial wilt as a soil-borne disease was caused byRalstonia solanacearum, and seriously damages the growth of tobacco. Integrated biocontrol method was explored to control bacterial wilt. Nevertheless, the long-term effects of the integrated biocontrol method on soil bacterial community, soil physicochemical properties and the incidence of bacterial wilt are not well understood. In this study,B. amyoliquefaciensZM9, calcium cyanamide and rice bran were applied to tobacco fields in different ways. The disease index and incidence of tobacco bacterial wilt (TBW), soil physicochemical properties, colonization ability ofB. amyoliquefaciensZM9, and rhizopshere bacterial community were investigated. The results showed that the integrated application ofB. amyoliquefaciensZM9, rice bran and calcium cyanamide had the highest control efficiency of TBW and bacteria community diversity. Additionally, the integrated biocontrol method could improve the colonization ability ofB. amyoliquefaciensZM9. Furthermore, the integrated biocontrol method could effectively suppress TBW by regulating soil physicochemical properties, promoting beneficial bacteria and antagonistic bacteria of rhizopshere soil. This strategy has prospect of overcoming the defects in application of a single antagonistic bacteria and provides new insights to understand how to improve the colonization capacity of antagonistic bacteria and control efficacy for TBW.

Marigold is reported to have antibacterial activity, and effectively protect crops against soil-borne diseases. However, it is not known whether and how tobacco bacterial wilt (TBW) could be mitigated via intercropping with marigold under field conditions. In this study, a field experiment was performed to measure and compare the occurrence of TBW, the soil chemical properties, and soil microbial composition and diversity between a tobacco-marigold intercropping system and a tobacco monocropping system. At 100 days (d) post-transplantation, the incidence (I) and disease index (DI) for the tobacco-marigold intercropping system were 30.12% and 58.25% lower than that for tobacco monocropping system, respectively. The results showed that Sobs, Shannon and Chao 1 index of soil bacterial communities in the tobacco-marigold intercropping system were 10.34%, 1.41% and 5.13% higher than that in the tobacco monocropping system at 100 d post-transplantation, respectively. It exhibited a higher richness and diversity of soil bacterial communities in the tobacco-marigold intercropping system. The relative abundance of some beneficial genera in tobacco-marigold intercropping system, such as Lysobacter, Burkholderia, Trichoderma, Mortierella, Chaetomium, Penicillium, was 1.50, 1.61, 3.35, 1.67, 4.40 and 4.50 fold higher than that in tobacco monocropping system. The presence of the intercropping system inhibited soil acidification and loss of soil calcium ions. The redundancy analysis (RDA) indicated that soil pH and exchange Ca²⁺ were the main environmental factors which seemed to influence the bacterial and fungal community. The results from this study provided valuable insight into the possible mechanisms enhancing soil health in the tobacco-marigold intercropping system.