Effects of <i>Cyperus rotundus</i> root exudates on <i>Ralstonia solanacearum</i> and <i>Bacillus velezensis</i> in relation to tobacco bacterial wilt occurrence

ABSTRACT Root exudates, functioning as chemical signaling molecules in the rhizosphere, regulate the structure and function of rhizosphere microbial communities, and play vital roles in plant disease resistance. This study characterized the rhizosphere microecological characteristics of tobacco and its accompanying weed Cyperus rotundus across different disease stages and explored the mechanisms by which C. rotundus root exudates affect Ralstonia solanacearum and its antagonistic strain Bacillus velezensis . The results showed that as soil temperature, humidity, and concurrent increases in R. solanacearum in the tobacco rhizosphere increased, the severity of tobacco bacterial wilt disease intensified. Additionally, the α-diversity of the rhizosphere soil microbial community exhibited a declining trend as the disease progressed. The rhizosphere of C. rotundus was more conducive to the stable enrichment of disease-suppressing bacterial groups such as Actinobacteria and Acidobacteria. In contrast, beneficial bacterial groups in the tobacco rhizosphere, including the phylum Pseudomonadota and the Burkholderia – Caballeronia – Paraburkholderia complex, declined continuously as the disease progressed. The active substances exerted significantly different effects on the two bacterial strains. At 50 μM, ferulic acid and phenylglyoxylic acid promoted the growth, biofilm formation, and motility of R. solanacearum . At 150 μM, phenylglyoxylic acid and 2-methoxycinnamaldehyde promoted the growth and motility of B. velezensis . Pot experiments confirmed that phenylglyoxylic acid and 2-methoxycinnamaldehyde at concentrations above 150 μM exerted certain control effects against bacterial wilt. In conclusion, the combined effects of soil environmental factors and root exudates alter the rhizosphere microbial community structure, creating a favorable microenvironment for R. solanacearum proliferation and thereby accelerating disease progression. IMPORTANCE Interactions between plants and rhizosphere microbial communities are key factors governing plant resistance to pathogen stress. This study investigated the regulatory effects of C. rotundus root exudates on R. solanacearum and its antagonistic bacteria from the perspective of tripartite interactions among weeds, pathogens, and crops, thereby providing new insights into the microecological regulatory mechanisms of tobacco bacterial wilt. Furthermore, C. rotundus exhibited an enrichment effect on R. solanacearum at the early disease stage, while it selectively reshaped the rhizosphere microbiome via recruiting beneficial microbial communities during critical disease development stages. These findings deepen the understanding of the mechanisms by which associated weeds influence crop diseases and provide theoretical support for green prevention and control strategies against bacterial wilt.