Effects of Continuous Cropping on Chili Root Rot: Insights from Rhizosphere Microbial Communities and SynCom Applications

Continuous cropping often results in stunted plant growth and a higher incidence of soil-borne diseases. Soil microbial communities play a crucial role in promoting plant growth, maintaining plant health, and enhancing plant resistance to various diseases. This study examines the impact of continuous cropping on chili root rot and explores the contribution of soil microbial communities in alleviating this issue. The results revealed that prolonged continuous cropping significantly altered the composition and structure of the rhizosphere bacterial community, as evidenced by the integration of 16S rRNA and ITS high-throughput sequencing. Specifically, the biomass of soil pathogens from the genus Fusarium increased, while the relative abundance of antagonistic bacteria from the genera Bacillus and Pseudomonas decreased significantly. LEfSe analysis showed that Bacillus and Pseudomonas were the core bacterial biomarkers in chili continuous cropping soil, which were successfully isolated and demonstrated significant antagonistic effect against Fusarium solani. Utilizing these antagonistic bacteria, nine different synthetic communities (SynComs) were constructed. Among them, the T7 SynCom exhibited excellent biocontrol efficacy. It effectively suppressed the pathogen, reduced the incidence of root rot, and enhanced systemic induced resistance, and enhanced systemic induced resistance by activating the plant immune associated pathways, including the MAPK signaling pathway, ethylene signaling pathway, and pathways mediated by Jasmonic acid (JA) and Salicylic acid (SA). These findings offer new insights into using functional SynCom as a sustainable agricultural solution and open new avenues for overcoming the challenges posed by continuous cropping.