Reductive soil disinfestation alleviates Paulownia fortunei replant disease via Fusarium suppression by microbially produced 2,6-pyridinedicarboxylic acid

Reductive soil disinfestation (RSD) technology not only facilitates the recycling of agricultural waste but also effectively suppresses soil-borne pathogens. However, the mechanism by which RSD suppresses soil-borne pathogens in soil for Paulownia fortunei planting is not yet fully understood. Here, we combined pot experiments with high-throughput amplicon sequencing, untargeted metabolomics and microbial isolation to elucidate how RSD suppresses P. fortunei replant disease caused by soil-borne pathogens. Compared with the control treatment (CK), RSD increased shoot and root biomass by 73.63% and 120.47%, respectively, and plant height by 20.91%. These benefits were primarily associated with RSD-induced shifts in soil bacterial and fungal communities, marked by the enrichment of potentially beneficial taxa such as Arthrobotrys and Devosia and a decline in the phytopathogen Fusarium . Functional assays confirmed the pathogenicity of Fusarium strains isolated from replanted soils, which significantly reduced P. fortunei biomass in both pot and plate experiments. Untargeted metabolomic analysis revealed that RSD induced the accumulation of 2,6-pyridinedicarboxylic acid, which was negatively correlated with Fusarium abundance. Furthermore, both Fusarium isolate assays and pot experiments with the addition of 2,6-pyridinedicarboxylic acid showed that Fusarium growth was significantly suppressed, thereby alleviating its inhibitory effect on the growth of P. fortunei . Random forest modeling coupled with culture-based validation identified that Clostridium may be a key contributor to 2,6-pyridinedicarboxylic acid production, with its abundance significantly increased in the RSD treatment. Overall, RSD alleviates replant disease by simultaneously modulating microbial community composition and stimulating antifungal metabolite production, offering new insights and practical strategies for sustainable disease control.