Application of microalgae reduces the incidence of bacterial wilt in flue-cured tobacco by altering soil properties and microbial community characteristics.

Introduction: To elucidate the mechanisms by which microalgae reduce tobacco bacterial wilt incidence through modifying soil properties and microbial community structure. Methods: Flue-cured tobacco (K326) was used as the test plant. Three microalgal suspension treatments-T1 (14 mL·L Results: 1. Compared with CK, yield in T1, T2, and T3 increased by 12.2%, 17.2%, and 14.8%, respectively, while disease incidence at maturity decreased by 43.7%, 18.9%, and 71.9%, respectively; 2. Pathogen abundance at maturity in T1, T2, and T3 decreased by 74.1%, 90.7%, and 90.7%, respectively, relative to CK, and soil pathogen abundance was significantly positively correlated with disease indices; 3. Microalgae suppressed soil pathogen abundance and disease incidence by increasing soil pH and dissolved organic carbon while decreasing available potassium and available phosphorus; 4. Compared with CK, bacterial abundance at maturity in T1, T2, and T3 increased by 12%, 23%, and 33%, respectively, and biocontrol functional genera (e.g., Sphingomonas, Bacillus) were enriched; 5. Microalgae reshaped the bacterial co-occurrence network by enhancing its modularity, and this highly modular network structure significantly suppressed pathogen proliferation. Discussion: Microalgae suppressed pathogens and reduced disease incidence by modulating soil chemical properties, increasing bacterial diversity, enriching biocontrol functional genera (e.g., Sphingomonas, Bacillus), and optimizing network topology. Under the experimental conditions, microalgae application at 28 mL·L