Mechanism by which cinnamic acid regulates the fungal community structure in the rhizosphere soil and exacerbates soil-borne diseases in Lanzhou lily under consecutive replant conditions: a case study of Lanzhou lily wilt disease

Aims Consecutive replant problems (CRPs) in Lanzhou lily are linked to soil degradation, autotoxin accumulation, and pathogen proliferation. This study investigated how cinnamic acid, a model autotoxin, interacts with soilborne pathogens to influence plant health, soil properties, and rhizosphere fungal communities under simulated CRP conditions. Methods An artificial simulation was conducted by adding cinnamic acid to soil to induce autotoxic stress and concurrently inoculating lily plants with pathogens ( Fusarium oxysporum and Ilyonectria sp. ) to induce wilt. Growth parameters, disease incidence, root activity, leaf defense enzymes, proline, soil properties, and fungal community composition were analyzed. Results Cinnamic acid at 0.24–2.40 mg/L promoted pathogen growth in vitro and soil colonization. In planta, it induced autotoxic stress, inhibiting growth and root activity while elevating leaf defense responses. Co-application with pathogens significantly increased disease index and incidence compared to pathogen-only treatments. Rhizosphere soil properties and fungal community structure were markedly altered, with enrichment of pathogenic genera ( Fusarium , Ilyonectria , Gibberella ) and species ( Fusarium_oxysporum , Ilyonectria_liriodendri ). RDA showed soil properties (OM, pH, AK) explained 63.92–66.97% of community variation, with stronger effects than cinnamic acid. Conclusion Cinnamic acid exacerbates lily wilt by promoting pathogen proliferation and modifying soil properties, which collectively reshape the fungal community. Its indirect regulation of the microbial community via alterations in soil properties outweighs its direct effects. The synergy between autotoxin accumulation and pathogen enrichment drives CRP severity in lily.