Biochar mitigates Fusarium wilt by regulating the rhizosphere microbial community structure

BACKGROUND: Continuous cropping of faba bean severely degrades the soil ecosystem, leading to the accumulation of autotoxic compounds and pathogenic fungi, which further aggravates soilborne diseases. Among available strategies, the rational application of biochar has the potential to reshape soil microbial communities. This study aimed to elucidate the rhizosphere microbial mechanisms by which biochar (BC) mitigates Fusarium wilt. Wheat straw BC was applied at 0%, 0.5%, 1%, 1.5%, 2% and 3% to evaluate its effects on soil microbial community. Based on this, a pot experiment was conducted to systematically assess the effects of BC on Fusarium wilt incidence, autotoxic compound accumulation, soil microbial diversity and root pathogenesis-related protein (PR) expression following inoculation with BC-conditioned soils. RESULTS: Compared with the control, BC application mitigated Fusarium wilt, reducing the disease index by 16.66%-52.11%, with the greatest effect observed at 1%. At this level, BC decreased soil phenolic acid accumulation, increased the relative abundance of Proteobacteria, and reduced that of Ascomycota. BC-induced shifts enhanced the diversity, structure, and composition of rhizosphere microbial communities. Specifically, 1% BC increased the absolute abundance of Bacillus sp. by 119.01% and Sphingomonas sp. by 98.93%, decreased the absolute abundance of Fusarium commune sp. by 77.41%, and upregulated root PR protein gene expression, thereby alleviating Fusarium wilt. CONCLUSION: The application of 1% wheat straw BC effectively reshaped the soil microbial community, reduced autotoxic compound accumulation, improved soil health and suppressed Fusarium wilt.