Spent mushroom substrate adsorbs fusaric acid, stabilises the cucumber rhizosphere microbiome, and alleviates Fusarium wilt

Cucumber Fusarium wilt caused by Fusarium oxysporum f. sp. cucumerinum (FOC) threatens cucumber production worldwide. The Fusarium virulence factor fusaric acid (FA) is phytotoxic and can disrupt rhizosphere microbial communities, potentially weakening beneficial bacteria and exacerbating disease. Here we show that spent mushroom substrate (SMS) derived from Lentinula edodes reduces FA bioavailability through adsorption and thereby alleviates FA-driven rhizosphere dysbiosis and disease aggravation. SMS removed FA from FOC culture supernatants without detectable changes in expression of the FA biosynthetic gene FUB1 , supporting adsorption rather than suppressed biosynthesis. In vitro adsorption exhibited rapid, saturable uptake and was best described by a Langmuir–Freundlich isotherm, with a maximum adsorption capacity of 52.72 µg/g, while kinetics were consistent with a pseudo-second-order model. Scanning electron microscopy revealed a porous SMS surface, and Fourier transform infrared spectroscopy combined with functional group blocking by acetylation indicated that surface polar functionalities contribute to FA binding. In a dual-chamber pot system that physically separated FA exposure from disease assessment, SMS amendment in the outer compartment markedly reduced FA transfer into the rhizosphere compartment and mitigated FA-associated disease aggravation in non-sterile soil but not in sterile soil, decreasing disease severity by up to approximately 25%. 16S rRNA gene amplicon sequencing further showed that elevated FA reduced rhizosphere bacterial richness and diversity and shifted community composition, whereas SMS treatment attenuated these changes. Notably, FA reduced the relative abundance of FA-sensitive taxa such as Bacillus , while SMS-mediated FA removal preserved Bacillus abundance. Together, our results support an adsorption-centred, microbiome-dependent mechanism whereby SMS immobilises FA, protects sensitive beneficial bacteria, stabilises the rhizosphere microbiome and suppresses cucumber Fusarium wilt, highlighting SMS as a microbiome-friendly strategy for managing toxin-driven soil-borne diseases.