Brassicaceae-Based Biosolarization Reduces Lettuce Fusarium Wilt (FOLac) in Naturally Infested Soils

Brassicaceae-based bio-disinfestation is a promising non-chemical option to manage lettuce Fusarium wilt caused by Fusarium oxysporum f. sp. lactucae (FOLac), but evidence integrating pathogen suppression, residue chemistry, and soil microbiome response remains limited. We conducted a greenhouse mesocosm assay with naturally infested soil to compare biofumigation (uncovered soil) and biosolarization (plastic-covered soil for 40 days) using five Brassicaceae residues (Brassica carinata, B. juncea, B. napus, Sinapis alba and Raphanus sativus) applied at two field-equivalent doses. Biosolarization created a distinct disinfestation environment, increasing soil temperature by an average of 2.74 °C and shifting oxidation–reduction potential toward reducing conditions. This strategy consistently reduced culturable Fusarium populations, F. oxysporum-assigned colony-forming units (CFU) and lettuce wilt severity compared with uncovered biofumigation. The strongest disease suppression was observed under plastic-covered conditions, including the soil-only control, indicating that the covered microenvironment was a major driver of suppressiveness, while Brassicaceae residues modulated the magnitude and consistency of the response. Glucosinolate profiling revealed contrasting residue chemistries among species, providing a biochemical context for interpreting species-dependent effects. Shotgun metagenomics further showed that biosolarization and biofumigation produced distinct genus-level microbial community structures, with significant effects of strategy, timepoint and their interaction, and higher Shannon diversity under biosolarization. Overall, the integration of disease severity, culture-based inoculum quantification, physicochemical indicators, residue chemistry and metagenomics supports Brassicaceae-based biosolarization as a promising pre-plant approach for suppressing FOLac wilt in naturally infested soils, with the plastic-covered disinfestation environment emerging as the main driver of suppression and Brassicaceae residues modulating the response.