Microplastic-pathogen interactions differentially modulate tomato Fusarium wilt severity: The dependence of polymer biodegradability

Microplastics (MPs) are pervasively present in agricultural soils, adversely affecting rhizosphere ecology and plant physiology; however, their influence on soil-borne pathogens and crop health remains poorly understood. Here, we systematically investigate the effects of exogenous MPs on Fusarium oxysporum f. sp. lycopersici (FOL) colonization, virulence and antagonistic network in tomato rhizosphere using hydroponic, soil-based, and in vitro co-culture assays. We found that conventional polyethylene (PE) exacerbated wilt severity by 19 %, whereas biodegradable polylactic acid (PLA) reduced it by 14 %. This divergence arose from MP-mediated pathogen colonization patterns: PE adhered to root surfaces and facilitated colonization, whereas PLA leachates generated during degradation suppressed growth. Gas chromatography-mass spectrometry analysis and in vitro antifungal assays identified two key antifungal pathways: the intermediate L-lactide induced rhizosphere acidification, and the leached plasticizer tris(2-butoxyethyl) phosphate, which exhibited direct antifungal activity (minimum inhibitory concentration = 50 mg·L; inhibition rate = 15.5 %). Transcriptomic profiling revealed that PE upregulated N transport and metabolism genes in FOL, whereas PLA downregulated the expression of the plant cell wall-degrading enzyme gene FOXG_11947 (log fold change = -3.18), reducing β-1,3-glucanase activity by 75.5 %, and consequently impairing pathogen virulence toward the host roots. Beyond singular interaction with FOL, PLA shifted rhizosphere microbiome toward an antagonistic network, which consequently reduced Fusarium abundance by 1.31 %. Our findings establish a polymer-dependent mechanism by which MPs regulate soil-borne disease and underscore an underappreciated co-exposure threat, providing a scientific basis for sustainable plastic use in agriculture.