Wheat–faba bean intercropping reduces Fusarium wilt by enhancing root resistance under combined Fusarium oxysporum f. sp. fabae and microplastics stress

Fusarium oxysporum f. sp. fabae Schltdl. (1824) (FOF) causes Fusarium wilt in faba bean. Microplastics (MPs) pollution in agricultural soils may exacerbate this disease by serving as a vector for FOF. By contrast, faba bean-wheat intercropping enhances agroecosystem biodiversity and is an important strategy for managing Fusarium wilt. To investigate how combined MPs and FOF stress promotes Fusarium wilt and elucidate how intercropping mitigates disease development through physiological and biochemical root resistance, a pot experiment was conducted. The experiment included faba bean monocropping and faba bean-wheat intercropping under three stress treatments: control (CK), FOF stress alone (F) and combined FOF and MPs stress (F + P). Key measurements included disease incidence, plant growth, nutrient uptake, root morphology, antioxidant enzyme activities, callose and lignin deposition, cellular ultrastructure and defence gene expression. Compared with F stress alone, combined F + P stress increased Fusarium wilt incidence by 26.3% and disease index by 54.1%. By contrast, intercropping improved plant growth and nutrient uptake. It also reduced disease incidence by 20.0% and disease index by 21.1%. These benefits were associated with enhanced root development, elevated antioxidant enzyme activities, reduced oxidative damage, improved structural resistance and upregulation of defence-related genes. These results indicate that combined F + P stress significantly aggravated Fusarium wilt, whereas intercropping effectively alleviated disease development by strengthening root growth, antioxidant capacity, structural defence and defence gene expression.