Benzoic Acid Reduced Nutrient Absorption and Photosynthesis of Faba Bean to Promote Fusarium Wilt Occurrence

The allelopathic compounds in the soil can be accumulated through the continuous cultivation of faba bean, intensifying the soilborne disease advancement. In this study, we aimed to elucidate the photosynthesis-related mechanisms by which benzoic acid, an allelopathic compound, promotes faba bean Fusarium wilt (Fusarium commune) development. The sample plants were treated with and without F. commune and exposed to varying concentrations of benzoic acid. The effects on seedling growth, Fusarium wilt occurrence, nutrient absorption, photosynthetic pigments, chlorophyll fluorescence, photosynthetic enzyme activities, photosynthetic assimilates, and the levels of pathogenesis-related (PR) gene expression were explored. Compared with the control, F. commune inoculation substantially decreased the leaf growth and increased the Fusarium wilt instances. Different from the F. commune-alone treatment, the treatment of benzoic acid and F. commune decreased the zinc, magnesium, manganese, iron, total phosphorus, total nitrogen, and total potassium in roots and leaves; reduced carotenoid, chlorophyll a, and chlorophyll b levels; decreased the quantum yield and photochemical quenching coefficient of PSII; increased the non-photochemical quenching coefficient; reduced the activities of H⁺-ATPase, ribulose bisphosphate carboxylase, fructose-1,6-bisphosphatase, sucrose synthase, and activator; increased starch content; decreased soluble sugar and sucrose levels; and upregulated PR1, PR2, and PR10 in leaves. Additionally, benzoic acid and F. commune treatment further reduced leaf growth and increased Fusarium wilt occurrence in faba bean. The investigation indicated that benzoic acid exacerbated the Fusarium wilt development and inhibited faba bean growth by reducing mineral nutrient absorption and impairing photosynthesis. This research might provide more information and enhance our understanding of plant soilborne disease in agriculture.