Fe₂O₃ nanoparticles enhance soybean resistance to root rot by modulating metabolic pathways and defense response

Four doses of Fe₂O₃ NPs suspension (10, 50, 100, and 500 mg/L) and one dose of EDTA-FeNa₂ solution (10 mg/L) were foliar applied to two soybean (Glycine max) varieties (ND12 and C103) with Fusarium oxysporum. Notably, soybean disease indices were significantly reduced following foliar application of Fe₂O₃ NPs. At 50 mg/L Fe₂O₃ NPs, disease indices were reduced by 60.29 % and 43.75 % in ND12 and C103, respectively; these values were significantly better than EDTA-FeNa₂, which reduced disease indices by 22.02-28.10 % compared to infected control. Furthermore, root biomass increased by 54.28 % and 42.95 %; chlorophyll a increased by 31.03 % and 43.78 %; SOD activity increased by 40.82 % and 45.59 %; and GmPAL expression increased by 16.64 and 7.23-fold with 50 mg/L Fe₂O₃ NPs on ND12 and C103, respectively, compared to the infected control. Importantly, the control efficiency of Fe₂O₃ NPs was 3-6 times higher than that of EDTA-FeNa₂. Metabolomic analysis indicated that 50 mg/L Fe₂O₃ NPs significantly increased the metabolite content of TCA biomolecules in both soybeans; for example, citric acid increased by 102.06 % and 29.88 % compared to the infected control. The results suggest that Fe₂O₃ NPs mitigate root rot through multiple mechanisms, including augmentation of antioxidant enzyme activity to mitigate disease-induced oxidative stress, activation of relevant defense genes to enhance resistance, and increased levels of TCA and amino acid metabolites to provide energy for soybean response. These findings underscore the significant potential of Fe₂O₃ NPs in disease suppression for an environmentally friendly sustainable agriculture.