Physiological and biochemical responses of Vicia faba L. to folic acid treatments and their relation to Aphis fabae infestation

Introduction: This study investigated the effects of foliar-applied folic acid (FA) on growth, biochemical traits, and antioxidant defenses of faba bean (Vicia faba L.) and evaluated associations with black bean aphid (Aphis fabae) infection. Bean plants were collected from agricultural fields in Iraq during the 2024 growing season and treated with FA at 0, 50, 100, and 150 mg/L producing the strongest responses. Folic acid significantly improved plant growth, photosynthetic pigments and biochemical composition, with the highest concentration (150 mg/liter) producing the strongest effect. Aphid infestation markedly reduced biomass and pigment content; However, FA at 100–150 mg/L partially restored these parameters. FA treatments also increased secondary metabolites and antioxidant enzyme activities, infected plants showed a strong defense response, indicating a priming effect against biotic stress. Novelty: This study demonstrates a dual role of folic acid as both a growth-promoting biostimulant and defense-promoting agent against Aphis faba in Vicia faba. Unlike previous studies focused primarily on abiotic stress, this work integrates physiological, biochemical and insect-related responses, supporting folic acid as a sustainable tool to increase crop productivity and resistance under biotic stress. Conclusion: Folic acid acts as an effective biostimulant that improves growth, photosynthetic efficiency and antioxidant defense in faba bean while reducing aphid-induced damage. These findings support its use as a sustainable strategy to enhance pest tolerance and increase crop productivity. Keywords: Vicia faba, folic acid, Aphis fabae, antioxidant enzymes, metabolites, plant resistance.