Nanoscale selenium confers broad-spectrum antifungal activity and reprograms antioxidant, phenylpropanoid and hormonal defense metabolism in tomato

Sustainable crop protection requires strategies that suppress pathogens while supporting host defense. Here, selenium nanomaterials (SeNMs) were investigated for their combined antifungal activity and effects on tomato defense metabolism across three pathogens with contrasting infection strategies. SeNMs inhibited mycelial growth of phytopathogenic fungi in a concentration-dependent manner and disease severity was significantly reduced in planta against Colletotrichum gloeosporioides , Fusarium oxysporum and Fusarium solani . SeNMs treatment alleviated infection-induced physiological damage, restoring plant growth, chlorophyll content, gas-exchange parameters and PSII efficiency. Oxidative injury, indicated by H 2 O 2 , malondialdehyde and proline accumulation, was consistently greater in roots than shoots and was reduced by SeNMs in both tissues. Antioxidant and phenylpropanoid responses diverged sharply between tissues: infection suppressed SOD, CAT and APX activities and lignin accumulation in shoots while inducing them in roots and SeNMs treatment restored shoot responses and further amplified root responses. Phytohormone profiling revealed a strongly root-biased response, with salicylic acid (SA), jasmonic acid (JA) and abscisic acid (ABA) rising under the soil-borne pathogens; SeNMs treatment significantly lowered root SA under both Fusarium species and root ABA under F. oxysporum , indicating attenuation rather than induction of stress-associated hormonal signaling. Transcript profiling of antioxidant, phenylpropanoid and defense-signaling genes, including SlPAL , SlMYB14 , SlPR1 , SlCHS and SlFLS , mirrored these tissue-specific patterns. Together, these findings show that tomato concentrates defense metabolism at the site of infection and that SeNMs act differentially on directly challenged and systemically affected tissues, supporting their potential in broad-spectrum fungal disease management.