Molecular insights into fusaric acid-induced cellular damage and hormonal modulation in watermelon suspension cells

• Fusaric acid (FA) induces concentration-dependent cell death and growth inhibition in watermelon suspension cultures. • FA exposure triggers lipid peroxidation, oxidative stress, and selective changes in antioxidant enzyme activities. • Significant increases in extracellular pH and conductivity indicate membrane destabilization under FA stress. • Pretreatment with plant hormones (IAA, MeJA, ABA, SA) mitigates FA-induced damage, with SA showing the highest recovery effect. • DNA methylation inhibition by 5-azacytidine alters hormone-related gene expression during FA stress response. Watermelon ( Citrullus lanatus ), a key global crop in the Cucurbitaceae family, is significantly impacted by wilt disease caused by Fusarium oxysporum . This study used suspension-cultured watermelon cells to examine the physiological and molecular effects of fusaric acid (FA), a major phytotoxin produced by the pathogen, at final concentrations of 0, 50, 100, 200, and 300 μM. The 100 μM FA treatment, used for most assays, reduced fresh cell weight by ∼52%, decreased packed cell volume by ∼70%, and more than doubled malondialdehyde (MDA) content, indicating severe lipid peroxidation. Antioxidant enzyme activities showed differential responses: superoxide dismutase (SOD) activity declined significantly at both 2 h and 24 h, peroxidase (POD) remained largely unchanged, and catalase (CAT) showed no significant variation. FA exposure also caused a progressive increase in extracellular pH and conductivity, reflecting loss of membrane integrity. Pretreatment with exogenous plant hormones (IAA, MeJA, ABA, SA; 100 μM each for 12 h) mitigated several FA-induced effects, with SA showing the greatest recovery in fresh weight and most pronounced reduction of POD activity. Transcriptome profiling revealed thousands of FA-responsive genes within 2–24 h, and inhibition of DNA methylation with 5-azacytidine altered the expression of multiple hormone-related genes. These results demonstrate that FA rapidly impairs growth, membrane stability, and antioxidant defense in watermelon cells, and that targeted hormonal and epigenetic interventions can partially counteract these effects. The findings provide a mechanistic basis for developing priming strategies to enhance watermelon resistance to Fusarium wilt