Unveiling the Interplay: Salinity‐Modulated Defence Mechanisms in <i>Medicago truncatula</i> Against <i>Phoma medicaginis</i> Infection

ABSTRACT In nature, plants are subjected to an interplay of biotic and abiotic stresses that impede their growth and overall productivity. The study used the Medicago truncatula plant model to explore the relationship between salinity and Phoma medicaginis infection, focusing on its effect on plant defence mechanisms. Low sodium chloride (NaCl) concentrations (50–100 mM) enhanced growth and plant resistance to P . medicaginis infection, while high concentrations reduced growth and resistance, demonstrating a synergistic effect. The increase in total polyphenol was linked to an increase in NaCl concentration, regardless of the presence of the fungal pathogen in the plants. The study found that under salt stress, potassium levels in both infected and noninfected M. truncatula plants decreased, while sodium ions increased in infected leaves and roots. Salinity stress and P . medicaginis infection affected M. truncatula membrane fatty acid composition, increasing saturated fatty acids (C18:0 and C18:1) and decreasing unsaturated ones (C18:3), possibly as an adaptive response to modulate membrane fluidity. Furthermore, the study analysed gene expression involving allene oxide synthase 1, catalase, chalcone reductase, lipoxygenase 2 and phenylalanine ammonia‐lyase in M. truncatula , revealing their role in the early response to salt– P . medicaginis stress and suggesting a crosstalk between jasmonic acid and salicylic acid pathways in shaping M. truncatula 's resilience to P . medicaginis infection under salt stress conditions.