Exogenous Cadaverine Alters Polyamine Metabolism in Flax, Thereby Limiting the Colonisation of Flax Roots by <i>Fusarium oxysporum</i>

ABSTRACT Fungal infections of plants cause major losses in agriculture. Recent studies highlight the potential role of secondary metabolites including polyamines in improving plant defence against infections. This study examined the effect of exogenous cadaverine (Cad) on flax infections with Fusarium oxysporum f. sp. lini (Foln), using it as a priming factor to test whether increased Cad levels enhance resistance. It also explored how exogenous Cad and infection influence endogenous polyamines and their metabolism. The findings suggest that applying an appropriate amount of Cad to the medium reduces the development of flax fusariosis. According to phenotypic and molecular analyses, a concentration of 10 mM Cad was optimal. Excessive amounts of Cad (100 mM) in the substrate, and consequently in the plant, resulted in increased fungal content in plant shoots without changing phenotypic disease symptoms and significantly altered polyamine content, the expression of polyamine metabolism genes, and induced oxidative stress. Plants treated with 10 mM Cad followed by Foln during early colonisation stages had lower fungal presence in both roots and shoots. This reduction may be due to inhibited fungal growth in the substrate and restricted root penetration in plants with elevated Cad levels. Additionally, altered polyamine metabolism and levels of other polyamines could contribute to limiting disease progression. Therefore, Cad plays an important role in plant–fungus interactions and holds promise for enhancing flax resistance to fusariosis.