Ionones in flax: an open question of their role in fungal resistance and metabolic shifts of flax

BACKGROUND: Flax (Linum usitatissimum L.) is a valuable crop that suffers significant losses due to Fusarium oxysporum f. sp. lini (Foln) infections. Apocarotenoids, especially volatiles have recently attracted attention as potential regulators of plant defence, but their functions remain poorly understood. RESULTS: Ionones exhibited concentration-dependent effects: low doses induced defence-related responses, including H₂O₂ accumulation and upregulation of defence-associated genes, whereas higher concentrations were phytotoxic. Foln infection was associated with increased ionone levels in planta, suggesting their involvement in plant responses to pathogen challenge. CCD inhibitor treatments altered H₂O₂ levels, ionone accumulation, and infection dynamics. Notably, similar patterns of H₂O₂ and ionone responses were observed in plants treated with selected inhibitors (B2 and D1) and during Foln infection. CONCLUSIONS: Overall, our findings indicate that ionones are unlikely to be effective fungicides, as their phytotoxic effects outweigh their limited impact on Foln infection. However, they appear to be associated with modulation of ROS levels and plant responses to pathogen challenge. Changes observed following CCD inhibition further point to coordinated redox-related processes, although their precise role in plant-pathogen interactions remains to be clarified.