Antifungal activity and mechanism of limonene against Fusarium oxysporum, a pathogen of potato dry rot

Potato is a pivotal food crop throughout the world. However, potato dry rot, a major potato disease caused by Fusarium species, seriously threatens potato production and quality worldwide. Chemical pesticides are widely used in agricultural practices for disease prevention and control, but their long–term use is harmful to human physical health and the environment. Therefore, there is an urgent need to develop environmentally friendly, antifungal, bio–based fungicides. Limonene, as a main component of plant essential oils, has strong antibacterial activity and is harmless to the human body. Limonene is easily degraded in the natural environment, making it a highly promising bio–based fungicide. However, the use of limonene to control potato dry rot has not yet been reported. This study determines the inhibitory mechanism of limonene on potato dry rot caused by Fusarium oxysporum. Limonene effectively suppressed colony growth of Fusarium oxysporum (half maximal inhibitory concentration (IC50) = 8.32μL/mL), changed its hyphal morphology, reduced its pathogenicity, decreased its spore germination rate, viability, toxicity, cell membrane integrity, and stability, and caused abnormalities during transcription and translation processes and an imbalance in the plant–fungus interaction and its intracellular ion homeostasis of transition metals. In addition, limonene affected its stress resistance. The combined antibacterial activity of limonene and chemical fungicides showed that limonene and mancozeb had an additive effect, whereas its combination with hymexazol had a synergistic effect. At the phenotypic, cytological, and transcriptomic levels, this study elucidated the mechanism underlying the antifungal activity of limonene against Fusarium oxysporum. By integrating mechanistic insights with application prospects, this study offers new avenues for developing bio–based, environmentally friendly pesticides and a theoretical foundation for potato dry rot management.