The Synergy of Chitosan and Azoxystrobin Against Fusarium graminearum Is Modulated by Selected ABC Transporters

The development of innovative and effective strategies to combat fungal pathogens is critical to sustainable crop protection. Fungicides have been used for over two centuries, with traditional copper- and sulfur-based formulations still in use due to their broad-spectrum, multisite mode of action, which minimizes the risk of pathogen resistance. In contrast, modern systemic fungicides, though potent, often target a single site of action, leading to the accelerated emergence of resistant fungal strains. This study explores synergistic interactions between chitosan (CS) and selected fungicides, focusing on their antifungal activity against <i>Fusarium graminearum</i>. Among the fungicides tested, azoxystrobin (Amistar) exhibited the highest 44.88 synergy score when combined with CS (30 kDa, degree of deacetylation ≥ 90), resulting in significantly improved antifungal efficacy. Furthermore, the combination of CS and Amistar with double-stranded RNA (dsRNA) targeting selected ABC transporter genes further amplified antifungal activity by silencing genes critical for fungal tolerance to treatment. This dual synergy highlights the potential of RNA interference (RNAi) as both a functional tool to investigate fungal physiology and an effective antifungal strategy. These findings reveal a promising and environmentally friendly approach to mitigate resistance while improving fungal control. Furthermore, the remarkable synergy between azoxystrobin and CS presents a novel mechanism with significant potential for sustainable agricultural applications, which warrants further investigation to elucidate its molecular basis.