Field surveillance reveals limited triazole resistance in Aspergillus fumigatus in bean and strawberry soils, and that propiconazole application does not alter its populations

Demethylase inhibitor (DMI) fungicides have been implicated in the emergence of triazole-resistant Aspergillus fumigatus (TRAF) in agricultural environments. To assess whether propiconazole (a triazole DMI) application exerts selective pressure for TRAF, field trials were conducted in strawberry and snap bean crop production systems. Three different treatments (T1, four (strawberry) three (snapbean) applications; T2, two (strawberry) one (snapbean) applications; and T3, no application) were applied at labelled rates. Soil samples were collected at baseline and after each fungicide application and screened for A. fumigatus and TRAF isolates. Linear mixed-effects models revealed no significant alteration in A. fumigatus counts (colony forming units/gram of soil) across treatment intensities, indicating that propiconazole application did not impact overall A. fumigatus population levels. Significant variation was noted across time points, though without a consistent trend. Four putative TRAF isolates were recovered from propiconazole field trials and one from the control field; all exhibited resistance to tebuconazole and propiconazole, with cross-resistance to medical triazoles. Multiplex qPCR assay using commercial AsperGenius kit identified two isolates harboring TR34/L98H environmental mutation in the cyp51A gene, while three isolates were identified as A. fischeri, which belongs to Aspergillus Section Fumigati. Despite the abundant presence of A. fumigatus in strawberry and snap bean compost samples, no TRAF were recovered at any sampling stage. These findings suggest that while propiconazole use does not significantly alter A. fumigatus population dynamics, further investigations are required into environmental selection pressures and resistance mechanisms.