Fluopicolide is a selective inhibitor of V-ATPase in oomycetes

Fungicide resistance to crop protection products is a critical sustainability issue in modern agriculture that requires constant monitoring of the field situation considering different environmental conditions and agricultural practices. Regulation strategies based on resistance risk ranking of both pathogen and active compound, underpinned by fast and broad field monitoring, shall result in recommendations for suitable practices with the aim to stabilize or even to restore the sensitivity situation. Alternating and mixing various products according to their modes of action belong to the most common and the most efficient mitigation methods. Though, these resistance management measures can be implemented best when precise knowledge of both the molecular target and the cell biology of the pathogen as well as of the resistance mechanism is acknowledged. To this end, we have investigated the molecular target and cellular effects of fluopicolide, one of the most effective Oomyceticides in the market. By combining data of genomic analysis of resistant field isolates of Plasmopara viticola and Phytophthora infestans with UV-mutagenized strains of P. infestans, we identified the enzyme vacuolar H⁺-ATPase as the target protein. Biochemical assays confirmed that fluopicolide inhibits specifically Oomycetes targets and has no residual activity on true fungi or insect orthologs.