Use of copper, silver and zinc nanoparticles against foliar and soil-borne plant pathogens

Nano-fungicides are expected to play an important role in future plant disease management as eco-friendly alternatives of conventional synthetic fungicides. In the present study, the sensitivity of seven fungal species, known to cause foliar and soil-borne diseases, to nanoparticles (NPs) containing copper (Cu-NPs, CuO-NPs), silver (Ag-NPs) and zinc (ZnO-NPs) was assessed in vitro. Mycelial growth assays revealed that Cu-NPs with mean inhibition rates, EC₅₀, ranging between 162 and 310 μg/mL were most effective among the NPs tested in inhibiting fungal growth, followed by ZnO-NPs with EC₅₀ ranging between 235 and 848 μg/mL. All fungal species were practically insensitive to CuO-NPs and Ag-NPs except for B. cinerea, which was equally sensitive to Ag-NPs and Cu-NPs (EC₅₀ = 307 μg/mL). Cu-NPs were more fungitoxic in terms of mycelial growth, to almost all species tested, than a protective fungicide containing Cu(OH)₂, which was used as a reference. Fungitoxicity experiments with the NPs tested and bulk size reagents containing the respective metals revealed that ZnO-NPs were more toxic to all fungal species tested than ZnSO₄, whereas Cu-NPs were more fungitoxic than CuSO₄ in all cases, except for B. cinerea, A. alternata and M. fructicola. The existence of a positive correlation between Cu-NPs and CuO-NPs toxicity and, at the same time, the absence of any correlation between NPs tested and their respective bulk metal counterparts indicated potential differences in the mode of action between bulk and nanosized antifungal ingredients. Although there was considerable variation between fungal species, all NPs were generally 10 to 100 fold more fungitoxic to spores than hyphae and in the majority of cases more effective than Cu(OH)₂, as revealed by colony formation bioassays. NPs significantly suppressed grey mold symptoms on plum fruit, especially Ag-NPs, which completely inhibited disease development. Consequently, tested NPs have the potential to be used as protective antifungal agents.