Impact of metal nanoparticles on tomato growth, physiology and symbiosis with the Fusarium solani FsK strain

Metal nanoparticles constitute promising, eco-compatible alternatives to be used as nano-fertilizers or nano-fungicides although their potential impact on the agroecosystem is poorly studied. In the present study, the impact of copper (Cu-NPs, CuO-NPs), silver (Ag-NPs) and zinc oxide (ZnO-NPs) nanoparticles (NPs) on tomato plant development, physiological properties and the symbiotic relationship with the endophytic Fusarium solani FsK strain was assessed in comparison with their respective bulk/ionic counterparts. Both NPs and their counterparts did not affect the number of germinated tomato seeds even at higher concentrations except for AgNO₃, which significantly decreased seed germination rates. On the contrary, a dose dependent decrease of root length was observed in most NP/bulk treatment cases. This was also the case for dry weight of tomato plants which was also significantly reduced upon treatment with NPs and counterparts especially in the cases of AgNO₃, Cu-NPs, ZnO-NPs, and ZnSO₄. Although differences between NPs and bulk counterparts varied, root and shoot length of grown tomato plants was also negatively affected by treatments. NPs/bulk counterpart treatments resulted in a marked oxidative stress response as indicated by increased MDA and H₂O₂ levels of treated plants. Photosynthetic pigments were also significantly affected by NP/bulk treatments, a fact evident from the reduced chlorophyl-a and carotenoid levels recorded. The FsK tomato-symbiotic strain was significantly more sensitive to Cu-NPs and ZnO-NPs than CuO-NPs and Ag-NPs as revealed in both mycelial growth and spore germination fungitoxicity tests. With the exception of AgNO₃,which was 8 to 9-fold more toxic than Ag-NPs, all NPs were more fungitoxic to FsK than their bulk/ionic counterparts. FsK colonization of roots was not significantly affected by treatments with NPs and counterparts indicating that, once established inside the roots, the endophyte is shielded against the toxic effect of metals. At the same time, an alleviation of CuO-NPs, ZnO-NPs,and ZnSO₄ phytoxicity was observed when FsK was present inside tomato roots in terms of plant dry weight. Concluding, results suggest that phytotoxicity of NPs in tomato treated plants should be considered before nano-fertilizer/fungicide treatments while the benefits of FsK inoculation of tomato plants may extent to resistance towards these toxic agents for both organisms.