Immune response of root-knot nematode-infected tomato is improved by biogenic copper nanoparticles

"Green" synthesized copper nanoparticles from hemp plant waste (Cu-G-NPs) identified as brochantite, together with chemically synthesized copper nanoparticles (Cu-C-NPs), and copper sulfate (CuSO₄) were tested as foliar spray against Meloidogyne incognita in tomato (Solanum lycopersicum).The materials were evaluated in two separate greenhouse experiments designed to assess their effectiveness at the different temperatures: one under warmer growth conditions and another stimulating cold stress. In both experiments treatments were applied at 200 mg/L of Cu and effects were assessed over a 45-day-period. Cu-G-NPs decreased nematode egg numbers by 41 % (significantly more than CuSO₄ (35 %) and Cu-C-NPs (20 %)) and the number of galls by 38 % (significantly more than Cu-C-NP (24 %) and comparable to CuSO₄ (43 %)). In treatments with Cu-G-NPs, plants had a lower content of malondialdehyde (41 % decrease, compared to 25 % and 28 % decreases with Cu-C-NPs and CuSO₄, respectively) compared to infected control plants. Addition of Cu-G-NPs modulated hormonal response in the plants, by upregulating ethylene biosynthesis in leaves and downregulating salicylic acid-mediated response in roots. The presence of bioactive compounds, such as amines, carboxylic acids, esters, and sterols, on the surface of Cu-G-NPs (as determined using attenuated total reflectance Fourier-transform infrared spectroscopy) increased their effectiveness when compared to Cu-C-NPs and CuSO₄.