In vitro effects of copper nanoparticles on plant pathogens, beneficial microbes and crop plants

Copper-based chemicals are effectively used as antimicrobials in agriculture. However, with respect to its nanoparticulate form there has been limited number of studies. In this investigation, in vitro tests on effect of copper nanoparticles (CuNPs) against plant pathogenic fungi, oomycete, bacteria, beneficial microbes Trichoderma harzianum and Rhizobium spp., and wheat seeds were conducted. Integration of CuNPs with non-nano copper like copper oxychloride (CoC) at 50 mg/L concentration each recorded 76% growth inhibition of the oomycete Phytophthora cinnamomi in vitro compared to the control. CuNPs also showed synergistic inhibitory effect with CoC on mycelial growth and sporulation of A. alternata. Pseudomonas syringae was inhibited at 200 mg/L of CuNPs. CuNPs were not significantly biocidal against Rhizobium spp. and Trichoderma harzianum compared to CoC. Evaluation of the effect of CuNP on wheat revealed that rate of germination of wheat seeds was higher in presence of CuNPs and CoC compared to control. Germination vigor index, root length, shoot dry weight and seed metabolic efficiency of wheat were negatively affected. At low concentration, CuNPs promoted the growth of the plant pathogenic fungi Botrytis fabae, Fusarium oxysporum f.sp. ciceris, F.oxysporum f.sp. melonis, Alternaria alternate and P. syringae, and sporulation of T. harzianum. Synergistic effect of CuNPs and CoC in inhibiting P. cinnamomi offers a possibility of developing new fungicide formulation for better control of the oomycetes. Non-biocidal effect of CuNPs against beneficial microbes indicates its potential use in the agri-ecosystem.