Synthesis of gold nanoparticles and assessment of in vitro toxicity against plant pathogens

Gold ions and gold-based compounds are extremely lethal to different plant pathogens. This characteristic of gold is well known for numerous roles in the medical field as these nanoparticles have enormous surface area accessible to the microbes. In the present study, gold nanoparticles were synthesized through the bacterium, Bacillus sonorensis. Fourier Transform Infrared Spectroscopy (FTIR) analysis of the reaction mixture assisted to comprehend the nature of the biomolecules elaborate in the development of gold nanoparticles. FTIR spectrogram of the reaction mixture confirmed the existence of bands at 3700 cm−1 and 1500 cm−1, which could be assigned to N–H stretch of 1° and 2° amines, amides and C =C bending of aromatic amino acid of protein involved in reduction of Au3+ to Au0. Transmission electron microscopy was used to measure the shape and size of gold nanoparticles, which were spherical, circular and hexagonal with size ranging between 10–35 nm, indicating that the synthesized gold particles were of nano-dimensions with satisfactory level of mono-dispersity. In this study, role of gold nanoparticles in different concentrations (0, 20, 40, 60, and 80 ppm) was explored for their toxicity to six plant pathogens i.e., Dematophora necatrix, Fusarium oxysporum, Alternaria aternata, Alternaria mali, Sclerotium rolfsii and Colletotrichum capsici. Significant growth inhibition was observed in Sclerotium rolfsii at 80 ppm concentration of gold nanoparticles. Gold nanoparticles preparation (80 ppm) changed the morphology and resulted in 70% growth inhibition of Fusarium oxysporum after one week of incubation. Similarly, in case of Alternaria alernata, 60%–70% growth inhibition and change in morphology was also observed. Inhibition of Alternaria mali up to 50%–60% was observed at 60 and 80 ppm with considerable change in morphology of mycelium after one week of incubation. © 2021, Indian Phytopathological Society.