Antibacterial activity of synthesized silver nanoparticles by sumac aqueous extract and silver-chitosan nanocomposite against Pseudomonas syringae pv. syringae

The considerable damages caused by plant pathogenic bacteria have prompted the use of a wide variety of chemical pesticides which cause harmful effects on human health and environment. Application of safe and eco-friendly methods for controlling plant pathogens is very important in sustainable agricultural systems. In this present study, the biosynthesis of silver nanoparticles was conducted using sumac aqueous extract. Antibacterial activity of synthesized AgNPs (with the average size of 35 nm) and their combination with chitosan (Cs) was evaluated against Pseudomonas syringae pv. syringae (Pss), the causal agent of bacterial canker disease of stone fruit trees in vitro and in vivo. The structure and physical properties of nanoparticles were investigated by scanning electron microscope, X-ray diffraction, and UV-visible spectrophotometer. Green synthesized AgNPs and Cs-Ag nanocomposite indicated minimum inhibitory concentration at 12 ppm and 9.2 ppm Cs/4 ppm AgNPs, respectively. Also, in vitro evaluations showed that chitosan could improve the antimicrobial property of silver nanoparticles. In greenhouse experiments, the results showed that different concentrations of AgNPs and Cs-Ag nanocomposite reduced disease severity of bacterial canker of stone fruits on two-year-old peach trees when compared to the control. The highest decreases were caused using 100 ppm concentration of AgNPs (89.40%) and then a combination of 100 ppm AgNPs/231.48 ppm chitosan (86.61%). This study suggests that the synthesized AgNPs act as eco-friendly antibacterial agents. But, further studies should be conducted to develop nanoparticles with the minimum toxicity and maximum antimicrobial effect to apply as proper alternatives for antibiotics and pesticides.