Biosynthesized silver nanoparticles using Trichoderma harzianum reduce charcoal rot disease in bean

Charcoal rot, caused by the soil-born fungus Macrophomina phaseolina, is one of the most important bean diseases in hot, arid regions of the world, which sometimes damages up to 100% of the yield. Trichoderma harzianum is a potent antagonist of many plant pathogens. Nanotechnology is a promising method to produce biological fungicides for the management of plant diseases and to produce safe plant products. Among metals, silver has shown powerful antimicrobial properties. This study was conducted to investigate the possibility of silver nanoparticles (AgNPs) biosynthesis using T. harzianum and its impact on the charcoal rot disease of beans. Two isolates of the pathogen were collected from bean fields in southwestern Iran. The pathogenicity of these isolates was tested on three beans and one hyper-virulent isolate was identified. Also, the effect of liquid culture extract of four T. harzianum isolates on colony growth of these two isolates was studied in vitro and a superior T. harzianum isolate has been identified. Silver nanoparticles were produced by this isolate. Ultraviolet–visible spectrophotometer, scanning electron microscopy, and dynamic light scattering were used to study the shape and size of the AgNPs. The effect of 12 concentrations of the AgNPs on colony growth of the hyper-virulent isolate of the pathogen was examined, and its effective concentration 50 percent value was calculated. The effect of three concentrations of the AgNPs and silver nitrate on the severity of charcoal rot in bean was studied under greenhouse conditions. The absorption spectrum of the AgNPs ranged from 400 to 600 nm, with maximum absorption at 450–500 nm, and most of the particles were spherical and 50.7–58.80 nm diameters. The EC50 value of the AgNPs for the hyper-virulent isolate of the pathogen was 444.522 ppm. The AgNPs was more effective than silver nitrate in reducing charcoal rot disease severity in bean. Therefore, the AgNPs, with EC50 = 444.522 ppm, can be recommended as a biological fungicide to control the charcoal rot disease of beans. The effect of biosynthesized AgNPs using T. harzianum, in reducing the charcoal rot disease of beans is reported for the first time.