Biocontrol of chocolate spot disease of broad bean (Vicia faba L.) caused by Botrytis fabae using biosynthesized reduced graphene oxide/silver nanocomposite

Abstract

This study was demonstrated to investigate the effects of reduced graphene oxide/silver nanocomposite (rGO/AgNC) on controlling the chocolate spot disease of broad bean (Vicia faba L.) caused by Botrytis fabae. rGO/AgNC was green synthesized using the cell-free supernatant of Escherichia coli D8 in the presence of sunlight and room temperature. rGO/AgNC revealed a broad UV–vis absorption peak at 433 nm. Transmission electron microscopy (TEM) images of rGO/AgNC confirmed the presence of spherical-shaped silver nanoparticles (AgNPs) with an average size of 7–26 nm. Zeta analysis of rGO/AgNC displayed their positive charge (+18.9 mV) and the good dispersion of AgNPs on the surface of rGO. rGO/AgNC had good antifungal activity against B. fabae in a dose-dependent pattern. In vivo, rGO/AgNC-treatment study on faba bean plants showed the biocidal action of rGO/AgNC (150 μg/ml) against B. fabae and completely prevented the pathogen infection. In addition, there was an increase in total phenolic content, peroxidase, and polyphenol oxidase activity, and protein content of rGO/AgNC-treated plants. Plants treated with rGO/AgNC displayed a typical cell morphology in their ultrastructure, including cell membranes and chloroplasts with ellipsoidal shapes and large starch grains. These are all encouraging findings for the use of the biosynthesized rGO/AgNC as a safe and efficient antifungal agent against B. fabae.