Green Synthesized Silver Nanoparticles Prepared from the Antimicrobial Crude Extracts of two Brown Seaweeds Against Plant Pathogens

This study aimed for green synthesis of silver nanoparticles (Ag-NPs) from the antimicrobial crude extracted in chloroform: methanol(1:1 v/v) from the two brown seaweeds Spatoglossum asperum and Hedophyllum sessile active against two pathogenic bacteria (Xanthomonas axonopodis pv. citri and X. oryzae pv. oryzae) and a fungus Ustilaginoidea virens cause diseases in plants under in vitro assay. Crude extracts exhibit high antibacterial activity and low antifungal activity. Green synthesized Ag-NPs showed very high antimicrobial properties on comparing its crude extracts. Among the crudes, extract of Spatoglossum asperum exhibits higher bioactivity than the extract of Hedophyllum sessile but Ag-NPs prepared from the extract of H. sessile possess very strong bioactivity over Ag-NPs of Spatoglossum asperum. Reduction of Ag-NPs was confirmed by UV spectra. FTIR data indicate that active groups related to terpenoids and phenols found in the crude extracts were responsible for the reduction of Ag-NPs. The XRD data showed that the pure three types of crystal silver structure at 2θ values 32.51, 46.50 and 74.62 corresponding to 111, 200 and 220 planes for silver, respectively. This study concludes that chloroform: methanol (1:1 v/v) extracts of Hedophyllum sessile and Spatoglossum asperum containing active groups related to terpenoids and phenols and they are acting as reducing agents for green synthesis of silver nanoparticles which are potential source for controlling the plant pathogens studied.