Nano-Magnesium Oxide: A Novel Bactericide Against Copper-Tolerant Xanthomonas perforans Causing Tomato Bacterial Spot

Abstract

Bacterial spot caused by Xanthomonas perforans causes significant damage on tomatoes in Florida. Due to the presence of copper (Cu)-tolerant X. perforans strains, Cu bactericides are not effective in disease management. Hence, there is a critical need to find alternatives for Cu. Anti-bacterial activity of magnesium oxide (Nano-MgO), and other metal oxide nanoparticles, were evaluated against a Cu-tolerant and sensitive X. perforans strain. In vitro experiments demon-strated high antibacterial activity of Nano-MgO against both strains compared to the commercial Cu. The minimum inhibitory concentration (MIC) of Nano-MgO is 25 µg/ml and the minimum bactericidal concentration (MBC) is 100 µg/ml against a Cu-tolerant X. perforans strain after 4h of exposure. Structural changes in the bacterial membrane following exposure to Nano-MgO treatments compared to the controls were observed using transmission electron microscopy. In two greenhouse experiments with a Cu-tolerant strain, bacterial spot severity was significantly reduced by Nano-MgO at 200 µg/ml compared to Cu-ethylene bis-dithiocarbamate (grower standard), and the untreated control (P = 0.05). In three field experiments, Nano-MgO at 200 µg/ml significantly reduced disease severity with no negative impact on yield compared to the untreated control. Inductively Coupled Plasma Mass Spectrometric analysis of the fruits confirmed that Nano-MgO application did not lead to the accumulation of Mg, Cu, Ca, K, Mn, P and S. This study is the first to demonstrate the potential of Nano-MgO against bacterial spot of tomato.

Bactericidal Activity of Copper-Zinc Hybrid Nanoparticles on Copper-Tolerant Xanthomonas perforans

“…This can be achieved in part by understanding the structural and biochemical changes on bacterial cells by nanoparticle exposure. Epifluorescence microscopy has previously provided insight into whether the nano materials are bactericidal or bacteriostatic in nature 26 . Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) have been shown to provide information on structural modifications on the surface and interior of bacterial cells upon exposure to the Cu/Zn hybrid nanoparticles 26 .…”

“…Various antibacterial nanoparticles have been developed and studied for disease management of copper-tolerant Xanthomonas spp. 8,23–26 . For example, the use of silver (Ag) nanoparticles merged in a dsDNA-graphene oxide matrix (Ag-dsDNA-GO).…”

“…Another example is the development of three copper composites (copper-core shell silica, copper-multivalent and copper-fixed quat) that were shown to be effective in vitro , and unlike Ag-dsDNA-GO, they were cheaper and prepared using industrial grade nanoparticles 8 . Moreover, magnesium oxide nanoparticles were found to effectively reduce disease severity of bacterial spot under both greenhouse and field conditions 26 . In the same study, it was shown nano sized particles of Cu 2 O had bactericidal activity against a copper-tolerant Xanthomonas spp.…”

Mechanistic insights into host adaptation, virulence and epidemiology of the phytopathogenXanthomonas

“…Recent advances in nanoparticle technology should enable effective modification resulting in a more potent product. Accordingly, different metal-ion-based nanoparticles have been successfully utilised as antimicrobial compound in greenhouse and field trials against tomato infecting Xanthomonas strains (Ocsoy et al 2013;Paret et al 2013;Makarovsky et al 2018;Liao et al 2019).…”

In vitro antimicrobial effect of metallic nanoparticles on phytopathogenic strains of crop plants

“…Metallic nanoparticles (NPs) such as silver, zinc and copper oxide, among others, have proven to inhibit the growth of phytopathogenic viruses, fungi and bacteria, demonstrating the enormous potential that NPs have to formulate new and advanced commercial antimicrobial agents (Yah & Simate, 2015). Current research has demonstrated that metallic NPs have an active bactericidal effect against plant pathogenic strains such as P. syringae, C. michiganensis (Banik & Luque, 2017;Cumplido-Nájera et al, 2019) as well as Xanthomonas perforans (Liao et al, 2018). The effectiveness of NPs depends on their size and shape.…”