1.
Nanomaterials: new weapons in a crusade against phytopathogens.
Rajwade, JM, Chikte, RG, Paknikar, KM
Applied microbiology and biotechnology. 2020;(4):1437-1461
Abstract
Bacteria, fungi, viruses, and nematodes are the major causal agents of plant diseases. These phytopathogens are responsible for about 10-40% losses in productivity and quality of food crops and horticultural produce. Although eradication of pathogens is not possible, control of plant diseases has been an area of continuous improvement/research. Use of antimicrobials, bacteriophages, and biocontrol agents, natural and synthetic agrochemicals along with best farm management practices constitute integrated measures for disease control. However, the quest for new materials continues due to pesticide resistance in the pathogens, emergence of new serotypes, and accumulation of high quantities of agrochemical contaminants in the ecosystem and associated environmental hazards, specificity of biocontrol agents, succession of pathogens during the plant growth phase, etc. The emergence of "nanotechnology," a multidisciplinary field of research, has provided a plethora of nanomaterials for potential applications in the agricultural sector. Control of plant diseases requires agents that reduce the pathogen to manageable levels, tools for early-stage detection of pathogen, and compounds that elicit immune response in the host plants. Nanomaterials have in fact been assessed for their utility in all these approaches for disease control. The present review discusses nanomaterials for controlling phytopathogens, nanomaterials in plant disease diagnostics, and nanomaterials as elicitors of the plant immune system. These nanomaterials thus represent new weapons in the fight against the phytopathogens. Recent studies indicate that nanomaterials will be a crucial component in the agroecosystem.
2.
Recent Advances in Zinc Oxide Nanostructures with Antimicrobial Activities.
Li, Y, Liao, C, Tjong, SC
International journal of molecular sciences. 2020;(22)
Abstract
This article reviews the recent developments in the synthesis, antibacterial activity, and visible-light photocatalytic bacterial inactivation of nano-zinc oxide. Polycrystalline wurtzite ZnO nanostructures with a hexagonal lattice having different shapes can be synthesized by means of vapor-, liquid-, and solid-phase processing techniques. Among these, ZnO hierarchical nanostructures prepared from the liquid phase route are commonly used for antimicrobial activity. In particular, plant extract-mediated biosynthesis is a single step process for preparing nano-ZnO without using surfactants and toxic chemicals. The phytochemical molecules of natural plant extracts are attractive agents for reducing and stabilizing zinc ions of zinc salt precursors to form green ZnO nanostructures. The peel extracts of certain citrus fruits like grapefruits, lemons and oranges, acting as excellent chelating agents for zinc ions. Furthermore, phytochemicals of the plant extracts capped on ZnO nanomaterials are very effective for killing various bacterial strains, leading to low minimum inhibitory concentration (MIC) values. Bioactive phytocompounds from green ZnO also inhibit hemolysis of Staphylococcus aureus infected red blood cells and inflammatory activity of mammalian immune system. In general, three mechanisms have been adopted to explain bactericidal activity of ZnO nanomaterials, including direct contact killing, reactive oxygen species (ROS) production, and released zinc ion inactivation. These toxic effects lead to the destruction of bacterial membrane, denaturation of enzyme, inhibition of cellular respiration and deoxyribonucleic acid replication, causing leakage of the cytoplasmic content and eventual cell death. Meanwhile, antimicrobial activity of doped and modified ZnO nanomaterials under visible light can be attributed to photogeneration of ROS on their surfaces. Thus particular attention is paid to the design and synthesis of visible light-activated ZnO photocatalysts with antibacterial properties.