Organic Nanoparticles as Delivery Tools for Bio-Based Antimicrobials

The application of antibiotics and agrochemicals has been increasingly restricted due to health and environmental concerns and the development of resistance by phytopathogens. There is an urge to develop eco-friendly and sustainable strategies for phytopathogen management. Recently, a myriad of natural antimicrobials such as plant-based products (e.g., essential oils, plant extracts, and secondary metabolites), antimicrobial peptides (e.g., peptaibiotics), and other less-studied molecules, like enzymes, have been proposed as green solutions. However, there are some important challenges to the application of these natural antimicrobials in the field, mainly related to their rapid degradation and/or volatility, as well as quick lixiviation from the plant. Several strategies to overcome these handicaps have been proposed, with the most promising being the encapsulation of these natural antimicrobials in stable, organic-based nanoparticles (e.g., lignin, chitosan, and zein). Recent works have shown that nanoparticle encapsulation increased the antimicrobial activity of natural antimicrobials against multiresistant plant pathogens, as well as their solubility and stability, while being nontoxic for the plant. Furthermore, recent research points to the possibility that chitosan and zein-based nanoparticles might present antimicrobial activity against some important plant pathogens, and thus could pose an interesting alternative to the more common Ag or Zn-based nanoparticles, currently employed for phytopathogen management. These were recently found to affect root morphology and impair the growth of maize as well as to be potentially harmful to the central nervous system of mammals. Moreover, nature-based nanoparticles might display a potential elicitation effect on the plant, enhancing its ability to respond to pathogen infection. Due to the insufficient knowledge in this field, nanoparticles should be the focus of future research regarding their antimicrobial properties against plant pathogens. Furthermore, their elicitor potential should be further investigated. This review provides the first insight into the current strategies employed for antimicrobials’ encapsulation and the effectiveness of current nanoformulations to control plant pathogens.