Daniele Schiavi

Scientific research, within the framework of a circular and sustainable economy, has increasingly focused on wild plants and agricultural by-products as valuable sources of bioactive compounds for innovative applications. In this study, the plant species selected for extract preparation and evaluation of their dyeing properties included Isatis tinctoria L., Castanea sativa, Juglans regia L., Rumex crispus L., Arbutus unedo L., and Punica granatum L. Each extract was analyzed to assess its dyeing performance on cotton and other cellulosic fabrics. Cellulose pads dyed with peels of P. granatum extract (PPGE) proved to be versatile and effective, showing potential for use in extending the shelf life of various fruits such as strawberries, apples, cherries, and persimmons. The optimum dyeing condition for cellulose and cotton fabrics was found to be 6% w/v dye. These findings support the development of natural, multifunctional materials suitable for food packaging applications aimed at preserving fresh produce, as well as for sustainable textile dyeing.

Olive Quick Decline Syndrome (OQDS), caused by the bacterium Xylella fastidiosa, subsp. pauca, has devastated olive groves in Italy’s Apulia region since 2013. Despite significant scientific progress, the solution remains elusive. This study investigated the link between olive tree nutritional status and OQDS severity, aiming to uncover potential mitigation strategies. We analyzed leaf nutrient profiles from olive trees in naturally infected areas, categorizing them as asymptomatic (AS), mildly symptomatic (MS), or severely symptomatic (SS). Distinct nutritional differences were observed across these groups. The integration of univariate statistical analysis, hierarchical clustering, and Principal Component Analysis (PCA) revealed a complex relationship between plant nutritional status and disease progression. Notably, the PCA results highlighted the importance of sulfur metabolism, suggesting its role in olive trees’ defense mechanisms and metabolic responses to OQDS. These results provide promising evidence with potential application for dealing with OQDS, and the question of whether plant nutritional status plays a role in the development of OQDS symptoms deserves to be further examined in depth.

Xylella fastidiosa ( Xf) is a quarantine plant pathogen capable of colonizing the xylem of a wide range of hosts. Currently, there is no cure able to eliminate the pathogen from a diseased plant, but several integrated strategies have been implemented for containing the spread of Xf. Nanotechnology represents an innovative strategy based on the possibility of maximizing the potential antibacterial activity by increasing the surface-to-volume ratio of nanoscale formulations. Nanoparticles based on chitosan and/or fosetyl-Al have shown different in vitro antibacterial efficacy against Xf subsp. fastidiosa ( Xff) and pauca ( Xfp). This work demonstrated the uptake of chitosan-coated fosetyl-Al nanocrystals (CH-nanoFos) by roots and their localization in the stems and leaves of Olea europaea plants. Additionally, the antibacterial activity of fosetyl-Al, nano-fosetyl, nano-chitosan, and CH-nanoFos was tested on Nicotiana tabacum cultivar SR1 (Petite Havana) inoculated with Xff, Xfp, or Xf subsp. multiplex ( Xfm). The bacterial load was evaluated with qPCR, and the results showed that CH-nanoFos was the only treatment able to reduce the colonization of Xff, Xfm, and Xfp in tobacco plants. Additionally, the area under the disease progress curve, used to assess symptom development in tobacco plants inoculated with Xff, Xfm, and Xfp and treated with CH-nanoFos, showed a reduction in symptom development. Furthermore, the twitching assay and bacterial growth under microfluidic conditions confirmed the antibacterial activity of CH-nanoFos.

Essential oil-based pesticides, which contain antimicrobial and antioxidant molecules, have potential for use in sustainable agriculture. However, these compounds have limitations such as volatility, poor water solubility, and phytotoxicity. Nanoencapsulation, through processes like micro- and nanoemulsions, can enhance the stability and bioactivity of essential oils. In this study, thyme essential oil from supercritical carbon dioxide extraction was selected as a sustainable antimicrobial tool and nanoencapsulated in an oil-in-water emulsion system. The investigated protocol provided high-speed homogenisation in the presence of cellulose nanocrystals as stabilisers and calcium chloride as an ionic crosslinking agent. Thyme essential oil was characterised via GC-MS and UV-vis analysis, indicating rich content in phenols. The cellulose nanocrystal/essential oil ratio and calcium chloride concentration were varied to tune the nanoemulsions’ physical–chemical stability, which was investigated via UV-vis, direct observation, dynamic light scattering, and Turbiscan analysis. Transmission electron microscopy confirmed the nanosized droplet formation. The nanoemulsion resulting from the addition of crosslinked nanocrystals was very stable over time at room temperature. It was evaluated for the first time on Pseudomonas savastanoi pv. savastanoi, the causal agent of olive knot disease. In vitro tests showed a synergistic effect of the formulation components, and in vivo tests on olive seedlings demonstrated reduced bacterial colonies without any phytotoxic effect. These findings suggest that crosslinked cellulose nanocrystal emulsions can enhance the stability and bioactivity of thyme essential oil, providing a new tool for crop protection.

Nanotechnology could play a huge role in ensuring safer and greener agriculture in the years ahead by providing sustainable tools to control plant diseases. In this study, the possibility of using cellulose nanocrystals (CNCs) obtained from tomato waste to control the bacterial speck disease’s causal agent was evaluated for the effects on plant development. Biocompatibility was assessed by studying seeds’ germination, leaf area, biomass and nitrogen balance index of tomato seedlings treated with CNC. Since epiphytic survival represents a relevant phase in early and later infections provoked by Pseudomonas syringae pv. tomato (Pst), the CNC’s ability to lower the level of bacterial cells in the plant canopy was evaluated in treated seedlings at 1, 7 and 14 days after being artificially inoculated. Leaflets were collected and washed to quantify the epiphytic bacterial population and observed through electron microscopy. Obtained results indicate that CNCs are non-toxic, compatible nanomaterials, highlighting at the same time their potential in counteracting bacterial speck disease by decreasing the level of epiphytic population after two weeks from inoculation by up to one log unit (3.08 CFU cm⁻²) compared to the control (3.94 CFU cm⁻²). Moreover, we were able to demonstrate that it is possible to cut in half the amount of copper without losing effectiveness in controlling the bacteria by mixing it with CNCs, concluding that CNCs could be used to design innovative sustainable plant protection strategies.

Quarantine pathogens require the investigation of new tools for effective plant protection. In particular, research on sustainable agrochemicals is the actual challenge. Plant extracts, essential oils, and gels are natural sources of efficient biocides, such as aromatic secondary metabolites. Thymol is the major phenolic constituent of thyme and oregano essential oils, and it can inhibit many pathogenic microbes. Thymol nanoparticles were obtained through adsorption on CaCO₃ nanocrystals, exploiting their carrier action. High loading efficiency and capability were reached as verified through UV and TGA measurements. We report the first study of thymol effect on Xylella fastidiosa, conducing both fluorometric assay and in vitro inhibition assay. The first test confirmed the great antibacterial effect of this compound. Finally, an in vitro test revealed an interesting synergistic action of thymol and nanocarriers, suggesting the potential application of thymol-nanoparticles as effective biocides to control Xylella fastidiosa infection.

Nanotechnology is rapidly gaining ground in crop protection, with the growing quest for sustainable nanopesticides and nanocarriers for plant pathogen management. Among them, cellulose nanocrystals (CNC) are emerging as innovative agrofood-waste-derived antimicrobial materials. In this work, new chemical and enzymatic CNC extraction methods from tomato harvest residues were evaluated. The obtained nanomaterials were characterized and tested for their antimicrobial properties on Pseudomonas syringae pv. tomato (Pto), the causal agent of bacterial speck disease on tomato. Both protocols were efficient. The enzymatic extraction method was greener, producing purer CNC at slightly lower yield. The obtained CNC, although they weakly inhibited cell growth and did not promote reactive oxygen species (ROS) formation, provoked bacterial aggregation and the inhibition of biofilm production and swimming motility. Both protocols produced CNC with similar morpho-chemical features, as well as promising antimicrobial activity against plant bacterial pathogens, suggesting their potential role in sustainable crop protection strategies. The new protocols could be a valuable alternative to conventional methods.

Agri-food waste management represent for several supply-chains a pending issue, since most of the lignocellulosic biomasses produced by the agricultural practices are often intended for energy production, due to their high disposal costs. Nanotechnology could represent a sustainable way to valorise agricultural waste by extracting highly performing nanomaterials and reusing them as nanocarriers or nanopesticides to protect crops. Cellulose and lignin, which are the main component of plant residues display antimicrobial properties when reduced to their nanosized forms, being able to act as innovative tools to counteract plant pathogens, both bacterial and fungal ones. In particularly cellulose can be extracted from different matrices to obtain cellulose nanocrystals (CNC), while lignin is often reduced in nanoparticles (LNP). In this mini review the current and most recent results in terms of antimicrobial activities against plant pathogens by waste-based lignocellulosic nanomaterial are showed.