Chitosan- and gallic acid-based (NPF) displayed antibacterial activity against three Pseudomonas spp. plant pathogens and boosted systemic acquired resistance in kiwifruit and olive plants.

BACKGROUD: Pseudomonas syringae pv. actinidiae (Psa), P. syringae pv. tomato (Pst) and P. savastanoi pv. savastanoi (Psav) are bacterial plant pathogens with worldwide impact that are mainly managed by the preventive application of cupric salts. These are dangerous for ecosystems and have favoured the selection of resistant strains, so they are candidates to be replaced in the next few years. Thus, there is an urgent need to find efficient and bio-based solutions to mitigate these bacterial plant diseases. Nanotechnology could represent an innovative way to control plant diseases, providing alternative solutions to the agrochemicals traditionally employed, thanks to the formulation of the so-called third-generation and nanotechnology-based agrochemicals. RESULTS: In this work, a novel nanostructured formulation (NPF) composed of cellulose nanocrystals (CNC) as carrier, high amylose starch (HAS) as excipient, and chitosan (CH) and gallic acid (GA) as antimicrobials, was tested at 2% in vitro and in vivo with respect to the three different Pseudomonas plant pathogens. In vitro agar assays demonstrated that the NPF inhibited ≤80% Psa, Pst and Psav. Moreover, the NPF did not decrease biofilm synthesis and it did not influence bacterial cells flocculation and adhesion. On plants, the NPF displayed complete biocompatibility and boosted the transcript levels of the major systemic acquired resistance responsive genes in kiwifruit and olive plants. CONCLUSION: This works provides novel and valuable information regarding the several modes-of-action of the novel NPF, which could potentially be useful to mitigate Psa, Pst and Psav infections even in organic agriculture. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Thymol-Nanoparticles as Effective Biocides against the Quarantine Pathogen Xylella fastidiosa.

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.

A new inclusive MLVA assay to investigate genetic variability of Xylella fastidiosa with a specific focus on the Apulian outbreak in Italy.

The Olive Quick Decline Syndrome by Xylella fastidiosa subspecies pauca is among the most severe phytopathological emergencies nowadays. In few years, the outbreak devastated olive groves in Apulia (Italy), potentially endangering the entire Mediterranean basin. This research aimed to develop a multiple locus VNTR analysis assay, a molecular tool to differentiate between populations of the pathogen. It has already been successfully applied to different X. fastidiosa subspecies from various plant hosts. The previously published TR loci, together with a set of new design, have been tested in silico on the genome of the Apulian De Donno strain. The resulting selection of 37 TR loci was amplified on the genomic DNAs of the Apulian strains AND from representatives of X. fastidiosa subspecies, and directly on DNA extracted from infected plants. The assay clearly discerned among subspecies or even sequence types (ST), but also pointed out variants within the same ST so as to provide more detailed information on the dynamics and pathogen diffusion pathways. Its effective application even on total DNAs extracted from infected tissues of different host plants makes it particularly useful for large-scale screening of infection and for the strengthening of containment measures.