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.

Abstract

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. 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. 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.