Chitosan-Coated Fosetyl-Al Nanocrystals efficacy on Nicotiana tabacum colonized by Xylella fastidiosa

: 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, whereas 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 subspecies 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 Chitosan-Coated Fosetyl-Al nanocrystals (CH-nanoFos) was tested on Nicotiana tabacum cv. 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 of reducing the colonization of Xff, Xfm, and Xfp in tobacco plants. Additionally, the Area Under Disease Progress Curve (AUDPC), used to assess symptoms 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.