Xylella fastidiosa is one of the most harmful bacterial plant pathogens worldwide, causing a variety of diseases in different host plants, with a huge economic impact on agriculture and the environment. Nowadays, the measures adopted in Europe are eradication of the infected plants, combined with the application of insecticides to control the vector population, and the use of pathogen-free plant material. These methods have been only partially successful and, therefore, there is a need for new treatments for disease control in infected plants. Antimicrobial peptides of synthetic or microbial origin could be considered promising candidates. These peptides exhibit high activity against a wide range of plant pathogens, low toxicity, high biodegradability and a mode of action that hinders the development of bacterial resistance. Moreover, they also possess antibiofilm properties. Since X. fastidiosa is a xylem-limited pathogen that can occlude sap flow in the xylem vessels by biofilm development, peptides displaying both activities are interesting candidates to control the disease. In this work, peptides with antibacterial and antibiofilm properties have been selected from the literature and synthesized. Also, peptides of bacterial origin have been obtained from cultures such as Bacillus spp., Pantoeas spp. and Pseudomonas spp. of selected strains from our collection. All these sequences have been tested for their antibacterial and antibiofilm activities against X. fastidiosa. Antibacterial activity was determined using a contact test combined with a viability q-PCR. Antibiofilm activity was tested by biofilm quantification using violet crystal staining. Haemolytic activity of the peptides was evaluated by exposing them to horse erythrocytes and phytotoxicity was assessed by infiltrating them into tobacco leaves. Peptides with a good biological activity profile in terms of high antibacterial and/or antibiofilm activity and moderate to low toxicity have been identified.

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