Prunus dulcis response to novel defense elicitor peptides and control of Xylella fastidiosa infections

Xylella fastidiosa is a plant pathogenic bacterium that has been introduced in the European Union (EU), threatening the agricultural economy of relevant Mediterranean crops such as almond (Prunus dulcis). Plant defense elicitor peptides would be promising to manage diseases such as almond leaf scorch, but their effect on the host has not been fully studied. In this work, the response of almond plants to the defense elicitor peptide flg22-NH₂ was studied in depth using RNA-seq, confirming the activation of the salicylic acid and abscisic acid pathways. Marker genes related to the response triggered by flg22-NH₂ were used to study the effect of the application strategy of the peptide on almond plants and to depict its time course. The application of flg22-NH₂ by endotherapy triggered the highest number of upregulated genes, especially at 6 h after the treatment. A library of peptides that includes BP100-flg15, HpaG23, FV7, RIJK2, PIP-1, Pep13, BP16-Pep13, flg15-BP100 and BP16 triggered a stronger defense response in almond plants than flg22-NH_2. The best candidate, FV7, when applied by endotherapy on almond plants inoculated with X. fastidiosa, significantly reduced levels of the pathogen and decreased disease symptoms. Therefore, these novel plant defense elicitors are suitable candidates to manage diseases caused by X. fastidiosa, in particular almond leaf scorch.