Synthetic peptides that target key processes of Xylella fastidiosa and its host for the leaf scorch control in almond plants

ENG- Food security is critical for sustaining the growing global population, but it is increasingly threatened by plant diseases that lead to significant food losses. The frequency of emerging and reemerging plant disease outbreaks has risen in recent years, driven by factors like climate change and globalization. One of the most damaging bacterial plant pathogens is Xylella fastidiosa, which attacks economically relevant crops such as grapevine and citrus, almond, and olive trees, causing diseases like Pierce’s disease, citrus variegated chlorosis, almond leaf scorch, and olive quick decline syndrome. Originally from the Americas, X. fastidiosa was detected in Italy in 2013 for the first time. Since then, it has spread to other European countries, including France and Spain, posing a serious threat to important agricultural industries. In Europe alone, the economic impact of this pathogen is estimated at 5.5 billion euros annually, highlighting the urgent need for effective control measures. The main spreading mechanism of the bacterium is through vectors, specifically insects. Currently, there are no effective treatments for plants infected with X. fastidiosa, so most control strategies focus on preventing the spread of the bacterium by controlling its vector. Although several strategies are under research, no therapeutic solutions are available for the control of X. fastidiosa in infected plants and trees. In addition, as the agricultural sector transitions toward more sustainable practices, there is growing interest in alternatives that are both environmentally friendly and effective. In this context, antimicrobial peptides (AMPs) have emerged as a promising alternative to chemical pesticides. In previous studies, some peptides had been reported to display antibacterial activity in vitro against X. fastidiosa. Nevertheless, the effect of peptides on key processes of disease development of X. fastidiosa, such as biofilm formation and motility, had not yet been studied when this doctoral thesis was started. Therefore, the aim of this PhD Thesis entitled “Synthetic peptides that target key processes of Xylella fastidiosa and its host for the leaf scorch control in almond plants“ was to identify synthetic peptides that affect these key processes and to determine their capability to control X. fastidiosa infections in almond plants. In this thesis, several screening methods were established to determine the activity of peptides targeting key processes of X. fastidiosa for disease development and its host. Using these methods, several peptides were tested against X. fastidiosa and many were able to block the bacteria's ability to move or form biofilms. Other peptides were shown to trigger the immune defense response of the plant, helping it fight back against infections. In particular, the most promising peptides were FV7 and BP100 which are able to reduce disease severity in almond plants. These peptides could be developed into new and eco-friendly treatments to protect crops against diseases caused by X. fastidiosa