Mitigation of Almond Leaf Scorch by a Peptide that Inhibits the Motility of Xylella fastidiosa

Xylella fastidiosa is a xylem-limited plant pathogenic bacterium that is a menace to the agriculture worldwide, threating economically relevant crops such as almond. The pathogen presents a dual lifestyle in the plant xylem, consisting of sessile microbial aggregates and mobile independent cells that move by twitching motility. The latter is essential for the systemic colonization of the host and is mediated through type IV pili. In previous reports, it has been demonstrated that peptides can affect different key processes of X. fastidiosa, but their effect on motility has never been assessed. In the present work, peptides previously identified and newly designed analogs were studied for their effect in vitro on the motility of X. fastidiosa, and their protective effect against almond leaf scorch was determined. By assessing the twitching fringe width in colonies and using microfluidic chambers, the inhibitory effect of BP100 on twitching motility was demonstrated. Interestingly, type IV pili of BP100-treated cells were similar in frequency and length and presented no morphological differences when compared with the nontreated control. The application of BP100 by endotherapy in almond plants inoculated with X. fastidiosa under greenhouse conditions significantly reduced population levels and showed less affected xylem vessels, which correlated with decreased disease symptoms. Therefore, BP100 is a promising candidate to manage almond leaf scorch caused by X. fastidiosa.