This research focused on studying the dynamics of the bacterial pathogen Xylella fastidiosa in almond trees across different developmental stages. The objective was to understand the seasonal distribution and concentration of X. fastidiosa within almond trees. Different tree organs, including leaves, shoots, branches, fruits, flowers, and roots, from ten X. fastidiosa-infected almond trees were sampled over two years. The incidence and concentration of X. fastidiosa were determined using qPCR and isolation. Throughout the study, X. fastidiosa was consistently absent from fruits, flowers, and roots, while it was detected in leaves as well as in shoots and branches. We demonstrate that the absence of X. fastidiosa in the roots is likely linked to the inability of this isolate to infect the peach-almond hybrid rootstock, GF677. X. fastidiosa incidence in shoots and branches remained consistent throughout the year, while in leaf petioles it varied across developmental stages, with lower detection during early and late stages of the season. Similarly, viable X. fastidiosa cells were isolated from shoots and branches at all developmental stages, but no successful isolations were achieved from leaf petioles during the vegetative and nut growth stage. Studying the progression of almond leaf scorch symptoms in trees with initial infections showed that once symptoms emerged on one branch, symptomless branches were likely already infected by the bacterium. Therefore, selectively pruning symptomatic branches is unlikely to cure the tree. This study enhances our understanding of X. fastidiosa dynamics in almond trees and may have practical applications for its detection and control.
Keywords: Bacterial Pathogens; Epidemiology; Pathogen Detection.