Mapping Xylella fastidiosa infection and xylem microbiome composition on olive tree branches

Trabajo presentado en la 3rd European Conference on Xylella fastidiosa (Building knowledge, protecting plant health), celebrada online el 29 y 30 de abril de 2021.The plant-pathogenic bacterium Xylella fastidiosa, widely distributed in the Americas and with several recent outbreaks in EU, emerged as a serious threat to olive crop and the typical Mediterranean landscape. This xylem-limited plant pathogen spreads by xylem sap-feeding insects, causes symptoms of marginal leaf scorch, leaf chlorosis, defoliation, and a general decay in olive trees. Research on plant-associated microorganisms has gained importance in the last decade as a key component in plant health. However, the role of the xylem microbiome and its contribution to plant health is still scarce. Therefore, this work is focused on mapping X. fastidiosa infection and deciphering the changes in the composition of microbial communities on symptomatic and asymptomatic olive tree branches. Three olives trees of cultivar Grappolo growing at Sao Paulo state (Brazil) were selected and within each tree three main branches were sampled showing different severity of symptoms development; one branch presenting typical X. fastidiosa symptoms of pathogen infection in contrast to the other two branches that were asymptomatic. X. fastidiosa infection was verified by qPCR. Leaves and stem samples were collected in a gradual scale above and below the symptomatic branches. Chips extracts of xylem tissue from its stems and leaf veins and petioles were used for DNA extraction to undergo metagenomic analysis (NGS) for microbial composition estimation and to diagnose the presence of the pathogen by real-time PCR, respectively. These results will help to understand the occurrence of step-wise changes in olive xylem microbiome as a consequence of X. fastidiosa infection and determine which microorganisms respond faster or can be associated to a symptom progression on infected trees.Study supported by Projects 727987 XF-ACTORS (EU-H2020) and AGL2016-75606-R (MEIC Spain and FEDER-EU) and SEGIB – Carolina Foundation