AUTHOR=Anguita-Maeso Manuel , Ares-Yebra Aitana , Haro Carmen , Román-Écija Miguel , Olivares-García Concepción , Costa Joana , Marco-Noales Ester , Ferrer Amparo , Navas-Cortés Juan A. , Landa Blanca B. 

TITLE=Xylella fastidiosa Infection Reshapes Microbial Composition and Network Associations in the Xylem of Almond Trees

JOURNAL=Frontiers in Microbiology

VOLUME=Volume 13 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.866085

DOI=10.3389/fmicb.2022.866085

ISSN=1664-302X

ABSTRACT=<p><italic>Xylella fastidiosa</italic> represents a major threat to important crops worldwide including almond, citrus, grapevine, and olives. Nowadays, there are no efficient control measures for <italic>X. fastidiosa</italic>, and the use of preventive measures and host resistance represent the most practical disease management strategies. Research on vessel-associated microorganisms is gaining special interest as an innate natural defense of plants to cope against infection by xylem-inhabiting pathogens. The objective of this research has been to characterize, by next-generation sequencing (NGS) analysis, the microbial communities residing in the xylem sap of almond trees affected by almond leaf scorch disease (ALSD) in a recent <italic>X. fastidiosa</italic> outbreak occurring in Alicante province, Spain. We also determined community composition changes and network associations occurring between xylem-inhabiting microbial communities and <italic>X. fastidiosa</italic>. For that, a total of 91 trees with or without ALSD symptoms were selected from a total of eight representative orchards located in five municipalities within the <italic>X. fastidiosa</italic>-demarcated area. <italic>X. fastidiosa</italic> infection in each tree was verified by quantitative polymerase chain reaction (qPCR) analysis, with 54% of the trees being tested <italic>X. fastidiosa</italic>-positive. Globally, <italic>Xylella</italic> (27.4%), <italic>Sphingomonas</italic> (13.9%), and <italic>Hymenobacter</italic> (12.7%) were the most abundant bacterial genera, whereas <italic>Diplodia</italic> (30.18%), a member of the family Didymellaceae (10.7%), and <italic>Aureobasidium</italic> (9.9%) were the most predominant fungal taxa. Furthermore, principal coordinate analysis (PCoA) of Bray–Curtis and weighted UniFrac distances differentiated almond xylem bacterial communities mainly according to <italic>X. fastidiosa</italic> infection, in contrast to fungal community structure that was not closely related to the presence of the pathogen. Similar results were obtained when <italic>X. fastidiosa</italic> reads were removed from the bacterial data set although the effect was less pronounced. Co-occurrence network analysis revealed negative associations among four amplicon sequence variants (ASVs) assigned to <italic>X. fastidiosa</italic> with different bacterial ASVs belonging to <italic>1174-901-12</italic>, <italic>Abditibacterium</italic>, <italic>Sphingomonas</italic>, <italic>Methylobacterium–Methylorubrum</italic>, <italic>Modestobacter</italic>, <italic>Xylophilus</italic>, and a non-identified member of the family Solirubrobacteraceae. Determination of the close-fitting associations between xylem-inhabiting microorganisms and <italic>X. fastidiosa</italic> may help to reveal specific microbial players associated with the suppression of ALSD under high <italic>X. fastidiosa</italic> inoculum pressure. These identified microorganisms would be good candidates to be tested in planta, to produce almond plants more resilient to <italic>X. fastidiosa</italic> infection when inoculated by endotherapy, contributing to suppress ALSD.</p>