Drought influences the fungal community structure, diversity, and functionality inhabiting the grapevine xylem and enhances the abundance of Phaeomoniella chlamydospora

Grapevine productivity worldwide is increasingly threatened by global warming, potentially exacerbating water scarcity. This study examines drought's effects on grapevine xylem's fungal communities, particularly regarding Phaeomoniella chlamydospora, linked to esca and Petri diseases. Investigating one-year-old grafted grapevines under varied water regimes, including severe, moderate, and no water deficit, the research assesses how drought influences fungal diversity, structure, and interactions within the xylem. Utilizing ITS high-throughput amplicon sequencing and droplet-digital PCR, the study tracks changes in fungal composition and P. chlamydospora prevalence over two growing seasons. The induced water stress not only altered the diversity and composition of the fungal microbiome in the xylem vessels but also affected co-occurrence networks, resulting in less complex networks with fewer correlations between taxa, potentially increasing grapevine vulnerability to various biotic and abiotic stresses. Severe water deficit significantly reduced microbial diversity, leading to a shift in the abundance of pathotrophs such as P. chlamydospora in the xylem. This underscores the interconnectedness between water stress, microbiome dynamics, and plant health. The combination of compromised plant defenses, altered physiological conditions, and shifts in the surrounding microbial community may create conditions conducive to increased P. chlamydospora abundance in the xylem vessels of young vines following water stress.