Natural and Urban Forest Viromes and the Tree-Associated Microbiome: Composition, Properties, and Interactions

Dear Colleagues,

Recent insights on viral abundance in forest tree holobionts—which had previously only been explored to a limited extent­—has been driven by the rapid rise of metagenomics. The total diversity of viruses in forests now includes more than 120 identified species, at least twice the number known a decade ago. These viruses have a wide range of hosts: they are found on trees as plant pathogens or can be harboured by all tree-associated organisms, including pathogenic fungi, mutualistic fungi, and saprotrophs, while some others parasitize arthropods. A high occurrence of cross-kingdom transmission events between fungi, oomycetes, plants, and arthropods has also been clearly shown.

What is the impact of the newly defined forest virome on forest health? How can information on the health and vitality of forest ecosystems enable the assessment of their capacity for resilience? These questions become even more relevant when we consider the many stress factors affecting forests: deforestation, air and soil pollution, forest fires, storms, droughts, and heat waves, recently exacerbated by climate change. Additionally, trees in urban environments face fragmentation and limited root space, soil compaction, and heat and drought stress, making them more susceptible to pathogens. Under these circumstances, the likelihood that these viral pathogens will trigger an emerging infectious disease in forests or urban environments in the future is considerable.

At the same time, forest health relies on the variability of microorganisms interacting with the host tree holobiont; symbiotic microbiota and pathogens are in a constant interplay that influences the host. Through interactions between pathogens, synergistic relationships can develop, which can drastically improve the health of the holobiont. Additionally, changes in the microbiome genome can also lead to genetic variations in the hologenome.

For this Special Issue, we invite the contribution of studies related to the forest virome. Possible topics include, but are not limited to, the following:

• the diversity and evolution of viruses in forest and urban ecosystems;
• the microbiota in natural and urban forests and interactions with the holobiont;
• forest plant protection based on endophytes and biocontrol agents.

We look forward to receiving your contributions.

Best regards,

Dr. Julio J. Diez
Dr. Artemis Rumbou
Guest Editors

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• virome
• plant pathogenic virus
• mycovirus
• biocontrol agent
• microbiota