Viruses in Forest and Urban Trees and Shrubs

Investigations of viruses in forest ecosystems are extremely rare as compared to viruses of the agricultural and horticultural environment and they are far outnumbered by the number of studies focussed on fungal pathogens and pest insects of forest trees. Many well-characterized viruses and viroids are known from different agricultural cultivars, but only a few viruses have been commonly detected in urban and forest trees and shrubs; viroids have not been detected yet. This lack of knowledge misleads to the impression that viral diseases in forest trees are unimportant. However, viruses are probably responsible for far greater economic losses in these hosts than generally recognized because of the insidious nature of the losses since symptoms are often inconspicuous and may therefore go unnoticed.

Studies of virus diseases in tree fruit crops, grape and citrus have shown that in extreme situations causal viruses can eliminate a tree species over a very broad region. Plant viruses can alter host physiology and predisposition leading to diseased and damaged tissues or to reductions in metabolism and yield and therefore play a central role in plant health status. In contrast to other pathogens, viruses cannot be controlled by curative treatments.

A comprehensive understanding of the impact of viruses on forest tree health is therefore an important research focus, starting with their proper characterization at genome level and their association with plant stress and disease. The availability of detection protocols is also a cornerstone in the study of these viruses while a deeper understanding of their biology (host range, symptoms, transmission pathways) is required to develop appropriate prophylactic and control measures when needed to ensure a long-term economic forest stand.

We welcome articles that deal with the identification and the characterization of known and novel viruses (single or as a virome) affecting woody host species. Suitable diagnostic tools for detection of plant viruses infecting these hosts can also be reported. Emphasis is given to viruses and virus complexes that affect host species which are important in forestry or urban greens, but virus diseases and disease complexes of trees and shrub species in general will also be considered. Research reports may also focus on epidemiological issues, for instance the importance of long-lived host species as virus reservoirs, or the effects of viruses on tree health in combination with other biotic (pathobiome) and abiotic stress factors. Moreover, knowledge of viruses affecting pathogens of trees is needed. This includes plant viruses bringing benefits to their hosts. For example, knowledge of mycoviruses will provide understanding of their role in the fungal host and their potential to reduce virulence of the pathogen. Studies providing information about effects of virus infection on wood quality and yield will be of interest to the special issue as well as the report of management strategies and best practices to minimize virus diseases and prevent virus infection.

Dr. Susanne von Bargen
Prof. Dr. Carmen Büttner
Dr. Thierry Candresse
Dr. Risto Jalkanen
Prof. Dr. Sebastien Massart
Dr. Tod Ramsfield
Guest Editors

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