IsXylella fastidiosaa serious threat to European forests?

Abstract

The recent emergence of Olive Quick Decline Syndrome in Italy, caused by Xylella fastidiosa, has drawn attention to the risks posed by this vector-borne bacterium to important crops in Europe (especially fruit trees and grapevine). Comparatively very little is known on actual and potential impacts of this pathogen in forests, in the native (North American) and introduced (European) regions, respectively. The present review aims to address important questions related to the threat posed by X. fastidiosa to European forests, such as the following: What are the symptoms, hosts and impact of bacterial leaf scorch caused by X. fastidiosa on trees in North America? Which forest tree species have been found infected in the introduction area in Europe? How does X. fastidiosa cause disease in susceptible hosts? Are there any X. fastidiosa genotypes (subspecies and sequence types) specifically associated with forest trees? How is X. fastidiosa transmitted? What are the known and potential vectors for forest trees? How does vector ecology affect disease? Is the distribution of X. fastidiosa, especially the strains associated with trees, restricted by climatic factors? Is disease risk for trees different in forest ecosystems as compared with urban settings? We conclude by pointing to important knowledge gaps related to all these questions and strongly advocate for more research about the Xylella-forest pathosystems, in both North America and Europe.

Xylella fastidiosa in Europe: From the Introduction to the Current Status

“…Aimed to determining the possibility of vector transmission In France, after the first discovery of X. fastidiosa in Corsica on P. myrtifolia plants, the bacterium was also found in mainland regions. Analyses involving 45,000 samples of different plant species revealed presence of this bacterium in approximately 3% of plant material taken from 49 plant species, including mainly ornamental plants and shrubs, but also several forest species, such as Acer pseudoplatanus, P. avium, Quercus suber, and Q. ilex (Desprez-Loustau et al, 2021). In France, 72 X. fastidiosa host plants are currently identified-including P. myrtifolia, rosemary, lavender, as well as olive and almond-which are typical for this region, but also Afghan lavender and Jerusalem sage (European Food Safety Authority et al, 2022b).…”

“…According to Markheiser et al (2020) , cherry and grapevine may be seriously threatened by the further spread of this pathogen in Europe. Among woody and forest species in Europe, natural infections have been recorded on plants from the genera Acer ( A. pseudoplatanus ), Ficus ( F. carica ), Fraxinus ( F. angustifolia ), Juglans ( J. regia ), Olea ( O. europaea ), Prunus ( P. avium , P. cerasifera ), and Quercus ( Q. ilex , Q. suber ) ( Desprez-Loustau et al, 2021 ). Symptoms caused on the economically important plant species such as grapevine, citrus, peach, coffee, olive, plum, and sweet orange were described by Baldi and La Porta (2017) .…”

Drivers of Forest Pathogen Invasions

“…Some affected plants that are widely planted in Europe, such as A. platanoides L. and Q. rubra, have not yet been confirmed to be infected. Xylella fastidiosa is currently restricted to Mediterranean Europe, where these species are uncommon (Desprez-Loustau et al 2021). A current notable problem of relevance to south-eastern Europe and beyond is that of 'olive quick decline syndrome' occurring in olive groves in Apulia, Southern Italy (Elbeaino et al 2014, Loconsole et al 2014.…”

Insect‐plant‐fungus interactions in mycorrhizal associations, with a focus on spittlebugs and ectomycorrhizal host plants

“…have tested positive for X. fastidiosa in the Eastern United States (refs. in Thompson et al, 2020), but positive tests in Europe are few (Desprez‐Loustau et al, 2021). Pines do not appear to host X. fastidiosa , perhaps because their specialised xylem vessels render them immune or resistant (Desprez‐Loustau et al, 2021).…”

“…in Thompson et al, 2020), but positive tests in Europe are few (Desprez‐Loustau et al, 2021). Pines do not appear to host X. fastidiosa , perhaps because their specialised xylem vessels render them immune or resistant (Desprez‐Loustau et al, 2021). In the Eastern United States, spittlebugs have experimentally transmitted X. fastidiosa to C. illinoinensis (Sanderlin & Melanson, 2010) and have been implicated in transmission to Quercus spp.…”