Emerging diseases in forest ecosystems:
challenges, prospects and role of NRL
plant diseases
Anne Chandelier
Walloon centre of agronomic research, Life sciences Department, Biology of pest and biovigilance Unit (Centre
wallon de Recherches agronomiques, Département Sciences du Vivant, Unité Biologie des Nuisibles et Biovigilance)
During the past 30 years, emerging diseases have been reported at an increasing rate in forest ecosystems in
Europe. These diseases have economical (loss in value of forest products, loss of employment in the wood sector,
financial loss for nurseries), ecological (loss of biodiversity, dysfunctional ecosystems) and societal (landscape
alteration, disappearance of forest species valued by the public) impacts. The Dutch elm disease, caused by the
fungus Ophiostoma novo-ulmi, the alder disease caused by Phytophthora alni (fig. 1a), the ash dieback caused by
the fungus Hymenoscyphus pseudoalbidus (fig. 1b) or more recently the “Sudden Larch Death” caused by Phytophthora ramorum are some examples of emerging diseases. Two of the causing agents (P. alni and H. pseudoalbidus)
have already caused a lot of damage in forest ecosystems in Belgium.
What is the origin of an emerging disease?
Intensified international trade constitute the main introduction pathway of pathogenic organisms. Plants or parts
of plants (seeds, cutting, living plants for nurseries), wood or wood packaging are potential ‘gateways’ for fungi, insects or nematodes in forests. The role of the public is also not to be put aside, whether by the direct introduction
of plants or seeds brought back in the luggage and escaping border inspection or by the indirect introduction of
pathogenic organisms polluting their cloths or present in soil sticking to their shoes. In parallel, climatic changes
modify temperature and humidity conditions of a region making local host plants more susceptible to infections.
Moreover, changed climatic conditions can also lead to the expansion of the distribution area of a pathogenic
organism.
Although the causes of introduction are known (but sometimes difficult to control), the factors which contribute
to the establishment and subsequent dispersal of a pathogenic exotic agent are hard to control because of the
complexity of invasions. While the directive 2000/29/EC (interceptions of non-conforming products) has shown
to be useful for regulated pathogens, it has no impact on emerging agents because the diseases they cause are
not foreseeable. Moreover, most of the time, they do not cause major plant health problems in their place of
origin (due to the co-evolution of host plants and the pathogenic agent). This means that the emerging organisms escape, at least initially, plant health inspections. Finally, it is also important to notice that emerging diseases
which occur in natural environments are very difficult to control by emergency phytosanitary measures because
they spread rapidly.
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Fig. 1. Symptoms caused by emerging diseases in Belgian forests. A: Alder (Alnus glutinosa) disease caused by Phytophthora alni – symptoms on the trunk and crown dieback; B : ash (Fraxinus excelsior) dieback caused by
Hymenoscyphus pseudoalbidus - symptoms in the wood and crown dieback (photos, A. Chandelier)
How to respond to these new phytosanitary threats?
At the European level, the scientific community is involved in different projects notably FORTHREAT (1) or ISEFOR
(2). Several options are proposed to limit the development of emerging diseases of tree species (Stenlid and al.
2011) (3):
• to intensify monitoring in Europe;
• to introduce Early Warning Systems for pathogenic organisms and especially spore traps (fig. 2);
• to introduce ‘sentinel’ plants (i.e. forest species found in Europe) in different regions of the world to evaluate
their behaviour in new environment;
• to adapt plant health legislation (better implementation of existing norms, reinforcement of phytosanitary
analysis in developing countries from which the plants come from, phytosanitary risk assessment by using
PRA (« Pest Risk Analysis »).
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Fig. 2. Installation of spore traps in forest to monitor airborne inoculum of pathogenic fungi (photo, A. Chandelier)
What does the NRL “plant diseases” do?
In Belgium, the NRL “plant diseases” participates to studies on forest pathogens in several nationally and internationally financed research projects. By its participation to different European meetings dealing with regulated
pathogens (especially meetings of the European and Mediterranean Plant Protection Organisation, EPPO), it
informs regional and federal political authorities about potential new phytosanitary threat to forest environment.
Ultimately, it also advises the FASFC on diseases for which trainings dealing with symptoms identification could be
organised. Moreover, as the reference laboratory of the Walloon Observatory of Forest Health for fungal diseases,
the laboratory of mycology of the CRAW carry out phytosanitary survey in forests and organizes trainings on disease identification for forest managers.
Bibliography:
1.
2.
3.
European network on emerging diseases and threats through invasive alien species in forest ecosystems
(FORTHREATS, FP6, 2007-2009)
Increasing Sustainability of European forests : modelling for security against invasive pests and pathogens
under climate changes (ISEFOR, FP7, 2011-2013)
Stenlid J, Oliva J, Boberg JB, Hopkins AJM (2011). Emerging diseases in European forest ecosystems and
responses in society. Forests 2, 486-504
[email protected]
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