Abstract
Introduction of and invasion by alien plant pathogens represents the main cause of emerging infectious diseases affecting domesticated and wild plant species worldwide. The trade in living plants is the most common pathway of introduction. Many of the alien tree pathogens recently introduced into Europe were not previously included on any quarantine lists. To help determine the potential risk of pest introduction through trading of ornamental plants, a sentinel nursery was established in Beijing, China in 2008. The sentinel nursery planting included four of the most common ornamental woody species shipped to Europe including Ilex cornuta var. fortunae, Zelkova schneideriana, Fraxinus chinensis and Buxus microphylla. Symptoms developing on these species within the sentinel nursery were detected in 2013 and consisted of necrotic spots on leaves, canker and stem necrosis, shoot blight and shoot necrosis. Fungi associated with the trees and their symptoms included Alternaria alternata detected from all hosts; Diaporthe liquidambaris and Diaporthe capsici from bark and leaf necrosis of Zelkova schneideriana; Botryosphaeria dothidea and Nothophoma quercina from stem cankers on Fraxinus chinensis and leaf necrosis on Ilex cornuta; and Pseudonectria foliicola from leaf necrosis on Buxus microphylla. Next generation sequencing analysis from asymptomatic tissues detected eighteen OTU’s at species level among which some taxa had not been previously recorded in Europe. These results clearly demonstrate that looking at trees of internationally traded species in the region of origin can reveal the presence of potentially harmful organisms of major forestry, landscape or crop trees. Results of this study also provide an indication as to how some disease agents can be introduced using pathways other than the co-generic hosts. Hence, sentinel nurseries represent one potential mechanism to address the current lack of knowledge about pests in the countries from where live plants are shipped and the threats they represent to native flora and crops in importing countries.
Highlights
Introduction and invasion by alien plant pathogens represent the main cause of emerging infectious diseases (EIDs) affecting domesticated and wild plant species worldwide [1]
The ash fungal pathogen H. fraxineus was known to be non-pathogenic in its native range, Far East Asia, but its introduction into Europe has led to widespread dieback of the native European ash species Fraxinus excelsior and Fraxinus angustifolia, with which it had not co-evolved [8]
Four woody plants species were selected among the live plants commonly imported from China to Europe at the beginning of the experiments: Ilex cornuta var. fortunei (Lindl.) S.Y.Hu, Buxus microphylla Siebold & Zucc, Fraxinus chinensis Roxb. and Zelkova schneideriana Hand.-Mazz
Summary
Introduction and invasion by alien plant pathogens represent the main cause of emerging infectious diseases (EIDs) affecting domesticated and wild plant species worldwide [1]. Of the more than 125 taxa listed in the European Database of the Invasive Forest Pathogens (IFPs) (https://www.eustafor.eu/eu-projects/isefor/), including fungi and oomycetes, 54 (43%) are believed to have been introduced through trading of exotic living hosts. Most recent examples are sudden oak death caused by Phytophthora ramorum both in Europe and in USA [3]; alder decline caused by Phytophthora alni; ash dieback caused by Hymenoscyphus fraxineus [4] and root and butt rot of conifers caused by Heterobasidion irregulare in Europe [5] Most of these pathogens become invasive as the result of novel host—pathogen interactions, which often involve a new host species (host jump) or different populations of the same host. The above examples highlight the difficulty in predicting and preventing the spread of EIDs caused by alien invasive plant pathogens (AIPP)
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