Editorial - May 2013: Tracking the advance of devastating diseases of trees and shrubs

The discovery of ash dieback (Chalara fraxinea) in several parts of the UK in 2012 prompted debate about the circumstances surrounding its arrival but also focused attention more generally on the state of plant pathology and biosecurity in the UK and EU. The British Society for Plant Pathology (BSPP) had already been producing evidence of the decline of human resources involved in plant pathology (http://www.bspp.org.uk/news.php?id=54). This helped politicians focus on the importance of a topic on which they had already been briefed (Wentworth, 2011)). As a resource for this debate, a Virtual Issue* of Plant Pathology has appeared with new and reprinted articles on relevant topics. This Editorial’s contribution focuses on New Disease Reports (NDR) on emerging or spreading diseases of trees and bushes. The emphasis is on Europe with limited attention paid to reports from other parts of the world.

The benchmark for present purposes is the review by Brasier (2008), in which pathogens already known to science (Brasier’s Table 2) are distinguished from those new to science when the disease was first described (Brasier’s Table 1). Table I of this editorial records Phytophthora species (Oomycetes) and Table II fungal, bacterial and viral pathogens, respectively, in relation to this benchmark. The most salient features of Table I are the diseases caused by P. ramorum on many different hosts in UK and the Balkans. Equally significant, however, are the 12 species of Phytophthora not included in Brasier (2008). Some of these species are characteristic of warmer climates (P. boehmeriae and P. palmivora reported from South America) but of potential significance in Europe. Olive which is grown commercially in SW England has already been reported to be affected by the introduced olive leaf-spot pathogen, Pseudocercospora cladosporioides (Henricot et al., 2009). Not surprisingly given that NDR is a journal of choice for these purposes, many of these reports were first reports for the country and/or host in question.

Table II records 11 species of fungal pathogens, two bacterial pathogens and one virus of trees or bushes from the archives of NDR. This includes, for the UK, ash dieback (Bakys et al., 2009), bleeding canker of horse chestnut (Pseudomonas syringae pv. aesuculi; Steele et al., 2010) and (sweet) chestnut blight (Cryphonectria parasitica). Pathogens featuring in Brasier (2008) not reported in NDR are Discula destructiva on dogwood (Cornus spp.) and fireblight of pome trees (Erwinia amylovora) but both these introductions pre-date the start of NDR as part of Plant Pathology in 2000. Erysiphe platani is present in UK (not reported in NDR).

NDR does not claim to be the only internationally recognised outlet for reporting new and emerging plant diseases nor does it claim comprehensive coverage. For example, EPPO Reporting Service is of particular interest, indexing a wide range of publications including NDR. However, NDR has utility as a resource for risk assessment and horizon scanning, especially given the changing distribution of pests and host plants (cultivated or not) due to climate change. For the UK and NW Europe, (more) diseases of olive and blueberry and bilberry (Vaccinium spp.) may be on the horizon as well as Thielaviopsis populi on poplar (Table II). A pathogen covered in the special Plant Pathology issue to look out for is Phytophthora obscura (Grünwald et al., 2012). To reflect the need for more focused information on disease distribution, NDR has introduced ‘Follow-up Reports’ (http://ndrs.org.uk/article.php?id=027002) so that spread or indeed eradication may be recorded.

*Available at http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-3059/homepage/virtual_issue_-_emerging_diseases_of_trees_and_their_management.htm