New plant disease outbreaks and a woolly diagnosis

26 Jul 2016

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It is far from easy to keep track of major disease outbreaks. Leading UK-based newspapers and their websites (especially The Guardian and the Economist) do a creditable job, but tend to focus internationally on diseases that signal the ‘end of chocolate’ or some other major recognizable commodity that is deemed newsworthy. There was a recent spate of articles on Fusarium wilt of bananas following fears about the spread of Tropical Race 4. Fortunately bananas have yet to disappear from the shops.

National reporting of plant diseases has been dominated in recent years by tree diseases, particularly following the discovery of ash dieback. I sometimes reflect that my career would have taken a different path if this irruption had occurred back in the 1980s, when I finished my PhD on a bacterial canker or gall disease. As a budding tree pathologist I willed Pseudomonas savastanoi to be serious enough to warrant a post-doc, or at least qualify me uniquely for some other major ash disease. This perverse but whispered wish was not to be.

Ash dieback continues to garner a lot of attention while Phytophthora ramorum has become mere background noise, even though the removal of millions of larch trees is having a dramatic impact in many parts of the UK. One report I’ve just seen said that six million infected larch have been removed in Wales. A Forestry Commission map from 2013 shows zones at risk the length and breadth of Britain and the most recent update I've found shows where the disease has got to. No, I didn't know this either until I looked more carefully on the web. We all rely heavily on mass media to tell us what is going on. Farmers Weekly does a good job in raising awareness of plant diseases (and pests) in the UK, with tweets on the BSPP home page to remind you what’s happening. The UK Plant Health Risk Register is a treasure trove of information though the homepage lacks any photos and is rather dull. The European Plant Protection Organisation issues regular alerts, and has one of the most attractive plant health logos around. The homepage is otherwise uninspiring.

From a plant pathology point of view, the star of the media show is for me a relatively little known service provided by the International Society for Infectious Diseases (shouldn’t that be 'against'?), known as Pro-Med Mail. The homepage doesn’t win any design awards either, but click on the plant tab and you get a wonderful snapshop of diseases around the world. OK, so it’s just a list of hyperlinked disease reports. But look at the diversity and regularity of reports!

Each disease alert is sent as an email, in which the inestimable (and unpaid) Dagmar Hanold at the University of Adelaide, provides a succinct summary of the latest outbreak. Her short paragraphs beneath the original report are a wonderful example of how to condense up to date information on a pathogen and host, including comments on control methods.

On the 21 July I read about an 'undiagnosed potato disease' in Turkey. Alarm bells might have started to ring and even PCR machines switched on ready for the latest molecular insights on a new pathogen. Any perverse, plant pathological hopes for a new disease were quickly dampened, however, when the original report from the Fresh Plaza website was analysed. The report said that downy mildew had broken out in Nigde Province in Central Anatolia. Except there is no recorded downy mildew on potato. It doesn’t take a lot of analysis to suggest that what journalists saw was fluffy, grey growth on leaves due to late blight. Downy mildew? A woolly diagnosis.