Publication of report of powdery mildew found on popular garden plant

After submitting my report to the British Society of Plant Pathology in mid-April 2016 it was published this week. The ‘First report of Podosphaera macrospora on Heuchera in the United Kingdom’ can now be found in one of their online journals. New Disease Reports records novel plant disease outbreaks and aims for this information to be useful to plant trade when protecting against infection of host plants in future.

Reports can range from diseases, such as ash dieback, being found in a country for the first time (hugely significant) to a disease found commonly in a country being found on a new host plant (less significant). However, while much of the terminology is useful, leaving no doubt over the identity of a disease, I feel it, like in many specific disciplines, makes the information unobtainable to a general audience.

The report, written with Royal Horticultural Society scientists, logs the first record of a certain species of powdery mildew on the popular garden plant, Heuchera. There are many varieties of Heuchera grown around the world each offering flowers in spring and year round ground cover with leaves often brightly coloured: vibrant greens, greys, purples, oranges, and everything in between. The plant is native to North America and as such this is also the original home of the associated powdery mildew species.

The identification of the fungus was particularly problematic as its microscopic features are almost identical to that of a powdery mildew infecting the plant Saxifraga. This complication is fairly common and one of the main issues behind relying solely on plant host identification or analysis of fungal appearance. Fortunately we were able to discriminate the species via its fungal spores (some small fraction of a mm larger in this species than its sister). This was backed up by the similarity of DNA to additional samples of this powdery mildew species from the Kew Fungarium.

The presence of this fungus in the UK is likely to be due to plant trade; with Heuchera being transported across borders unchecked. This is not uncommon. Our report will allow UK growers of Heuchera to be increasingly vigilant and aware of another potentially harmful disease to their multimillion pound trade.