First report of Pleuroceras pseudoplatani on Acer rubrum, A. griseum, A. saccharinum, A. negundo, A. circinatum and A. macrophyllum in Scotland

In September 2016, large necrotic lesions were observed on the foliage of several maples in Aberdeenshire, Scotland. Symptoms resembled giant leaf blotch disease caused by Pleuroceras pseudoplatani (formerly Gnomonia pseudoplatani; Ophiognomia pseudoplatani) on sycamore maple (Acer pseudoplatanus), a common disease in Europe. Other than A. pseudoplatanus, no other Acer species have previously been reported as hosts for this pathogen. Symptomatic leaves were collected from Acer rubrum, A. rubrum var. Somerset, A. griseum, A. saccharinum, A. negundo, A. macrophyllum, and A. circinatum, and the known host of P. pseudoplatani, A. pseudoplatanus. Next generation sequencing was used to determine presence of the suspected P. pseudoplatani and other associated fungi in symptomatic leaves. P. pseudoplatani was predominant in all symptomatic samples with 99-100% identity with reference ITS sequences of P. pseudoplatani deposited in GenBank (NCBI). This is the first report of P. pseudoplatani associated with leaf blotch on Acer species other than A. pseudoplatanus. The newly reported damage on North American Acer species may be of particular concern because of the economic importance of maples for timber products, syrup production and as ornamental trees in urban landscapes. Precautions should be taken to limit trade of plants from infested areas in Europe.