Massaria Disease: Identify the Fungus

Identify the spores of Splanchnonema platani and diagnose Massaria disease

S. platani sporesPlane trees (Platanus x hispanica) in Britain are suffering from Massaria disease, which causes large lesions on tree branches. The fungus Splanchnonema platani (formerly called Massaria platani) has been found in association with these lesions and may be the primary cause of the disease.

  • Characteristic brown, multi-septate pycnidiospores are 40-50 μm long x 12.5 to 17.5 μm wide
  • Characteristic ascospores are 67-75 x 17.5 to 20μm

In Europe the fungus seems to produce an abundant number of spores on the surface of the bark or cambium (the layer beneath the bark) that surrounds the lesion. These European spores are easily seen under the microscope. Spores on UK lesions were more difficult to find until recently (2013-)  since when we have seen a number of samples in the Autumn/ winter with abundant sporulation. In 2011 Forest Research isolated spores from lesions taken from trees in London and Bristol; sequencing ribosomal DNA confirmed at least some of the spores to be S. platani. During this molecular analysis other fungi – such as common basidiomycete decay fungi - were also found. This suggests that several fungi have played a role in the extensive decay associated with the lesions.

S. platani is usually considered to be a weak parasite that only causes minor damage - such as twig dieback - in warmer Mediterranean climates. It has not previously caused any major problems in the UK.