First reports of Cryptostroma corticale causing sooty bark disease in Acer sp. in Canton Geneva, Switzerland.
In June 2014, characteristic symptoms of sooty bark disease were observed on the trunk of an approximately 40-year-old maple tree (Acer sp.) in Canton Geneva, Switzerland. Five other nearby maple trees of identical age displayed similar symptoms on several branches but not on the trunk. Symptoms consisted of bark blistering and shedding, with long and broad black stripes, resulting in thick layers of fungal spores forming blackish stains under the bark. Samples were taken from the dark stains and by coring into the trunk with an increment borer at 1.5 m height. The core cut in 16 equal pieces, 1 cm long, yielded 16 isolates of Cryptostroma corticale only. Bark yielded 53 isolates from 30 samples that resolved into 20 different fungal species. Cryptostroma corticale amounted to 23% of total isolates while the yield of Cytospora chrysosperma [Valsa sordida], a common canker agent of Populus spp. was 15% of total isolates. Plant pathogens often observed in decaying trees, such as Dothiorella iberica, Mucor spp., Phomopsis spp. and Fusarium sp. yielded another 25% altogether. Cryptostroma corticale was present in symptomatic bark and was the only microorganism retrieved from cores taken from the internal wood. This is thought to be the first report of an isolated and identified strain in Switzerland.