Stem Cankers in Urban and Forest Trees: Identification, Impact, and Management

In this study, we report the first identification of Paraconiothyrium brasiliense and Querciphoma minuta causing stem cankers on previously unreported tree host species. P. brasiliense and Q. minuta were isolated for the first time from Carpinus betulus, Fagus sylvatica, and Aesculus hippocastanum. Additionally, P. brasiliense was newly isolated from Ulmus spp. and Platanus × hispanica, while Q. minuta was also found for the first time on Acer platanoides. These trees originate from different cities in Germany, located in different geographical regions. Fungal isolates were initially grouped by morphotyping based on visually recognizable culture characteristics. The taxonomy of these fungi was verified by sequencing with multiple primers, including ITSu1/4, and LSU/LR6. The pathogenicity of each fungus was confirmed using Koch’s postulates on the corresponding host trees. P. brasiliense and Q. minuta are opportunistic pathogens on several plant species, but this is the first report of their pathogenic activity on the corresponding urban trees, confirmed through stem inoculations with fungal agar plugs. This report indicates the emergence of fungal pathogens causing stem necrosis on tree hosts that have not previously been reported.