The fungus Pseudodidymella fagi
is spreading in Europe and causing leaf blotch of European beech, Fagus sylvatica
. Between 2008 and 2017, outbreaks of P. fagi
were observed on European beech in Switzerland, Germany (also on F. orientalis
), Austria, and Slovakia. In Slovenia, leaf blotch symptoms were first observed on F. sylvatica
in 2018. P. fagi
was identified as the causal agent of the observed symptoms in Slovenia by morphological examinations together with sequencing of the internal transcribed spacer (ITS) region of the rDNA. This study links the fungus to the expansion of the known distribution of the disease to Slovenia, and based on in vitro pathogenicity trials, also to a new potential host, Quercus petraea.
The pathogenicity tests confirmed F. sylvatica
and F. orientalis
as hosts for P. fagi
, but not Castanea sativa
, where pathogenicity to F. orientalis
was proved for first time in vitro. Although Koch’s postulates could not be proven for C. sativa
, it seems to be partially susceptible in vitro because some of the inoculation points developed lesions. Additionally, damage to Carpinus betulus
related to P. fagi
near heavily infected beech trees was observed in vivo but was not tested in laboratory trials. Based on the results and our observations in the field, it is likely that P. fagi
has a wider host range than previously thought and that we might be witnessing host switching.
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