First reports of Pseudodidymella fagi and Petrakia deviata in Europe
Two unusual tree pathogens associated with leaf blotch symptoms have recently been reported for the first time in Europe. Pseudodidymella fagi has been found on Fagus sylvatica in Switzerland and Germany. Leaves of F. sylvatica showing brown to dark-brown necrotic leaf spots were observed for the first time near Zurich in 2008. Similar symptoms were then observed on numerous sites in Switzerland, as well as in several localities in Southern Germany, including one case on F. orientalis in the botanical garden of Munich. Ps. fagi was described in 1997 as a pathogen causing leaf blotch on F. crenata in Japan, and until these records in Europe, it was only known to occur in Japan. The pathogenicity of Ps. fagi was tested on F. sylvatica by inoculation on detached leaves in vitro and Koch’s postulates were fulfilled. The other species which is reported in Europe for the first time is Petrakia deviata which causes a leaf blotch disease on Acer campestre. There was an old record from the central Caucasus region in 1929, but the fungus has never been found again there. In Switzerland, P. deviata was found in 2 locations on A. campestre and A. platanoides. It is noted that compared to Ps. fagi, P. deviata was rarely found and caused a rather weak infection, suggesting that it has probably only a minor impact on tree vigour. The identity of both fungus species has been confirmed by morphological and molecular methods. It is not known whether these two species have simply been overlooked, favoured by climate change, altered management practices, or represent newly introduced and invasive species. Finally, phylogenetic analyses have revealed a close relationship between Ps. fagi and P. deviata. In subsequent taxonomic studies, it has been proposed that both the genus Petrakia and the genus Pseudodidymella should be placed in a new family called Pseudodidymellaceae fam. nov.
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Gross A, Beenken L, Dubach V, Queloz V, Tanaka K, Hashimoto A, Holdenrieder O (2017) Pseudodidymella fagi and Petrakia deviata: two closely related tree pathogens new to central Europe. Forest Pathology 00:e12351. https://doi.org/10.1111/efp.12351
Hashimoto A, Matsumura M, Hirayama K, Fujimoto R, Tanaka K (2017) Pseudodidymellaceae fam. nov.: phylogenetic affiliations of mycopappus-like genera in Dothideomycetes. Studies in Mycology (in press). http://www.sciencedirect.com/science/article/pii/S0166061617300271