First Report of Cryphonectria carpinicola in Croatia

Cryphonectria carpinicola, the most recently described species in the genus Cryphonectria, is gaining research interest due to its involvement in common hornbeam (Carpinus betulus) decline. So far, no symptoms of hornbeam decline have been observed in Croatian forests. However, following a chance observation of a Cryphonectria-like stromata on the bark of a dead hornbeam branch, we conducted a targeted sampling campaign to verify the presence of C. carpinicola, determine its distribution and assess its potential impact on the host. We confirmed the presence of C. carpinicola in four out of five sampled populations and isolated pure cultures from 28 out of 53 sampled trees, making it the largest collection of C. carpinicola in Europe to date. The population network analysis inferred from nucleotide sequences of C. carpinicola ITS region, including this and previous research, has grouped them all in a single cluster with only a few isolates differing by a single nucleotide polymorphism. The isolation of C. carpinicola was possible only from bark samples with visible sporulation. The majority (24) of C. carpinicola isolates were obtained from dead stems or branches. However, in two different populations, we isolated the fungus from branches on four living trees that had died off distally to the area of the observed fungal sporulation, suggesting the fungus to be at least a weak pathogen on susceptible hornbeam trees.