Fungi associated with dieback of Abies alba seedlings in naturally regenerating forest ecosystems

Dieback of young Abies alba seedlings was identified as an important limitation for natural regeneration of this species in the mountain regions of Central Europe. Approximately 2-4 weeks after emergence, during cool and wet weather, necrotic spots developed on seedling cotyledons. Later they expanded and merged to finally cover all above-ground tissues. Symptomatic seedlings of A. alba were sampled at 16 stands, and fungi were isolated from the cotyledons, stems, and roots. Morphological and molecular methods based on ITS rDNA sequencing were then used for isolate identification. In total, 105 distinct taxa were identified, with Ascomycota dominating, representing 97.4% of the isolates. The most frequently isolated taxa were Allantophomopsis lycopodina, Gyoerffyella rotula, Leptosphaeria sp., Phialocephala fortinii, Pseudaegerita sp., Scirrhia aspidiorum, Sydowia polyspora, Peyronellaea sp., Phomopsis sp., and Varicosporium elodeae. The frequency of colonization by individual fungal species differed among the three plant organs and among forest types. In symptomatic cotyledons, the dominant species were G. rotula, S. polyspora, and Pseudaegerita sp. whose pathogenicity, together with that of Gyoerffyella sp., V. elodeae, and Hormonema carpetanum, was tested on young A. alba seedlings. Only G. rotula and Gyoerffyella sp. caused serious dieback of above-ground seedling tissues and necrotic symptoms on cotyledons. This study is one of the few comprehensive reports showing that aquatic hyphomycetes commonly occur in forests beyond their preferred habitat.