Fungi as potential factors limiting natural regeneration of pedunculate oak (Quercus robur) in mixed‐species forest stands in Poland

Abstract

AbstractDieback of youngQuercus roburseedlings can limit natural regeneration in mixed‐species forest stands in Poland. The aim of this study was to examine the role of fungi in the dieback of oak seedlings in central Europe. Fungi were isolated from the stems and roots ofQ.robur, from both healthy seedlings and seedlings with symptoms, that were sampled from four stands in Poland. In total, 111 distinct taxa were identified. Ascomycota was dominant, representing 95.6% of the isolates. Among the taxa identified,Alternaria alternata,Colletotrichum fioriniae,Colletotrichumgodetiae,Coniella quercicola,Diaporthe eres,Gnomoniopsis paraclavulata,Ilyonectria rufa,Mucor genevensis,Penicillium glandicola,Tubakia dryina, andUmbelopsis changbaiensiswere most frequently isolated, and were consistently found in stems and roots of both healthy and diseased plants. The community compositions of fungi in healthy and diseased stems were similar, althoughFusariumspecies, especiallyFusariumsp. 1 (FTSC 5) andF.sporotrichioides, were found mainly in seedlings with symptoms. The pathogenicity of the most consistently isolated species from stems and roots of diseased seedlings was tested onQ.roburseedlings.F.sporotrichioidescaused the largest lesions on inoculated seedlings. Six weeks after inoculation,D.eres,C.fioriniae,G.paraclavulata,T.dryina, andF.sporotrichioideskilled 0%–18.8% of seedlings, whileI.rufaandIlyonectriapseudodestructansdid not cause any lesions or other symptoms. This study is the first comprehensive report suggesting that massive fungal attack can lead to oak seedling dieback in mixed‐species forest stands in central Europe.