First Report of Fomitopsis Marianiae as a Causal Agent of Brown Wood Rot in Hazelnut (Corylus Avellana) Worldwide

Abstract

Hazelnut (Corylus avellana L.) is a cornerstone of Türkiye's agricultural economy, accounting for over 60% of global production. In 2022, a wood decay disease was observed in orchards of Samsun Province, affecting 3% (15 of 500) of surveyed trees. Symptoms included branch dieback and canopy chlorosis, while internal inspection revealed extensive brown rot of the xylem. Fungal isolates consistently produced white, fast-growing colonies with clamp connections. Multilocus sequencing of the internal transcribed spacer (ITS), large subunit (LSU) and small subunit (SSU) ribosomal DNA regions, and the partial translation elongation factor 1-alpha (tef1) gene identified the pathogen as Fomitopsis marianiae. Phylogenetic analysis of ITS + tef1 datasets placed the Turkish isolate within the F. marianiae clade. Pathogenicity was confirmed by inoculating 1-year-old hazelnut seedlings, which developed necrotic lesions averaging 3.88 ± 0.22 cm within 3.5 months; the fungus was successfully reisolated, fulfilling Koch's postulates. This study represents the first report of F. marianiae as a pathogen of hazelnut and, more broadly, its first documentation in any agricultural system. These findings identify F. marianiae as an emerging threat to a globally important nut crop and highlight the need for targeted disease surveillance and management strategies. © 2026 Wiley-VCH GmbH. Published by John Wiley & Sons Ltd.