# First Report of Ophiostoma clavatum and Fusarium verticillioides Associated With Ips acuminatus‐Infested Scots Pine in Western Ukraine

## TL;DR

This study reports new fungal species linked to bark beetles in Ukraine, which may be contributing to the decline of pine trees.

## Contribution

The first record of Ophiostoma clavatum with Ips acuminatus in Ukraine and the first evidence of Fusarium verticillioides co-occurring with ophiostomatoid fungi in infested pines.

## Key findings

- Ophiostoma clavatum was identified as a weak phytopathogen causing localized lesions in pine trees.
- Fusarium verticillioides induced severe necrosis and tissue maceration on pine seedlings.
- Fusarium verticillioides showed strong competitive dominance over Ophiostoma clavatum in dual culture.

## Abstract

Over the past two decades, dieback of
Pinus sylvestris
L. stands has increased across Europe, largely due to mass outbreaks of the bark beetle, in particular, Ips acuminatus Gyll. (Coleoptera: Curculionidae). This beetle causes mechanical damage and vectors pathogenic fungi, including ophiostomatoid species that induce blue stain. Ophiostoma clavatum Math.‐Käärik is the most frequently reported fungal associate, yet its occurrence has not been documented in Ukraine. While ophiostomatoid fungi are well studied in pine pathogenesis, the role of fast‐growing co‐occurring associates such as Fusarium spp. remains poorly understood. This study aimed to identify the dominant Ophiostoma and Fusarium species associated with
I. acuminatus
in western Ukraine and to evaluate their pathogenicity and in vitro interactions. Isolates from surface‐sterilized beetle abdomens and blue‐stained wood were identified as O. clavatum based on morphology and multi‐locus molecular markers (ITS, TUB, TEF1‐α). Pathogenicity tests showed that O. clavatum acts as a weak phytopathogen, primarily inducing localized lesions. The dominant Fusarium morphotype from blue‐stained wood was identified as Fusarium verticillioides (Sac) Nirenberg, which induced severe necrosis and tissue maceration on pine seedlings. In dual culture, F. verticillioides displayed strong asymmetric competitive dominance over O. clavatum, reducing its growth by more than 45%. This study provides the first record of O. clavatum associated with
I. acuminatus
in Ukraine, extending its known European distribution. The observed pathogenicity and competitive ability of F. verticillioides suggest it may synergistically contribute to Scots pine decline, warranting further investigation into its role within the beetle–fungus complex.

This study provides the first record of Ophiostoma clavatum associated with Ips acuminatus in Ukraine, and the first evidence of Fusarium verticillioides coexisting with ophiostomatoid fungi in infested Scots pines. This fungal association may contribute to the decline of Scots pine stands.