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.
Yusypovych et al. (Wed,) studied this question.
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