Fungal Needle Communities and Dothistroma septosporum Occurrence in Pinus sylvestris Stands in Slovakia.

Dothistroma needle blight (DNB), caused by Dothistroma septosporum, is a globally important disease of pines, yet its ecological role within native host systems remains incompletely understood. We combined species-specific quantitative PCR (qPCR) with ITS2 metabarcoding to investigate the occurrence of D. septosporum and associated needle mycobiomes of Pinus sylvestris in natural stands in Slovakia with a pooled non-natural positive-reference group included for comparison. D. septosporum was detected in the Vernár natural stand (11 of 16 samples), where visible DNB symptoms were also observed, and in all samples of the non-natural positive-reference group (15 of 15 samples). The pathogen was not detected in the other three sampled natural stands. Fungal community analyzes revealed significant differences in community composition among sample groups, while alpha diversity patterns showed comparatively minor variation. The most abundant genus across all sites was Lophodermium, whereas Dothistroma was highly abundant only in the non-natural positive-reference group. Co-occurrence network analysis indicated that fungal communities were dominated by positive associations; however, patterns involving Dothistroma primarily reflected the positive-reference group, where the pathogen was highly abundant. Our results suggest that D. septosporum is not a consistently detectable component of needle mycobiomes in native P. sylvestris stands in Slovakia and that its high abundance in the non-natural positive-reference group was associated with a distinct fungal community composition.