Fusarium Community Composition and Co-Occurrence with Other Fungi and Bacteria in Finnish Oat Crop

Fusarium species are major contributors to Fusarium head blight (FHB) and mycotoxin contamination in cereal production. To characterize microbial co-occurrence associated with toxin accumulation in oats, the Fusarium , fungal, and bacterial communities of 51 Finnish oat grain samples were analyzed using a multi-marker metabarcoding approach targeting Fusarium translation elongation factor 1‑alpha (EF1α), fungal ITS2, and bacterial 16 S regions. Microbial profiles were compared between grains with high and low deoxynivalenol (DON) concentrations. High‑DON samples were dominated by F. graminearum , whereas F. langsethiae prevailed in low‑DON grains. Bacterial diversity was higher in high‑DON samples, while fungal diversity remained similar across groups. Several bacterial genera, including Pseudomonas , Paenibacillus , Massilia , and Curtobacterium , exhibited negative correlations with Fusarium species, indicating competition in the same niche, whereas Duganella and Xylophilus showed positive association with Fusarium abundance. Microdochium consistently co-occurred with Fusarium . Results show differences in microbial communities associated with mycotoxin levels and Fusarium community composition, identifying taxa that may influence FHB or indicate mycotoxin risk.