Fusarium community composition and co-occurrence with other fungi and bacteria in Finnish oat crop. Multi-marker metabarcoding Fusarium EF region, fungal ITS region and bacterial 16S region

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 EF1α, ITS2, and 16S 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, 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 shifts in microbial communities linked to mycotoxins and Fusarium community composition, identifying taxa that may influence FHB or indicate mycotoxin risk.