| Summary: | Oat (<i>Avena sativa</i>) is susceptible to Fusarium head blight (FHB). The quality of oat grain is threatened by the accumulation of mycotoxins, particularly the trichothecene deoxynivalenol (DON), which also acts as a virulence factor for the main pathogen <i>Fusarium graminearum</i>. The plant can defend itself, e.g., by DON detoxification by UGT-glycosyltransferases (UTGs) and accumulation of PR-proteins, even though these mechanisms do not deliver effective levels of resistance. We studied the ability of the fungal biocontrol agent (BCA) <i>Clonostachys rosea</i> to reduce FHB and mycotoxin accumulation. Greenhouse trials showed that <i>C. rosea</i>-inoculation of oat spikelets at anthesis 3 days prior to <i>F. graminearum</i> inoculation reduced both the amount of <i>Fusarium</i> DNA (79%) and DON level (80%) in mature oat kernels substantially. DON applied to <i>C. rosea</i>-treated spikelets resulted in higher conversion of DON to DON-3-Glc than in mock treated plants. Moreover, there was a significant enhancement of expression of two oat UGT-glycosyltransferase genes in <i>C. rosea</i>-treated oat. In addition, <i>C. rosea</i> treatment activated expression of genes encoding four PR-proteins and a WRKY23-like transcription factor, suggesting that <i>C. rosea</i> may induce resistance in oat. Thus, <i>C. rosea</i> IK726 has strong potential to be used as a BCA against FHB in oat as it inhibits <i>F. graminearum</i> infection effectively, whilst detoxifying DON mycotoxin rapidly.
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