To
assess the in vitro activity of five naturally occurring phenolic
compounds (ferulic acid, apocynin, magnolol, honokiol, and thymol)
on mycelial growth and type B trichothecene mycotoxin accumulation
by Fusarium graminearum, three complementary
approaches were adopted. First, a high-throughput photometric continuous
reading array allowed a parallel quantification of F. graminearum hyphal growth and reporter TRI5 gene expression directly on solid medium. Second, RT-qPCR
confirmed the regulation of TRI5 expression by the
tested compounds. Third, liquid chromatography–tandem mass
spectrometry analysis allowed quantification of deoxynivalenol (DON)
and its acetylated forms released upon treatment with the phenolic
compounds. Altogether, the results confirmed the activity of thymol
and an equimolar mixture of thymol–magnolol at 0.5 mM, respectively,
in inhibiting DON production without affecting vegetative growth.
The medium pH buffering capacity after 72–96 h of incubation
is proposed as a further element to highlight compounds displaying
trichothecene inhibitory capacity with no significant fungicidal effect.