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Trichothecenes are sesquiterpenoid toxins produced by diverse ascomycetes, including <i>Fusarium</i>. The trichothecene analog deoxynivalenol (DON) produced by the Fusarium head blight (FHB) pathogen <i>Fusarium graminearum</i> is a virulence factor on wheat and a major food and feed safety concern. In <i>Fusarium</i>, the trichothecene biosynthetic gene (<i>TRI</i>) cluster consists of 7–14 genes. Most <i>TRI</i> cluster genes are conserved and their specific roles in trichothecene biosynthesis have been determined. An exception is <i>TRI14</i>, which is not required for DON synthesis in vitro but is required for spread of <i>F. graminearum</i> in wheat heads. In the current study, gene expression analyses revealed that TRI14 was highly induced in infected wheat heads. We demonstrated that TRI14 was not only required for <i>F. graminearum</i> spread but also important for initial infection in wheat. Although a prior study did not detect DON in infected seeds, our analyses showed significantly less DON and fungal biomass in <i>TRI14</i>-mutant (designated ∆<i>tri14</i>)-inoculated heads than wild-type-inoculated heads. Gene expression comparison showed that the level of expression of <i>TRI</i> genes was similar in the wheat tissues infected with ∆<i>tri14</i> or the wild type, indicating the reduced toxin levels caused by ∆<i>tri14</i> may be due to less fungal growth. ∆<i>tri14</i> also caused less lesion and grew less in wheat coleoptiles than the wild type. The growth of ∆<i>tri14</i> in carboxymethylcellulose medium was more sensitive to hydrogen peroxide than the wild type. The data suggest that <i>TRI14</i> plays a critical role in <i>F. graminearum</i> growth, and potentially protects the fungus from plant defense compounds.