Background: Fusarium head blight (FHB) is a serious fungal disease of crop plants due to substantial yield reduction and production of mycotoxins in the infected grains. The breeding progress in increasing resistance with maintaining a high yield is not possible without a thorough examination of the molecular basis of plant immunity responses; Methods: LC-MS based metabolomics approaches powered by three-way ANOVA and differentially accumulated metabolites (DAMs) selection, correlation network and functional enrichment were conducted on grains of resistant and susceptible to FHB genotypes of barley and wheat as well as model grass Brachypodium distachyon (Bd) still poorly known at metabolomic level; Results: We selected common and genotype-specific DAMs in response to F. culmorum inoculation. Immunological reaction at metabolomic level was strongly diversified between resistant and susceptible genotypes. DAMs common for all tested species from porphyrins, flavonoids and phenylpropanoids metabolic pathways were highly correlated and reflects conservativeness in FHB response in Poaceae family. Resistant related DAMs belonged to different structural classes including tryptophan derived metabolites, pirimidines, amino acids proline and serine as well as phenylpropanoids and flavonoids. Physiological response to F. culmorum of Bd was close to barley and wheat genotypes however, metabolomic changes were strongly diversified. Conclusions: Combined targeted and untargeted metabolomics provides comprehensive knowledge about significant elements of plant immunity with potential of being molecular biomarkers of enhance resistance to FHB in grass family. Thorough examination of Bd21 metabolome in juxtaposition with barley and wheat diversified genotypes facilitate their setting as model grass for plant-microbe interaction.