Root exudates as a nutrient source play a significant role in the formation of the rhizosphere bacterial community. The effect of exudates on the development of phytopathogenic fungi and their interactions with the antagonistic microorganisms so far remain largely unexplored. The aim of this study is to estimate the effect of low molecular weight components of root exudates of barley, as a nutrients source, on the development of the phytopathogenic fungus Fusarium culmorum 30, the antagonistic strain Pseudomonas fluorescens 2137 and the interaction between them. The obtained data will clarify the role of the plant in the regulation of the colonization ability of the facultative phytopathogen and in its interaction with the antagonistic strain. The quantitative composition of sugars, organic acids and amino acids in root exudates of sterile barley plants was determined by ultra performance liquid chromatography (UPLC). Using the UPLC, the trophic needs and preferences of these microorganisms were determined as