Changes induced by vesicular-arbuscular fungus Rhizophagus irregularis in aerial parts of Echinacea purpurea

•Greenhouse and open field experiments were set up with control and treated plants.•Treatment with the AMF R. irregularis had no positive effect on growth parameters.•For some substrates, control plants showed significantly higher phenol content.•Higher essential oil yields were observed for control plants on Stagnic Luvisol.•AMF R. irregularis was not efficient on the used substrates. The majority of studies conducted on Echinacea purpurea regarding elicitor (e.g. arbuscular-mycorrhizal fungi – AMF) induction have been carried out in vitro, using controlled conditions. The application of elicitors had conducted to elevated levels of various secondary metabolites. The aim of this study was to test the competitive ability of Rhizophagus irregularis on different substrates (greenhouse and open field conditions) in the presence of local microorganism communities, in order to induce quantitative and qualitative changes in the active principles of E. purpurea. Greenhouse and open field experiments were conducted with E. purpurea inoculated with R. irregularis and control plants. In the greenhouse experiment three different soil types and sterile peat were used. Dried leaves (foliage) of E. purpurea plants were subjected to HPLC analyses to determine their phenolic compounds. The dried herba was analyzed with GC-MS for volatile oil composition. According to the HPLC analyses six phenolic acids were detected. The two dominant compounds were chicoric and chlorogenic acids. Control plants presented significantly higher values in phenolic content compared to treated plants, on sterile peat and open field Stagnic Luvisol in case of caftaric (with 59 and 48%), chlorogenic (16 and 28%), caffeic (6 and 5%), chicoric acids (51 and 56%), and echinacoside (38 and 61%). AMF colonization rate favored caftaric, chlorogenic, and chicoric acids content on several substrates. The quantitative analyses of the essential oil showed significantly higher yield for potted control plants on Stagnic Luvisol (70%). The qualitative analyses revealed 35 constituents, the most abundant were caryophyllene oxide and germacrene D. According to the PCA analyses the essential oil obtained from treated plants contained γ-cadinene and humulene epoxide-2 in higher proportions, while the essential oil of the control plants was abundant in spatulenol and shyobunol. Observations on AMF effect on root essential oil yield and composition would be of high interest. Further studies with other AMF species