The cultivation of Echinacea purpurea for commerce and obtaining high-quality plant material on a large scale remain a challenge for growers. Another challenge for the following decades is to create sustainable agriculture that meets society’s needs, has no environmental impact, and reduces the use of fertilizers and pesticides. The aims of this overview were: (1) to present the importance of the chemical compounds reported in E. purpurea; (1) to synthesize results about cultivation of the E. purpurea with arbuscular mycorrhizal fungi (AMF) and associated microorganisms; (2) to exemplify similar research with plants from the Asteraceae family, due to the limited number of published Echinacea studies; (3) to collect recent findings about how the inoculation with AMF affects gene expressions in the host plants; (4) to propose perspective research directions in the cultivation of E. purpurea, in order to increase biomass and economic importance of secondary metabolite production in plants. The AMF inocula used in the Echinacea experiments was mainly Rhizophagus irregularis. The studies found in the selected period (2012–2022), reported the effects of 21 AMFs used as single inocula or as a mixture on growth and secondary metabolites of 17 plant taxa from the Asteraceae family. Secondary metabolite production and growth of the economic plants were affected by mutualistic, symbiotic or parasitic microorganisms via upregulation of the genes involved in hormonal synthesis, glandular hair formation, and in the mevalonate (MVA), methyl erythritol phosphate (MEP) and phenylpropanoid pathways. However, these studies have mostly been carried out under controlled conditions, in greenhouses or in vitro in sterile environments. Since the effect of AMF depends on the variety of field conditions, more research on the application of different AMF (single and in various combinations with bacteria) to plants growing in the field would be necessary. For the identification of the most effective synergistic combinations of AMF and related bacterial populations, transcriptomic and metabolomic investigations might also be useful.

Echinacea purpurea is a widely used medicinal plant valued for its bioactive constituents; however, cultivation presents several challenges (poor and imbalanced germination, slow initial development). Arbuscular mycorrhizal fungi (AMF), especially Rhizophagus irregularis, are known to influence plant growth and metabolite accumulation, yet limited multi-year field data exist. This is the first study that evaluates the effect of R. irregularis inoculation on root biomass, phenolic acid content, essential oil yield and its composition in two-year-old E. purpurea under greenhouse (four substrate types) and open-field conditions. Chicoric acid was the predominant phenolic in all samples. Significant substrate- and environment-dependent effects were found for other compounds: AMF-treated plants showed increased caftaric (2.87-fold) and caffeic (2.15-fold) acid levels on sterile peat and elevated cynarin (2.13-fold) under field conditions, but decreased caffeic acid (3.39-fold) and echinacoside (1.98-fold) on gleyic calcaric Fluvisol. On stagnic Luvisol and gleyic calcaric Fluvisol, treated plants showed a higher proportion of oxygenated sesquiterpenes in oil composition, while controls contained fatty acids along with sesquiterpene hydrocarbons. A negative correlation was found between AMF colonization rate and both phenolic content and essential oil yield under open-field conditions. The results suggest that the effects of R. irregularis are strongly influenced by substrate type and environmental conditions, indicating the need for further research.

Production of health-promoting substances in plants’ metabolism may be modulated by treatment with chemical stress factors and natural bioactive compounds, which enhance stress tolerance through stimulation of biosynthesis of several protective metabolites. The aim of this work is to reveal metabolic interactions between high salinity stress (exerted by the presence of 100 mM NaCl in the mineral nutrient solution) and treatment of plants with 0.1 mM S-methylmethionine (also known as vitamin U). This plant-derived bioactive compound enhances the production of antioxidants such as carotenoids, ascorbate and other phenoloids in leaves of rocket plantlets exposed to salt stress, while reducing the concentration of toxic malondialdehyde and related catabolic products of membrane lipid peroxidation. Thus, a suitable combination of high salinity and plant hardening with S-methylmethionine may improve the quality of fresh rocket leaves upon human and animal consumption.