Improving growth and phenolic compounds of Echinacea purpurea root by integrating biological and chemical resources of phosphorus under water deficit stress

The global viewpoint toward crop production is to increase the quantitative and qualitative yield of medicinal plants through management techniques such as the use of bio-fertilizers and the reduction of chemical fertilizers consumption. Improving the growth and phenolic compounds in E. purpurea root by combining the phosphorous fertilizer with biological resources at different irrigation intervals was the research proposes in this study. A split-plot experiment was performed in a randomized complete block design with three replications. The main plots consisted of soil irrigation at 25, 50, and 75 % of available water depletion (AWD) to retain field capacity moisture. The subplots were six different treatments to supply phosphorus (P) for plant growth (control without P fertilizer, 100 % plant required P from triple super-phosphate, sole application of mycorrhizal arbuscular fungi (AMF) and Pseudomonas fluorescens bacteria (PFB), and AMF or PFB combination with 50 % of the plant's P requirement. Results showed that 75 % of AWD decreased root biomass and increased root cichoric and caftaric acid. The highest root colonization was observed when P fertilizer and AMF were applied together. Complete supply of plant phosphorus from triple superphosphate (100 kg/ha) increased root biomass and echinacoside yield by 57 % and 47 %, respectively compared to control (P < 0.05). Moreover, the use of phosphorus with PFB significantly increased chlorogenic and caftaric acid content by 29 % and 62 %, respectively. In 25 % of AWD, the highest root cynarin (0.583 mg/g dry matter) was observed in the joint application of phosphorus + AMF. Root colonization with beneficial soil microorganisms partially increased drought stress tolerance in E. purpurea through root development. The incorporation of chemical P with bio-fertilizers also played a vital role in the synthesis of secondary compounds in E. purpurea.