Physiological and biochemical response of Echinacea purpurea to combined application of biofertilizers and salicylic acid under different irrigation regimes in saline conditions

Ameliorating resources (AR), by creating a balance in physiological and biochemical traits, play a key role in regulating signaling pathways and inducing tolerance to environmental stresses. This study was conducted as a factorial experiment based on a randomized complete block design during the 2022 and 2023 growing seasons, with two harvests of Echinacea purpurea . The main factor consisted of three irrigation regimes applied after 25, 50, and 75 % available water depletion (AWD) from field capacity, and the sub-factor included eight levels of AR: control, sole application of arbuscular mycorrhiza fungus (AMF), Pseudomonas fluorescens bacteria (PF), salicylic acid (SA), and their various dual and triple combinations. The results showed that ion leakage and the activities of catalase and peroxidase enzymes increased significantly under 75 % AWD. Moreover, the combined application of AMF + PF + SA reduced malondialdehyde content by 26 % and 25 % compared with the control under 50 and 75 % AWD, respectively. The combined treatment of AMF + PF + SA produced the highest chlorogenic acid content, reaching 0.802 mg g - ¹ dry weight, and resulted in an 18 % increase in cichoric acid compared with the control. Under 50 % AWD, cynarin content increased by 18 % in the combined treatment compared with the control. Furthermore, the triple combined treatment enhanced biological yield by 15 % at the first harvest and by 13 % at the second harvest relative to the control. The highest biological yield was obtained under the 25 % AWD, reaching 277.8 kg ha - ¹ at the first harvest and 655.0 kg ha - ¹ at the second harvest. Overall, due to the positive effects of the combined treatment on the physiological and biochemical traits of Echinacea purpurea , this treatment can be recommended under conditions of simultaneous drought and salinity stress. • A field experiment was conducted during two consecutive years (2022 and 2023) with Echinacea purpurea . • The main factor was irrigation regimes included 25, 50, and 75 % available water depletion (AWD) and the subfactor consisted of AR in eight levels including control, arbuscular mycorrhiza fungus (AMF), Pseudomonas fluorescens bacteria (PF), salicylic acid (SA), AMF + PF, AMF + SA, PF + SA and AMF + PF + SA. • Results showed that due to the regulation of physiological and biochemical traits in Echinacea purpurea , the combination of AMF + PF + SA can be recommended under salt stress conditions.