Effects of Foliar Application of Salicylic Acid and Spermine on the Growth and Root Morphological Characteristics of Purple Coneflower (Echinacea purpurea L.) Under Drought Stress

In order to study the effects of water deficit and foliar application of salicylic acid and spermine on dry matter production and biochemical and morphological treats of Echinacea purpurea, a split plot experiment was conducted based on randomized complete block design with three replicated during 2016- 2017 growing seasons at research field of Institute of Forests and Rangelands, Iran. In this experiment, irrigation regimes of three levels (irrigation after 20, 40 and 60% depletion of soil available water) were accommodated in main plots and salicylic acid (SA) and spermine (SPM) spray treatments (75 mg/l SA, 150 mg/l SA, 75 mg/l SPM, 75 mg/l SA+75 mg/l SPM and 150 mg/l SA+75 mg/l SPM) were considered as sub plots. The effects of irrigation regime and spray treatments were significant on studied traits. Water stress increased phenol, flavonoid, root length, volume, area, weight and density but decreased plant height, number of tillers, leaf area index, shoot weight, specific root length and protein. The application of salicylic acid and spermine increased plant height, number of tillers, leaf area index, flavonoid, root volume, root weight and protein but decreased phenol, shoot weight root length. The interactions between water deficit and foliar application were significant on the concentration of phenol and flavonoid in shoot and also on root length, volume, weight and density. The highest flavonoid, root volume and root weight were obtained in plants sprayed by combined application of high rate of SA with SPM and the highest phenol, root length and root density were achived in unsprayed plants; both under irrigation after 60% water depletion. Based on the results from this experiment, the foliar application of salicylic acid and spermine improved the growth of coneflower plants under both normal and water stress conditions and the positive effects of salicylic acid were greater as compared with spermine.