Foliar salicylic acid application to mitigate the effect of drought stress on isabgol (Plantago ovata forssk)

Abstract

The aim of this study was to identify the effect of drought stress on physiological and biochemical characteristics of isabgol and to clarify whether the foliar application of salicylic acid is able to mitigate the stress impacts. This study was carried out as a factorial field experiments at Gonbad Kavous, north-eastern Iran during the growing seasons of 2016 and 2017.The treatments were 3 regimes of irrigation, namely irrigation every week throughout the growth period based on field capacity (Non stress = NS), cut-off the irrigation at the seed filling stage for 60 days (Moderate stress = MS) and at the flowering stage for 50 days (Severe stress = SS). Salicylic acid (SA) application with three levels, 0 (distilled water spray), 0.4 and 0.8 mM SA per 5 m−2were assigned as the subplot treatments. Foliar application of salicylic acid was performed simultaneously with cut-off irrigation treatments (in three times).The studied traits included: membrane stability index, catalase activity, proline content, soluble sugars content, total phenol contents in plant leaves and seed yield. According to the results of the two-year experiment, the highest seed yield was obtained by foliar spraying of 0.8 mM salicylic acid at the moderate stress condition. Application of salicylic acid at a concentration of 0.8 mM improved the cell membrane stability from 71 to 98%, water productivity by 53–99 m3 ha−1, water used efficiency from 2 to 4 m3 ha−1the soluble sugar content from 62 to 125 mg g−1 DW and the total phenol content from 2 to 10 mg g−1 DW. In both years of the study, the highest catalase activity was recorded for the normal irrigation treatment under foliar application of 0.4 and 0.8 mM salicylic acid. Application of SA at 0.8 mM under MS and SS conditions increased seed yield, cell membrane stability, catalase activity and proline concentration compared to NS, which indicates the positive effect of this compound.