Can licorice root extract be used as an effective natural biostimulant for salt-stressed common bean plants?

Green approaches for promoting plant performance using natural supplementations are highly requested. After a field preliminary study was carried out in 2015 on saline (EC = 7.2 dS m− 1) and normal (EC = 1.2 dS m− 1) soils, two field trials were conducted to evaluate the potential effects of licorice root extract; LRE (0.5%; 5 g roots L− 1 distilled water), used as seed soaking (SS) and/or foliar spray (FS) on growth and green yield, physio-biochemical attributes, and antioxidant defense systems of Phaseolus vulgaris plants grown on a saline (EC = 7.15 dS m− 1) soil. The preliminary study results showed that plant growth, yield, RWC, and chlorophylls content were significantly reduced due to salt stress (EC = 7.2 dS m− 1), however, LRE application significantly increased these parameters. On the other hand, these parameters were not altered with LRE application on the normal soil. Field studies reported significant increases in growth and yield parameters, photosynthetic pigments, free proline, total soluble carbohydrates (TSC), total soluble sugars (TSS), nutrients, and selenium (Se), ratio of K+/Na+, relative water content (RWC), membrane stability index (MSI), activities of all enzymatic antioxidants, and all anatomical features, while represented significant decreases in electrolyte leakage (EL), malondialdehyde (MDA), Na+, hydrogen peroxide (H2O2), and superoxide radical (O2•−) by the application of LRE as SS and/or FS compared to the controls (SS and FS using distilled water) under salt stress. Best results were recorded when SS was integrated with FS using LRE. Therefore, results of the present study recommend using this integrative (SS + FS) LRE treatment for growing common beans on saline soils.