<div>Background: Glycyrrhiza is an important medicinal plant that has been in shortage in recent years because of high demand and exhaustive harvesting. Investigating the drought tolerance of liquorice species can inform the artificial cultivation of liquorice under different water conditions and help address the shortage. 
 
Methods: Seeds of G. uralensis, G. glabra&nbsp;and G. inflata were treated with different concentrations of polyethylene glycol (PEG)-6000 solutions to simulate different levels of drought stress. The germination process germination rate, germination index, vigour index, stress tolerance index and recovery germination percentage of seeds were measured. Drought tolerance was evaluated using the membership function. 
 
Result: Low concentrations of PEG promoted the seed germination of G. glabra and G. inflata, whereas high concentrations inhibited the seed germination of all three plants. The degree of inhibition increased with increasing PEG concentration. Under mild PEG stress, the drought tolerance of G. uralensis was highest and that of G. glabra was the lowest. However, under severe PEG stress, the drought tolerance of G. glabra was the highest and that of G. uralensis was the lowest. Therefore, seeds of G. uralensis should be sown in relatively moist soil and those of G. glabra in relatively arid soil.</div>

Effect of PEG-simulated Drought Stress on Seed Germination of Three Medicinal Liquorice (Glycyrrhiza) Species

<div>Background: Although both the root and rhizome of Glycyrrhiza inflata have been used as medicinal material, the sales volume and price of its root are much higher than its rhizomes. Limiting the growth of liquorice rhizomes while improving the yield and quality of its root has become an important problem.&nbsp; 
 
Methods: Two irrigation patterns (surface drip irrigation and subsurface drip irrigation, i.e. DI and SDI) and three irrigation levels (40%-50%, 60%-70% and 80%-90% of the maximum soil water capacity) were used in this study.&nbsp; 
 
Result: The plant height, crown width, root length, root biomass and concentrations of the five medicinal components (glycyrrhizic acid, glycyrrhetinic acid, glycyrrhizin, liquiritigenin and isoliquiritigenin) of the SDI treatments were significantly higher than those of the DI treatments. The above parameters reached their maximum under the SDI90 treatment (SDI with 80%-90% of the maximum soil water capacity). The rhizome growth of the liquorice was promoted with an increase in irrigation amount, but the biomass of the rhizomes under SDI treatment was significantly lower than that under DI treatment. Thus, the regime of SDI with a relatively high water supply can effectively promote the yield and medicinal quality of liquorice roots, while inhibiting the development of its rhizomes.</div>

Effect of PEG-simulated Drought Stress on Seed Germination of Three Medicinal Liquorice (Glycyrrhiza) Species

Effect of Irrigation Pattern and Irrigation Level on Growth of Glycyrrhiza inflata and the Medicinal Quality of its Root