Effect of seedling grade standard on improving the quality of licorice (Glycyrrhiza uralensis F.): changes in the seven bioactive components and root biomass during two-year growth

Licorice cultivated is one of the most popular herbal medicines, while its quality is unstable. The aim of present study is to investigate the effect of licorice seedling grade standard on improving its quality. One-year-old Glycyrrhiza uralensis seedlings were classified into three grades 1, 2, and 3 by weight per plant. The major root biomass indexes (root fresh weight, root dry weight and taproot diameter) and contents of 7 bioactive components (glycyrrhizin, liquiritin, liquiritin apioside, liquiritigenin, isoliquiritin, isoliquiritin apioside, and isoliquiritigenin) varied in different grades seedlings. Further, the contents of 7 investigated compounds of 3-year-old licorice produced by grade 1 seedlings were 1.5–2 times as much as those produced by grade 2 and 3. Additionally, the contents of liquiritin apioside and isoliquiritin apioside were positively correlated with licorice root biomass. These results indicated that establishing licorice seedling grade standard is an effective way to improve and control its quality.