Abstract:Hybridization is one of the traditional methods to breed new cultivars, pollen viability is important for the successful transmission of genetic material to generations.Glycyrrhiza inflata is one of the three licorice species recorded in Chinese Pharmacopoeia, with many specialized active compounds. In order to determine the optimal pollen development periods for licorice hybridization, the pollen viability of five bloom stages (a, b, c, d, and e) of two G. inflata cultivars (GJJ-7 and GJJ-9) were measured by TTC staining and in vitro pollen germination methods. The result of TTC staining method showed that the pollen viability of GJJ-7 trended in a wave pattern and peaked at a and d stages. The pollen viability of GJJ-9 increased with the opening process of petals, and peaked at e stage. But the result of in vitro pollen germination method showed that the pollen viability of both GJJ-7 and GJJ-9 was highest at c stage, which was consistent with fruiting rate in the hybridization, and further indicating the higher reliability of the in vitro germination method compared with the TTC staining. Hybridization results of the three medicinal licorice species showed that a low fruiting rate but highest seed germination rate was obtained when G. glabra cultivars S-7 and S-12 were used as the female parents. High fruiting rate but low seed germination rate was observed when G. uralensis cultivar GDN-16 was used as the female parent, indicating the importance of parent selection during licorice hybridization. These provides an important reference for improving the field hybridization efficiency of licorice.