Objective In order to enrich the breeding methods of Lagerstroemia speciosa, the optimum conditions of EMS mutagenesis were studied..

Method The seeds of Lagerstroemia speciosa were used as the study material to compare and analyse the effects of different combination of EMS concentrations and treatment times on seed germination and seedling growth ofLagerstroemia speciosa.

Result It was observed that EMS treatment could inhibit the germination of Lagerstroemia speciosa seeds. The concentration and treatment time were found to have a significant impact on the degree of inhibition. All seeds were killed by treating with 20g·L⁻¹EMSfor 12 h. The starting time of seed germination was delayed and the germination duration became longer with the increase of EMS concentration and treatment time. The inhibition of hypocotyl and radicle growth was more significant. The relative lethal rates of the 16g·L⁻¹ EMS treatment for 12 h and the 18g·L⁻¹ EMS treatment for 10 h were 47.99% and 55.02%, respectively, which were the closest to the Lethal concentration 50(LC50). Consequently, the 1.6% EMS treatment for 12 h and the 18g·L⁻¹ EMS treatment for 10 hours were identified as the optimal treatment combinations for EMS mutagenesis of Lagerstroemia speciosa. The growth of Lagerstroemia speciosa seedlings was inhibited by EMS treatment, with the greatest impact observed at 20g·L⁻¹ EMS treatment for 8 h. The plant height, crown width, ground diameter and leaf area were 8.28 cm, 9.66 cm, 1.70 mm and 29.32 cm². The leaf shape index was found to be the highest at 16g·L⁻¹ EMS treatment for 12 h and 18g·L⁻¹ EMS treatment for 10 h, with a value of 2.42.

Conclusion In this study, the treatment combination close to the LC50 of EMS mutagenesis of Lagerstroemia speciosa seeds was determined, and the effects of EMS concentration and treatment time on seed germination and seedling growth of Lagerstroemia speciosa were explored, which could provide a basis for the cultivation of new varieties of this plant.