Objective This study aimed to determine the optimal conditions for ethyl methanesulfonate (EMS) mutagenesis in lavender, providing a methodological reference for constructing a lavender mutant library and enhancing germplasm innovation.

Methods Seeds of the main lavender cultivar 'Xinxun No. 1' were soaked in EMS solutions at concentrations of 0.00% (CK), 0.85%, 1.00%, 1.25%, 1.50%, and 2.00% for 4, 8, 12, and 16 h, respectively. The effects of different treatments on seed germination potential, germination rate, relative germination rate, germination index, radicle length, plumule length, and seedling length were analyzed to identify the optimal EMS treatment for achieving a semi-lethal rate.

Results Increasing EMS concentration or prolonging treatment duration significantly inhibited seed germination and seedling growth, and induced morphological abnormalities. Compared with the CK, when the treatment duration was 4 h, no significant differences were observed in germination potential, germination rate, or relative germination rate across concentrations, indicating that excessively short treatment is insufficient to induce mutagenic effects. However, at treatment durations of 8, 12, and 16 h, germination potential, germination rate, relative germination rate, germination index, plumule length, radicle length, and seedling length all exhibited significant inhibition, and the inhibitory effects became more pronounced with increasing EMS concentration, even leading to lethality. Among all traits, radicle length was the most sensitive to EMS, showing highly significant differences from the CK across all four treatment durations.

Conclusion High-concentration or prolonged EMS treatment significantly reduces seed germination rate and germination index, while also markedly inhibiting radicle and plumule growth. For constructing a lavender mutant library via EMS mutagenesis, the optimal treatment condition is 2.00% EMS for 8 h.