Ethyl Methane Sulphonate (EMS) is a chemical mutagen widely used to improve rice characters by mutation breeding. The experiment was conducted to find out the optimum lethal dose (LD50) of EMS on four rice varieties viz., Aye Yar Min, Rice Berry, Jasmine 105 and Paw San (Black) for creating genetic variation. Dry seeds of four rice varieties were directly treated with different doses of EMS 0.00%, 0.25%, 0.50%, 0.75%, 1.00% and 1.25% for 22 hours. The effects of different EMS doses and varieties and their interaction showed for the traits like germination %, shoot length and root length were significant differences. The lethal dose (LD50) values were detected by regression analysis for different varieties. The lethal dose (LD50) values for germination %, shoot length and root length were observed at Aye Yar Min (0.52 to 0.55%), Rice Berry (0.55 to 0.68%), Jasmine 105 (0.57 to 0.60%) and Paw San (Black) (0.62 to 0.66%). The three studied traits were decreased with increase in dose of EMS. The sensitivity of EMS appeared to be related to the type of variety. The lethal dose (LD50) values determined for the different rice varieties could be useful while formulating future rice varietal improvement breeding programmes.

Keywords : Rice Varieties, Ethyl Methane Sulphonate (EMS), Lethal Dose (LD50) .