Abstract
Effect of simetryn [2, 4-bis (ethylamino)-6-methylthio-s-triazine] and dimethametryn [2-(1, 2-dimethylpropylamino)-4-ethylamino-6-methylthio-s-triazine] on growth and photosynthesis of rice (Oryza sativa L.) cultivars Nihonbare and Choseng Tongil, and barnyardgrass (Echinochloa oryzicola Vasing.) was compared. Dimethametryn showed greater phytotoxicity than simetryn in all plants, but difference in susceptibility of the plants to the herbicides was greater in Nihonbare cultivar than in other plants. It is believed that this results from very high tolerance of the cultivar to simetryn.
Both herbicides inhibited in photosynthesis with very low concentrations, and dimethametryn was the stronger inhibitor. The I50 values in the reaction were approximately 4 or 5×10-8M and 2×10-8M for simetryn and dimethametryn respectively.
This difference in inhibiting activity at the site of action is considered to be one of the factors determining their phytotoxicity.
