Abstract
Effect of root-applied bensulfuron methyl {3-(4, 6-dimethoxypyrimidin-2-yl)-1-[(2-methoxycarbonylbenzyl) sulfonyl] urea} on growth of five rice cultivars (Oryza sativa L. cv. Milyang 30, Shingwang, Sangpung, Shinseonchalbyeo, and Nihonbare) was investigated under applied concentrations of 10-6, 5×10-6 and 10-5M. Based on effects of the herbicide on growth of the plant parts (the 4th to 6th leaves and roots) which grew largely after its application, the order of sensitivity among tested cultivars to the herbicide is Nihonbare>Sangpung, Shinseonchalbyeo>Shingwag>>Milyang 30. Root absorption of the 14C-herbicide and translocation from roots to shoots were investigated at 10-6 and 10-5M concentrations. There was no clear relation between the absorption or the translocation rates and the growth inhibition. Metabolism of root-absorbed 14C-bensulfuron methyl was studied in four of the cultivars, excluding Shinseonchalbyeo. Milyang 30 and Shingwang had lower percentages of the parent compound in roots than Sangpung and Nihonbare; they also had higher percentages of O-demethyl bensulfuron methyl and water soluble metabolites than the latter two. In Milyang 30, bensulfuron methyl was less translocated from roots to shoots and largely degraded in roots, and these may contribute to its resistance. The low sensitivity of Shingwang may be related to its high degradation ability in roots, while in Nihonbare and Sangpung the rate of degradation of the herbicide was much lower than Milyang 30.
