Cross-resistance pattern and alternative herbicides for Rotala indica resistant to imazosulfuron in Korea

Abstract

A Rotala indica accession from Chonnam province, Korea was tested for resistance to sulfonylurea (SU) herbicide, imazosulfuron. The accession was confirmed to be resistant (R) and was cross-resistant to other SU herbicides, bensulfuron-methyl, cyclosulfamuron, and pyrazosulfuron-ethyl, but not to imidazolinone herbicides, imazapyr, and imazaquin. Multiple resistance was tested using eight herbicides with target sites other than acetolactate synthase (ALS). The R biotype was susceptible to other herbicides with different modes of action, such as fentrazamide and mefenacet. Herbicide mixtures, butachlor + pyrazolate and MCPB + molinate + simetryne can also control R biotype of R. indica. Although mixtures of SU herbicides with other modes of action can control the R biotype, use of these mixtures should be avoided. In vivo ALS activity of the R biotype was 35-, 26-, 278-, and 7-fold more resistant to bensulfuron-methyl, cyclosulfamuron, imazosulfuron, and pyrazosulfuron-ethyl, respectively, than the S biotype. The resistance mechanism of R. indica to imazosulfuron was mainly due to an alteration in the target enzyme, ALS. Since the level of resistance to other SU herbicides in the enzyme assay was much lower than that in the whole-plant assay, other mechanisms of resistance, such as herbicide metabolism, or reduced absorption and translocation may be involved. There was no indication of fitness difference between the R and S biotypes.