Assessment of acetolactate synthase (ALS) tolerance to imazethapyr in red rice ecotypes (Oryza spp) and imidazolinone tolerant/resistant rice (Oryza sativa) varieties

Three red rice ecotypes (Oryza spp), including LA 5, MS 5 and TX 4, were evaluated for acetolactate synthase resistance/tolerance to imazethapyr. The red rice ecotypes were compared with a tolerant line (CL-121), a resistant line (CL-161) and a conventional rice variety (Cypress). Based on enzymatic activity, the mean 150 values were 1. 5, 1. 1, 1. 5, 1.6, 20.8 and 590.6 L-Nt imazethapyr., respectively, for LA S, MS 5, TX 4, Cypress, CL-121 and CL-161. CL-161 was 32 times more resistant than CL-121 and at least 420 times more resistant than the average of the red rice ecotypes and Cypress. Results from the acetolactate synthase (ALS) assay showed that red rice ecotypes and Cypress had high susceptibility to imazethapyr when compared with the tolerant CL-121 and the resistant CL-161. Measurable enzymatic tolerance to ALS-inhibiting herbicides has not yet developed in these red rice ecotypes. (C) 2004 Society of Chemical Industry.