A Comparison of Two Genes for Sulfonylurea Herbicide Resistance in Transgenic Tobacco Seedlings

Abstract

Previous work in tobacco (Nicotiana tabacum L.) showed the csr1‐1 gene for sulfonylurea resistance was inadequate for use in conjunction with a new, low residual sulfonylurea herbicide, DPX‐R9674 {a mixture of (methyl 2[[[[N‐4‐methoxy‐6‐methyl‐1,3,5‐triazin‐2‐yl)methylamino]‐carbonyl]amino]sulfonyl) benzoate) and (methyl 1‐3‐[[[[(4‐methoxy‐6‐methyl‐1,3,5‐triazin‐2‐yl)amino] carbonyl]amino]sulfonyl]‐2‐thiophenecarboxylate}. This study compared a new sulfonylurea resistance gene, ahas3r, with csr1‐1 in order to determine if ahas3r confers superior resistance to DPX‐R9674. The genetic material used in the study consisted of transgenic tobacco seedlings carrying either one of the two genes alone or both genes together. These genotypes were compared with each other and untransformed controls using acetohydroxyacid synthase (AHAS) assays and contrast comparisons of absolute growth rates of tobacco seedlings 10 and 20 d following herbicide application. Both the AHAS assays and the growth analyses of tobacco seedlings showed the genes to confer similar levels of resistance to chlorsulfuron {2‐chloro‐N‐[(4‐methoxy‐6‐methyl‐1,3,5‐triazin‐2‐yl)aminocarbonyl] benzenesulfonamide}. However, the ahas3r gene clearly conferred a greater degree of resistance to DPX‐R9674 than the csr1‐1 gene and may therefore be a good candidate for use with this herbicide.