A COMPARISON OF 2 GENES FOR SULFONYLUREA HERBICIDE RESISTANCE IN TRANSGENIC TOBACCO SEEDLINGS

Previous work in tobacco (Nicotiana tabacum L.) showed the csr1-1 gene for sulfonylurea resistance was inadequate for use in conjunction wit h a new, low residual sulfonylurea herbicide, DPX-R9674 (a mixture of (methyl triazin-2-yl)methylamino]-carbonyl]amino]sulfonyl] benzoate) a nd (methyl -[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl ] amino]sulfonyl]-2-thiophenecarboxylate). This study compared a new s ulfonylurea resistance gene, ahas3r, with csr1-1 in order to determine if ahas3r confers superior resistance to DPX-R9674. The genetic mater ial used in the study consisted of transgenic tobacco seedlings carryi ng either one of the two genes alone or both genes together. These gen otypes were compared with each other and untransformed controls using acetohydroxyacid synthase (AHAS) assays and contrast comparisons of ab solute growth rates of tobacco seedlings 10 and 20 d following herbici de application. Both the AHAS assays and the growth analyses of tobacc o seedlings showed the genes to confer similar levels of resistance to chlorsulfuron methoxy-6-methyl-1,3,5-triazin-2-yl)aminocarbonyl] benz enesulfonamide). However, the ahas3r gene clearly conferred a greater degree of resistance to DPX-R9674 than the csr1-1 gene and may therefo re be a good candidate for use with this herbicide.