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GENOMICS, MOLECULAR GENETICS & BIOTECHNOLOGY

Physiological and Molecular Characterization of Mutation-Derived Imidazolinone Resistance in Spring Wheat

^a Crop Development Centre, Dep. of Plant Sciences, Univ. of Saskatchewan, 51 Campus Drive, Saskatoon, SK, Canada, S7N 5A8
^b BASF Plant Sciences, Research Triangle Park, Raleigh, NC 27709 USA
^c DNA LandMarks Inc., 84 Richelieu Street, Saint-Jean-sur-Richelieu, QC, Canada, J3B 6X3

^* Corresponding author (curtis.pozniak{at}usask.ca).

While imidazolinone herbicides are an attractive alternative for weed control, spring wheat (Triticum aestivum L.) is susceptible to most of these herbicides. Three mutant alleles conferring resistance to the imidazolinone herbicides were previously identified in spring wheat following seed mutagenesis, but little is known about the physiological and molecular basis of resistance conferred by these alleles. On the basis of acetohydroxyacid synthase (AHAS; E.C. 4.1.3.18) assays, imazethapyr resistance in genotypes TealIMI 10A (AhasL-D1), TealIMI 11A (AhasL-B1), TealIMI 15A, and BW755 (AhasL-D1) was due to a herbicide resistant form of AHAS. TealIMI 15A, which is homozygous for two resistance alleles, was the most resistant at the enzyme level, suggesting resistance in wheat is additive. Nucleotide sequence analysis of clones derived from susceptible cultivar CDC Teal and resistant lines indicated the presence of three genes coding for the catalytic subunit of AHAS. Using a collection of T. aestivum cv. Chinese Spring aneuploid and deletion lines, ahasL-D1, ahasL-B1, and ahasL-A1 mapped to the long arm of chromosomes 6D, 6B, and 6A, respectively. Comparison of partial AhasL-D1, and AhasL-B1 deduced amino acid allele sequences with wild-type sequences indicated resistance was due to a Ser-Asn substitution near the carboxyl terminal of resulting AHAS catalytic subunits. This substitution was not present on the single isolated clone of AhasL-A1 from TealIMI 15A. This is the first report of the molecular characterization of the AHAS gene family from wheat.

Abbreviations: AHAS, acetohydroxyacid synthase • N6AT6B, Nullisomic 6A Tetrasomic 6B • N6BT6D, Nullisomic 6B Tetrasomic 6D • N6DT6A, Nullisomic 6D Tetrasomic 6A • DT6AS, Ditelosomic 6AS • DT6AL, Ditelosomic 6AL • DT6BS, Ditelosomic 6BS • DTBL, Ditelosomic 6BL • DT6DS, Ditelosomic 6DS • DT6DL, Ditelosomic 6DL

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