Barley productivity in this region and elsewhere. The group of herbicides belonging to the imidazolinone family targets acetohydroxyacid synthase or acetolactate synthase, an octameric enzyme with four catalytic and four regulatory subunits. The enzyme AHAS catalyses two parallel reactions in the synthesis of branched chain amino acids. The first reaction is condensation of two pyruvate molecules to yield acetolactate leading to the production of valine and leucine, and the other reaction is the condensation of pyruvate and aketobutyrate that give rise to acetohydroxybutyrate, which subsequently results in the synthesis of isoleucine. The AHAS-inhibiting herbicides are known to bind at the substrate access channel, blocking the path of substrate to the active site. When AHAS is inhibited, deficiency of the amino acids causes a decrease in protein synthesis, which in turn slows down the rate of cell division. This process eventually kills the plant, with symptoms observed in meristematic tissues where biosynthesis of amino acids primarily takes place. Amino acid substitutions at Ala122 and Ser653 confer high levels of resistance to imidazolinone herbicides, whereas substitutions at Pro197 endow high level of resistance against sulfonylureas and provide low-level resistance against imidazolinone and triazolopyrimidine herbicides. Likewise, substitutions at Trp574 provide high levels of resistance to imidazolinones, sulfonylureas and triazolopyrimidines, while substitutions at Ala205 confer resistance against all Carfilzomib AHASinhibiting herbicides. In the case of barley, there is no IMI-resistance reported for any of the varieties cultivated in the PNW. Thus, introduction of a barley variety with IMI-resistance will provide greater flexibility to barley as a rotational crop after winter wheat. An IMI resistant mutant was earlier isolated by our group from an extensive screening of two million seeds of ‘Bob’ treated with sodium azide. Molecular characterization of the mutant revealed an amino acid substitution in the substrate access channel of the catalytic subunit of the AHAS enzyme, changing a serine to asparagine at amino acid location 653. This mutation in the substrate access channel does not allow imazamox to block the path of the substrate to the active site, thus allowing the plant to survive with no obvious effects on plant fitness even when exposed to field recommended dose of herbicide used on the IMI-tolerant winter wheat. The major reason behind selecting markers from chromosome 6H lies in the fact that this chromosome carries the gene encoding for the catalytic subunit of acetohydroxyacid synthase enzyme and the mutation providing IMI-resistance. It is known through traitintrogression studies that due to linkage-drag, it always takes longer to recover the recipient parent genotype for the carrier chromosome in comparison with non-carrier chromosomes, which assort independently. Thus, to identify the rare recombinant carrying the precise gene introgression in the early generation, it is important to screen large segregating populations with the markers derived from the carrier chromosome. Of the 56 polymorphic markers, one marker detected three loci.