In this study we determined the genetic diversity among 13 barley cultivars/breeding lines, which benefitted the present study and is expected to prove useful in future breeding efforts. Chromosomal localization of the gene encoding the catalytic subunit of the barley AHAS enzyme will also prove useful in future gene-transfer studies leading to the development of herbicide-resistant cultivars with other agronomically important traits. Determination of the working dose of herbicide used for phenotypic screening of this trait will be used in future breeding efforts to transfer IMI-resistance. This pilot study with a limited number of selected F2 lines shows that it is possible to identify genotypes showing good recovery of the recipient parent genome by screening large F2:3 populations and following a strategic selection scheme. Our future objective is to take the recently developed IMIresistant food, feed and malting barley genotypes from the glasshouse to the field by i) screening large numbers of F3 families, representing the 250 top ranking F2 lines selected per cross combination, based on their vigor a month after herbicide spray, for their genetic backgrounds using DNA markers; ii) fixing heterozygosity in selected lines by doubled haploid production; iii) field evaluation of the DH lines for their performance on herbicide residue and under spray trials. This will allow identification of barley lines showing more genetic proximity to their respective recipient parents. For the first objective, F3 seeds belonging to the 250 F2 lines which survived the herbicide spray and showed early vigor a month after spray are currently being propagated in herbicide treated soil in the glasshouse. Cultivating plants on herbicide treated soil will allow elimination of susceptible individuals, which are expected in a segregating population at a proportion of one in four individuals. Genotype of the survivors will be determined at the AHAS locus by DNA sequencing following the procedure described above. It is of considerable importance to differentiate homozygotes from heterozygotes at the AHAS locus, as the two genotypic states at this locus are undistinguishable from each other using herbicide treatment alone. This is due to the semi-dominant nature of the AHAS mutation. The lines possessing the mutant allele at the AHAS locus either in homo- or heterozygous state will be evaluated for their genetic background in a stepwise fashion first using 10 carrier chromosome specific microsatellite markers followed by 4 DNA markers per non-carrier chromosomes. The second step of background selection will be performed on the F3 plants showing good carrier chromosome recovery in the first step. The lines showing good recovery of recipient parent genome will be converted to doubled haploids via a microspore culture based method following Kasha et al.. The resultant doubled haploids will be evaluated for their performance in the field on herbicide residue and herbicide spray trials. The major outcome of this project will be the development of IMI-resistant barley varieties and BU 4061T germplasm with a combination of beneficial traits.