Rapeseed is a very important oil crop in China;however,its production is challenging due to the absence of effective weed management strategies.This is predominantly because of a shortage of herbicide resistance genes.Acetohydroxyacid synthase(AHAS) herbicides inhibit AHAS,a key enzyme involved in branched-chain amino acid synthesis that is required for plant growth.A rapeseed line designated M342 with AHAS herbicide resistance was developed through seed mutagenesis and was studied to assess the level and mode of inheritance of the resistance and to identify the molecular basis of resistance.M342 possessed a high level of cross-resistance to sulfonylureas(SUs) and imidazolinones(IMIs).This resistance was due to AHAS insensitivity to these herbicides and was inherited as a dominant trait conferred by a single nuclear-encoded gene.Molecular analysis revealed the presence of a Trp574 Leu mutation in M342,and an allele-specific cleaved amplified polymorphic sequence(AS-CAPS) marker was developed and cosegregated with herbicide resistance in the F2,BC1,and BC2 populations.This mutation altered the transcript levels of Bn AHAS1 and Bn AHAS3 in M342 compared with those in the wild type,but it did not affect the agronomic or quality traits.The simple genetic inheritance of this mutation and the availability of the cleaved amplified polymorphic sequence(CAPS) marker and herbicide resistance gene should facilitate the development of herbicide-resistant rapeseed cultivars for effective weed control in China. Rapeseed is a very important oil crop in China; however, its production is suspended due to the absence of effective weed management strategies. This is predominantly because due to a shortage of herbicide resistance genes. Acetohydroxyacid synthase (AHAS) herbicides inhibit AHAS, a key enzyme involved in branched-chain amino acid synthesis that is required for plant growth. A rapeseed line designated M342 with AHAS herbicide resistance was developed through seed mutagenesis and was studied to assess the level and mode of inheritance of the resistance and to identify the molecular basis of resistance. M342 possessed a high level of cross-resistance to sulfonylureas (SUs) and imidazolinones (IMIs). This resistance was due to AHAS insensitivity to these herbicides and was inherited as a dominant trait conferred by a single nuclear-encoded gene. Molecular analysis revealed the presence of a Trp574 Leu mutation in M342, and an allele-specific cleaved amplified polymorphic sequence (AS-CAPS) marker was dev eloped and cosegregated with herbicide resistance in the F2, BC1, and BC2 populations. This mutation altered the transcript levels of Bn AHAS1 and Bn AHAS3 in M342 compared with those in the wild type, but it did not affect the agronomic or quality traits. simple genetic inheritance of this mutation and the availability of the cleaved amplified polymorphic sequence (CAPS) marker and herbicide resistance gene should facilitate the development of herbicide-resistant rapeseed cultivars for effective weed control in China.