Polymorphisms at DNA loci flanked by inverted long terminal repeats (LTRs) of the Cassandra retrotransposon were analyzed, using the IRAP technique, in bread wheat cell lines resistant to metabolites produced by the pathogen of Ophiobolus root rot (G. graminis var. tritici) in the process of selecting for resistance to osmotic stress, as well as in regenerant plants obtained from them. Differences in DNA polynucleotide sequences have been identified between direct and multistep cell selection. An assessment of the level of genetic divergence has shown that calluses obtained by direct selection and calluses derived at later multistep selection stages were the most genetically distant forms from the original samples (D NL = 0.4855); i.e., the most significant genomic mutations occurred in the investigated objects at sublethal doses of a selective factor. In contrast to the original forms, the spectra of DNA amplification products from calluses and regenerants showed the emergence of an amplicon of approximately 638 bps in length which may be evidence of Cassandra retrotransposon activation.