The application of DNA intercalator 9-aminoacridine allowed us to increase the resolution of chromosome C-banding and DAPI-banding patterns and to investigate chromosomal polymorphism in karyotypes of seven spring and six winter rape varieties. It was shown that the pericentromeric and intercalary C-bands of most of the chromosomes in spring rape were smaller in size and less polymorphic than those of winter rape. More 26S and 5S rDNA sites were found in the winter rape karyotypes than the spring varieties. Separate or colocalized 26S and 5S rDNA sites were revealed on chromosomes 4, 5, 6, 8, 10, 14, 15, 16 and 18. Intervarietal and intravarietal polymorphism of the number and chromosomal localization of rDNA sites were detected. The generalized idiogram of chromosomes of 13 Brassica napus varieties with account of all possibilities of C-banding patterns as well as localization of 26S and 5S rDNA sites were constructed. Polymorphism of the examined molecular and cytogenetic markers as well as the heterozygosis level of FAE1.1 gene controlling erucic acid synthesis in rapeseed was higher in the winter varieties than in the spring ones. The obtained data were in a atisfactory agreement with increased tolerance to environmental stress conditions of winter rape.

The phenotypic, biochemical and genetic variability was studied in M2-M5 generations of ethyl methansulfonat (EMS, 0.2%) mutagenized rapeseed lines generated from canola, ‘00’, B . napus cv. Vikros. EMS mutagenesis induced extensive diversity in morphological and agronomic traits among mutant progeny resulted in selection of EMS populations of B . napus - and B . rapa- morphotypes. The seeds of the obtained mutant lines were high-protein, low in oil and stabilized in contents of main fatty acids which make them useful for feed production. Despite the increased level of various meiotic abnormalities revealed in EMS populations, comparative karyotype analysis and FISH-based visualization of 45S and 5S rDNA indicated a high level of karyotypic stability in M2-M5 plants, and therefore, the obtained mutant lines could be useful in further rapeseed improvement. The revealed structural chromosomal reorganizations in karyotypes of several plants of B . rapa- type indicate that rapeseed breeding by chemical mutagenesis can result in cytogenetic instability in the mutant progeny, and therefore, it should include the karyotype examination. Our findings demonstrate that EMS at low concentrations has great potential in rapeseed improvement.

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