<p>Frequency and spectrum of cytogenetic disorders in the cells of root meristem sprouts of <em>Triticum aestivum L.,</em> induced by soil contamination with hexachlorobenzene in the territory of toxic waste ground and Dombrovskyi potassium ore mine (Kalush city, Ivano-Frankivsk oblast), were studied. The concentration of hexachlorobenzene exceeded MPC (maximum permissible concentration) by 1233.3–18350 times. It has been established that chemical soil contamination causes the increase of the frequency of cytogenetic aberrations by 1.8-3.8 times. Its highest indicators were found under the most intensive soil contamination with hexachlorobenzene in the areas of toxic waste ground which were not recultivated. Frequency of cytogenetic disorders exceeded the control level by 3.4-3.8 times. The maintenance of high mutagenic activity of hexachlorobenzene remains in the soil of the recultivated area of the ground is confirmed by statistically reliable increase of the number of aberrant cells by 2.6-3 times. It has been shown that soil contamination of Dombrovskyi mine with the complex of natural-mineral compounds of mining-chemical raw materials causes the increase of mutagenic activity level of low concentrations of chemical gene-toxic factors of techno-genic origin, which is seen in the induction of higher level of cytogenic disorders compared with spontaneous indicators by 1.8-2.4 times. Spectrum of chromosome aberrations, which mostly included acentric fragments, expanded due to induced bridges, ring chromosomes and micronuclei. The share increase of the cells with dicentrics, caused by the effect of soil contamination with hexachlorobenzene in the territory of toxic waste ground, confirms the radiomimetic effect, resulted from the effect of chemical mutagen in high concentrations. Chemical pollutants of the soil of all the studied areas show the ability to cause mitosis disorder, connected with the damage of mitotic apparatus. A significant increase of disorder frequency of chromosome segregation can be the result of the interaction of mutagens not only with microtube proteins of division spindle but also with heterochromatin of near-center areas of chromosomes, which is typical for the mechanism of the emergence of cytogenetic aberrations under the effect of chemical supermutagens in high concentrations. The increase of the cell number with multiple aberrations under the effect of soil contamination with hexachlorobenzene in different concentrations proves high gene-toxicity of the chemical compound and the threat of severe genetic outcomes when it gets into the environment.</p>

Induced mutagenesis opens great perspectives for radical genetic improvement of cultivated plants. Scientists seeking new sources and methodological approaches to improve the frequency and extend the range of mutations have drawn attention to the Zone of Alienation around the Chornobyl Nuclear Power Plant, where unique conditions of the influence of mutagenic factors have developed, and therefore needs to be studied for possible use of its territory in propagating parent material for selective breeding of wheat. Plants of winter wheat of Albatros Odesky and Zymoiarka varieties were grown within 10 km of the Chernobyl Plant, inside the Alienation Zone, in Chystohalivka, Kopachi and Yaniv villages of Chornobyl district of Kyiv Oblast. The exposure occurred in the dose of 7.2 ∙ 10–12– 50.0 ∙ 10–12 A/kg. As the control, we used the territory of the Research Institute of Physiology of Plants and Genetics of the Academy of Sciences of Ukraine (Hlevaha urbanized settlement of Vasylkivsky District of Kyiv Oblast), where the power of the exposure dose equaled 0.93 ∙ 10–12 A/kg. Frequency and spectrum of mutant forms were determined in M2–M3 generations according to the ratio of the number of families with mutagenic plants to studied M2 families. Among the observed mutations, we determined the share of the ones important for selective breeding. Chronic ionizing radiation throughout the vegetation period of winter wheat increased the level of noticeable mutations, the frequency of which exceeded the control parameters by 8.0–14.9 times. In the conditions of cultivation of winter wheat in the territory of Kopachi village, where the dose was the lowest, we recorded a high level of mutation variability which exceeded the control parameters by 8.0–9.2 times and was notably different from the frequency of mutations induced by radionuclide contamination of soil in the territories of Chystohalivka and Yaniv villages. The mutation range contained 12–20 types and depended on the density of soil contamination with radio nuclides, magnitude of exposure dose and genotype of plants. The predominant mutations were the ones related to the duration of vegetation period, length of the stem, morphology and awns of the ear. Among the detected mutations, the important selective ones accounted for 24.3–49.3%, predominant being low height, intense growth and long cylindrical ear. Because beneficial agronomic traits are highly likely to be inherited in complex with mutations that reduce the productivity of winter wheat, efficiency of direct selection of mutant forms that are valuable for selective breeding is limited. Enlargement of genetic diversity of the initial selection material using the radionuclide-induced mutagenesis resulting from contamination creates the possibility of using it in cross breeding for the purpose of implementing selective breeding genetic programs of improving wheat varieties.