The article discusses the effect of copper oxide (CuO) and silver (Ag) nanoparticles on expression of genes asr3 , icdh , PR-1 , PR-10 , DREB2 , used as markers of the development of stress tolerance, in poplar in vitro clones of the “POK” variety under conditions of artificial infection with the filamentous ascomycete Alternaria alternata . The exposure to the phytopathogen activates the asr3 , icdh , PR-1 , PR-10 , DREB2 genes in microclones on a medium without nanoparticles, which indicates development of adaptation mechanisms in them. The expression indicators of stress tolerance marker genes in in vitro clones on a medium with CuO and Ag nanoparticles were reduced or did not exceed the values obtained for plants on a medium without nanoparticles. The observed suppression of the stress response under cultivation with CuO and Ag may be governed by the inhibitory effect of nanoparticles on the development of Alternaria alternata , as well as their influence on the development processes of poplar in vitro clones of the POK variety, which is associated with the peculiarities of the plant genotype and the concentration of nanoparticles.

The widespread introduction of highly productive and rot-resistant forms and hybrids of aspen (Populus tremula L.) into the forest production is constrained by the lack of effective methods of their vegetative reproduction. Achievements of modern forest biotechnology enable in vitro cloning of economically valuable aspen genotypes and obtain planting material for plantation forest growing. The study of the manifestation features of valuable traits and genetic stability of in vitro clones propagated in the field (ex vitro) is important for the development of effective and reliable propagation methods that guarantee the preservation of the genetic and economic value of parent trees for their sustainable and targeted reproduction. The results of genetic stability evaluation, growth dynamics, productivity and wood quality of three in vitro propagated aspen clones (6/3, 15/01, and 20/4) in the field are presented. Micropropagation was carried out by direct organogenesis using hormone-free nutrient media. According to the results of 17-year field trials, clones demonstrate good growth and sufficiently high productivity of stands; preserve the growth characteristics of parent trees, showing no signs of somaclonal variability. At the age of 17, the average height of the trees was 18-20 m; the trunk diameter was 25-30 cm; the trunk volume was 0.391-0.553 m(3); the timber volume was 111-227 m(3)/ha at trees placing 4x4 and survival rate 44-71 %. High genetic stability of clones in vitro and ex vitro was revealed based on the results of analysis of microsatellite loci, ploidy level and mixoploidy. It is shown that the triploid clone 15/01, which has high myxoploidy level, is characterized by a higher preservation and better wood quality attributes (wood density and fiber length) than diploid clones. This is probably due to the optimal balanced ratio of cells with different ploidy levels (triploid, diploid, and aneuploid), which provides the most effective expression of genes in specific environmental conditions.