The effect of chemically synthesized nanocomposites (NCs) of selenium (Se/AG NC), copper oxide (Cu/AG NC) and manganese hydroxide (Mn/AG NC) based on the natural polymer arabinogalactan (AG) on the processes of growth, development and colonization of potato plants in vitro was studied upon infection with the causative agent of potato blackleg – the Gram-negative bacterium Pectobacterium carotovorum and the causative agent of ring rot – the Gram-positive bacterium Clavibacter sepedonicus (Cms). It was shown that infection of potatoes with P. carotovorum reduced root formation of plants and the concentration of pigments in leaf tissues. Treatment of plants with Cu/AG NC before infection with P. carotovorum stimulated leaf formation and increased the concentration of pigments in them. A similar effect was observed when potatoes were exposed to Mn/AG NC, and an increase in growth and root formation was also observed. Infection of plants with Cms inhibited plant growth. Treatment with each of the NCs mitigated this negative effect of the phytopathogen. At the same time, Se/AG and Mn/AG NCs promoted leaf formation. Se/AG NC increased the biomass of Cms-infected plants. Treatment of plants with NCs before infection showed a decrease in the intensity of colonization of plants by bacteria. The Se/AG NC had the maximum effect, which is probably due to its high antioxidant capacity. Thus, the NCs are able to mitigate the negative effect of bacterial phytopathogens on vegetation and the intensity of colonization by these bacteria during infection of cultivated plants.