The master thesis examines the potential interaction between the plant (Solanum tuberosum L., cultivar Igor and genotype NahG-Ryawl), bacteria (Bacillus mycoides or Bacillus subtilis) and PVYNTN virus, by measuring concentration of IAA and hydrolytic enzymes (proteinase, chitinase, cellulase) in cell suspension and comparing growth and appearance of symptoms among uninfected and infected plants after addition of the suspension of various bacterial strains mentioned above. It was assumed that strains of B. mycoides (a species is widely recognized as PGPR against fungal pathogens when applied on leaves), isolated from a potato field in the Netherlands, differ in the production of IAA and hydrolytic enzymes, and that they develop a mutualistic relationship with potato plant meaning they can inhibit viral infection, especially the strains that excrete high concentrations of IAA. We have found a varietal difference in response: in Igor there is several types of lesions while there is only one in NahG-Rywal, but the latter exhibits more scarce response and occurrence of signs of infection on uninoculated leaves. Nutrients-rich substrate did not stop the spreading of infection but favorably affected the growth of young plants. B. mycoides by means of measured concentration of IAA and enzymes did not exhibit as high PGP potential as B. subtilis, but in vivo the strain of M2E-7 and M3E-14 exhibits some beneficial effects, for instance accelereted growth of cultivar Igor and good leave condition of cultivar Igor plus strong reaction in terms of lesions, seen in genotype NahG-Rywal, respectively. Strains B. subtilis PS-216 and T16-8 are apropriate for further analysis whether they could be used in crop protection products.