Effect  of  phytoviruses  on  tomato  plants was  assessed  on  the  basis  of  four  genotypes:  susceptible  cultivar  Elvira,  spontaneous  form  S.pimpinellifolium,  the  varieties  with  resistance genes to TMV – Craigella (Tm-22/Tm-22) and Craigella (Tm-1/Tm-1). The ultrastructural  study of the mesophyll cells in control and virus-infected plants have been shown   changes   with    degree   of   cell   organelles   organization.   More   pronounced modifications were noticed in  susceptible cultivar. A clear and smooth cell wall with a well-organized chloroplast can be found  in the leaf of plants with genes of resistance and tolerant tomato variety. The degree of  ultrastructural reorganizations depends in more part  on  the  type  of  the  host  reaction  to   viral  infection.  The  defense  reactions  of  host genotypes to Tomato Aspermy Virus and Tobacco  Mosaic Virus were evaluated on base of  peroxidase  and  polyphenol  oxidase  activity.  The   analyzed  viruses  contributed  to fluctuation in peroxidase and polyphenol oxidase activity  depending on the genotype. The antioxidant activity is more significant in tolerant and genotypes  with resistance genes, while the variation in activity of polyphenol oxidase is higher expressed in  genotype-virus systems that presented more deep pathological changes.