This study presents some results regarding the treatment of Lycopersicon esculentum seeds with hydrolyzed collagen and thyme oil in different concentrations, in order to assess germination. Also, to evaluate the in vitro activity of collagen combined with antifungal substances on the tomato seeds infected with Alternaria alternata f.sp. lycopersici, this paper emphasizes the importance of using alternative non-polluting methods as essential oils in plant pathogens management. A control (untreated) and experimental (pre-treated and treated) lots were used, and the observations focused on the development of the pathogen, as well as the occurrence of the necrosis and alternariosis symptoms. Overall, three in vitro experiments were performed, as follows; seed germination; fungus prevention; infected seed treatment. In terms of growing, collagen alone delayed the germination of the tomato seeds, acting as a film on the seed surface. On the other hand, the mixture of collagen (stock solution and 50%) and thyme oil (0.5 ml, 0.25 ml respectively) inhibited germination. As for the preventive stage, the mixture of collagen and thyme oil 1 ml remained on the tomato seed surface, preventing the infection. Finally, the treatment of infected seeds with collagen and thyme oil 0.1 ml did not prevent the development of the pathogen, which was evidenced by the occurrence of necrotic radicles in tomatoes.