## 4 Discussion  
Preventing the development of undesirable microbiota seems to be one of the main topics of research on the practical application of preparations containing active agents such as silver nanoparticles, as evidenced by the works [9; 10; 11; 44] carried out over several years. Due to their antimicrobial activity, components containing biologically active silver nanoparticles could be a potential alternative to disinfectants used so far in in vitro cultures. However, for this to happen, a number of analyses should be carried out to assess the degree of germination of seeds and other plant structures used in vitro. The potential lack of necrotic changes in seedlings, presented in this paper, raises some hopes for a non-toxic, time-delayed release of silver nanoparticles from the structure of sodium alginate. MS medium is commonly used in in vitro cultures of tomato [45]. Sucrose is usually added to the medium as an easy source of carbon chains for plants [46; 47], but it can also be used by microorganisms [48]. Sometimes sugar is omitted from the nutrient solution to reduce infection [34], but there is a risk of slower plant growth. The possibility of using silver nanoparticles to decontaminate _Arabidopsis_ seeds and tomato leaf explants were demonstrated by [PERSON] and co-worker [49]. However, it was observed that with complete sterilising effect (no culture infection) long exposure to silver nanoparticle solutions (30 and 60 min) has an inhibitory effect on _Arabidopsis_ seed germination and high concentrations of silver nanoparticles (250-2000 ppm) even at shorter exposure inhibit germination. Therefore, silver nanoparticles are a promising sterilizing agent but it is important to select an appropriate concentration and assess the risk of seed germination inhibition. Toxic effects of silver nanoparticles on plants in vitro cultures were also observed in _Aldrovanda vesiculosa_[50]. Therefore, work on the application of nanoparticles to in vitro cultures is still ongoing and requires, on the one hand, the search for new methods of producing silver nanoparticles and, on the other, testing their effect on specific cultures. In the presented work, a modern method of nanoparticle production using alginate was used and, most importantly, no toxic effect on germinating tomato plants was observed at any of the concentrations used. However, not every concentration used was equally effective in protecting against culture infection. In experiment 1 (non-sterile seeds were placed on culture media), the application of a 75 ppm silver nanoparticle solution gave the highest inhibitory effect on infection development. In contrast, the application of a 15 ppm solution did not reduce the development of infection. In the second experiment (seeds were treated with different solutions before placing them on the plates), the greatest reduction in infection development was obtained with a 75 and 30 ppm solution of nanosilver and a solution of sodium hypochlorite. Despite the best performance of these solutions, infections of 50% were still observed. In addition, in other studies, the appearance of microorganisms was observed after the application of hypochlorite [34]. Infections were also observed in barley embryo cultures after hypochlorite treatment [51]. The addition of silver nanoparticles to the MS medium decreased the frequency of these infections which points to the effectiveness of nanosilver in reducing infection--as in our experiments. The use of silver nanoparticles as a solution poured on the surface of the medium in the first experiment improved seed germination compared to the control. In the second experiment, seeds germinated at similar levels in all treatments. In the study by [PERSON] et al. [52], similarly to this study, the stimulation of plant seedlings growth was demonstrated on the example of garden petunias in in vitro cultures. [PERSON] et al.