# Antifungal Activity of Quaternary Pyridinium Salts Against _Fusarium culmorum_ in Wheat Seedlings
## 4 Discussion
In our study, some nicotinamide derivatives improved the growth parameters of wheat seedlings, particularly root biomass. However, not all compounds were effective, and a lower disease index did not always result in increased biomass. This indicates that the antifungal activity of the compounds and their effects on plant growth may be governed by different mechanisms (Table 4, Figure 4). Similar findings have been reported for nicotinamide mononucleotide (NMN), which activated plant defenses against _Fusarium_ without significantly influencing plant growth [59]. Some derivatives also showed a positive effect on shoot development, and all tested compounds improved shoot and root length under pathogen stress (Figures 5 and 6). These effects may be related to healthier root systems, improved nutrient uptake, or reduced infection intensity. Similar findings have been reported for vitamin B3-based compounds (nicotinic acid), where treated plants showed better growth and vitality under stress conditions [58]. In barley (_Hordeum vulgare_ L) exposed to lead stress, nicotinamide treatment also improved shoot and root development, higher pigment levels, and reduced oxidative damage. Although the stress factor was abiotic, these outcomes further highlight the potential of vitamin B3 derivatives in enhancing plant tolerance to various stress conditions [60]. All applied isonicotinamide derivatives positively affected fresh root and shoot mass compared to the control (Figures 7 and 8), although their effects on dry biomass varied. In particular, some compounds led to lower fresh mass but higher lyophilized mass, which may indicate an impact on the plant's water content. The results suggest that compounds **(6)** and **(7)** may lead to higher dry biomass while reducing the water content in plant tissue. This could indicate that the compounds affect how plants regulate internal water balance. A similar pattern has been described as part of a stress-priming response,where isonicotinamide was shown to enhance plant defense mechanisms and stimulate the production of secondary metabolites under stress conditions [61]. Similar patterns (lower fresh mass but higher dry weight) have been reported in drought-stressed plants as part of a physiological strategy to conserve water. A study on maize (_Zea mays_ L.) showed that, under drought conditions, the plant reduces water content in aboveground tissues and reallocates resources to root development to improve water-use efficiency [62]. Although our study did not focus on drought stress, these observations may indicate a similar adaptive response. Furthermore, previous research indicates that nicotinamide derivatives can help alleviate the effects of soil salinity, a stress that often reduces plant height, root length, leaf area, and overall biomass production [63]. In our study, several isonicotinamide derivatives stimulated shoot and root elongation, with the most pronounced effects observed at lower concentrations, while higher doses were generally less effective (Figure 9). For instance, compound **(6)** at 10 \(\upmu\)g/mL significantly increased shoot length compared to the fungicide, whereas this effect was not observed at 100 \(\upmu\)g/mL. These results show that vitamin B3-based compounds may promote plant growth but also highlight the importance of dose optimization. Compound **(6)** promoted plant growth at 10 \(\upmu\)g/mL but not at 100 \(\upmu\)g/mL, suggesting a hormetic effect--a biphasic response where low doses stimulate and high doses inhibit growth [64]. Such non-monotonic responses are known for many plants' bioactive compounds [65, 66]. Although this study did not investigate the underlying mechanisms, lower concentrations may enhance physiological responses such as hormone-like activity or stress protection. At the same time, higher doses may disrupt cellular balance. These results emphasize the importance of dose optimization when evaluating the dual role of bioactive compounds in pathogen control and plant development.