# Antifungal Activity of Quaternary Pyridinium Salts Against _Fusarium culmorum_ in Wheat Seedlings
## 1 Introduction  
Among the most widespread and economically significant fungal genera is _Fusarium_, which includes numerous species responsible for crop diseases affecting wheat, maize, barley, tomato, cucumber, potato, and many other plants. Diseases caused by _Fusarium_ species are seed rot, seedling blight, root and stem rot, late blight, and wilt disease. The primary sources of infection are contaminated seeds, infected soil, and alternative hosts [1]. Among the _Fusarium_ species, _Fusarium culmorum_ (Wm. [PERSON].) Sacc. is considered one of the most important fungal pathogens, causing significant crop losses, particularly in wheat(_Triticum aestivum_ L.), its primary host [2]. Many researchers have identified _F. culmorum_, _Fusarium graminearum_ [PERSON], and _Fusarium pseudograminearum_ [PERSON] as the most critical wheat pathogens globally [3; 4; 5; 6]. Wheat is cultivated at approximately 161.80 thousand ha in Croatia, with an annual yield of around 971.40 thousand t, while globally, it is grown at 219.20 million ha, with an annual production of 99.96 million t [7]. These figures highlight the crucial role of wheat in food security, especially in Croatia, where it is one of the most important agricultural products. According to [PERSON] and [PERSON] [8], _F. culmorum_ is one of the most pathogenic species for wheat in Croatia. Among the pathogens affecting wheat, _F. culmorum_ causes several economically significant diseases, particularly Fusarium root rot (FRR), which is especially damaging during the early growth stages. FRR symptoms usually appear soon after sowing and can result in seedling death either before or after emergence. Infected plants often show brown lesions on the roots and lower stem, with reddish-pink sporodochia forming under humid conditions due to intense sporulation. In later stages, lesions may extend to the stem internodes, further compromising plant development [9]. Although _F. culmorum_ is also a recognized agent of Fusarium head blight (FHB) [10], this study primarily focuses on FRR because of its impact on early seedling health. _Fusarium_ species, including _F. culmorum_, are not only plant pathogens but also potent producers of mycotoxins such as deoxynivalenol (DON), zearalenone (ZEA), and fumonisins. These toxic secondary metabolites can contaminate grains and pose a serious food safety risk due to their potential to disrupt protein synthesis, hormonal balance, and nervous system function [11; 12; 13]. Beyond visible crop damage, their presence in food and feed poses a hazard to immunocompromised individuals [14]. Beyond food safety concerns, DON also acts as a virulence factor in plants--it promotes disease development in wheat by disrupting normal cellular processes, inducing oxidative stress, and triggering programmed cell death (PCD). This leads to tissue damage and bleaching, which are characteristic symptoms of Fusarium head blight (FHB). Specific wheat genotypes can convert DON into a less toxic form (DON-3-glucoside), contributing to increased resistance to the disease [15; 16; 17; 18]. In addition to DON, other mycotoxins produced by _Fusarium_, such as fusaric acid, fumonisin B1, and zearalenone, can also harm plants. They can slow down root and shoot growth, damage cell membranes, cause oxidative stress, and lead to cell death, which weakens the plant and helps the disease spread [19]. Effective control of _Fusarium_ diseases requires multiple preventive measures, including crop rotation, selection of healthy seeds, appropriate fertilization, and moisture management. In intensive cereal production systems, chemical fungicides are widely applied. However, excessive use, particularly of fungicides with the same mode of action, promotes the development of resistant pathogen strains and accelerates the emergence of resistance [20; 21]. As a result, interest in alternative strategies is growing, including the application of synthetic compounds such as quaternary pyridinium salts.