## 3 Results and Discussion
### Mycotoxin Occurrence
Critical period for contamination with mold and mycotoxins is the end of the growing season, when the crops are mature and begin to dry, as well as during harvesting and immediately after harvest. Rainfall is a very important factor at the crop maturity stage, since it slows down the drying process and causes the development of _Fusarium_ and production of its mycotoxins. Colonies of these fungi can be moved to storage and continue to grow if the relative humidity remains high. Prolongation of rainfall during harvest create ideal conditions for the development of many postharvest fungi [12]. [PERSON] and [PERSON] (2017) also confirmed that the occurrence and growth of fungi producing mycotoxins are controlled by various environmental and ecological factors [46]. Pre-harvest contamination by mycotoxin-producing fungi is mainly influenced by interactions between the host plant genotype, soil type and a number of biological factors. The growth and development of fungi after harvest depends on the pre-harvest soil and plant condition (i.e., nutrient-impor ished soils and damaged grain increase susceptibility), environmental factors (temperature and humidity) and the presence of biotic factors such as pests and microorganisms. In general, high humidity and temperature increase the susceptibility of crops to mycotoxin contamination. According to [PERSON] and [PERSON], the optimum temperatures for growth and mycotoxin production of the major mycotoxicine fungal species range from 20 to 35 \({}^{\circ}\)C, but its activity may continue even below 0 \({}^{\circ}\)C. Very interesting observations were made by [PERSON] et al. (2013), who monitored the levels of mycotoxins and the presence of fungal DNA as well as their correlations in samples of Finnish oats [47]. Their investigations indicate that in Europe it is possible to distinguish two populations of F. _graminetarum_ occurring in different host plants. According to their research, the 3-AcDON chemotype source population is dominant in northern Europe and has recently spread from Finland to northwest Russia, while the 15-AcDON chemotype population is dominant in Central and Southern Europe and has spread to Denmark. The 3-AcDON chemotype is rare in Germany, England, Poland, Hungary, Luxembourg and Italy. These findings suggest possible correlation between mycotoxins occurrence and geographical area/climate conditions. Other studies have shown similar observations confirming the existence of geographical differences in the composition of _Fusarium_ community in different regions of Sweden, where F. _graminetarum_ was more abundant in the western part of the country [20]. The average FB2 concentration of all barley grain samples tested was 139.05 \(\upmu\)g kg\({}^{-1}\) (Table 7), whereas in the case of oat it was 39.16 \(\upmu\)g kg\({}^{-1}\) (Table 8). High contents of FB2, within a range of 289.52-645.34 \(\upmu\)g kg\({}^{-1}\), were found in a few individual barley grain samples of SU Lolek, Britney and Natasia cultivars. The concentrations of fumonisins in the oat samples were rather low, not far above the limit of quantification, which is 10 \(\upmu\)g kg\({}^{-1}\). The DON, ZEA, T-2 and HT-2 toxins were detected only in Soldo cultivar of barley. However, the contents of all four toxins were very low. 15-AcDON was found only in Fariba barley and Arden oat samples. Most of the tested barley and oat grain samples contained OTA contamination. It was not detected only in the grain samples of three barley (Olimpic, Fariba and Fabienne) and one oat (Amant) cultivars. Among all the barley and oat grain samples tested, no mycotoxin contaminations were found only in the case of one oat cultivar--Amant (Table 8). According to [PERSON] (2007), genetic susceptibility and several environmental factors and agricultural practices, such as tillage, soil fertilization, planting dates, pest and weed control, physiological stage of plants and pre- and post-harvest conditions, can influence the crop mycotoxin contamination [17]. [PERSON] et al.