Sari Rämö

Fusarium proliferatum is one of the main pathogens causing Fusarium basal rot of onion, which is a major problem in onion cultivation worldwide. In this work, three Fusarium proliferatum isolates from onion (Allium cepa), two from imported sets and one from a mature bulb grown in Finland, were tested for pathogenicity and mycotoxin production. Symptom development in the inoculated onion bulbs and production of fumonisins, beauvericin, and moniliformin were measured at 1–5 weeks post-inoculation (wpi). Symptoms were observed in all the bulbs inoculated with F. proliferatum, starting as water-soaked lesions and developing into dead brown scales. When colonizing the bulbs, all three F. proliferatum isolates were confirmed by qPCR to express the genes FUM1, required for fumonisin production, and SIX2, encoding a putative virulence factor. Fumonisin B₁ (FB₁) was detected already at 2 wpi in a symptomatic onion inoculated with Fpr047, and at 3 wpi, fumonisin production was confirmed for all three isolates. At 4 wpi, all the isolates had produced quantifiable amounts of FB₁, ranging from 3.9 to 177 µg/kg, and fumonisin B₂, ranging from 3.4 to 89 µg/kg. At 5 wpi, FB₁ was even detected in a symptomless sample. Beauvericin and moniliformin were quantified at 5 wpi in the symptomatic onion tissues with Fpr047 and Fpr049, but not with FUS16163, which was unable to produce moniliformin and produced less beauvericin than the other F. proliferatum isolates also in the rice culture. The results showed that onions infected with F. proliferatum can contain high amounts of fumonisins.

When thick wet snow covers unfrozen ground at the beginning of winter, herders fear the development of a hard, icy bottom snow layer and the appearance of noxious moulds (microfungi) in semi-domesticated reindeer pastures. Such winter onsets were experienced in 2019 and 2021 in the reindeer herding area of Finland, after which significant reindeer losses, along with collapses in calf production and slaughter animals, were encountered. We studied the development of weather and snow conditions in the late autumn and early winter of 2021–2022 and measured snow conditions in March 2022 in 11 reindeer cooperatives. We also collected samples from reindeer winter forage plants for mycotoxin analysis. We found that the weather and snow conditions during the late autumn and early winter of 2021 caused the formation of a hard, icy bottom snow layer and the development of mycotoxins in pastures. Alternariol (AOH) and alternariol monomethyl ether (AME), produced by Alternaria spp., were found in all 33 samples (104–2562, 61–808 µg/kg DM) and zearalenone (ZEN) by Fusarium spp. in 16 samples (14–206 µg/kg). Certain significant correlations in the concentrations of mycotoxins with snow conditions and ground surface temperatures were found. We assume that besides difficult grazing conditions in the winters of 2019–2020 and 2021–2022, the presence of mycotoxins in pastures has contributed to reindeer losses and reduced the body condition, health, and reproduction of reindeer. As onsets of winters become warmer and rainier, the risk of similar pasture conditions in reindeer herding may increase.

At the same time as the strong ambition to improve sustainability and the healthiness of food systems through a transition towards a more plant-based diet, climate change is increasing the risk of plant diseases. Consequently, mycotoxigenic fungi have become a food safety issue of major importance. A variety of strategies to suppress fungal growth in the pre- and postharvest stages of plant production have been established, and the potential of various biological methods has been assessed to ensure food safety. Of the various food microbes, lactic acid bacteria are known for their capacity to suppress the growth of toxigenic fungi and adsorb free mycotoxins. The current study showed that lactic acid fermentation could mitigate aflatoxin risk in plant-based foods through a reduction in free aflatoxin B1. In line with previous studies, in which Lactiplantibacillus plantarum (formerly Lactobacillus plantarum) was shown to reduce the level of free aflatoxin B1 in vitro, L. plantarum was shown to achieve up to a 90% reduction in free aflatoxin B1 in food fermentation. The results showed that traditional lactic acid fermentation, using L. plantarum as the starter strain, could be applied to mitigate aflatoxin B1 contamination risk in proteinaceous plant-based foodstuffs. In a wider context, fermentation using selected strains of lactic acid bacteria as starters could also enhance the availability of nutritious and safer food in terms of mycotoxin risk in low-income countries.

Mycotoxin incidence in forage may heavily affect the amount of toxins consumed by cattle. However, many studies have focused on mycotoxin occurrence in cereals and there are less studies of forages, particularly of grass silages. For determining the occurrence of mycotoxins in farm silages under Northern European conditions in Finland, 37 grass silage and 6 whole-crop cereal silage batches were analysed separately for surface, core and, if present, visibly mouldy spots. Mycotoxins were found in 92% of the samples. All mouldy samples contained mycotoxins. Beauvericin was the most common mycotoxin in grass silages and roquefortine C in whole-crop cereal silages. In mouldy samples, beauvericin, mycophenolic acid and roquefortine C were the most common mycotoxins in the grass silage and mycophenolic acid in the whole-crop cereal silage. Aflatoxins were not found in any of the samples. On average, all samples contained more than one type of mycotoxin. Concentrations of mycotoxins varied considerably from very low to very high values. The results of this survey indicate that silage-fed ruminants can be exposed to a broad range of mycotoxins. The absence of visible moulds does not always indicate mycotoxin-free feed. All moulded samples contained mycotoxins and some at very high concentrations, and they contained more different types of mycotoxins than samples without visible mould. Thus, feeding mouldy feeds to animals should be avoided.

Fusarium head blight (FHB) is an economically important plant disease. Some Fusarium species produce mycotoxins that cause food safety concerns for both humans and animals. One especially important mycotoxin-producing fungus causing FHB is Fusarium graminearum. However, Fusarium species form a disease complex where different Fusarium species co-occur in the infected cereals. Effective management strategies for FHB are needed. Development of the management tools requires information about the diversity and abundance of the whole Fusarium community. Molecular quantification assays for detecting individual Fusarium species and subgroups exist, but a method for the detection and quantification of the whole Fusarium group is still lacking. In this study, a new TaqMan-based qPCR method (FusE) targeting the Fusarium-specific elongation factor region (EF1α) was developed for the detection and quantification of Fusarium spp. The FusE method was proven as a sensitive method with a detection limit of 1 pg of Fusarium DNA. Fusarium abundance results from oat samples correlated significantly with deoxynivalenol (DON) toxin content. In addition, the whole Fusarium community in Finnish oat samples was characterized with a new metabarcoding method. A shift from F. culmorum to F. graminearum in FHB-infected oats has been detected in Europe, and the results of this study confirm that. These new molecular methods can be applied in the assessment of the Fusarium community and mycotoxin risk in cereals. Knowledge gained from the Fusarium community analyses can be applied in developing and selecting effective management strategies for FHB.

Fusarium basal rot (FBR) of onion is a serious disease problem worldwide. The Fusarium species causing FBR can also produce mycotoxins that are potentially harmful to humans and animals. In this study, a multiple reaction monitoring technique with ultra-high-performance liquid chromatography–tandem mass spectrometry (MRM UHPLC-MS/MS) was developed and validated for onion matrix to study Fusarium mycotoxins in the harvested onions. This study was focused on fumonisins B₁, B₂, and B₃ (FB₁, FB₂, and FB₃), beauvericin (BEA), and moniliformin (MON), which are the main mycotoxins produced by Fusarium oxysporum and Fusarium proliferatum. In the in-house validated protocol, the onion samples were extracted with methanol:water (3:1) using magnetic stirring for 15 min. FBs and BEA were determined directly from the filtered extracts, whereas MON required sample concentration prior to analysis. No cleanup of extracts was needed prior to analysis. The target mycotoxins were separated on an Acquity UPLC system BEH C18 column with gradient elution. Mycotoxins were identified and quantified using ¹³C-FB₁ as internal standard. Minor matrix effect was compensated using multi-point matrix-matched calibration curves with uninfected onion sample. For the mycotoxins studied, a good linearity was obtained (R² ≥ 0.99) and the recoveries were in the range of 67–122%, with the highest standard deviation for MON, 22%. The limits of quantification were from 2.5 to 10 ng g⁻¹ in onion matrix. The method was successfully employed for the analysis of mycotoxins in harvested onions showing FBR symptoms and found to be infected with F. oxysporum and F. proliferatum.