First report of Pectobacterium versatile causing blackleg of potato in Serbia

Potato blackleg is frequently observed on the production fields in the Bačka region of Vojvodina province, which is one of the largest potato-growing areas in Serbia. This disease usually occurs during June and July. In July 2020, blackleg symptoms in the form of stem necrotic lesions, vascular discoloration, hollow stems, and wilting of whole plants were noted on potato cultivar VR808 on a field 28 ha in size located in Maglić village (GPS coordinates 45.349325 N, 19.542768 E). Disease incidence was estimated at 20-25%. Isolations were performed from 12 potato samples on Crystal Violet Pectate medium (CVP). Stem sections consisted of brown lesions and healthy tissue (c.10 cm) were surface sterilized with ethyl alcohol 70% (w/v) and rinsed with sterile distilled water. Small pieces of tissue were taken at the edges of stem lesions (between healthy and diseased tissue) were soaked in phosphate buffer saline for 20 min and plated using a standard procedure (Klement et al. 1990). Single colonies that formed pits after 48 hours at 26 °C were re-streaked onto Nutrient Agar (NA) where creamy white colonies with smooth surfaces were formed. A total of 30 isolates were selected and DNA isolated from the colonies was further analyzed by polymerase chain reaction (PCR) using the partial dnaX gene (DNA polymerase subunit III gamma/tau) with primer pair dnaXf/dnaXr for Pectobacterium and Dickeya species identification (Slawiak et al. 2009). A single characteristic band of 535 bp was amplified in all isolates (Slawiak et al. 2009). DNA sequence alignment showed two distinct groups of isolates (Fig.S1), which were genetically uniform within each group. Using BLASTn search, it was established that the dnaX sequence of the first group (consisting of 19 Serbian potato isolates) had 99.79% identity with NCBI-deposited Pectobacterium versatile strains 14A and 3-2 from potato from Belarus (Acc. No. CP034276 and CP024842, respectively) as well as SCC1 from Finland (Acc. No. CP021894). The remaining 11 dnaX sequences had 100% identity with Pectobacterium carotovorum subsp. carotovorum strain CFBP7081 originating from water in Spain (Acc. No. MK516961). The partial dnaX sequences of three Serbian P. versatile isolates (Pv1320, Pv1520, and Pv1620) and one P. carotovorum subsp. carotovorum (Pcc2520) were deposited in GenBank under Acc. No. MW839571, MW805306, MW839572, and MW805307, respectively. These results, indicating combined infection in the observed field, signify the first identification of P. versatile in Serbia. Multilocus sequence analysis (MLSA) performed with proA (proAF1/ proAR1) and mdh (mdh2/mdh4) genes (Ma et al. 2007; Moleleki et al. 2013) grouped three tested Serbian potato P. versatile isolates together with P. versatile strains from NCBI (Fig.S2). For both tested genes, BLASTn search revealed 100% homology with P. versatile strain SCC1 from Finland. Three Serbian P. versatile potato isolates were deposited under Acc. Nos. MZ682623-25 for proA and MZ682620-22 for mdh genes. According to the routine tests suggested for Pectobacteriaceae (Schaad et al. 2001), Serbian isolates possessed microbiological traits identical to P. versatile description (Portier et al. 2019). Pathogenicity was performed on potato cultivar VR808 with three selected P. versatile isolates (Pv1320, Pv1520, and Pv1620) in the following assays: (i) surface-sterilized tuber slices with holes in the center filled with 100 µL of bacterial suspensions (adjusted to 109 CFU mL-1) to test the isolates' ability to cause soft rot, and (ii) young, four-week old plants with developed 3rd true leaf (c. 30 cm tall) were inoculated by injecting stems with bacterial suspension adjusted to 107 - 108 CFU mL-1 at a height 5 cm above the soil line. Negative controls were treated with sterile distilled water. Inoculated plants were kept under controlled conditions (25 °C temperature and >70% relative humidity). Each assay was replicated twice. Soft rot appeared on tuber slices 24 h after inoculation. On inoculated stems, initial symptoms manifested as greasy elongated spots at inoculation sites two days after inoculation (DAI), and subsequently extended along the vascular tissue and became necrotic. Whole plant's decay was recorded in five DAI, while negative controls remained healthy. To complete Koch's postulates, bacteria were re-isolated from symptomatic potato plants and confirmed by PCR and sequencing of dnaX. This first report of P. versatile in potato indicates that blackleg currently present in Serbia is caused by a diverse bacterial population. This pathogen was first identified in genome comparison as 'Candidatus Pectobacterium maceratum' (Shirshikov et al. 2018) and was later renamed as Pectobacterium versatile sp. nov. (Portier et al. 2019). Thus far, bacterium Pectobacterium carotovorum subsp. brasiliensis has been recognized as dominant pathogen on most of the infected fields in Vojvodina province, and was recently noted on one plot subjected to a combined infection with Dickeya dianthicola (Marković et al. 2021). Findings achieved in this study are highly relevant, as they point to the diversity in potato blackleg pathogens, likely due to the increasingly widespread distribution of imported seed potatoes.

The impact of management practices to prevent and control mycotoxins in the European food supply chain: MyToolBox project results

The presence of mycotoxins in cereals has led to large economic losses in Europe. In the course of the European project MyToolBox, prevention and control measures to reduce mycotoxin contamination in cereals were developed. This study aimed to estimate the impact of these prevention and control measures on both the reduction in crop losses and the increased volume of crops suitable for food and/or feed. It focused on the following measures: the use of fungicides during wheat cultivation, the use of resistant maize cultivars and/or biocontrol during maize cultivation, the use of real time sensors in storage silos, the use of innovative milling strategies during the pasta making process, and the employment of degrading enzymes during the process of bioethanol and Dried Distillers Grains with Solubles (DDGS) production. The impact assessment was based on the annual volume of cereals produced, the annual levels of mycotoxin contamination, and experimental data on the prevention and control measures collected in the course of the MyToolBox project. Results are expressed in terms of reduced volumes of cereals lost, or as additional volumes of cereals available for food meeting the current European legal limits. Results showed that a reduction in crop losses as well as an increase in the volume of crops suitable as food and/or feed is feasible with each proposed prevention or control measure along the supply chain. The impact was the largest in areas and in years with the highest mycotoxin contamination levels but would have less impact in years with low mycotoxin levels. In further research, the impact assessment may be validated using future data from more years and European sites. Decision makers in the food and feed supply chain can use this impact assessment to decide on the relevant prevention and control strategies to apply.

The MyToolbox EU-China Partnership-Progress and Future Directions in Mycotoxin Research and Management

Affordable and practical tools for farmers and food processors along the chain are required to efficiently reduce the risk of mycotoxin contamination of crops, feeds and foods. Developing new tools and enhancing existing ones was the mission of MyToolBox-a four-year EU-project that included important Chinese partners and joint research efforts. To identify future directions in mycotoxin research and management in China and their role in China-EU relations, a unique stakeholder workshop including group discussions was organized in Beijing. Six related topics: biocontrol, forecasting, sampling and analysis, silo management, detoxification, and the development of safe use options for contaminated materials were covered. The discussions clearly identified a critical need for smart, integrated strategies to address mycotoxin issues to attain safer food and feed, and to minimize losses and export rejections. Managing data on when, where and the size of mycotoxin contamination events and identifying the institution(s) to manage them are complex issues in China. Studies of microbes and novel, genetically-altered enzymes to limit pre-harvest contamination and to manage post-harvest product detoxification and alternate uses of contaminated materials are in the early stages in China. Further efforts are needed to increase the visibility of mycotoxin problems beyond the scientific and research communities.

Biological Control of Aflatoxin in Maize Grown in Serbia

Aspergillus flavus is the main producer of aflatoxin B1, one of the most toxic contaminants of food and feed. With global warming, climate conditions have become favourable for aflatoxin contamination of agricultural products in several European countries, including Serbia. The infection of maize with A. flavus, and aflatoxin synthesis can be controlled and reduced by application of a biocontrol product based on non-toxigenic strains of A. flavus. Biological control relies on competition between atoxigenic and toxigenic strains. This is the most commonly used biological control mechanism of aflatoxin contamination in maize in countries where aflatoxins pose a significant threat. Mytoolbox Af01, a native atoxigenic A. flavus strain, was obtained from maize grown in Serbia and used to produce a biocontrol product that was applied in irrigated and non-irrigated Serbian fields during 2016 and 2017. The application of this biocontrol product reduced aflatoxin levels in maize kernels (51–83%). The biocontrol treatment had a highly significant effect of reducing total aflatoxin contamination by 73%. This study showed that aflatoxin contamination control in Serbian maize can be achieved through biological control methods using atoxigenic A. flavus strains.

Emerging Fusarium Mycotoxins Fusaproliferin, Beauvericin, Enniatins, and Moniliformin in Serbian Maize

Emerging mycotoxins such as moniliformin (MON), enniatins (ENs), beauvericin (BEA), and fusaproliferin (FUS) may contaminate maize and negatively influence the yield and quality of grain. The aim of this study was to determine the content of emerging Fusarium mycotoxins in Serbian maize from the 2016, 2017, and 2018 harvests. A total of 190 samples from commercial maize production operations in Serbia were analyzed for the presence of MON, ENs, BEA, and FUS using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The obtained results were interpreted together with weather data from each year. MON, BEA, and FUS were major contaminants, while other emerging mycotoxins were not detected or were found in fewer samples (<20%). Overall contamination was highest in 2016 when MON and BEA were found in 50–80% of samples. In 2017 and 2018, high levels of MON, FUS, and BEA were detected in regions with high precipitation and warm weather during the silking phase of maize (July and the beginning of August), when the plants are most susceptible to Fusarium infections. Since environmental conditions in Serbia are favorable for the occurrence of mycotoxigenic fungi, monitoring Fusarium toxins is essential for the production of safe food and feed.

Effect of Wheat Milling Process on the Distribution of Alternaria Toxins

Alternaria toxins are mycotoxins produced by various Alternaria species which, besides the Fusarium species, represent the principal contaminants of wheat worldwide. As currently, only limited information on the behaviour of Alternaria toxins during processing of cereals is available, the objective of this study was to investigate the effect of the dry milling process of wheat on Alternaria toxins distribution. Alternariol (AOH), alternariol monomethyl ether (AME) and tenuazonic acid (TeA) content were analysed by high performance liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) in all milling fractions of untreated (control), fungicide-treated, Alternaria tenuissima inoculated and commercial wheat sample. After dry milling process, in last break and milling flows and by-products, increased concentration of examined Alternaria toxins was detected. TeA was quantified in almost all milling fractions in all tested wheat samples, while AOH and AME were detectable mostly in last break and milling flows and by-products. In respect to the contamination with Alternaria toxins, white flour can be considered as relatively safe product. Since Alternaria toxins are concentrated mainly in the peripheral parts of the kernel, a special attention should be given to their content in low-grade flours and milling by-products.

Safe food and feed through an integrated toolbox for mycotoxin management: the MyToolBox approach

There is a pressing need to mobilise the wealth of knowledge from the international mycotoxin research conductedover the past 25-30 years, and to perform cutting-edge research where knowledge gaps still exist. This knowledgeneeds to be integrated into affordable and practical tools for farmers and food processors along the chain inorder to reduce the risk of mycotoxin contamination of crops, feed and food. This is the mission of MyToolBox – a four-year project which has received funding from the European Commission. It mobilises a multi-actorpartnership (academia, farmers, technology small and medium sized enterprises, food industry and policystakeholders) to develop novel interventions aimed at achieving a significant reduction in crop losses due tomycotoxin contamination. Besides a field-to-fork approach, MyToolBox also considers safe use options ofcontaminated batches, such as the efficient production of biofuels. Compared to previous efforts of mycotoxin reduction strategies, the distinguishing feature of MyToolBox is to provide the recommended measures to theend users along the food and feed chain in a web-based MyToolBox platform (e-toolbox). The project focuseson small grain cereals, maize, peanuts and dried figs, applicable to agricultural conditions in the EU and China. Crop losses using existing practices are being compared with crop losses after novel pre-harvest interventionsincluding investigation of genetic resistance to fungal infection, cultural control (e.g. minimum tillage or cropdebris treatment), the use of novel biopesticides suitable for organic farming, competitive biocontrol treatment and development of novel modelling approaches to predict mycotoxin contamination. Research into post-harvestmeasures includes real-time monitoring during storage, innovative sorting of crops using vision-technology, novelmilling technology and studying the effects of baking on mycotoxins at an industrial scale.

The protective effect of hulls on the occurrence of Alternaria mycotoxins in spelt wheat

BACKGROUND

Since there is an increasing demand on the world market for alternative crops suitable for organic production, spelt wheat (Triticum aestivum spp. spelta L.) is a highly attractive farming option. Alternaria species are widespread and infect a great variety of economically important crops. Certain species are known producers of mycotoxins. The aim of this study was to assess the protective effect of hulls covering the spelt kernels on Alternaria toxins.

RESULTS

Alternariol (AOH) and alternariol monomethyl ether (AME) were evaluated in hulls and dehulled kernels after plant inoculation with one A. alternata and two different A. tenuissima isolates. Mycotoxins were determinated using high-performance liquid chromatography with dioade array detection. The detected levels of AOH and AME were four times higher in hulls compared to kernels in inoculation treatments. AOH was registered at levels ranging from 227 to 331 µg kg(-1) in dehulled kernels and from 433 up to 1647 µg kg(-1) in hulls. AME was predominant toxin detected in the range of 277 to 398 µg kg(-1) in dehulled kernels and from 1844 to 2183 µg kg(-1) in hulls, with highly significant difference to water control treatment.

CONCLUSION

Obtained results indicate the significantly higher concentrations of Alternaria toxins in hulls than in dehulled kernels which implicate the possible protective effect of spelt wheat hulls.