Überregionales Monitoring zur Epidemie- und Schadensdynamik von Fusariumerregern sowie Strategien zur Befalls- und Risikominimierung der Mykotoxinbelastung in der Weizen- und Maiskultur Schleswig-Holsteins (2008 – 2012)

Der überregional vermehrte Maisanbau in Schleswig-Holstein, mitunter in Monokulturen, führt insgesamt zu einem erhöhten Befallsdruck mit resultierend erhöhter Mykotoxinbelastung durch Fusarium-Pilze. Eine zusätzliche und zukünftig zu erwartende Problematik ergibt sich durch die Biologie der Fusarium-Pilze, welche nicht nur an der Maiskultur, sondern auch an Weizen parasitieren. Demnach erhöht der zunehmende Maisanbau auch das überregionale Infektionspotential einerseits für die Mais-, andererseits für die Weizenkultur. In den Jahren 2008 bis 2012 wurden überregional Weizenkorn- (Sorte Ritmo, 2012 zusätzlich Inspiration und Dekan; unbehandelte Kontrolle und fungizide Gesundvariante) sowie 2011 und 2012 Silomaisproben (Sorten Lorado, LG 30222, P 8000, Torres) von verschiedenen Standorten aus ganz Schleswig-Holstein auf das Auftreten verschiedener Fusarium-Arten sowie deren Mykotoxinbelastung untersucht. Als Ergebnis der überregional unter den Bedingungen der Kulturführung und Umwelt durchgeführten Untersuchungen können Aussagen zur strategischen Nutzung verschiedener Anbausystemfaktoren (Sortenwahl, Fruchtfolge, Bodenbearbeitung) zur pflanzenhygienischen Befallskontrolle gegenüber den in Schleswig-Holstein auftretenden Fusarium-Arten abgeleitet werden. Im Winterweizen konnten in den Versuchsjahren 2008 bis 2012 die Fusarium-Arten F. graminearum, F. culmorum, F. poae, F. avenaceum, F. equiseti, F. langsethiae und F. tricinctum nachgewiesen werden, wobei F. graminearum, F. culmorum, F. poae und F. avenaceum die dominierenden Arten darstellten. In allen Versuchsjahren wurden die Mykotoxine Deoxynivalenol (DON), Nivalenol (NIV) und Zearalenon (ZEA) nachgewiesen. Die höchsten Mykotoxinwerte wurden 2011 detektiert, wobei im Mittel 2126 µg/kg DON und 518 µg/kg ZEA gefunden wurden. In 2009 und 2012 konnten mittlere Belastungen von 1049 µg/kg bzw. 807 µg/kg DON und 158 bzw. 108 µg/kg ZEA festgestellt werden. 2008 und 2010 stellten befallsschwache Jahre dar mit geringen DON- und ZEA-Werten (2008: 82 µg DON/kg, 7 µg ZEA/kg; 2010: 173 µg DON/kg, 49 µg ZEA/kg). Ursächlich für diese unterschiedlichen Mykotoxin-Gehalte waren die jahrespezifischen Witterungsbedingungen während der Weizenblüte. Während in 2011 durchschnittliche Niederschläge von 37,9 mm und Temperaturen von 16,1 °C verantwortlich für die erhöhten Mykotoxinwerte waren, konnten diese hohen Werte trotz ähnlich hoher Niederschläge in 2009 (46,2 mm) und 2012 (28,1 mm) nicht diagnostiziert werden, was auf die niedrigeren durchschnittlichen Temperaturen während der Weizenblüte in diesen Jahren zurückzuführen war (2009: 12,7 °C; 2012: 14,2 °C). Die sehr geringen Niederschlagsmengen zur Weizenblüte in den Jahren 2008 und 2010 (3,2 mm bzw. 3,9 mm) bedingten entsprechend geringe Mykotoxingehalte. Im Vergleich zur fusariumspezifisch hochanfälligen Sorte Ritmo konnte in der als gering anfällig eingestuften Sorte Dekan die DON- und ZEA-Belastungen deutlich reduziert werden, während in der Sorte Inspiration, welche als mittel bis stark anfällig eingestuft ist, eine geringere Minderung der DON- und ZEA-Belastung vergleichend zur Referenzsorte Ritmo nachgewiesen wurde. Durch den überregionalen Einsatz fusariumwirksamer Triazolfungizide zum Zeitpunkt der Blüte konnten die DON- bzw. ZEA-Belastungen des Winterweizens in Schleswig-Holstein 2008 bis 2012 überregional deutlich vermindert werden. In den Silomaisproben konnten 2011 die Fusarium-Arten F. graminearum, F. culmorum, F. poae, F. avenaceum und F. equiseti an allen Standorten nachgewiesen werden, während F. langsethiae und F. tricinctum nicht an allen Standorten präsent waren. In den Proben konnten die Mykotoxine DON, NIV und ZEA detektiert werden. In der anfälligen Sorte Lorado wurden DON-Gehalte von 1225 bis 26068 µg/kg TM und ZEA-Gehalte von 671 bis 5991 µg/kg TM analysiert. Der Einfluss von Anbausystemfaktoren zeigte hierbei deutlich, dass die Kombination von Monokultur Mais und pflugloser Bodenbearbeitung in den höchsten Mykotoxingehalten im Vergleich zum Maisanbau in Fruchtfolgen und wendender Bodenbearbeitung mit dem Pflug resultierten. Der Anbau von Sorten mit einer geringeren Anfälligkeit gegenüber Fusarien (LG 30222, P 8000, Torres) resultierte in einer deutlichen Reduktion der Mykotoxinbelastung. Jedoch waren selbst diese Sorten an Standorten mit pflugloser Bodenbearbeitung und Monokultur Mais ähnlich stark mit Mykotoxinen belastet wie die hoch anfällige Sorte Lorado. Die Ergebnisse zeigen, dass der Anbau einer gering anfälligen Sorte, der Anbau von Mais in Fruchtfolgen sowie die Nutzung des Pfluges zur wendenden Bodenbearbeitung wertvolle Werkzeuge darstellen, um die Mykotoxinbelastungen im Silomais zu reduzieren. In 2012 wurden deutlich geringere Mykotoxingehalte nachgewiesen, jedoch konnten an den Standorten mit Maismonokultur und pflugloser Bodenbearbeitung wiederum die höchsten Belastungen detektiert werden

Temporal Changes in Sensitivity of Zymoseptoria tritici Field Populations to Different Fungicidal Modes of Action

Septoria tritici blotch (STB; Zymoseptoria tritici), one of the most important foliar diseases in wheat, is mainly controlled by the intensive use of fungicides during crop growth. Unfortunately, Z. tritici field populations have developed various extents of resistance to different groups of fungicides. Due to the complete resistance to quinone outside inhibitors (QoIs), fungicidal control of STB relies mainly on demethylation inhibitors (DMIs) and succinate dehydrogenase inhibitors (SDHIs) as well as multi-site inhibitors. In this study, temporal changes in the sensitivity of Z. tritici to selected DMIs (tebuconazole, propiconazole, prothioconazole, prochloraz), SDHIs (boscalid, bixafen), and multi-site inhibitors (chlorothalonil, folpet) were determined in microtiter assays using Z. tritici field populations isolated in 1999, 2009, 2014, and 2020 in a high-disease-pressure and high-fungicide-input area in Northern Germany. For the four tested DMI fungicides, a significant shift towards decreasing sensitivity of Z. tritici field populations was observed between 1999 and 2009, whereby concentrations inhibiting fungal growth by 50% (EC50) increased differentially between the four DMIs. Since 2009, EC50 values of tebuconazole, propiconazole, and prochloraz remain stable, whereas for prothioconazole a slightly increased sensitivity shift was found. A shift in sensitivity of Z. tritici was also determined for both tested SDHI fungicides. In contrast to DMIs, EC50 values of boscalid and bixafen increased continuously between 1999 and 2020, but the increasing EC50 values were much smaller compared to those of the four tested DMIs. No changes in sensitivity of Z. tritici were observed for the multi-site inhibitors chlorothalonil and folpet over the last 21 years. The sensitivity adaptation of Z. tritici to both groups of single-site inhibitors (DMIs, SDHIs) mainly used for STB control represents a major challenge for future wheat cultivation

Composition and Predominance of Fusarium Species Causing Fusarium Head Blight in Winter Wheat Grain Depending on Cultivar Susceptibility and Meteorological Factors

Fusarium head blight (FHB) is one of the most important diseases of wheat, causing yield losses and mycotoxin contamination of harvested grain. A complex of different toxigenic Fusarium species is responsible for FHB and the composition and predominance of species within the FHB complex are determined by meteorological and agronomic factors. In this study, grain of three different susceptible winter wheat cultivars from seven locations in northern Germany were analysed within a five-year survey from 2013 to 2017 by quantifying DNA amounts of different species within the Fusarium community as well as deoxynivalenol (DON) and zearalenone (ZEA) concentrations. Several Fusarium species co-occur in wheat grain samples in all years and cultivars. F. graminearum was the most prevalent species, followed by F. culmorum, F. avenaceum and F. poae, while F. tricinctum and F. langsethiae played only a subordinate role in the FHB complex in terms of DNA amounts. In all cultivars, a comparable year-specific quantitative occurrence of the six detected species and mycotoxin concentrations were found, but with decreased DNA amounts and mycotoxin concentrations in the more tolerant cultivars, especially in years with higher disease pressure. In all years, similar percentages of DNA amounts of the six species to the total Fusarium DNA amount of all detected species were found between the three cultivars for each species, with F. graminearum being the most dominant species. Differences in DNA amounts and DON and ZEA concentrations between growing seasons depended mainly on moisture factors during flowering of wheat, while high precipitation and relative humidity were the crucial meteorological factors for infection of wheat grain by Fusarium. Highly positive correlations were found between the meteorological variables precipitation and relative humidity and DNA amounts of F. graminearum, DON and ZEA concentrations during flowering, whereas the corresponding correlations were much weaker several days before (heading) and after flowering (early and late milk stage)

Will Triazoles Still Be of Importance in Disease Control of Zymoseptoria tritici in the Future?

Septoria tritici blotch (STB), caused by Zymoseptoria tritici, is one of the most important foliar wheat diseases worldwide. Current control strategies of STB rely mainly on fungicides, whereby triazoles (demethylation inhibitors; DMIs) have been the backbone in the control of Z. tritici in the last decades. However, in recent years a gradual loss of sensitivity of Z. tritici to several active ingredients of the triazole group has been reported in several European wheat-growing areas. Nevertheless, a new triazole fungicide, namely, mefentrifluconazole, has recently become available in disease management of STB, which belongs to a completely new triazole subclass, the so-called isopropanol triazoles. In this study, the trend in sensitivity development of Z. tritici towards older triazoles (tebuconazole, prothioconazole, and propiconazole) and the new isopropanol triazole mefentrifluconazole was determined in microtiter assays using Z. tritici field populations isolated in 1999, 2009, 2014, and 2020 in a high-disease-pressure and high-fungicide-input area in northern Germany in order to investigate whether the loss of sensitivity of Z. tritici to older triazoles also applies to mefentrifluconazole. For the three triazole fungicides tebuconazole, prothioconazole and propiconazole, a significant shift towards decreasing sensitivity of Z. tritici field populations was observed from 1999 to 2020, whereas the efficacy of mefentrifluconazole in reducing the in vitro fungal growth by 50% (EC50) remained unchanged over the investigated period, demonstrating a stable sensitivity of Z. tritici towards mefentrifluconazole. Although older triazoles are suffering from a loss of sensitivity of Z. tritici field populations due to the selection and spread of less triazole sensitive strains within the Z. tritici population, the efficacy of the new triazole mefentrifluconazole with its unique isopropanol unit was not affected by these changes within the Z. tritici population. Thus, the introduction of such new molecular units could also represent an important contribution for older groups of active ingredients, which previously suffered from a loss of sensitivity

Spatio-Temporal Prediction of the Epidemic Spread of Dangerous Pathogens Using Machine Learning Methods

Real-time identification of the occurrence of dangerous pathogens is of crucial importance for the rapid execution of countermeasures. For this purpose, spatial and temporal predictions of the spread of such pathogens are indispensable. The R package papros developed by the authors offers an environment in which both spatial and temporal predictions can be made, based on local data using various deterministic, geostatistical regionalisation, and machine learning methods. The approach is presented using the example of a crops infection by fungal pathogens, which can substantially reduce the yield if not treated in good time. The situation is made more difficult by the fact that it is particularly difficult to predict the behaviour of wind-dispersed pathogens, such as powdery mildew (Blumeria graminis f. sp. tritici). To forecast pathogen development and spatial dispersal, a modelling process scheme was developed using the aforementioned R package, which combines regionalisation and machine learning techniques. It enables the prediction of the probability of yield- relevant infestation events for an entire federal state in northern Germany at a daily time scale. To run the models, weather and climate information are required, as is knowledge of the pathogen biology. Once fitted to the pathogen, only weather and climate information are necessary to predict such events, with an overall accuracy of 68% in the case of powdery mildew at a regional scale. Thereby, 91% of the observed powdery mildew events are predicted

Can Decision Support Systems Help Improve the Sustainable Use of Fungicides in Wheat?

Wheat is one of the most economically important field crops worldwide. Foliar diseases are a major threat to wheat productivity and are primarily managed by implementing less susceptible cultivars and using fungicides. With the “Farm to Fork” strategy under consideration by the European Union to reduce pesticide usage by 50% by 2030, this elucidates the importance of utilizing decision support systems (DSS) to optimize fungicide applications. Therefore, three DSSs of different origins, namely the IPM-Wheat Model Schleswig-Holstein (scientific), the ISIP system (federal), and the xarvio© FIELD MANAGER (commercial), were analysed under maritime climate conditions at three locations in a high input area of wheat cultivation in northern Germany from 2019 to 2021. Fungicide efficacy was evaluated for yield as well as for the management of prevalent pathogens (Septoria tritici blotch, glume blotch, tan spot, powdery mildew, stripe rust, and leaf rust) on two different commercially available cultivars (highly and moderately susceptible). Compared to a stage-oriented standard system, no significant decrease in yield was observed in both cultivars, despite up to a 50% reduction in fungicide use through the use of DSSs. This was attributed to an optimized timing of fungicide applications, which resulted in slightly lower but still tolerable disease suppression efficacy compared to the stage-oriented system. In conclusion, minor disease severities are often overestimated, and DSSs can help improve the sustainability of fungicide use in wheat and pesticides in general

Evaluation of High-Resolution Mass Spectrometry for the Quantitative Analysis of Mycotoxins in Complex Feed Matrices

The selective and sensitive analysis of mycotoxins in highly complex feed matrices is a great challenge. In this study, the suitability of OrbitrapTM-based high-resolution mass spectrometry (HRMS) for routine mycotoxin analysis in complex feeds was demonstrated by the successful validation of a full MS/data-dependent MS/MS acquisition method for the quantitative determination of eight Fusarium mycotoxins in forage maize and maize silage according to the Commission Decision 2002/657/EC. The required resolving power for accurate mass assignments (<5 ppm) was determined as 35,000 full width at half maximum (FWHM) and 70,000 FWHM for forage maize and maize silage, respectively. The recovery (RA), intra-day precision (RSDr), and inter-day precision (RSDR) of measurements were in the range of 94 to 108%, 2 to 16%, and 2 to 12%, whereas the decision limit (CCα) and the detection capability (CCβ) varied from 11 to 88 µg/kg and 20 to 141 µg/kg, respectively. A set of naturally contaminated forage maize and maize silage samples collected in northern Germany in 2017 was analyzed to confirm the applicability of the HRMS method to real samples. At least four Fusarium mycotoxins were quantified in each sample, highlighting the frequent co-occurrence of mycotoxins in feed

Occurrence of Fusarium Mycotoxins and Their Modified Forms in Forage Maize Cultivars

Forage maize is often infected by mycotoxin-producing Fusarium fungi during plant growth, which represent a serious health risk to exposed animals. Deoxynivalenol (DON) and zearalenone (ZEN) are among the most important Fusarium mycotoxins, but little is known about the occurrence of their modified forms in forage maize. To assess the mycotoxin contamination in Northern Germany, 120 natural contaminated forage maize samples of four cultivars from several locations were analysed by liquid chromatography-high resolution mass spectrometry (LC-HRMS) for DON and ZEN and their modified forms deoxynivalenol-3-glucoside (DON3G), the sum of 3- and 15-acetyl-deoxynivalenol (3+15-AcDON), α- and β-zearalenol (α-ZEL, β-ZEL). DON and ZEN occurred with high incidences (100 and 96%) and a wide range of concentrations, reaching levels up to 10,972 and 3910 µg/kg, respectively. Almost half of the samples (46%) exceeded the guidance value in complementary and complete feeding stuffs for ZEN (500 µg/kg), and 9% for DON (5000 µg/kg). The DON related mycotoxins DON3G and 3+15-AcDON were also present in almost all samples (100 and 97%) with amounts of up to 3038 and 2237 µg/kg and a wide range of concentrations. For the ZEN metabolites α- and β-ZEL lower incidences were detected (59 and 32%) with concentrations of up to 423 and 203 µg/kg, respectively. Forage maize samples were contaminated with at least three co-occurring mycotoxins, whereby 95% of all samples contained four or more mycotoxins with DON, DON3G, 3+15-AcDON, and ZEN co-occurring in 93%, together with α-ZEL in 57% of all samples. Positive correlations were established between concentrations of the co-occurring mycotoxins, especially between DON and its modified forms. Averaged over all samples, ratios of DON3G/DON and 3+15-AcDON/DON were similar, 20.2 and 20.5 mol%; cultivar-specific mean ratios ranged from 14.6 to 24.3 mol% and 15.8 to 24.0 mol%, respectively. In total, 40.7 mol% of the measured DON concentration was present in the modified forms DON3G and 3+15-AcDON. The α-ZEL/ZEN ratio was 6.2 mol%, ranging from 5.2 to 8.6 mol% between cultivars. These results demonstrate that modified mycotoxins contribute substantially to the overall mycotoxin contamination in forage maize. To avoid a considerable underestimation, it is necessary to analyse modified mycotoxins in future mycotoxin monitoring programs together with their parent forms

Location of Pathogen Inoculum in the Potting Substrate Influences Damage by Globisporangium ultimum, Fusarium culmorum and Rhizoctonia solani and Effectiveness of Control Agents in Maize Seedlings

The aim of this study was to determine the impact of the location of the pathogen inoculum on damage caused by Globisporangium (syn. Pythium) ultimum, Fusarium culmorum and Rhizoctonia solani in pot tests with maize. For this purpose, pathogen inoculum was added to potting substrate, and the resulting mix was used to fill the whole pot volume, the upper half, or the lower half of pots. The remaining volume was filled with non-inoculated substrate. In a second experimental approach, maize seeds were germinated in non-inoculated potting substrate and the seedlings were transferred to inoculated substrate. The seeds were untreated, treated with the chemical thiram, or treated with a bacterial or a fungal biocontrol agent. With each of the pathogens, the damage to the developing maize seedlings was the strongest when the seeds germinated in the inoculated potting substrate. When only the roots were in contact with the inoculum, there was limited damage by R. solani and F. culmorum, and no damage by G. ultimum. This implies that in experiments with artificial inoculation, the seeds should always be in immediate contact with the inoculum if a strong pathogenic effect is desired. Conversely, seed treatments must, in the first place, be able to protect the spermosphere, while the requirement to protect the roots at a distance from the seed seems to depend on the pathogen

Efficiency and Effectivity of a Biological–Epidemiological Fungal Disease Management System in Wheat—A Study of 26 Years

Foliar diseases are a major threat to worldwide wheat production, especially during the vegetative period in maritime climates. Despite advancements in agronomic practices, infestations by foliar diseases are possible under favourable weather conditions, thus, fungicides are essential for maintaining control. Stage-oriented applications are therefore common in farm practices. The optimization of fungicide use according to biological–epidemiological thresholds reduces the total amount of fungicides used, which is of political interest, especially in the European Union. Therefore, the efficiency and effectivity of the fungicides used to control the six major foliar diseases (Septoria tritici blotch, glume blotch, tans spot, powdery mildew, stripe rust, and leaf rust) were analysed in a long-term study of 26 years in northern Germany under favourable maritime conditions. Of those diseases, Septoria tritici blotch was the most dominant recurring disease, with high severity noted in every year of the study. The threshold-based disease management system was compared to a fungicide untreated control and a healthy-standard fungicide treatment (according to growth stages). The usage of the threshold-based system reduced the disease severities significantly compared to the fungicide untreated control, without any loss of yield compared to the healthy-standard fungicide treatment. Thereby, the use of fungicides was reduced by two thirds compared to the stage-oriented healthy-standard treatment. Thus, the advantages of the threshold-based system were obvious, and this approach will be an important tool for future evaluations of current farm practices