Reduction ofFusariumhead blight and deoxynivalenol in wheat with early fungicide applications of prothioconazole

Effects of wheat varieties, fungicides and application time on Fusarium head blight and deoxynivalenol contamination control in wheat

BACKGROUND

Yield loss and toxin contamination caused by wheat Fusarium head blight (FHB) have always been a worldwide concern. Cultivating disease-resistant varieties and fungicide application are effective measures to control FHB. The comprehensive control technology system for FHB and toxin contamination of wheat in Anhui Province needs further improvement. This study compared the control efficacy of different wheat varieties, fungicides and application times on wheat FHB and deoxynivalenol (DON) contamination, and the dynamic change of DON accumulation after application.

RESULTS

Among the 93 main wheat varieties in Anhui Province, the disease-resistant and low-toxic wheat variety "Ningmai 26" was more suitable for planting in the central part of Anhui Province. At the same time, "Yangmai 22" was used for subsequent experiments. The field efficacy trials of different fungicides showed that 30% prothioconazole oil dispersion (OD) had the highest control efficacy on FHB and DON contamination, reaching 94.33 and 77.49%, respectively. The study on the optimum application time of prothioconazole showed that the 0-20% flowering stage was the key point of DON control. The survey of the dynamic changes of DON accumulation showed that prothioconazole could significantly reduce the level of DON accumulation while inhibiting the accumulation rate of DON. At the same time, the control fungicide carbendazim increased the level of DON contamination.

CONCLUSION

This study will provide excellent germplasm resources for cultivating disease-resistant and low-toxic wheat varieties, and provide a theoretical reference for establishing a collaborative prevention and control system of disease control and toxin reduction. © 2023 Society of Chemical Industry.

Resistance risk assessment of Fusarium pseudograminearum from wheat to prothioconazole

Fusarium crown rot (FCR), primarily caused by Fusarium pseudograminearum, poses significant threats to cereal crops worldwide. Prothioconazole is a demethylation inhibitor (DMI) fungicide used to control FCR. However, the risk of resistance in F. pseudograminearum to prothioconazole has not yet been evaluated. In this study, the sensitivity of a total of 255 F. pseudograminearum strains obtained from Henan Province, China to prothioconazole were determined by the mycelial growth inhibition. The results showed that the effective concentration to 50% growth inhibition (EC₅₀) of these strains ranged from 0.4228 μg/mL to 2.5284 μg/mL, with a mean EC₅₀ value of 1.0692 ± 0.4527 μg/mL (mean ± SD). Thirty prothioconazole-resistant mutants were obtained out of six selected sensitive parental strains by means of fungicide taming. The resistant mutants exhibited defects in vegetative growth, conidia production, and pathogenicity on wheat seedlings compared to their parental strains. Under ion, cell wall, and temperature stress conditions but not osmotic stress, all the mutants exhibited decreased growth rates compared with their parental strains, which was consistent with the control treatment. Cross-resistance test showed that there was a cross-resistance relationship between prothioconazole and four DMI fungicides, including prochloraz, metconazole, tebuconazole and hexaconazole, but no cross-resistance was observed between prothioconazole and carbendazim, phenamacril, fludioxonil, or azoxystrobin. Although no site mutation occurred on Cyp51a and Cyp51b genes, the constitutive expression level of the Cyp51a gene was significantly increased in all mutants. After being treated with prothioconazole, the Cyp51a and Cyp51b genes were significantly increased in both the resistant mutants and their parents. These results suggested that the resistance to prothioconazole of the mutants may be attributed to the changes of the relative expression level of Cyp51a and Cyp51b genes. Taken together, these results could provide a theoretical basis for the scientific use of prothioconazole in the field and fungicide resistance management strategies.

Biocontrol Effect of Clonostachys rosea on Fusarium graminearum Infection and Mycotoxin Detoxification in Oat (Avena sativa)

Oat (Avena sativa) is susceptible to Fusarium head blight (FHB). The quality of oat grain is threatened by the accumulation of mycotoxins, particularly the trichothecene deoxynivalenol (DON), which also acts as a virulence factor for the main pathogen Fusarium graminearum. The plant can defend itself, e.g., by DON detoxification by UGT-glycosyltransferases (UTGs) and accumulation of PR-proteins, even though these mechanisms do not deliver effective levels of resistance. We studied the ability of the fungal biocontrol agent (BCA) Clonostachys rosea to reduce FHB and mycotoxin accumulation. Greenhouse trials showed that C. rosea-inoculation of oat spikelets at anthesis 3 days prior to F. graminearum inoculation reduced both the amount of Fusarium DNA (79%) and DON level (80%) in mature oat kernels substantially. DON applied to C. rosea-treated spikelets resulted in higher conversion of DON to DON-3-Glc than in mock treated plants. Moreover, there was a significant enhancement of expression of two oat UGT-glycosyltransferase genes in C. rosea-treated oat. In addition, C. rosea treatment activated expression of genes encoding four PR-proteins and a WRKY23-like transcription factor, suggesting that C. rosea may induce resistance in oat. Thus, C. rosea IK726 has strong potential to be used as a BCA against FHB in oat as it inhibits F. graminearum infection effectively, whilst detoxifying DON mycotoxin rapidly.

Genotoxic damage and apoptosis in rat glioma (F98) cell line following exposure to bromuconazole

Bromuconazole, a fungicide from the triazole family, is widely used to protect the crop from various fungal contaminations to increase product quality and productivity. Although the massive use of bromuconazole poses a serious risk to human health, the exact mechanism of bromuconazole toxicity, especially on brain support cells, called glia cells, remains unclear so far. This study aimed to determine the mechanism of cytotoxicity and genotoxicity of bromuconazole via inspection of apoptotic death in rat glioma (F98) cells. We observed that bromuconazole treatment caused concentration-dependent cell death with an IC50 of 60 µM, and disruption of the cytoskeleton was observed via immunocytochemical analysis. Further, bromuconazole inhibits cell proliferation, it arrests the cell cycle in the G0/G1 phase and so inhibits DNA synthesis. Genotoxic analysis showed that bromuconazole exposition causes DNA fragmentation (comet assay) and nuclear condensation (DAPI staining). Apoptotic cell death was confirmed through: positive Annexin-V/FITC-PI dyes, p53 and Bax overexpression, Bcl2 repression, an increase in Bax/BCL-2 ratios of the mRNA, mitochondrial membrane depolarization, and an increase of caspase-3 activity. All these results demonstrate that bromuconazole exerts its cytotoxic and genotoxic effects through apoptotic cell death, which could implicate mitochondria.

Bromuconazole fungicide induces cell cycle arrest and apoptotic cell death in cultured human colon carcinoma cells (HCT116) via oxidative stress process

BACKGROUND

Bromuconazole, a fungicide belonging to the triazole family, is a plant protection product used to control, repel or destroy fungi that may develop on crops. We investigated the pro-apoptotic effect of bromuconazole and the role of oxidative stress in the death mechanism induced by this fungicide in this study.

METHODS

The human colon HCT116 cell line was treated with Bromuconazole (IC50/4, IC50/2, and IC50) for 24 h. Cells were collected and analysed for biomarkers of apoptotic cell death and oxidative stress as well as for the assessment of genotoxic damage.

RESULTS

Our study showed that bromuconazole caused a concentration-dependent increase in cell mortality with an IC50 of 180 µM. Bromuconazole induced cell cycle arrest in the G0/G1 phase and DNA synthesis inhibition. The Comet assay showed that bromuconazole caused DNA damage in a concentration-dependent manner. Bromuconazole-induced apoptosis was observed by, Annexin-V/FITC-PI and BET/AO staining, by mitochondrial membrane depolarisation, and by increased caspase-3 activity. In addition, bromuconazole induced a significant increase in ROS and lipid peroxidation levels and a disruption in SOD and CAT activities. N-acetylcysteine (NAC) strongly prevents cytotoxic and genotoxic damage caused by bromuconazole.

CONCLUSION

Bromuconazole toxicity was through the oxidative stress process, which causes DNA damage and mitochondrial dysfunction, leading to cell cycle arrest and apoptotic death of HCT116 cells.

Enantioselective effect of chiral fungicide prothioconazole on Fusarium graminearum: Fungicidal activity and DON biosynthesis

Prothioconazole, a chiral triazole fungicide, is widely used to control Fusarium head blight (FHB) of wheat. Fusarium graminearum (F. graminearum), as the main pathogen of FHB, can produce many secondary metabolites including deoxynivalenol (DON), which threatens the health of humans and animals. However, some fungicides may stimulate F. graminearum to synthesize more DON under certain conditions. Until now, the fungicidal activity and enantioselective effect of prothioconazole enantiomers on DON production, transcriptome and metabolome of F. graminearum were unclear. The fungicidal activity of R-(-)-prothioconazole against F. graminearum was 9.12-17.73 times higher than that of S-(+)-prothioconazole under all conditions. Prothioconazole enantiomers can induce F. graminearum to synthesize more DON under 0.99 water activity (a_w) and 30 °C, especially R-(-)-prothioconazole. The expression levels of TRI6, TRI10 and TRI101 under R-(-)-prothioconazole treatment were significantly higher than those under S-(+)-prothioconazole treatment. Most genes in glycolysis, pyruvate metabolism, the target of rapamycin (TOR) signaling transduction pathway and the cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) signaling transduction pathway showed higher expression levels under R-(-)-prothioconazole treatment than uner S-(+)-prothioconazole treatment and the control. The peroxisome pathway displayed higher transcriptional activity under S-(+)-prothioconazole treatment compared with R-(-)-prothioconazole and the control. Based on metabolomic data, R-(-)-prothioconazole can significantly influence phenylalanine metabolism, and no significantly enriched pathway was found under S-(+)-prothioconazole treatment. These results are helpful to understand the risk of prothioconazole enantiomers on DON production of F. graminearum and uncover the relevant underlying mechanisms of prothioconazole enantiomers.

2-Methoxy-1,4-naphthoquinone regulated molecular alternation of Fusarium proliferatum revealed by high-dimensional biological data

Fungi Fusarium proliferatum and the toxins it produces are hazardous to agricultural plants, animals, and human health. However, there is a lack of more effective and environment-friendly natural anti-F. proliferatum agents. In the search for natural anti-fungal agents, we found that naturally originated 2-methoxy-1,4-naphthoquinone (MNQ) with a minimal inhibitory dose of 8.0 mg L^-1 possessed a potential inhibitory effect on F. proliferatum. The results of transcriptomic, proteomic, and metabolomic reveal a total of 1314 differential expression genes (DEGs, 873 up-regulated and 441 down-regulated), 259 differential expression proteins (DEPs, 104 up-regulated and 155 down-regulated), and 86 differential accumulation metabolites (DAMs, 49 up-regulated and 37 down-regulated) in MNQ-induced F. proliferatum. Further, the correlation analysis of transcriptomic, proteomic, and metabolomic indicated that these DEGs, DEPs, and DAMs were co-mapped in the pathways of glyoxylate and dicarboxylate metabolism, glycine, serine, and threonine metabolism, and pyruvate metabolism that linked to the TCA cycle. Furthermore, the key DEGs of the significantly co-mapped pathways were verified with qPCR analysis, which was related to the permeability of the cell membrane of F. proliferatum. Thus, these findings will provide fundamental scientific data on the molecular shifts of MNQ-induced F. proliferatum.

Effect of fungicides on spike characteristics in winter wheat inoculated with Fusarium culmorum

The impact of fungicides on the head blight (FHB) development disease index, percent spike harvest index (SHI), and deoxynivalenol (DON) accumulation in wheat kernels under field conditions was evaluated after artificial spike inoculation with Fusarium culmorum (S-14). The trial was carried out using commercially available fungicides and a sensitive cultivar of bread wheat (Flamura-85) in a field of a wheat producer located in the Trakya region of Turkey. Fungicides were applied at the beginning of anthesis (ZGS 61), 48 hours after the inoculation with the pathogen. Disease index was determined 10 days and 14 days post-inoculation. The application of fungicides containing tebuconazole, thiophanate methyl plus tetraconazole and prothioconazole plus trifloxystrobin reduced the FHB disease and increased kernel number, spike weight, and kernel weight, as compared to the inoculated/non-fungicide control. The efficacy of tebuconazole and of prothioconazole plus trifloxystrobin was higher than that of thiophanate methyl plus tetraconazole on FHB disease severity, percent spike harvest index (SHI), and DON accumulation in wheat kernels.

Bromuconazole caused genotoxicity and hepatic and renal damage via oxidative stress process in Wistar rats

Bromuconazole is a triazole pesticide used to protect vegetables and fruits against diverse fungi pathologies. However, its utilization may be accompanied by diverse tissue injuries. In this study, we evaluated the biochemical and histopathological modifications, and we analyzed genotoxic and oxidative stress, in the aim to examine bromuconazole effects in the liver and kidney. We subdivided animals into four groups, each one contains six adult male Wistar rats. Untreated rats received daily a corn oil (vehicle) orally. Three oral bromuconazole doses were tested (1, 5, and 10 % of LD50) daily for 28 days. Bromuconazole increased the plasma activities of alkaline phosphatase, lactate dehydrogenase, and transaminases. It also increased the plasma levels of creatinine and uric acid. Histopathological check showed that bromuconazole caused organ damage. This study makes known that bromuconazole caused conspicuous DNA damage either in hepatic or kidney tissues, with a significant increase in the levels of malondialdehyde and protein carbonyl followed by an enhancement in catalase and superoxide dismutase enzymatic activities, and these increases are in a dose-dependent manner. In other side, we found that Glutathione-S-transferase and peroxidase activities raised. Our outcomes highlight that bromuconazole exposure induced genotoxic damage and organ damage which may be caused by the disturbances of oxidative stress statue in the liver and kidney.

Bioprospecting Phenols as Inhibitors of Trichothecene-Producing Fusarium: Sustainable Approaches to the Management of Wheat Pathogens

Fusarium spp. are ubiquitous fungi able to cause Fusarium head blight and Fusarium foot and root rot on wheat. Among relevant pathogenic species, Fusarium graminearum and Fusarium culmorum cause significant yield and quality loss and result in contamination of the grain with mycotoxins, mainly type B trichothecenes, which are a major health concern for humans and animals. Phenolic compounds of natural origin are being increasingly explored as fungicides on those pathogens. This review summarizes recent research activities related to the antifungal and anti-mycotoxigenic activity of natural phenolic compounds against Fusarium, including studies into the mechanisms of action of major exogenous phenolic inhibitors, their structure-activity interaction, and the combined effect of these compounds with other natural products or with conventional fungicides in mycotoxin modulation. The role of high-throughput analysis tools to decipher key signaling molecules able to modulate the production of mycotoxins and the development of sustainable formulations enhancing potential inhibitors' efficacy are also discussed.

Pydiflumetofen Co-Formulated with Prothioconazole: A Novel Fungicide for Fusarium Head Blight and Deoxynivalenol Control

Fusarium head blight (FHB) is an important disease of small grain cereals worldwide, resulting in reduced yield and quality as well as the contamination of harvested grains with mycotoxins. The key mycotoxin of concern is deoxynivalenol (DON), which has legislative and advisory limits in numerous countries. Cereal growers have a number of control options for FHB including rotation, cultivation, and varietal resistance; however, growers are still reliant on fungicides applied at flowering as part of an IPM program. Fungicides currently available to control FHB are largely restricted to triazole chemistry. This study conducted three field experiments to compare a new co-formulation of pydiflumetofen (a succinate dehydrogenase inhibitor (SDHI) with the tradename ADEPIDYN^™) and prothioconazole (a triazole) against current standard fungicides at various timings (flag leaf fully emerged, mid-head emergence, early flowering, and late flowering) for the control of FHB and DON. Overall, the co-formulation showed greater efficacy compared to either pydiflumetofen alone or current fungicide chemistry. This greater activity was demonstrated over a wide range of spray timings (flag leaf fully emerged to late flowering). The availability of an SDHI with good activity against FHB and the resulting DON contamination of harvested grain will give growers an additional tool within an IPM program that will provide a greater flexibility of spray application windows and reduce fungicide resistance selection pressure.

Bacterial Communities in the Embryo of Maize Landraces: Relation with Susceptibility to Fusarium Ear Rot

Locally adapted maize accessions (landraces) represent an untapped resource of nutritional and resistance traits for breeding, including the shaping of distinct microbiota. Our study focused on five different maize landraces and a reference commercial hybrid, showing different susceptibility to fusarium ear rot, and whether this trait could be related to particular compositions of the bacterial microbiota in the embryo, using different approaches. Our cultivation-independent approach utilized the metabarcoding of a portion of the 16S rRNA gene to study bacterial populations in these samples. Multivariate statistical analyses indicated that the microbiota of the embryos of the accessions grouped in two different clusters: one comprising three landraces and the hybrid, one including the remaining two landraces, which showed a lower susceptibility to fusarium ear rot in field. The main discriminant between these clusters was the frequency of Firmicutes, higher in the second cluster, and this abundance was confirmed by quantification through digital PCR. The cultivation-dependent approach allowed the isolation of 70 bacterial strains, mostly Firmicutes. In vivo assays allowed the identification of five candidate biocontrol strains against fusarium ear rot. Our data revealed novel insights into the role of the maize embryo microbiota and set the stage for further studies aimed at integrating this knowledge into plant breeding programs.

Azole Use in Agriculture, Horticulture, and Wood Preservation - Is It Indispensable?

Plant pathogens cause significant damage to plant products, compromising both quantities and quality. Even though many elements of agricultural practices are an integral part of reducing disease attacks, modern agriculture is still highly reliant on fungicides to guarantee high yields and product quality. The azoles, 14-alpha demethylase inhibitors, have been the fungicide class used most widely to control fungal plant diseases for more than four decades. More than 25 different azoles have been developed for the control of plant diseases in crops and the group has a world market value share of 20-25%. Azoles have proven to provide long-lasting control of many target plant pathogens and are categorized to have moderate risk for developing fungicide resistance. Field performances against many fungal pathogens have correspondingly been stable or only moderately reduced over time. Hence azoles are still, to date, considered the backbone in many control strategies and widely used as solo fungicides or as mixing partners with other fungicide groups, broadening the control spectrum as well as minimizing the overall risk of resistance development. This review describes the historic perspective of azoles, their market shares and importance for production of major crops like cereals, rice, oilseed rape, sugar beet, banana, citrus, and soybeans. In addition, information regarding use in amenity grass, in the wood preservation industry and as plant growth regulators are described. At the end of the review azoles are discussed in a wider context including future threats following stricter requirements for registration and potential impact on human health.

Comparative assessment of spray nozzles efficacy in the control of fusarium head blight in the barley crops using developed quantitative PCR assay

Fusarium species infect cereal spikes during anthesis and cause Fusarium head blight (FHB), a destructive disease of cereal crops with worldwide economic relevance. The necessity for these phytopathogenic fungi effective control becomes increasingly important for the production of both cultivated plants and those plants seeds. Fungicide application is a key methodology for controlling the disease development and mycotoxin contamination in cereals. Polymerase chain reaction (PCR) is currently the most commonly admitted DNA-based technology for specific, rapid and precise Fusarium detection. We have developed and patented the method for detection and quantitative determination of phytopathogenic fungi F. avenaceum and F. graminearum in plant seeds using Real-Time PCR with a pair of primers, designed to amplify sequences of the internal transcribed spacer at the ribosomal RNA gene cluster of those phytopathogenic fungi. This study was aimed to perform a comparative assessment of the efficacy of different spray nozzles for antifungal treatment to control F. avenaceum and F. graminearum infection of barley grains using a developed qPCR diagnostic system. A single application of a fungicide (active ingredient's content: 250 g/l propiconazole, 80 g/l cyproconazole) at BBCH 65 (middle of flowering) was carried out. For this purpose, four spray nozzles with different technical characteristics were used: Flat Fan 030, Amistar 030, Defy 3D 030 and Vegetable 060 (Pentair, USA). DNA-based fungi detection and identification was performed using conventional PCR and developed qPCR. The level of mycotoxins in barley grain was determined using enzyme-linked immunosorbent assay (ELISA). Grain count in the ear of barley and thousand seed weight (TSW) were also examined. A single application of the fungicide inhibited the development of FHB and is accompanied by the slight increase of TSW values in treated plants. It was found, that the most effective fungicide was against F. avenaceum and F. graminearum. The inhibitory effect depended on sprayer type. According to qPCR results, the best performance was achieved when using Amistar 030 and Flat Fan (FF) 030 sprayers. The average concentration of deoxynivalenol (DON) content in all barley grain samples were up to 4 times higher than the permissible level. Overall, because of the high contamination levels, found in tested samples, it is possible to state that a single application of the fungicide at the flowering phase was not able to effectively reduce DON contamination in barley samples. The developed test-system for qPCR provides new important information in the study of the effectiveness of fungicides and development of strategies to control FHB in cereals, not achievable with conventional PCR.

The ASK1 gene regulates the sensitivity of Fusarium graminearum to carbendazim, conidiation and sexual production by combining with β2-tubulin

β-tubulin, a component of microtubules, is involved in a wide variety of roles in cell shape, motility, intracellular trafficking and regulating intracellular metabolism. It has been an important fungicide target to control plant pathogen, for example, Fusarium. However, the regulation of fungicide sensitivity by β-tubulin-interacting proteins is still unclear. Here, ASK1 was identified as a β-tubulin interacting protein. The ASK1 regulated the sensitivity of Fusarium to carbendazim (a benzimidazole carbamate fungicide), and multiple cellular processes, such as chromatin separation, conidiation and sexual production. Further, we found the point mutations at 50th and 198th of β₂-tubulin which caused carbendazim resistance decreased the binding between β₂-tubulin and ASK1, resulting in the deactivation of ASK1. ASK1, on the other hand, competed with carbendazim to bind to β₂-tubulin. The point mutation F167Y in β₂-tubulin broke the intermolecular H-bonds and salt bridges between β₂-tubulin and ASK1, which reduced the competitive effect of ASK1 to carbendazim and resulted in the similar carbendazim sensitivities in F167Y-ΔASK1 and F167Y. These findings have powerful implications for efforts to understand the interaction among β₂-tubulin, its interacting proteins and fungicide, as well as to discover and develop new fungicide against Fusarium.

Moving from qPCR to Chip Digital PCR Assays for Tracking of some Fusarium Species Causing Fusarium Head Blight in Cereals

Fusarium Head Blight (FHB) is one of the major diseases affecting small-grain cereals, worldwide spread and responsible for severe yield and quality losses annually. Diagnostic tools, able to track Fusarium species even in the early stages of infection, can contribute to mycotoxins' risk control. Among DNA-based technologies for Fusarium detection, qPCR (single and multiplex assays) is currently the most applied method. However, pathogen diagnostics is now enforced by digital PCR (dPCR), a breakthrough technology that provides ultrasensitive and absolute nucleic acid quantification. In our work, a panel of chip digital PCR assays was developed to quantify Fusarium graminearum, F.culmorum, F. sporotrichioides, F. poae and F. avenaceum. The primers/probes combinations were evaluated on pure fungal samples with cdPCR technique, in comparison with the qPCR approach. Moreover, the cdPCR assays were applied to quantify Fusarium in durum wheat and oat samples, naturally contaminated or spiked with fungal DNA. For a better evaluation of infection level in plants, duplex assays were developed, able to co-amplify both plant and fungal DNA. To the best of our knowledge, this is the first study directed to the application of digital PCR to Fusarium diagnosis in plants.

Effect of fungicides commonly used for Fusarium head blight management on growth and fumonisin production by Fusarium proliferatum

Fumonisin occurrence was reported in wheat grains and F. proliferatum has been suggested to be the main contributor to its presence in wheat. Thus, a survey was performed in order to study the impact of four commercial fungicides used in Argentina for controlling Fusarium head blight disease (epoxiconazole+metconazole, tebuconazole, pyraclostrobin+epoxiconazole, and prothioconazole) on growth and fumonisin production of two F. proliferatum strains in relation to water activity (a_W; 0.99, 0.97, 0.95) and temperature (15°C and 25°C). Most fungicides reduced growth rates when compared to the control (reduction increased as fungicide concentration increased), and reduced fumonisin production when they were used at high doses; however, most fungicides enhanced fumonisin production at sublethal doses, with the exception of prothioconazole. Thus, fungicides used for FHB management could enhance fumonisin production by F. proliferatum strains present in wheat grains.

Modeling Yield Losses and Fungicide Profitability for Managing Fusarium Head Blight in Brazilian Spring Wheat

Fusarium head blight (FHB) and wheat yield data were gathered from fungicide trials to explore their relationship. Thirty-seven studies over 9 years and 11 locations met the criteria for inclusion in the analysis: FHB index in the untreated check ≥ 5% and the range of index in a trial ≥ 4 percentage points. These studies were grouped into two baseline yields, low (Yl ≤ 3,631 kg ha^-1) or high (Yh > 3,631 kg ha^-1), defined based on the median of maximum yields across trials. Attainable (disease-free) yields and FHB index were predicted using a wheat crop and a disease model, respectively, in 280 simulated trials (10 planting dates in a 28-year period, 1980 to 2007) for the Passo Fundo location. The damage coefficient was then used to calculate FHB-induced yield loss (penalizing attainable yield) for each experiment. Losses were compared between periods defined as before and after FHB resurge during the early 1990s. Disease reduction from the use of one or two sprays of a triazole fungicide (tebuconazole) was also simulated, based on previous meta-analytic estimates, and the response in yield was used in a profitability analysis. Population-average intercepts but not the slopes differed significantly between Yl (2,883.6 kg ha^-1) and Yh (4,419.5 kg ha^-1) baseline yields and the damage coefficients were 1.60%^-1 and 1.05%^-1, respectively. The magnitudes and trends of simulated yield losses were in general agreement with literature reports. The risk of not offsetting the costs of one or two fungicide sprays was generally higher (>0.75) prior to FHB resurgence but fungicide profitability tended to increase in recent years, depending on the year. Our simulations allowed us to reproduce trends in historical losses, and may be further adjusted to test the effect and profitability of different control measures (host resistance, other fungicides, etc.) on quality parameters such as test weight and mycotoxin contamination, should the information become available.

Impact of microalgal phenolic extracts on the control of Fusarium graminearum and deoxynivalenol contamination in wheat

In this study, microalgal phenolic extracts (MPE) of Nannochloropsis sp. and Spirulina sp. were tested in in vitro experiments and, in comparison with synthetic fungicides, in field experiments, for their ability to control Fusarium graminearum development and limit deoxynivalenol (DON) contamination. In in vitro experiments, the Nannochloropsis and Spirulina extracts inhibited fungal biomass by 34 and 25%, respectively, compared with the untreated control. This effect was confirmed by a reduction in ergosterol production (-80% for Nannochloropsis and -75% for Spirulina) and in DON content (-97% for Nannochloropsis and -62% for Spirulina). In field experiments, application of the fungicide prothioconazole and prothioconazole + tebuconazole resulted in control of Fusarium head blight (FHB) and foliar disease, leading to a significant increase in grain yield (+13%) and a reduction in DON content (-46%) compared to the untreated control. The application of MPE at wheat flowering reduced the severity of FHB compared with the control (-35% for Spirulina and -39% for Nannochloropsis). However, the MPE did not significantly control foliar diseases (Septoria tritici blotch) and therefore did not enhance the grain yield. Moreover, no effect in reducing the DON content in comparison to the control was observed in the field. In view of that, the use of MPE in wheat fields as real alternatives to conventional fungicides requires the discovery of solutions to empower their persistence and efficacy.

Potential use of machine learning methods in assessment of Fusarium culmorum and Fusariumproliferatum growth and mycotoxin production in treatments with antifungal agents

Fusarium-controlling fungicides are necessary to limit crop loss. Little is known about the effect of antifungal formulations at sub-lethal doses, and their interaction with abiotic factors, on Fusarium culmorum and F. proliferatum development and on zearalenone and fumonisin biosynthesis, respectively. In the present study different treatments based on sulfur, trifloxystrobin and demethylation inhibitor fungicides (cyproconazole, tebuconazole and prothioconazole) under different environmental conditions, in Maize Extract Medium, are assayed in vitro. Several machine learning methods (neural networks, random forest and extreme gradient boosted trees) have been applied for the first time for modeling growth of F. culmorum and F. proliferatum and zearalenone and fumonisin production, respectively. The most effective treatment was prothioconazole, 250 g/L + tebuconazole, 150 g/L. Effective doses of this formulation for reduction or total growth inhibition ranged as follows ED₅₀ 0.49-1.70, ED₉₀ 2.57-6.02 and ED₁₀₀ 4.0-8.0 µg/mL, depending on the species, water activity and temperature. Overall, the growth rate and mycotoxin levels in cultures decreased when doses increased. Some treatments in combination with certain a_w and temperature values significantly induced toxin production. The extreme gradient boosted tree was the model able to predict growth rate and mycotoxin production with minimum error and maximum R² value.

Genomic Identification of the TOR Signaling Pathway as a Target of the Plant Alkaloid Antofine in the Phytopathogen Fusarium graminearum

Fusarium head blight caused by the fungal pathogen Fusarium graminearum is a devastating disease of cereal crops worldwide, with limited effective chemical treatments available. Here we show that the natural alkaloid compound antofine can inhibit fusarium head blight in wheat. Using yeast genomic screening, we identified the TOR pathway component RRD2 as a target of antofine that is also required for F. graminearum pathogenicity.

Antofine, a phenanthroindolizidine alkaloid, is a bioactive natural product isolated from milkweeds that exhibits numerous biological activities, including anticancer, antimicrobial, antiviral, and anti-inflammatory properties. However, the direct targets and mode of action of antofine have not been determined. In this report, we show that antofine displays antifungal properties against the phytopathogen Fusarium graminearum, the cause of Fusarium head blight disease (FHB). FHB does devastating damage to agriculture, causing billions of dollars in economic losses annually. We therefore sought to understand the mode of action of antofine in F. graminearum using insights from yeast chemical genomic screens. We used haploinsufficiency profiling (HIP) to identify putative targets of antofine in yeast and identified three candidate targets, two of which had homologs in F. graminearum. The Fusarium homologues of two targets, glutamate dehydrogenase (FgGDH) and resistance to rapamycin deletion 2 (FgRRD2), can bind antofine. Of the two genes, only the Fgrrd2 knockout displayed a loss of virulence in wheat, indicating that RRD2 is an antivirulence target of antofine in F. graminearum. Mechanistically, we demonstrate that antofine disrupts the interaction between FgRRD2 and FgTap42, which is part of the Tap42-phosphatase complex in the target of rapamycin (TOR) signaling pathway, a central regulator of cell growth in eukaryotes and a pathway of extensive study for controlling numerous pathologies.

Effect of Tebuconazole Enantiomers and Environmental Factors on Fumonisin Accumulation and FUM Gene Expression in Fusarium verticillioides

Fusarium verticillioides is an important corn pathogen that can produce fumonisins (FBs) under certain environmental conditions. In this study, we evaluated the enantioselective impact of tebuconazole enantiomers on the growth and FB production of F. verticillioides on maize-based media at different abiotic factors. The expression of FB biosynthetic genes ( FUM1 and FUM6) was quantified by real-time reverse transcription polymerase chain reaction. The results showed that water activity ( a_w), temperature, and types of tebuconazole significantly affected the growth of F. verticillioides. The order of fungicidal activity was (-)-tebuconazole > rac-tebuconazole > (+)-tebuconazole. (-)-tebuconazole exhibited the maximal selective fungicidal activity (242-fold) against F. verticillioides at 0.95 a_w and 35 °C. Production of fumonisin B₁ (FB₁) and fumonisin B₂ (FB₂) by F. verticillioides was influenced by a_w, temperature, types of tebuconazole, and dose. Under most conditions, (-)-tebuconazole showed stronger inhibition for FB₁ and FB₂ production than (+)-tebuconazole (1.87-2.85-fold reduction in FBs) and rac-tebuconazole. The optimal environmental condition for FB production was at 0.99 a_w and 25 °C. Tebuconazole enantiomers differently affected FB biosynthetic gene ( FUM1 and FUM6) expression, but the effects on FB production and gene expression showed no positive correlation. The present study provides a better understanding on ways to minimize FB production in corn treated with fungicides.

Meta-Analysis of the Effects of QoI and DMI Fungicide Combinations on Fusarium Head Blight and Deoxynivalenol in Wheat

Field trials were conducted in 17 U.S. states to evaluate the effects of quinone outside inhibitor (QoI) and demethylation inhibitor (DMI) fungicide programs on Fusarium head blight index (IND) and deoxynivalenol (DON) toxin in wheat. Four DMI-only treatments applied at Feekes 10.5.1, five QoI-only treatments applied between Feekes 9 or Feekes 10.5, three QoI+DMI mixtures applied at Feekes 10.5, and three treatments consisting of a QoI at Feekes 9 followed by a DMI at Feekes 10.5.1 were evaluated. Network meta-analytical models were fitted to log-transformed mean IND and DON data and estimated contrasts of log means were used to obtain estimates of mean percent controls relative to the nontreated check as measures of efficacy. Results from the meta-analyses were also used to assess the risk of DON increase in future trials. DMI at Feekes 10.5.1 were the most effective programs against IND and DON and the least likely to increase DON in future trials. QoI-only programs increased mean DON over the nontreated checks and were the most likely to do so in future trials, particularly when applied at Feekes 10.5. The effects of QoI+DMI combinations depended on the active ingredients and whether the two were applied as a mixture at heading or sequentially. Following a Feekes 9 QoI application with a Feekes 10.5.1 application of a DMI reduced the negative effect of the QoI on DON but was not sufficient to achieve the efficacy of the Feekes 10.5.1 DMI-only treatments. Our results suggest that one must be prudent when using QoI treatments under moderate to high risk of FHB, particularly where the QoI is used without an effective DMI applied in combination or in sequence.

Effects of Pre- and Postanthesis Applications of Demethylation Inhibitor Fungicides on Fusarium Head Blight and Deoxynivalenol in Spring and Winter Wheat

Anthesis is generally recommended as the optimum growth stage for applying a foliar fungicide to manage Fusarium head blight (FHB) and the Fusarium-associated toxin deoxynivalenol (DON) in wheat. However, because it is not always possible to treat fields at anthesis, studies were conducted to evaluate pre- and postanthesis treatment options for managing FHB and DON in spring and winter wheat. Network meta-analytical models were fitted to data from 19 years of fungicide trials, and log response ratio ([Formula: see text]) and approximate percent control ([Formula: see text]) relative to a nontreated check were estimated as measures of the effects of six treatments on FHB index (IND: mean percentage of diseased spikelets per spike) and DON. The evaluated treatments consisted of either Caramba (metconazole) applied early (at heading [CE]), at anthesis (CA), or late (5 to 7 days after anthesis; CL), or Prosaro (prothioconazole + tebuconazole) applied at the same three times and referred to as PE, PA, and PL, respectively. All treatments reduced mean IND and DON relative to the nontreated check, but the magnitude of the effect varied with timing and wheat type. CA and PA resulted in the highest [Formula: see text] values for IND, 52.2 and 51.5%, respectively, compared with 45.9% for CL, 41.3% for PL, and less than 33% for CE and PE. Anthesis and postanthesis treatments reduced mean IND by 14.9 to 29.7% relative to preanthesis treatments. The estimated effect size was also statistically significant for comparisons between CA and CL and PA and PL; CA reduced IND by 11.7% relative to CL, whereas PA reduced the disease by 17.4% relative to PL. Differences in efficacy against IND between pairs of prothioconazole + tebuconazole and metconazole treatments applied at the same timing (CE versus PE, CA versus PA, and CL versus PL) were not statistically significant. However, CA and CL outperformed PA and PL by 7 and 12.8%, respectively, in terms of efficacy against DON. All application programs had comparable efficacy against IND between spring and winter wheat types, but efficacy against DON was 10 to 16% greater for spring than winter wheat for applications made at or after anthesis. All programs led to an increase in mean grain yield and test weight relative to the nontreated check.

Tolerance of triazole-based fungicides by biocontrol agents used to control Fusarium head blight in wheat in Argentina

Fusarium head blight (FHB) caused by Fusarium graminearum species complex is a devastating disease that causes extensive yield and quality losses to wheat around the world. Fungicide application and breeding for resistance are among the most important tools to counteract FHB. Biological control is an additional tool that can be used as part of an integrated management of FHB. Bacillus velezensisRC 218, Brevibacillus sp. RC 263 and Streptomyces sp. RC 87B were selected by their potential to control FHB and deoxynivalenol production. The aim of this work was to test the tolerance of these biocontrol agents to triazole-based fungicides such as prothioconazole, tebuconazole and metconazole. Bacterial growth was evaluated in Petri dishes using the spread plating technique containing the different fungicides. Bacillus velezensisRC 218 and Streptomyces sp. RC 87B showed better tolerance to fungicides than Brevibacillus sp. RC 263. Complete growth inhibition was observed at concentrations of 20 μg ml^-1 for metconazole, 40 μg ml^-1 for tebuconazole and 80 μg ml^-1 for prothioconazole. The results obtained indicate the possibility of using these biocontrol agents in combination with fungicides as part of an integrated management to control FHB of wheat.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study evaluates the possibility to use biocontrol agents (Bacillus velezensisRC 218, Brevibacillus sp. RC 263 and Streptomyces sp. RC 87B) in combination with triazole-based fungicides to control Fusarium head blight in wheat. The evaluation of biocontrol agents' growth under in vitro conditions was carried out in Petri dishes containing either prothioconazole, tebuconazole or metconazole. Viability studies demonstrated that B. velezensisRC 218 and Streptomyces sp. RC 87B were more tolerant to the fungicides evaluated. Results obtained reflect the possibility to use fungicides at low doses combined with biocontrol agents.

Biocontrol of Fusarium graminearum sensu stricto, Reduction of Deoxynivalenol Accumulation and Phytohormone Induction by Two Selected Antagonists

Fusarium head blight (FHB) is a devastating disease that causes extensive yield and quality losses to wheat and other small cereal grains worldwide. Species within the Fusarium graminearum complex are the main pathogens associated with the disease, F. graminearum sensu stricto being the main pathogen in Argentina. Biocontrol can be used as part of an integrated pest management strategy. Phytohormones play a key role in the plant defense system and their production can be induced by antagonistic microorganisms. The aims of this study were to evaluate the effect of the inoculation of Bacillus velezensis RC 218, F. graminearum and their co-inoculation on the production of salicylic acid (SA) and jasmonic acid (JA) in wheat spikes at different periods of time under greenhouse conditions, and to evaluate the effect of B. velezensis RC 218 and Streptomyces albidoflavus RC 87B on FHB disease incidence, severity and deoxynivalenol accumulation on Triticum turgidum L. var. durum under field conditions. Under greenhouse conditions the production of JA was induced after F. graminearum inoculation at 48 and 72 h, but JA levels were reduced in the co-inoculated treatments. No differences in JA or SA levels were observed between the B. velezensis treatment and the water control. In the spikes inoculated with F. graminearum, SA production was induced early (12 h), as it was shown for initial FHB basal resistance, while JA was induced at a later stage (48 h), revealing different defense strategies at different stages of infection by the hemibiotrophic pathogen F. graminearum. Both B. velezensis RC 218 and S. albidoflavus RC 87B effectively reduced FHB incidence (up to 30%), severity (up to 25%) and deoxynivalenol accumulation (up to 51%) on durum wheat under field conditions.

Accumulation of Azole Drugs in the Fungal Plant Pathogen Magnaporthe oryzae Is the Result of Facilitated Diffusion Influx

Magnaporthe oryzae is an agricultural mold that causes disease in rice, resulting in devastating crop losses. Since rice is a world-wide staple food crop, infection by M. oryzae poses a serious global food security threat. Fungicides, including azole antifungals, are used to prevent and combat M. oryzae plant infections. The target of azoles is CYP51, an enzyme localized on the endoplasmic reticulum (ER) and required for fungal ergosterol biosynthesis. However, many basic drug-pathogen interactions, such as how the azole gets past the fungal cell wall and plasma membrane, and is transported to the ER, are not understood. In addition, reduced intracellular accumulation of antifungals has consistently been observed as a drug resistance mechanism in many fungal species. Studying the basic biology of drug-pathogen interactions may elucidate uncharacterized mechanisms of drug resistance and susceptibility in M. oryzae and potentially other related fungal pathogens. We characterized intracellular accumulation of azole drugs in M. oryzae using a radioactively labeled fluconazole uptake assay to gain insight on whether azoles enter the cell by passive diffusion, active transport, or facilitated diffusion. We show that azole accumulation is not ATP-dependent, nor does it rely on a pH-dependent process. Instead there is evidence for azole drug uptake in M. oryzae by a facilitated diffusion mechanism. The uptake system is specific for azole or azole-like compounds and can be modulated depending on cell phase and growth media. In addition, we found that co-treatment of M. oryzae with ‘repurposed’ clorgyline and radio-labeled fluconazole prevented energy-dependent efflux of fluconazole, resulting in an increased intracellular concentration of fluconazole in the fungal cell.

Bromuconazole-induced hepatotoxicity is accompanied by upregulation of PXR/CYP3A1 and downregulation of CAR/CYP2B1 gene expression

Despite widespread use of bromuconazole as a pesticide for food crops and fruits, limited studies have been done to evaluate its toxic effects. Here, we evaluated the hepatotoxic effect of bromuconazole using classical toxicological (biochemical analysis and histopathological examination) and gene-based molecular methods. Male rats were treated either orally or topically with bromuconazole at doses equal to no observed adverse effect level (NOAEL) and 1/10 LD50 for 90 d. Bromuconazole increased activities of liver enzymes (ALT, AST, ALP, and ACP), and levels of bilirubin. It also induced hepatic oxidative stress as evidenced by significant decrease in the activities of superoxide dismutase (SOD), and significant increase in levels of malondialdehyde (MDA) in liver. In addition, bromuconazole caused an increase in liver weights and necrobiotic changes (vacuolation and hepatocellular hypertrophy). It also strongly induced the expression of PXR and its downstream target CYP3A1 gene as well as the activity of CYP3A1. However, it inhibited the expression of CAR and its downstream target CYP2B1 gene without significant changing in CYP2B1 activity. Overall, the oral route showed higher hepatotoxic effect and molecular changes than the dermal route and all changes were dose dependent. This is the first investigation to report that bromuconazole-induced liver oxidative damage is accompanied by upregulation of PXR/CYP3A1 and downregulation of CAR/CYP2B1.

Assessment of azole fungicides as a tool to control growth of Aspergillus flavus and aflatoxin B1 and B2 production in maize

Aspergillus flavus is a highly aflatoxin (AF)-producing species infecting maize and other crops. It is dominant in tropical regions, but it is also considered an emerging problem associated with climate change in Europe. The aim of this study was to assess the efficacy of azole fungicides (prochloraz, tebuconazole and a 2:1 (w/w) mixture of prochloraz plus tebuconazole) to control the growth of A. flavus and AF production in yeast-extract-sucrose (YES) agar and in maize kernels under different water activities (a_w) and temperatures. Aflatoxins B₁ and B₂ were determined by LC with fluorescence detection and post-column derivatisation of AFB₁. In YES medium and maize grains inoculated with conidia of A. flavus, the growth rate (GR) of the fungus and AFB₁ and AFB₂ production were significantly influenced by temperature and treatment. In YES medium and maize kernels, optimal temperatures for GR and AF production were 37 and 25°C, respectively. In maize kernels, spore germination was not detected at the combination 37ºC/0.95 a_w; however, under these conditions germination was found in YES medium. All fungicides were more effective at 0.99 than 0.95 a_w, and at 37 than 25ºC. Fungicides effectiveness was prochloraz > prochloraz plus tebuconazole (2:1) > tebuconazole. AFs were not detected in cultures containing the highest fungicide doses, and only very low AF levels were found in cultures containing 0.1 mg l^-1 prochloraz or 5.0 mg l^-1 tebuconazole. Azoles proved to be highly efficient in reducing A. flavus growth and AF production, although stimulation of AF production was found under particular conditions and low-dosage treatments. Maize kernels were a more favourable substrate for AF biosynthesis than YES medium. This paper is the first comparative study on the effects of different azole formulations against A. flavus and AF production in a semi-synthetic medium and in maize grain under different environmental conditions.

Synthesis and Characterization of 1-(1-chlorocyclopropyl)-2-(1,2,4-triazol-1-yl)ethan-1-one

A simple and efficient method to prepare 1-(1-chlorocyclopropyl)-2-(1,2,4-triazol-1-yl)ethan-1-one via nucleophilic substitution of 2-chloro-1-(1-chlorocyclopropyl)ethanone and 1,2,4-triazole is described. The title compound is the key intermediate required for the synthesis of prothioconazole, a promising agricultural fungicide. By exploring changes in the reaction time, temperature, ratio of starting reagents, acid binding agent, and the nature of phase transfer catalyst, the reaction conditions could be optimized to afford the desired N-alkylated material in near-quantitative yield. The ultimate yield of the product after recrystallization was 93%, with a purity of 99% based on its characterization by Gas Chromatography-Mass Spectrometer (GC-MS), Fourier Transform infrared spectroscopy (IR), Proton Magnetic Resonance (1H NMR), and Carbon-13 Nuclear Magnetic Resonance (13C NMR). The synthetic process is suitable for industrial application, with the advantages of high yield and facile preparation under mild operating conditions.

Functional Agents to Biologically Control Deoxynivalenol Contamination in Cereal Grains

Mycotoxins, as microbial secondary metabolites, frequently contaminate cereal grains and pose a serious threat to human and animal health around the globe. Deoxynivalenol (DON), a commonly detected Fusarium mycotoxin, has drawn utmost attention due to high exposure levels and contamination frequency in the food chain. Biological control is emerging as a promising technology for the management of DON contamination. Functional biological control agents (BCAs), which include antagonistic microbes, natural fungicides derived from plants and detoxification enzymes, can be used to control DON contamination at different stages of grain production. In this review, studies regarding different biological agents for DON control in recent years are summarized for the first time. Furthermore, this article highlights the significance of BCAs for controlling DON contamination, as well as the need for more practical and efficient BCAs concerning food safety.

Impact of post-anthesis rainfall, fungicide and harvesting time on the concentration of deoxynivalenol and zearalenone in wheat

Field experiments were conducted to identify the impact of post-anthesis rainfall on the concentration of deoxynivalenol (DON) and zearalenone (ZON) in harvested wheat grain. Winter wheat plots were inoculated with Fusarium graminearum at stem extension (GS31) and prothioconazole was applied at mid-anthesis (GS65) to split plots and plots were subsequently mist irrigated for 5 days. Plots were either covered by polytunnels, irrigated by sprinklers or left as non-irrigated uncovered control plots after medium-milk (GS75). Plots were harvested either when ripe (GS92; early harvest) or three weeks later (late harvest). Fusarium head blight (FHB) was assessed each week from inoculation. At harvest, yield and grain quality was measured and grains were analysed for DON and ZON. Differences in rainfall resulted in contrasting disease pressure in the two experiments, with low FHB in the first experiment and high FHB in the second. Difference in FHB resulted in large differences in grain yield, quality and mycotoxin content. DON concentration was significantly (P < 0.05) higher in irrigated compared to covered and control plots in the first experiment, whereas in the second experiment, DON was significantly (P < 0.05) higher in the covered plots compared to the control and irrigated plots. ZON concentration was significantly (P < 0.05) higher in irrigated plots in both experiments. Later harvesting resulted in an approximate fivefold increase in ZON in the first experiment, but was not significantly different in the second experiment. Prothioconazole significantly (P < 0.05) reduced DON in both experiments, but gave inconsistent reductions to ZON. This is the first report to show that the post-anthesis rainfall can significantly increase ZON in wheat, which can increase further with a delayed harvest but may be significantly reduced with the application of prothioconazole. Importantly, in the absence of moisture late season, ZON remains at very low concentrations even when wheat is severely affected by FHB.

The potential of antagonistic fungi for control of Fusarium graminearum and Fusarium crookwellense varies depending on the experimental approach

AIMS

To investigate the potential of fungal antagonists to control Fusarium head blight (FHB) causing pathogens (Fusarium graminearum and F. crookwellense) with two different experimental approaches.

METHODS AND RESULTS

Using two in vitro tests, Clonostachys rosea, Cladosporium cladosporioides and 10 Trichoderma strains were screened. In a co-culture assay, all Trichoderma strains significantly reduced the colony area of F. graminearum and F. crookwellense by 45-93%, whereas C. rosea and C. cladosporioides were not effective. In another assay, all antagonists from a chosen subset reduced the number of perithecia and ascospores on wheat straw by 88-100% when inoculated before the pathogen. Only C. rosea, a weak antagonist in the co-culture assay, was effective when inoculated after the pathogen, reducing perithecia and ascospore production by 73 and 100%, respectively.

CONCLUSIONS

For screening antagonists and to avoid sorting out highly effective strains, it is crucial to consider different experimental approaches since the efficacy might differ substantially depending on the incubation conditions. By using two distinct experimental set-ups, we identified promising biological control agents.

SIGNIFICANCE AND IMPACT OF THE STUDY

FHB is one of the most devastating fungal cereal diseases worldwide. As the pathogen overwinters on crop residues, application of antagonists on residues of the previous crop during harvest could be a promising approach to efficiently control FHB in cereals as an essential part of an integrated disease management.

Quantifying the effects of fusarium head blight on grain yield and test weight in soft red winter wheat

Fusarium head blight (FHB), caused by the fungus Fusarium graminearum, is known to negatively affect wheat grain yield (YLD) and test weight (TW). However, very little emphasis has been placed on formally quantifying FHB-YLD and FHB-TW relationships. Field plots of three soft red winter wheat cultivars-'Cooper' (susceptible to FHB), 'Hopewell' (susceptible), and 'Truman' (moderately resistant)-were grown during the 2009, 2010, 2011, and 2012 seasons, and spray inoculated with spore suspensions of F. graminearum and Parastagonospora nodorum to generate a range of FHB and Stagonospora leaf blotch (SLB) levels. FHB index (IND) and SLB were quantified as percent diseased spike and flag leaf area, respectively, and YLD (kg ha(-1)) and TW (kg m(-3)) data were collected. Using IND as a continuous covariate and cultivar (CV) and SLB as categorical fixed effects, linear mixed-model regression analyses (LMMR) were used to model the IND-YLD and IND-TW relationship and to determine whether these relationships were influenced by CV and SLB. The final models fitted to the data were of the generic form y=a+b (IND), where a (intercept) or b (slope) could also depend on other factors. LMMR analyses were also used to estimate a and b by combining the studies from these 4 years with an additional 16 experiments conducted from 2003 to 2013, and bivariate random-effects meta-analysis was used to estimate population mean b ([Formula: see text]) and a (ā) for the IND-YLD relationship. YLD and TW decreased as IND increased, with b ranging from -3.2 to -2.3 kg m(-3) %(-1) for TW. For the IND-YLD relationship, [Formula: see text] was -51.7 kg ha(-1) %IND(-1) and ā was 4,426.7 kg ha(-1). Neither cultivar nor SLB affected the IND-YLD relationship but SLB affected a of the IND-TW regression lines, whereas cultivar affected b. Plots with the highest levels of SLB (based on ordinal categories for SLB) had the lowest a and Hopewell had the highest b. The level of IND at which a 50-kg m(-3) reduction in TW was predicted to occur was 19, 16, and 22% for Cooper, Hopewell, and Truman, respectively. A yield loss of 1 MT ha(-1) was predicted to occur at 19% IND. The rate of reduction in relative TW or YLD per unit increase in IND was between -0.39 and -0.32%(-1) for TW and -1.17%(-1) for YLD. Results from this study could be integrated into more general models to evaluate the economics of FHB management strategies.

Efficacy and Economics of Integrating In-Field and Harvesting Strategies to Manage Fusarium Head Blight of Wheat

Fusarium head blight (FHB), a fungal disease of wheat caused by Fusarium graminearum, and its associated toxins, particularly deoxynivalenol (DON), are best managed by integrating multiple strategies. Experiments were established in 2011 and 2013 to evaluate the effects of integrating cultivar resistance, fungicide application, and grain harvesting strategy on FHB index (IND; field severity), DON, grain yield (YLD), and grain test weight (TW; weight per unit volume). Plots of two moderately resistant and two susceptible cultivars were either treated with 19% tebuconazole + 19% prothioconazole or left untreated, and then inoculated with F. graminearum. IND was rated as the mean percentage of diseased spikelets per spike. Separate subsets of the plots of each cultivar-treatment combination were harvested with one of two combine harvester configuration: C1 (the default, set at a fan speed of 1,375 rpm and a shutter opening of 70 mm) and C4 (modified, with the same fan speeds but a wider shutter opening of 90 mm). YLD and TW data were collected, and grain samples were rated for percent Fusarium-damaged kernels (FDK) and tested for DON. Results from linear mixed-model analyses showed that the cultivar-treatment interaction was significant for all FHB-related responses, with the magnitude of the difference in mean arcsine-square-root-transformed IND and FDK (arcIND and arcFDK) and log-transformed DON (logDON) between treated and untreated being higher for susceptible than moderately resistant cultivars. Plots harvested with the C4 combine configuration had significantly higher mean TW than those harvested with C1. Treated plots had significantly higher YLD and TW than untreated plots, regardless of cultivar and configuration. Relative to the reference management program (untreated, susceptible cultivar, harvested with C1), the greatest percent reduction in FDK and DON and increase in YLD was observed for programs that included moderate resistance and fungicide treatment. The greatest percent increase in TW relative to the reference was observed when C4 adjusted combine setting was integrated with resistance and fungicide. Overall, the most effective management programs all included fungicide treatment, two included moderate resistance, and two included C4 combine setting. Relative to the reference management program, these programs resulted in 30 to 51% reduction in total estimated price discount, $127 to 312 ha^-1 increase in gross cash income, and economic benefit of $31 to 272 ha^-1, depending on the level of FHB IND (5 to 15%), grain price ($118 to 276 metric ton^-1), and fungicide application cost ($40 to 96 ha^-1).

Efficacy of Fungicide Applications During and After Anthesis Against Fusarium Head Blight and Deoxynivalenol in Soft Red Winter Wheat

Seven field experiments were conducted in Ohio and Illinois between 2011 and 2013 to evaluate postanthesis applications of prothioconazole + tebuconazole and metconazole for Fusarium head blight and deoxynivalenol (DON) control in soft red winter wheat. Treatments consisted of an untreated check and fungicide applications made at early anthesis (A), 2 (A+2), 4 (A+4), 5 (A+5), or 6 (A+6) days after anthesis. Six of the seven experiments were augmented with artificial Fusarium graminearum inoculum, and the other was naturally infected. FHB index (IND), Fusarium damaged kernels (FDK), and DON concentration of grain were quantified. All application timings led to significantly lower mean arcsine-square-root-transformed IND and FDK (arcIND and arcFDK) and log-transformed (logDON) than in the untreated check; however, arcIND, arcFDK, and logDON for the postanthesis applications were generally not significantly different from those for the anthesis applications. Relative to the check, A+2 resulted in the highest percent control for both IND and DON, 69 and 54%, respectively, followed by A+4 (62 and 52%), A+6 (62 and 48%), and A (56 and 50%). A+2 and A+6 significantly reduced IND by 30 and 14%, respectively, relative to the anthesis application. Postanthesis applications did not, however, reduce DON relative to the anthesis application. These results suggest that applications made up to 6 days following anthesis may be just as effective as, and sometimes more effective than, anthesis applications at reducing FHB and DON.

Rainfastness of Prothioconazole + Tebuconazole for Fusarium Head Blight and Deoxynivalenol Management in Soft Red Winter Wheat

Fungicides are most warranted for control of Fusarium head blight (FHB), a disease of wheat caused by the fungal pathogen Fusarium graminearum, when wet, rainy conditions occur during anthesis. However, it is unclear whether rainfall directly following application affects fungicide efficacy against FHB and its associated toxin, deoxynivalenol (DON). The objective of this study was to determine the rainfastness of the fungicide tebuconazole + prothioconazole and the residual life of tebuconazole when applied to wheat spikes at anthesis in combination with the nonionic surfactant Induce. Three field experiments were conducted during 2012 and 2013 in Wooster, OH. Simulated rainfall of a fixed intensity and duration was applied to separate plots at five different times after the fungicide treatment (0, 60, 105, 150, or 195 min). Spike samples were collected at 4-day intervals after fungicide application and assayed for tebuconazole residue. A similar set of greenhouse experiments was conducted using six post-fungicide-application rainfall timing treatments (0, 15, 30, 60, 120, or 180 min). All experiments were inoculated at anthesis with spores of F. graminearum, and FHB index (IND) and DON were quantified. In four of the five experiments, all fungicide-treated experimental units (EUs) had significantly lower mean IND and DON than the untreated check, regardless of rainfall treatment. Among rainfall treatments, EUs that received the earliest rains after fungicide application tended to have the highest numerical mean IND and DON, but were generally not significantly different from EUs that received later rain or fungicide without rain. In both years, fungicide residue on wheat spikes decreased rapidly with time after application, but the rate of reduction varied somewhat between years, with a half-life of 6 to 9 days. Rainfall treatment did not have a significant effect on the rate of residue reduction or the level of residue at a fixed sampling time after fungicide application. In this study, tebuconazole + prothioconazole mixed with a nonionic surfactant was fairly rainfast for a fixed set of rainfall characteristics, and tebuconazole residue did not persist very long after application on wheat spikes.

Fusarium head blight control and prevention of mycotoxin contamination in wheat with botanicals and tannic acid

Suspensions or solutions with 1% of Chinese galls (Galla chinensis, GC) or 1% of tannic acid (TA), inhibited germination of conidia or mycelium growth of Fusarium graminearum (FG) by 98%-100% or by 75%-80%, respectively, whereas dried bark from buckthorn (Frangula alnus, FA) showed no effect at this concentration. In climate chamber experiments where the wheat variety "Apogee" was artificially inoculated with FG and F. crookwellense (FCr) and treated with 5% suspensions of TA, GC and FA, the deoxynivalenol (DON) content in grains was reduced by 81%, 67% and 33%, respectively. In field experiments with two commercial wheat varieties and artificial or semi-natural inoculations, mean DON reductions of 66% (TA) and 58% (FA), respectively, were obtained. Antifungal toxicity can explain the high efficacies of TA and GC but not those of FA. The Fusarium head blight (FHB) and mycotoxin reducing effect of FA is probably due to elicitation of resistance in wheat plants. With semi-natural inoculation, a single FA application in the first half of the flowering period performed best. However, we assume that applications of FA at the end of ear emergence and a treatment, triggered by an infection period, with TA or GC during flowering, might perform better than synthetic fungicides.

Translocation and degradation of tebuconazole and prothioconazole in wheat following fungicide treatment at flowering

BACKGROUND

Prothioconazole and tebuconazole are among the most effective fungicides against Fusarium head blight (FHB) of wheat (Triticum aestivum L.). The translocation between the ears and the flag leaves and the kinetics of degradation may influence field efficacy of these active ingredients (AIs).

RESULTS

In greenhouse experiments, only traces (<1%) of the total AI content translocated from the flag leaves to the ears, and a maximum of 3.55% from the ears to the flag leaves. From the treated to the non-treated side of the ears, 3.2-15.9% of the AI translocated, depending on cultivar, AI and time. In field experiments, the degradation kinetics in the first 8 days after treatment revealed a higher velocity in the flag leaf blades than in the ears, although both were dependent on the type of cultivar. The fungicide treatment resulted in 42.6-100% decreases in FHB traits.

CONCLUSIONS

There is no effective translocation of these AIs, only moderate redistribution in the ears, which can be decisive from the aspect of FHB management. The degradation of prothioconazole was faster than that of tebuconazole. Cultivar and environmental effects influenced the degradation kinetics of these AIs, but a high level of protection against FHB was maintained.

Influence of agronomic and climatic factors on Fusarium infestation and mycotoxin contamination of cereals in Norway

A total of 602 samples of organically and conventionally grown barley, oats and wheat was collected at grain harvest during 2002-2004 in Norway. Organic and conventional samples were comparable pairs regarding cereal species, growing site and harvest time, and were analysed for Fusarium mould and mycotoxins. Agronomic and climatic factors explained 10-30% of the variation in Fusarium species and mycotoxins. Significantly lower Fusarium infestation and concentrations of important mycotoxins were found in the organic cereals. The mycotoxins deoxynivalenol (DON) and HT-2 toxin (HT-2) constitute the main risk for human and animal health in Norwegian cereals. The impacts of various agronomic and climatic factors on DON and HT-2 as well as on their main producers F. graminearum and F. langsethiae and on total Fusarium were tested by multivariate statistics. Crop rotation with non-cereals was found to reduce all investigated characteristics significantly--mycotoxin concentrations as well as various Fusarium infestations. No use of mineral fertilisers and herbicides was also found to decrease F. graminearum, whereas lodged fields increased the occurrence of this species. No use of herbicides was also found to decrease F. langsethiae, but for this species the occurrence was lower in lodged fields. Total Fusarium infestation was decreased with no use of fungicides or mineral fertilisers, and with crop rotation, as well as by using herbicides and increased by lodged fields. Clay and to some extent silty soils seemed to reduce F. graminearum in comparison with sandy soils. Concerning climate factors, low temperature before grain harvest was found to increase DON; and high air humidity before harvest to increase HT-2. F. graminearum was negatively correlated with precipitation in July but correlated with air humidity before harvest. F. langsethiae was correlated with temperature in July. Total Fusarium increased with increasing precipitation in July. Organic cereal farmers have fewer cereal intense rotations than conventional farmers. Further, organic farmers do not apply mineral fertiliser or pesticides (fungicides, herbicides or insecticides), and have less problem with lodged fields. The study showed that these agronomic factors were related to the infestation of Fusarium species and the concentration of mycotoxins. Hence, it is reasonable to conclude that farming system (organic versus conventional) impacts Fusarium infestation, and that organic management tends to reduce Fusarium and mycotoxins. However, Fusarium infestation and mycotoxin concentrations may be influenced by a range of factors not studied here, such as local topography and more local climate, as well as cereal species and variety.