Detection and dynamics of different carbendazim-resistance conferring β-tubulin variants of Gibberella zeae collected from infected wheat heads and rice stubble in China

Characterization of Fusarium species causing head blight of highland barley (qingke) in Tibet, China

Most of the research on the characterization of Fusarium species focused on wheat, barley, rice, and maize in China. However, there has been limited research in highland barley (qingke). Recently, Fusarium head blight (FHB) of qingke was recently observed in Tibet, China, especially around the Brahmaputra River. To gain a better understanding of the pathogens involver, 201 Fusarium isolates were obtained from qingke samples in 2020. Among these isolates, the most abundant species was F. avenaceum (45.3 %), followed by F. equiseti (27.8 %), F. verticillioides (13.9 %), F. acuminatum (9.0 %), F. flocciferum (3.5 %), and F. proliferatum (0.5 %). The distribution of Fusarium species varied along the Brahmaputra River, with F. avenaceum being predominant in the midstream and downstream regions, while F. equiseti was more common in the upstream region. Chemical analyses of all the isolates revealed the production of different mycotoxins by various Fusarium species. It was found that enniatins were produced by F. acuminatum, F. avenaceum, and F. flocciferum, beauvericin (BEA) and fumonisins were produced F. proliferatum and F. verticillioides, and zearalenone (ZEN) and nivalenol (NIV) were produced by F. equiseti. Pathogenicity test showed that F. avenaceum was more aggressive in causing FHB compared to F. acuminatum, F. equiseti, and F. flocciferum. The disease severity, measured by the area under the disease progress curve (AUDPC), was significantly positively (P < 0.01) correlated with the concentration of total toxins produced by each species. Furthermore, all the Fusarium strains which were used for pathogenicity test were susceptible to carbendazim, and the 50 % effective concentration (EC50) ranged from 0.406 μg/mL to 0.673 μg/mL with an average EC50 of 0.551 ± 0.012 μg/mL.

Prevalence of gastrointestinal parasites and molecular identification of beta-tubulin mutations associated with benzimidazole resistance in Haemonchus contortus in goats from selected districts of Uganda

Gastrointestinal parasites are among the most economically important pathogens of small ruminants causing serious economic losses and animal welfare problems for the livestock industry worldwide. The emergence of anthelmintic resistant H. contortus in small ruminants is a serious problem because it undermines effective helminth control and results in reduced productivity. Little is known about resistance to benzimidazoles (BZ) in Haemonchus in goats and sheep in Uganda. The objective of this study was to determine the prevalence of gastrointestinal parasites and to identify the presence of benzimidazole resistance associated mutations in the β-tubulin isotype 1 gene of Haemonchus contortus in goats from selected districts of Uganda. A total of 200 goats from 10 districts of Uganda slaughtered at Kalerwe abattoir in Kampala were sampled for H. contortus adult worms. Faecal samples were also collected to detect other intestinal parasites. Faecal microscopy and analysis were performed using flotation and sedimentation techniques. DNA was extracted from adult worms and PCR and sequencing of the ITS- 2 region and β-tubulin isotype 1 gene performed to identify H. contortus species and to determine the presence of mutations associated with anthelmintic resistance respectively. Faecal microscopy showed that the most prevalent intestinal parasites were coccidia (98%), strongyles (97.5%), Strongyloides (82%), Paramphistomum (74.5%), Moniezia (46%), Fasciola (1.5%) and Trichuris (1%). Most goats had a high intestinal burden of coccidia (≥ 5000 oocyst per gram) and strongyles (≥ 1000 egg per gram), 65% and 67.5%, respectively. The prevalence of H. contortus adult worms was 63% (126/200). Sequencing of the partial β-tubulin isotype 1 gene of 54 Haemonchus contortus adult male isolates revealed the presence of mutations associated with anthelmintic resistance. The F200Y mutation was the most common mutation (13% of samples with good beta-tubulin sequences) followed by the E198A and E198K mutations, both found in 9% of sequenced samples. Mutation F167Y was not identified in any of the samples and there were no heterozygous individuals for any of the SNPS associated with BZ resistance that were identified in this study. These findings highlight the need for controlled use of anthelmintics especially benzimidazoles, to enable sustainable control of H. contortus in Uganda, and a need for further investigation to understand the resistance of other parasites identified in this study.

Dynamics of Carbendazim-Resistance Frequency of Pathogens Associated with the Epidemic of Fusarium Head Blight

Carbendazim resistance was detected using 4,701 Fusarium graminearum species complex isolates collected from major wheat-producing regions in China from 2018 to 2020. A total of 348 carbendazim-resistant isolates were identified. The majority of carbendazim-resistant isolates were detected in Jiangsu and Anhui Provinces. In total, 227 and 88 isolates were obtained from each of the Jiangsu and Anhui Provinces, with a high resistance frequency of 41.12 and 20.56%, respectively. The predominant resistant isolates harboring point mutations were F167Y (79.31%), followed by E198Q (16.38%) and F200Y (4.31%). Compared with F. graminearum, F. asiaticum isolates were more likely to produce carbendazim resistance. In this study, we first detected carbendazim-resistant isolates in Hebei, Shaanxi, Sichuan, and Hunan Provinces. In Jiangsu, Anhui, and Zhejiang, the frequency of carbendazim-resistant isolates maintained a high level, resulting in stable carbendazim-resistant populations. We also found the dynamic of carbendazim-resistance frequency in most provinces showed similar trends to the epidemic of Fusarium Head Blight (FHB). Our results facilitate the understanding of the current situation of carbendazim resistance of FHB pathogens and will be helpful for fungicides selection in different wheat-producing areas in China.

Enhancement of herbicolin A production by integrated fermentation optimization and strain engineering in Pantoea agglomerans ZJU23

BACKGROUND

The lipopeptide herbicolin A (HA) secreted by the biocontrol agent Pantoea agglomerans ZJU23 is a promising antifungal drug to combat fungal pathogens by targeting lipid rafts, both in agricultural and clinical settings. Improvement of HA production would be of great significance in promoting its commercialization. This study aims to enhance the HA production in ZJU23 by combining fermentation optimization and strain engineering.

RESULTS

Based on the results in the single-factor experiments, corn steep liquor, temperature and initial pH were identified as the significant affecting factors by the Plackett-Burman design. The fermentation medium and conditions were further optimized using the Box-Behnken response surface method, and the HA production of the wild type strain ZJU23 was improved from ~ 87 mg/mL in King's B medium to ~ 211 mg/mL in HA induction (HAI) medium. A transposon library was constructed in ZJU23 to screen for mutants with higher HA production, and two transcriptional repressors for HA biosynthesis, LrhA and PurR, were identified. Disruption of the LrhA gene led to increased mRNA expression of HA biosynthetic genes, and subsequently improved about twofold HA production. Finally, the HA production reached ~ 471 mg/mL in the ΔLrhA mutant under optimized fermentation conditions, which is about 5.4 times higher than before (~ 87 mg/mL). The bacterial suspension of the ΔLrhA mutant fermented in HAI medium significantly enhanced its biocontrol efficacy against gray mold disease and Fusarium crown rot of wheat, showing equivalent control efficacies as the chemical fungicides used in this study. Furthermore, HA was effective against fungicide resistant Botrytis cinerea. Increased HA production substantially improved the control efficacy against gray mold disease caused by a pyrimethanil resistant strain.

CONCLUSIONS

This study reveals that the transcriptional repressor LrhA negatively regulates HA biosynthesis and the defined HAI medium is suitable for HA production. These findings provide an extended basis for large-scale production of HA and promote biofungicide development based on ZJU23 and HA in the future.

The calcium-calcineurin and high-osmolarity glycerol pathways co-regulate tebuconazole sensitivity and pathogenicity in Fusarium graminearum

The calcium-calcineurin and high-osmolarity glycerol (HOG) pathways play crucial roles in fungal development, pathogenicity, and in responses to various environmental stresses. However, interaction of these pathways in regulating fungicide sensitivity remains largely unknown in phytopathogenic fungi. In this study, we investigated the function of the calcium-calcineurin signalling pathway in Fusarium graminearum, the causal agent of Fusarium head blight. Inhibitors of Ca²⁺ and calcineurin enhanced antifungal activity of tebuconazole (an azole fungicide) against F. graminearum. Deletion of the putative downstream transcription factor FgCrz1 resulted in significantly increased sensitivity of F. graminearum to tebuconazole. FgCrz1-GFP was translocated to the nucleus upon tebuconazole treatment in a calcineurin-dependent manner. In addition, deletion of FgCrz1 increased the phosphorylation of FgHog1 in response to tebuconazole. Moreover, the calcium-calcineurin and HOG signalling pathways exhibited synergistic effect in regulating pathogenicity and sensitivity of F. graminearum to tebuconazole and multiple other stresses. RNA-seq data revealed that FgCrz1 regulated expression of a set of non-CYP51 genes that are associated with tebuconazole sensitivity, including multidrug transporters, membrane lipid biosynthesis and metabolism, and cell wall organization. Our findings demonstrate that the calcium-calcineurin and HOG pathways act coordinately to orchestrate tebuconazole sensitivity and pathogenicity in F. graminearum, which may provide novel insights in management of Fusarium disease.

Novel Camphor Sulfonohydrazide and Sulfonamide Derivatives as Potential Succinate Dehydrogenase Inhibitors against Phytopathogenic Fungi/Oomycetes

To discover novel fungicidal agrochemicals for treating wheat scab, 39 novel camphor sulfonohydrazide/sulfonamide derivatives 4a-4t and 6a-6s were designed and synthesized. In the in vitro antifungal/antioomycete assay, compounds 4g, 4n, and 4o displayed significant inhibitory activities against Fusarium graminearum, Botryosphaeria dothidea, and Phytophthora capsici. Among them, 4n exhibited the best antifungal activity against F. graminearum with an EC₅₀ value of 0.41 mg/L, which was at the same level as that of pydiflumetofen. The in vivo experiment revealed that 4n presented excellent protective and curative efficacy toward F. graminearum. In the antifungal mechanism study, 4n could increase the cell membrane permeability and reduce the exopolysaccharide and ergosterol content of F. graminearum. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses revealed that 4n could significantly damage the surface morphology and the cell ultrastructure of mycelia to interfere with the growth of F. graminearum. Furthermore, 4n exhibited potent succinate dehydrogenase (SDH) inhibitory activity in vitro with an IC₅₀ value of 3.94 μM, which was equipotent to pydiflumetofen (IC₅₀ = 4.07 μM). The molecular dynamics simulation and docking study suggested that compound 4n could well occupy the active site and form strong interactions with the key residues of SDH. The above-mentioned results demonstrated that the title camphor sulfonohydrazide/sulfonamide derivatives could be promising lead compounds for further succinate dehydrogenase inhibitor (SDHI) fungicide development.

Protocooperative Effect of Sphaerodes mycoparasitica Biocontrol and Crop Genotypes on FHB Mycotoxin Reduction in Bread and Durum Wheat Grains Intended for Human and Animal Consumption

The occurrence of Fusarium Head Blight (FHB) mycotoxins in wheat grains is a major threat to global food safety and security. Humans and animals are continuously being exposed to Fusarium mycotoxins such as deoxynivalenol (DON) and its acetylated derivatives 3ADON and 15ADON through the ingestion of contaminated food or grain-based diet. In this study, a host-specific mycoparasite biocontrol agent (BCA), Sphaerodes mycoparasitica, significantly reduced FHB mycotoxin occurrence in harvested wheat grains from Fusarium graminearum 3ADON chemotype infected plants in greenhouse. Four genotypes of wheat, two common wheat and two durum wheat cultivars with varying FHB resistance levels were used in this study. Principal Coordinate Analysis (PCoA) using Illumina ITS sequences depicted beta diversity changes in Fusarium species indicating that both plant cultivar and BCA treatments influenced the Fusarium species structure and mycotoxin occurrence in grains. Fusarium graminearum complex (cluster A), F. avenaceum and F. acuminatum (cluster B), and F. proliferatum (cluster C) variants were associated with different FHB mycotoxins based on LC-MS/MS analyses. The predominant FHB mycotoxins measured were DON and its acetylated derivatives 3ADON and 15ADON. The BCA reduced the occurrence of DON in grains of all four cultivars (common wheat: 1000-30,000 µg·kg^-1.; durum wheat: 600-1000 µg·kg^-1) to levels below the Limit of Quantification (LOQ) of 16 µg·kg^-1. A relatively higher concentration of DON was detected in the two common wheat genotypes when compared to the durum wheat genotype; however, the percentage reduction in the wheat genotypes was greater, reaching up to 99% with some S. mycoparasitica treatments. Similarly, a higher reduction in DON was measured in susceptible genotypes than in resistant genotypes. This study's findings underscore the potential of a Fusarium-specific S. mycoparasitica BCA as a safe and promising alternative that can be used in conjunction with other management practices to minimize FHB mycotoxins in cereal grain, food and feed intended for human and animal consumption.

Biological characterization and in vitro fungicide screenings of a new causal agent of wheat Fusarium head blight in Tibet, China

Wheat (Triticum aestivum L.) is an important cereal crop, widely grown throughout the temperate zones, and also suitable for cultivation at higher elevations. Fusarium head blight (FHB) is a highly destructive disease of wheat throughout the globe. In July 2020, serious wheat FHB symptoms were observed in open fields located in Linzhi City, southeast of Tibet, China. The causal agent was identified as Fusarium avenaceum (Fr.) Sacc. by amplification and sequencing of the internal transcribed spacer (ITS) region, translation elongation factor 1-alpha (EF-1α) gene, and RNA polymerase II subunit (RPB-2) gene, as well as by morphological characterization. Koch’s postulates were confirmed by a pathogenicity test on healthy spikes, including re-isolation and identification. To our knowledge, this is the first report of F. avenaceum causing FHB on wheat in Tibet, China. Moreover, to determine pathogen characteristics that may be useful for future disease management, the utilization of different carbon and nitrogen resources, temperature, light, and ultraviolet (UV) irradiation on mycelium growth and conidia germination were studied. Soluble starch and peptone were the best carbon, and nitrogen source for the pathogen respectively. The optimal temperatures for the pathogen’s mycelium growth and conidia germination were 15–20°C, matching the average temperature during the growing season in Linzhi (Tibet). Meanwhile, alternating 8-h light and 16-h dark was shown to be conducive to mycelia growth, and complete darkness facilitated conidia germination. In addition, UV Irradiation of 48 MJ/cm², approximately 100 times of the local condition, did not inhibit the germination of conidia. Furthermore, in vitro screening of effective fungicides was conducted. Among the seven tested pesticides, carbendazim showed the best inhibition rate, with an EC₅₀ (concentration for 50% of maximal effect) value of 2.1 mg/L. Propiconazole also showed sufficient inhibitory effects against F. avenaceum, with an EC₅₀ value of 2.6 mg/L. The study provides insights into the newly identified causal agent of wheat FHB in Tibet, China, as well as first pathogen characteristics and promising candidate substances for its management.

Interactions of C. elegans β-tubulins with the microtubule inhibitor and anthelmintic drug albendazole

Parasitic nematodes are major human and agricultural pests, and benzimidazoles are amongst the most important broad spectrum anthelmintic drug class used for their control. Benzimidazole resistance is now widespread in many species of parasitic nematodes in livestock globally and an emerging concern for the sustainable control of human soil transmitted helminths. β-tubulin is the major benzimidazole target, although other genes may influence resistance. Among the six C. elegans β-tubulin genes, loss of ben-1 causes resistance without other apparent defects. Here, we explored the genetics of C. elegans β-tubulin genes in relation to the response to the benzimidazole derivative albendazole. The most highly expressed β-tubulin isotypes, encoded by tbb-1 and tbb-2, were known to be redundant with each other for viability, and their products are predicted not to bind benzimidazoles. We found that tbb-2 mutants, and to a lesser extent tbb-1 mutants, were hypersensitive to albendazole. The double mutant tbb-2 ben-1 is uncoordinated and short, resembling the wild type exposed to albendazole, but the tbb-1 ben-1 double mutant did not show the same phenotypes. These results suggest that tbb-2 is a modifier of ABZ sensitivity. To better understand how BEN-1 mutates to cause benzimidazole resistance, we isolated mutants resistant to albendazole and found that 15 of 16 mutations occurred in the ben-1 coding region. Mutations ranged from likely nulls to hypomorphs, and several corresponded to residues that cause resistance in other organisms. Null alleles of ben-1 are albendazole-resistant and BEN-1 shows high sequence identity with tubulins from other organisms, suggesting that many amino acid changes could cause resistance. However, our results suggest that missense mutations conferring resistance are not evenly distributed across all possible conserved sites. Independent of their roles in benzimidazole resistance, tbb-1 and tbb-2 may have specialized functions as null mutants of tbb-1 or tbb-2 were cold or heat sensitive, respectively.

Moving beyond the state of the art of understanding resistance mechanisms in hookworms: confirming old and suggesting new associated SNPs

Hookworms represent a serious problem for human and animal health in different parts of the world. One of the suggested control strategies for parasitosis caused by members of the Ancylostomatidae family is mass drug aministration with benzimidazole compounds. This strategy has been proven to lead to the establishment of resistant strains in several nematodes related to SNPs at codons 167, 198 and 200 of the beta-tubulin isotype-1 gene. Through bioassay and in vivo analysis, we successfully isolated an albendazole-resistant A. ceylanicum strain by drug selective pressure. We observed a strong correlation between the presence of SNPs at codon 198 and drug resistance. We also described for the first time, in hookworms, the presence of SNP A200L, already described at low frequencies in ruminant nematodes. The results presented here are important for updating the current knowledge about anthelmintic resistance in hookworms. The answers and the new questions raised may provide a basis for the establishment of more effective control strategies.

Fungicide Resistance in Fusarium graminearum Species Complex

Fusariosis affects cereal grain crops worldwide and is responsible for devastating crops, reducing grain quality and yield, and producing strong mycotoxins. Benzimidazoles and triazoles were recommended to combat fusariosis; however, there were reports of resistance, making it necessary to reflect on the reasons for this occurrence. The purpose of this review was to evaluate the fusariosis resistance to the main agricultural fungicides, to observe whether this resistance can cause changes in the production of mycotoxins, and to verify the influence of resistance on the cereal grain production chain. Scientific articles were selected from the ScienceDirect, Scopus, and Pubmed databases, published at maximum 10 years ago and covering the main fungicide classes that combat phytopathogenesis and mycotoxin production. A high occurrence of resistance to carbendazim was found, while few reports of resistance to triazoles are available. The effectiveness of strobilurins is doubtful, due to an increase of mycotoxins linked to it. It is possible to conclude that the large-scale use of fungicides can select resistant strains that will contribute to an increase in the production of mycotoxins and harm sectors of the world economy, not only the agriculture, but also sanitation and foreign trade.

Evolution of Fusarium Head Blight Management in Wheat: Scientific Perspectives on Biological Control Agents and Crop Genotypes Protocooperation

Over the past century, the economically devastating Fusarium Head Blight (FHB) disease has persistently ravished small grain cereal crops worldwide. Annually, losses globally are in the billions of United States dollars (USD), with common bread wheat and durum wheat accounting for a major portion of these losses. Since the unforgettable FHB epidemics of the 1990s and early 2000s in North America, different management strategies have been employed to treat this disease. However, even with some of the best practices including chemical fungicides and innovative breeding technological advances that have given rise to a spectrum of moderately resistant cultivars, FHB still remains an obstinate problem in cereal farms globally. This is in part due to several constraints such as the Fusarium complex of species and the struggle to develop and employ methods that can effectively combat more than one pathogenic line or species simultaneously. This review highlights the last 100 years of major FHB epidemics in the US and Canada, as well as the evolution of different management strategies, and recent progress in resistance and cultivar development. It also takes a look at protocooperation between specific biocontrol agents and cereal genotypes as a promising tool for combatting FHB.

Evolution of the Resistance of Botrytis cinerea to Carbendazim and the Current Efficacy of Carbendazim Against Gray Mold After Long-Term Discontinuation

Gray mold caused by Botrytis cinerea is a fungal disease that critically threatens agricultural production, and carbendazim was the first fungicide used to control B. cinerea. However, B. cinerea developed serious resistance to carbendazim, and this fungicide has thus rarely been used in the past decade in China. Due to the extended discontinuation of carbendazim use, the evolution of the resistance of B. cinerea to carbendazim in recent years is unclear, and whether carbendazim can effectively control gray mold is largely unknown. Therefore, this study determined the sensitivity of 407 B. cinerea isolates collected from 2014 to 2018 to carbendazim and the ability of carbendazim to control gray mold in the field. The results showed that the frequency of B. cinerea isolates resistant to carbendazim remained above 95%. Three different mutation types responsible for the resistance of B. cinerea to carbendazim were identified at codon 198 in the β-tubulin gene sequence: E198V (changed from GAG to GTG), E198A (changed from GAG to GCG), and E198K (changed from GAG to AAG). Over the last 5 years, E198V was the major mutation. However, an analysis of its evolution revealed that the percentage of the E198V mutation declined after 2017 to 56.5% in 2018. In addition, the proportion of isolates with the E198K mutation decreased over time, and no isolates with this mutation were found in either 2017 or 2018. The proportion of the E198A mutation increased over the 5-year test period to reach 43.5% in 2018. Furthermore, three greenhouse experiments demonstrated that carbendazim has lost its ability to control gray mold. We attribute the above findings to our results showing that the carbendazim-resistant isolates had no fitness penalties compared with the carbendazim-sensitive isolates for sporulation and mycelial growth. In particular, the E198A mutant isolates exhibited a strong ability to sporulate, suggesting that the E198A mutation might become dominant in the future. Interestingly, the results showed that carbendazim-sensitive isolates could be easily controlled by four conventional fungicides, namely boscalid, procymidone, iprodione, and pyrimethanil, with mean EC₅₀ values of 0.71 ± 0.2 mg liter^-1, 1.33 ± 0.39 mg liter^-1, 0.59 ± 0.33 mg liter^-1, and 6.02 ± 3.02 mg liter^-1, respectively. In conclusion, carbendazim has lost its application value and is ineffective for the control of gray mold.

Assessing anthelmintic resistance risk in the post-genomic era: a proof-of-concept study assessing the potential for widespread benzimidazole-resistant gastrointestinal nematodes in North American cattle and bison

As genomic research continues to improve our understanding of the genetics of anthelmintic drug resistance, the revolution in DNA sequencing technologies will provide increasing opportunities for large-scale surveillance for the emergence of drug resistance. In most countries, parasite control in cattle and bison has mainly depended on pour-on macrocyclic lactone formulations resulting in widespread ivermectin resistance. Consequently, there is an increased interest in using benzimidazole drugs which have been used comparatively little in cattle and bison in recent years. This situation, together with our understanding of benzimidazole resistance genetics, provides a practical opportunity to use deep-amplicon sequencing to assess the risk of drug resistance emergence. In this paper, we use deep-amplicon sequencing to scan for those mutations in the isotype-1 β-tubulin gene previously associated with benzimidazole resistance in many trichostrongylid nematode species. We found that several of these mutations occur at low frequency in many cattle and bison parasite populations in North America, suggesting increased use of benzimidazole drugs in cattle has the potential to result in widespread emergence of resistance in multiple parasite species. This work illustrates a post-genomic approach to large-scale surveillance of early emergence of anthelmintic resistance in the field.

New codon 198 β-tubulin polymorphisms in highly benzimidazole resistant Haemonchus contortus from goats in three different states in Sudan

Background

Benzimidazole (BZ) resistance in gastrointestinal nematodes is a worldwide problem for livestock production, particularly in small ruminants. Assignment of the emergence of resistance using sensitive and reliable methods is required to adopt the correct strategies for control. In Sudan, BZ resistant Haemonchus contortus populations were recently reported in goats in South Darfur. This study aimed to provide additional data regarding albendazole efficacy and to describe the prevailing molecular BZ resistance mechanisms.

Methods

Faecal egg count reduction and egg hatch tests (EHT) were used to evaluate albendazole efficacy in three different areas of South Darfur using naturally (Rehed Al-Birdi and Tulus) and experimentally infected (Tulus and Um Dafuq) goats. Using samples from Central, East and South Darfur, pyro- and Sanger sequencing were used to detect the polymorphisms F167Y, E198A and F200Y in H. contortus isotype 1 β-tubulin in DNA extracted from pooled third-stage larval (L3) samples (n = 36) on days 0 and 10 during trials, and from pooled adult male H. contortus (treated goats, n = 14; abattoirs, n = 83) including samples from populations previously found to be resistant in South Darfur.

Results

Albendazole efficacies at 5, 7.5 and 10 mg/kg doses were 73.5–90.2% on day 14 in natural and experimental infections while 12.5 mg/kg showed > 96.6% efficacy. EC₅₀ in the EHT were 0.8 and 0.11 µg/ml thiabendazole in natural and experimental infection trials, respectively. PCRs detected Haemonchus, Trichostrongylus and Cooperia in L3 samples from albendazole-treated goats. Haemonchus contortus allele frequencies in codons 167 and 200 using pyrosequencing assays were ≤ 7.4% while codon 198 assays failed. Sanger sequencing revealed five novel polymorphisms at codon 198. Noteworthy, an E198L substitution was present in 82% of the samples (L3 and adults) including all post-treatment samples. Moreover, E198V, E198K and potentially E198I, and E198Stop were identified in a few samples.

Conclusions

To our knowledge, this is the first report of E198L in BZ resistant H. contortus and the second where this is the predominant genotype associated with resistance in any strongyle species. Since this variant cannot be quantified using pyrosequencing, the results highlight important limitations in the general applicability of pyrosequencing to quantify BZ resistance genotypes.

Reduced sensitivity of azoxystrobin and thiophanate-methyl resistance in Lasiodiplodia theobromae from papaya

Stem-end rot caused by Lasiodiplodia theobromae is one of the most devastating diseases of papaya in northeastern Brazil. It is most effectively controlled by applications of fungicides, including site-specific fungicides at risk for resistance development. This study investigated the molecular mechanisms of reduced sensitivity to the QoI fungicide azoxystrobin and resistance to the MBC fungicide thiophanate-methyl in L. theobromae from Brazilian orchards. The EC₅₀ values for azoxystrobin in sixty-four isolates ranged from 0.36 μg/ml to 364.24 μg/ml and the frequency distribution of EC₅₀ values formed a multimodal curve, indicating reduced sensitivity to azoxystrobin. In detached fruit assays reduced sensitive isolates were not controlled as effectively as sensitive isolates at lowest label rate. Partial fragments were obtained from target genes β-tubulin (751 bp) and Cytb (687 bp) of isolates resistant to thiophanate-methyl and reduced sensitivity to azoxystrobin. Sequence analysis of the β-tubulin fragment revealed a mutation corresponding to E198K in all thiophanate-methyl-resistant isolates, while reduced sensitivity to axoxystrobin was not attributable to Cytb gene alterations. The target gene-based mechanism conferring resistance to thiophanate-methyl will likely be stable even if selection pressure subsides. However, the mechanism conferring reduced sensitivity to azoxystrobin is not based on target gene modifications and thus may not be as stable as other genotypes with mutations in Cytb gene.

Fusarium graminearum Trichothecene Mycotoxins: Biosynthesis, Regulation, and Management

Fusarium head blight (FHB) of small grain cereals caused by Fusarium graminearum and other Fusarium species is an economically important plant disease worldwide. Fusarium infections not only result in severe yield losses but also contaminate grain with various mycotoxins, especially deoxynivalenol (DON). With the complete genome sequencing of F. graminearum, tremendous progress has been made during the past two decades toward understanding the basis for DON biosynthesis and its regulation. Here, we summarize the current understanding of DON biosynthesis and the effect of regulators, signal transduction pathways, and epigenetic modifications on DON production and the expression of biosynthetic TRI genes. In addition, strategies for controlling FHB and DON contamination are reviewed. Further studies on these biosynthetic and regulatory systems will provide useful knowledge for developing novel management strategies to prevent FHB incidence and mycotoxin accumulation in cereals.

Tetra-primer ARMS PCR for rapid detection and characterisation of Plasmopara viticola phenotypes resistant to carboxylic acid amide fungicides

BACKGROUND

The occurrence of Plasmopara viticola populations resistant to carboxylic acid amide (CAA) fungicides is becoming a serious problem in the control of grapevine downy mildew worldwide. The resistance is caused by point mutations in the PvCesA3 gene. These isolates with this mutation have been detected mainly by determining the minimum inhibitory concentration of fungicides, which is always time consuming and inefficient.

RESULTS

To establish a suitable method for rapid detection of the G1105S mutation in P. viticola, an efficient and simple molecular method was developed, based on tetra-primer ARMS PCR. A set of four primers were designed and optimised to distinguish the different genotypes within one step. Only 2 h was required from the sampling of symptoms to the phenotyping of fungicide resistance. Using this method, CAA-resistant P. viticola were identified for the first time in China. Also, the finding of sensitive heterozygotes indicated that the resistant allele is spreading in the population in Ziyuan.

CONCLUSION

This new method proved to be useful as an early warning system for resistance outbreaks of P. viticola to CAA fungicides in the field and may be helpful in decisions concerning rotation of different fungicide groups. © 2016 Society of Chemical Industry.

A single-nucleotide-polymorphism-based genotyping assay for simultaneous detection of different carbendazim-resistant genotypes in the Fusarium graminearum species complex

The occurrence resistance to methyl benzimidazole carbamates (MBC)-fungicides in the Fusarium graminearum species complex (FGSC) is becoming a serious problem in the control of Fusarium head blight in China. The resistance is caused by point mutations in the β2-tubulingene. So far, five resistant genotypes (F167Y, E198Q, E198L, E198K and F200Y) have been reported in the field. To establish a high-throughput method for rapid detection of all the five mutations simultaneously, an efficient single-nucleotide-polymorphism-based genotyping method was developed based on the Luminex xMAP system. One pair of amplification primers and five allele specific primer extension probes were designed and optimized to specially distinguish the different genotypes within one single reaction. This method has good extensibility and can be combined with previous reported probes to form a highly integrated tool for species, trichothecene chemotype and MBC resistance detection. Using this method, carbendazim resistant FGSC isolates from Jiangsu, Anhui and Sichuan Province in China were identified. High and moderate frequencies of resistance were observed in Jiangsu and Anhui Province, respectively. Carbendazim resistance in F. asiaticum is only observed in the 3ADON genotype. Overall, our method proved to be useful for early detection of MBC resistance in the field and the result aids in the choice of fungicide type.

Identification of a novel phenamacril-resistance-related gene by the cDNA-RAPD method in Fusarium asiaticum

BACKGROUND

Fusarium asiaticum, a dominant pathogen of Fusarium head blight (FHB) in East Asia, causes huge economic losses. Phenamacril, a novel cyanoacrylate fungicide, has been increasingly applied to control FHB in China, especially where resistance of F. asiaticum against carbendazim is severe. It is important to clarify the resistance-related mechanisms of F. asiaticum to phenamacril so as to avoid control failures, and to sustain the usefulness of the new product.

RESULTS

A novel phenamacril-resistance-related gene Famfs1 was obtained by employing the cDNA random amplified polymorphic DNA (cDNA-RAPD) technique, and was validated by genetic and biochemical assays. Compared with the corresponding progenitors, deletion of Famfs1 in phenamacril-sensitive or highly phenamacril-resistant strains caused a significant decrease in effective concentrations inhibiting radial growth by 50% (EC50 value). Additionally, the biological fitness parameters (including mycelial growth under different stresses, conidiation, perithecium formation and virulence) of the deletion mutants attenuated significantly.

CONCLUSION

Famfs1 not only was involved in the resistance of F. asiaticum to phenamacril but also played an important role in adaptation of F. asiaticum to the environment. Moreover, our data suggest that the cDNA-RAPD method can be a candidate technique to clone resistance-related genes in fungi. © 2015 Society of Chemical Industry.

Metabolic effects of azoxystrobin and kresoxim-methyl against Fusarium kyushuense examined using the Biolog FF MicroPlate

Azoxystrobin and kresoxim-methyl are strobilurin fungicides, and are effective in controlling many plant diseases, including Fusarium wilt. The mode of action of this kind of chemical is inhibition of respiration. This research investigated the sensitivities of Fusarium kyushuense to azoxystrobin and kresoxim-methyl, and to the alternative oxidase inhibitor salicylhydroxamic acid (SHAM). The Biolog FF MicroPlate is designed to examine substrate utilization and metabolic profiling of micro-organisms, and was used here to study the activity of azoxystrobin, kresoxim-methyl and SHAM against F. kyushuense. Results presented that azoxystrobin and kresoxim-methyl strongly inhibited conidial germination and mycelial growth of F. kyushuense, with EC50 values of 1.60 and 1.79μgml(-1), and 6.25 and 11.43μgml(-1), respectively; while not for SHAM. In the absence of fungicide, F. kyushuense was able to metabolize 91.6% of the tested carbon substrates, including 69 effectively and 18 moderately. SHAM did not inhibit carbon substrate utilization. Under the selective pressure of azoxystrobin and kresoxim-methyl during mycelial growth (up to 100μgml(-1)) and conidial germination (up to 10μgml(-1)), F. kyushuense was unable to metabolize many substrates in the Biolog FF MicroPlate; while especially for carbon substrates in glycolysis and tricarboxylic acid cycle, with notable exceptions such as β-hydroxybutyric acid, y-hydroxybutyric acid, α-ketoglutaric acid, α-d-glucose-1-phosphate, d-saccharic acid and succinic acid in the mycelial growth stage, and β-hydroxybutyric acid, y-hydroxybutyric acid, α-ketoglutaric acid, tween-80, arbutin, dextrin, glycerol and glycogen in the conidial germination stage. This is a new finding for some effect of azoxystrobin and kresoxim-methyl on carbon substrate utilization related to glycolysis and tricarboxylic acid cycle and other carbons, and may lead to future applications of Biolog FF MicroPlate for metabolic effects of other fungicides and other fungi, as well as providing a carbon metabolic fingerprint of F. kyushuense that could be useful for identification.

α1-Tubulin FaTuA1 plays crucial roles in vegetative growth and conidiation in Fusarium asiaticum

The filamentous ascomycete Fusarium asiaticum contains two homologous genes FaTUA1 and FaTUA2 encoding α-tubulins. In this study, we found that FaTUA2 was dispensable for vegetative growth and sporulation in F. asiaticum. The deletion of FaTUA1 however led to dramatically reduced mycelial growth, twisted hyphae and abnormal nuclei in apical cells of hyphae. The FaTUA1 deletion mutant (ΔFaTuA1-5) also showed a significant decrease in conidiation, and produced abnormal conidia. Pathogenicity assays showed that ΔFaTuA1-5 exhibited decreased virulence on wheat head. Unexpectedly, the deletion of FaTUA1 led to resistance to high temperatures. In addition, ΔFaTuA2 showed increased sensitivity to carbendazim. Furthermore, increased FaTUA2 expression in ΔFaTuA1-5 partially restored the defects of the mutant in mycelial growth, conidial production and virulence, vice versa, increased FaTUA1 expression in the FaTUA2 deletion mutant also partially relieved the defect of the mutant in the delay of conidial germination. Taken together, these results indicate that FaTuA1 plays crucial roles in vegetative growth and development, and the functions of FaTuA1 and FaTuA2 are partially interchangeable in F. asiaticum.

The evolution of fungicide resistance

Fungicides are widely used in developed agricultural systems to control disease and safeguard crop yield and quality. Over time, however, resistance to many of the most effective fungicides has emerged and spread in pathogen populations, compromising disease control. This review describes the development of resistance using case histories based on four important diseases of temperate cereal crops: eyespot (Oculimacula yallundae and Oculimacula acuformis), Septoria tritici blotch (Zymoseptoria tritici), powdery mildew (Blumeria graminis), and Fusarium ear blight (a complex of Fusarium and Microdochium spp). The sequential emergence of variant genotypes of these pathogens with reduced sensitivity to the most active single-site fungicides, methyl benzimidazole carbamates, demethylation inhibitors, quinone outside inhibitors, and succinate dehydrogenase inhibitors illustrates an ongoing evolutionary process in response to the introduction and use of different chemical classes. Analysis of the molecular mechanisms and genetic basis of resistance has provided more rapid and precise methods for detecting and monitoring the incidence of resistance in field populations, but when or where resistance will occur remains difficult to predict. The extent to which the predictability of resistance evolution can be improved by laboratory mutagenesis studies and fitness measurements, comparison between pathogens, and reconstruction of evolutionary pathways is discussed. Risk models based on fungal life cycles, fungicide properties, and exposure to the fungicide are now being refined to take account of additional traits associated with the rate of pathogen evolution. Experimental data on the selection of specific mutations or resistant genotypes in pathogen populations in response to fungicide treatments can be used in models evaluating the most effective strategies for reducing or preventing resistance. Resistance management based on robust scientific evidence is vital to prolong the effective life of fungicides and safeguard their future use in crop protection.