Sensitivity to silthiofam, tebuconazole and difenoconazole of Gaeumannomyces graminis var. tritici isolates from China

Understanding the ecological effects of the fungicide difenoconazole on soil and Enchytraeus crypticus gut microbiome

Increasing knowledge of the impacts of pesticides on soil ecological communities is fundamental to a comprehensive understanding of the functional changes in the global agroecosystem industry. In this study, we examined microbial community shifts in the gut of the soil-dwelling organism Enchytraeus crypticus and functional shifts in the soil microbiome (bacteria and viruses) after 21 d of exposure to difenoconazole, one of the main fungicides in intensified agriculture. Our results demonstrated reduced body weight and increased oxidative stress levels of E. crypticus under difenoconazole treatment. Meanwhile, difenoconazole not only altered the composition and structure of the gut microbial community, but also interfered with the soil-soil fauna microecology stability by impairing the abundance of beneficial bacteria. Using soil metagenomics, we revealed that bacterial genes encoding detoxification and viruses encoding carbon cycle genes exhibited a dependent enrichment in the toxicity of pesticides via metabolism. Taken together, these findings advance the understanding of the ecotoxicological impact of residual difenoconazole on the soil-soil fauna micro-ecology, and the ecological importance of virus-encoded auxiliary metabolic genes under pesticide stress.

Deposition and dissipation of difenoconazole in pepper and soil and its reduced application to control pepper anthracnose

The initial deposition amount, dissipation dynamics, retention rate, and field control efficacy of difenoconazole in pepper-soil system were studied with different application dosages, planting regions and patterns. The initial deposition amount of difenoconazole under the same application dosage showed the following order: fruits < cultivated soils < lower stems < upper stems < lower leaves < upper leaves, open field < greenhouse, and Changjiang < Cixi < Hefei < Langfang, respectively, which increased with increasing application dosage. The dissipation rates in leaves, stems, fruits and cultivated soils exhibited an initially fast and then slow trend, while the retention rates displayed a tendency of first increasing and then stabilizing with increasing application dosages. After 7 d of difenoconazole application, the retention rates at five concentrations were 10.3%- 39.1%, and the field efficacy mostly reached the minimum effective dose. These results suggested that difenoconazole could be reduced by 25% based on the minimum recommended dose meeting the requirements of field control efficacy for controlling pepper anthracnose.

Impact of fumigants on non-target soil microorganisms: a review

Fumigants have been used for decades to control soil-borne pathogens of high-value crops, and increasing evidence indicates they can affect non-target soil microbial communities. Understanding the impacts of these products on soil microorganisms is of critical importance not only for evaluating their environmental safety, but also because soil microbial communities have a central role in soil quality and nutrient cycling, plant growth, and crop production. Thus, we conducted a systematic review and metanalysis study of fumigant impacts on non-target soil microorganisms. In general, we found that fumigation decreases the bacterial diversity and abundance of total bacteria and nitrogen-cycling genes by approximately 10-50% during the first four weeks after application compared to non-treated soils. These decreases appear transient and tend to diminish or disappear after four weeks. Increases in bacterial diversity and abundance can occur after fumigation but are less common. Fumigant application can also alter bacterial community composition during the first six weeks after treatment by significantly increasing and/or decreasing the relative abundance of bacterial taxa involved in key soil functions such as N-cycling and plant-growth promotion. Knowledge gaps and areas where future research efforts should be prioritized to improve our understanding of the impact of organic fumigants on non-target soil microorganisms are discussed.

Take-All Disease: New Insights into an Important Wheat Root Pathogen

Take-all disease, caused by the fungal root pathogen Gaeumannomyces tritici, is considered to be the most important root disease of wheat worldwide. Here we review the advances in take-all research over the last 15 years, focusing on the identification of new sources of genetic resistance in wheat relatives and the role of the microbiome in disease development. We also highlight recent breakthroughs in the molecular interactions between G. tritici and wheat, including genome and transcriptome analyses. These new findings will aid the development of novel control strategies against take-all disease. In light of this growing understanding, the G. tritici-wheat interaction could provide a model study system for root-infecting fungal pathogens of cereals.

Exposure to fungicide difenoconazole reduces the soil bacterial community diversity and the co-occurrence network complexity

Difenoconazole is a triazole fungicide that is widely used worldwide and has been frequently detected in agricultural soils, but its ecotoxicological effect on soil bacterial community remains unknown. Here, the degradation of difenoconazole and its effect on soil bacterial communities were investigated at three concentrations in five different agricultural soils. Difenoconazole degraded faster in non-sterilized soils than in sterilized soils, suggesting that biodegradation is a major contributor to the dissipation of difenoconazole in soils. Exposure to high concentrations of difenoconazole decreased the soil bacterial community diversity in most soils, and this influence was aggravated with the increasing concentration. The effect of difenoconazole on soil bacterial community diversity was also enhanced with the increasing content of organic matter and total nitrogen in soils. Moreover, difenoconazole exposure also reduced the soil bacterial community network complexity and exhibited a concentration-dependent characteristic. In addition, a core bacterial community (57 operational taxonomic units, OTUs) was identified, and some core OTUs were strongly linked to the degradation of difenoconazole in soils. It is concluded that high concentrations of difenoconazole may have a significant effect on the soil bacterial communities, and co-occurrence networks may improve the ecotoxicological risk assessment of fungicides on soil microbiome.

A functional analysis of mitochondrial respiratory chain cytochrome bc1 complex in Gaeumannomyces tritici by RNA silencing as a possible target of carabrone

Gaeumannomyces tritici, an ascomycete soilborne fungus, causes a devastating root disease in wheat. Carabrone, a botanical bicyclic sesquiterpenic lactone, is a promising fungicidal agent that can effectively control G. tritici. However, the mechanism of action of carabrone against G. tritici remains largely unclear. Here, we used immunogold for subcellular localization of carabrone and the results showed that carabrone is subcellularly localized in the mitochondria of G. tritici. We then explored the functional analysis of genes GtCytc1 , GtCytb, and GtIsp of the mitochondrial respiratory chain cytochrome bc1 complex in G. tritici by RNA silencing as a possible target of carabrone. The results showed that the silenced mutant ∆GtIsp is less sensitive to carabrone compared to ∆GtCytc1 and ∆GtCytb. Compared with the control, the activities of complex III in all the strains, except ∆GtIsp and carabrone-resistant isolate 24-HN-1, were significantly decreased following treatment with carabrone at EC20 and EC80 in vitro (40%-50% and 70%-80%, respectively). The activities of mitochondrial respiratory chain complex III and the mitochondrial respiration oxygen consumption rates in all the strains, except ∆GtIsp and 24-HN-1, were higher with respect to the control when treated with carabrone at EC20 in vivo. The rates of mitochondrial respiration of all strains, except ∆GtIsp, were significantly inhibited following treatment with carabrone at EC80 (ranging from 57% to 81%). This study reveals that the targeting of the iron-sulphur protein encoded by GtIsp is highly sensitive to carabrone and provides a direction for the research of carabrone's target.

Novel Fungicide 4-Chlorocinnamaldehyde Thiosemicarbazide (PMDD) Inhibits Laccase and Controls the Causal Agent of Take-All Disease in Wheat, Gaeumannomyces graminis var. tritici

Our aim was to investigate the bioactivity and mode of action of a novel fungicide 4-chlorocinnamaldehyde thiosemicarbazide (PMDD). As a result of its efficacy against various plant pathogens, its protective fungicidal activity, and systemic transport after root treatment, PMDD could be a promising fungicide to control wheat root diseases. In a field assay, PMDD showed good control efficacy on wheat take-all disease. A biochemical study indicated that PMDD acts as a laccase inhibitor, a to date unique mode of fungicidal action. Moreover, a total of seven stable PMDD-resistant Gaeumannomyces graminis var. tritici (Ggt) mutants were generated and demonstrated no cross-resistance with any commercial fungicides used for take-all disease control, and the gene expression profile further confirmed that laccase could be the target of PMDD. Taken together, we conclude that PMDD is a laccase inhibitor and could be used on wheat to control take-all diseases. The current study could strongly benefit the registration and application of PMDD.

Enantioselective Behavior of Chiral Difenoconazole in Apple and Field Soil

Difenoconazole is a universal chiral fungicide which is widely used in apples. Recently, it is still employed as racemic mixtures without distinction of the enantiomers, which may lead to an incomplete risk assessment. Here, we analyzed the stereoselective degradation of difenoconazole in apple fruits and open-field soil using an HPLC-UV system. Different trends were established in various apple varieties under identical environmental conditions. No significant differences were found in its enantioselectivity of the degradation processes applied in the field soil of an apple orchard. However, preferential dissipation of (2R,4R)-difenoconazole and (2R,4S)-difenoconazole was observed in Hanfu and Fuji apples, resulting in the enrichment of stereoisomers of (2S,4S)-difenoconazole and (2S,4R)-difenoconazole. Meanwhile, no significant enantioselectivity was detected in Huahong apples. The present study will provide additional information that contributes to the comprehensive evaluation of the risks posed by the application of chiral difenoconazole in agricultural production practices.

Evaluation of acute and developmental effects of difenoconazole via multiple stage zebrafish assays

Zebrafish, during embryo, larvae and adult stages were selected to investigate the potential environmental risk and aquatic toxicity of a widely used fungicide, difenoconazole. In addition to mortality, embryo development endpoints, teratogenic effects and behavior abnormity were measured. Finally, the developmental parameters of the adult fish were assessed after 14 days' exposure. This study concluded that the acute toxicity of difenoconazole to the three phases of zebrafish were larvae (1.17 mg/L) > adult fish (1.45 mg/L) > embryo (2.34 mg/L). A large suite of symptoms was induced in embryonic development by different dosages of difenoconazole, including hatching inhibition, abnormal spontaneous movement, slow heart rate, growth regression and morphological deformities. 0.50 mg/L of difenoconazole could cause significant body color blackening and decrease in the heart rate of zebrafish larvae over 24 h. In addition, 0.25 mg/L of difenoconazole apparently inhibited the growth weight of adult zebrafish measured after 14 days' exposure.