Systematic assessment of the antifungal mechanism of soil fumigant methyl isothiocyanate against Fusarium oxysporum.

Fusarium oxysporum is an important phytopathogenic fungus, it can be controlled by the soil fumigant methyl isothiocyanate (MITC). However, the antimicrobial mechanism of MITC against F. oxysporum, especially at the transcriptional level, is still unclear. In this experiment, the antimicrobial mechanism of MITC against F. oxysporum was investigated. Our results indicated that when F. oxysporum was exposed to 6 mg/L MITC for 12 h, the inhibitory rate of MITC on F. oxysporum was 80%. Transmission electron microscopes showed that the cell wall and membrane of F. oxysporum had shrunk and folded, vacuoles increased, and mitochondria swelled and deformed. In addition, the enzyme activity of F. oxysporum treated with MITC showed a decrease of 32.50%, 8.28% and 74.04% in catalase, peroxidase and superoxide dismutase, respectively. Transcriptome sequencing of F. oxysporum was performed and the results showed that 1478 differentially expressed genes (DEGs) were produced in response to MITC exposure. GO and KEGG analysis showed that the DEGs identified were involved in substance and energy metabolism, signal transduction, transport and catalysis. MITC disrupted cell homeostasis by influencing the expression of some key genes involved in chitin synthase and detoxification enzymes production, but F. oxysporum also protected itself by up-regulating genes involved in energy synthesis (such as upregulating acnA, CS and LSC2 in TCA). qRT-PCR data validated the reliability of transcriptome data. Our research used biochemical and genetic techniques to identify molecular lesions in the mycelia of F. oxysporum exposed to MITC, and provide valuable insights into the toxic mechanism of pathogenic fungi mediated by MITC. These techniques are also likely to be useful for rapidly screening and identifying new, environmentally-friendly soil fumigants that are efficacious against fungal pathogens.

Silica modified copper-based alginate/chitosan hybrid hydrogel to control soil fumigant release, reduce emission and enhance bioactivity.

Soil fumigant has been extensively used for excellent efficacy on soil-borne diseases. However, rapid emission and insufficient effective duration typically limit its application. In this study, hybrid silica/polysaccharide hydrogel was proposed (SIL/Cu/DMDS) by emulsion-gelation method to encapsulate dimethyl disulfide (DMDS). The orthogonal study was used to optimize the preparation parameters for LC and EE of SIL/Cu/DMDS, which was 10.39 % and 71.05 %, respectively. Compared with silica, the time for 90 % of the total emissions was extended by 4.36 times. The hydrogel possessed a longer persistent duration and the degradation half-life of DMDS was 3.47 times greater than that of silica alone. Moreover, the electrostatic interaction between abundant groups of polysaccharide hydrogel bestowed DMDS with pH-triggered release behavior. Additionally, SIL/Cu/DMDS had excellent water holding and water retention capacity. The bioactivity of the hydrogel was 58.1 % higher than that of DMDS TC due to the strong synergistic effect between DMDS and the carriers (chitosan and Cu2+), and showed obvious biosafety to cucumber seeds. This study seeks to provide a potential approach to develop hybrid polysaccharide hydrogel to control soil fumigants release, reduce emission and enhance bioactivity in plant protection.

Evaluation of ethylicin as a potential soil fumigant in commercial tomato production in China.

Recent increases in soil-borne plant disease have limited further expansion of some crops produced in protected agriculture. Soil fumigation effectively minimizes the impact of soil pathogens causing many diseases. We provide the first report of the efficacy of the Chinese fungicide ethylicin as a soil fumigant against the plant pathogens such as Fusarium spp. and Phytophthora spp., and against the plant parasitic nematode Meloidogyne spp. We also examined ethylicin's impact on the physicochemical properties of soil, the soil's bacterial and fungal taxonomic composition, the plant growth of tomatoes, the enzyme activity of soil and tomato yield. Ethylicin fumigation significantly decreased the abundance of Fusarium spp. and Phytophthora spp. by 67.7 %-84.0 % and 53.8 %-81.0 %, respectively. It reduced Meloidogyne spp. by 67.2 %-83.6 %. Ethylicin significantly increased the growth of tomato plants and tomato yield by 18.3 %-42.0 %. The soil's ammonium­nitrogen concentration increased significantly in answer to ethylicin fumigation, while nitrate­nitrogen concentration and the activity of soil urease decreased significantly. High-throughput gene sequencing had been used to show that ethylicin cut down the taxonomic soil bacteria diversity and bacterial abundance, but increased the soil fungi taxonomic diversity. Some genera of microorganisms increased, such as Firmicutes, Steroidobacter and Chytridiomycota, possibly due to changes in the physicochemical properties of soil that differentially favored their survival. We conclude that ethylicin is efficacious as a soil fumigant and it would be a useful addition to the limited number of soil fumigants currently available.

Metolachlor metal-organic framework nanoparticles for reducing leaching, ecotoxicity and improving bioactivity.

BACKGROUND: The adverse effects of pesticides has led to a series of ecological, environmental and public health issues. Amide herbicides are an important agrochemical, yet many are prone to leach and pollute the environment, which limits their further application. In this study, metolachlor (METO) was selected as a model pesticide and a controlled released nanoparticle (NP) system was constructed employing a zeolitic imidazolate framework-8 hybrid inorganic-organic porous material (METO@ZIF-8). RESULTS: The synthesis parameters of METO@ZIF-8 were optimized, and the loading content of METO@ZIF-8 was maximized by a central composite design of response surface test. The NPs were regular dodecahedron with uniform size (mostly 54.3 nm diameter). METO@ZIF-8 had high specific surface area and good dispersal in water. Moreover, it endowed the active ingredient with a pH-responsive release property. The nanocarrier effectively improved the adsorption capacity of METO in soil and reduce the leaching by 10.3-21.7%. Pot experiments suggested that the control effect of METO@ZIF-8 was 16.6 and 48.4% higher than that of METO emulsifiable concentrate (EC) and METO technical concentration (TC) at the recommended dose. Based on the excellent controlled release profiles, METO@ZIF-8 did not affect corn plant growth and significantly reduced the risk of phytotoxicity induced by METO. METO@ZIF-8 effectively reduced acute toxicity in zebrafish compared with METO EC. CONCLUSION: This study explored the fabrication of a nanocarrier for improving the efficacy and promoting the environmental safety of leachable amide herbicides. © 2022 Society of Chemical Industry.

Site-Specific Controlled-Release Imidazolate Framework-8 for Dazomet Smart Delivery to Improve the Effective Utilization Rate and Reduce Biotoxicity.

An accurate controlled-release strategy of pesticides is considered desirable in sustainable agriculture. A site-specific nanorelease system of dazomet (DZ) was proposed by employing the zeolitic imidazolate framework-8 composite (DZ@ZIF-8) by a one-pot method. The synthetic parameters of DZ@ZIF-8 were optimized, and the loading content of DZ was maximized. ZIF-8 endowed DZ with a pH-sensitive behavior. The collapse of the DZ@ZIF-8 structure and the site-specific release of DZ were triggered by acidic substances produced by Botrytis cinerea. In vitro and pot experiments showed that the fungicidal activity of DZ@ZIF-8 was about 36.3 and 42.7% higher than that of DZ, respectively. DZ is conventionally used before a crop is planted because of its volatility and toxicity. However, DZ@ZIF-8 could avoid phytotoxicity of DZ to plants, which made the application of DZ possible during plant growth. Moreover, the acute toxicity to zebrafish changed from high to moderate levels. This study highlights a potential strategy that improves DZ effective utilization and reduces side effects.

Organic fertilizers activate soil enzyme activities and promote the recovery of soil beneficial microorganisms after dazomet fumigation.

Soil fumigation can reduce the impact of soil-borne diseases, weeds and insect pests on commercial crop production. Unfortunately, fumigation also kills beneficial microorganisms. In this study, we explored if dazomet fumigation could be used in combination with organic fertilizers (silicon fertilizer, potassium humate organic fertilizer, Bacillus microbial fertilizer, and mixtures of the last two) to reduce its impact on soil beneficial microorganisms. We evaluated the effects of adding these fertilizers after fumigation on the soil's physical and chemical properties and its enzyme activities, as well as its effects on the soil microbial communities under continuous production for >20 years. We found that fertilizers applied after fumigation increased the soil nitrate nitrogen content by 11.6%-29.4%, increased available potassium content by 5.6%-26.3% and increased organic matter content by 28.5%-48.8%. In addition, soil conductivity and water content increased significantly by 8.2%-26.5% and 8.0%-16.0%, respectively. The activities of soil catalase and soil sucrase were significantly increased by 6.2%-15.9% and 133.1%-238.5%, respectively. High-throughput DNA sequencing showed that fertilizers applied after fumigation increased the relative abundance of the phyla Proteobacteria, Actinobacteria and Ascomycota; and the genera Sphingomonas, Chaetomium and Mortierella. Silicon fertilizer applied after fumigation has the most significant promotion effect on soil micro-ecological health. The results showed that organic fertilizers applied after fumigation can improve the soil's fertility, activate soil enzyme activities and promote the recovery of soil beneficial microorganisms, which are all factors that improve crop quality and yield.

Combination of modified biochar and polyurea microcapsules to co-encapsulate a fumigant via interface polymerization for controlled release and enhanced bioactivity.

BACKGROUND: Soil fumigants-the most effective agrochemicals for managing soil-borne diseases-have been used extensively. However, high volatility, moderate toxicity and insufficient effective duration considerably limit their application. In the present study, interface polymerization was used to combine modified biochar (BC) and polyurea microcapsules (MCs) to co-encapsulate allyl isothiocyanate (AITC), developing a model fumigant for controlled release (AITC@BC-MCs). RESULTS: The physical characteristics of BC modified by sand-milling were significantly improved. In addition, chemical properties and morphological features of AITC@BC-MCs characterized by integrated methods revealed successful preparation of BC-MCs. Compared with monolayer MCs, BC-MCs could significantly delay AITC release owing to the composite obstruction effect. Moreover, modifying BC endowed the cargo molecules with a pH-responsive release property. Additionally, this composite showed a longer persistent duration by prolonging AITC degradation half-life, which was 3.2-3.5-fold greater than that of the AITC technical concentrate under different soil conditions. Finally, the control efficacy of the AITC@BC-MC against pathogens, including nematodes and fungi, as well as against weeds was significantly enhanced at the same dose, but the composite did not inhibit seed germination and growth after 10 days when fumigated soil was aerated. CONCLUSION: Construction of a composite encapsulation system enhanced pesticide efficacy, reduced dose via controlled release and delayed fumigant degradation in soil, indicating the great potential of this strategy for developing an effective and environmentally friendly fumigant formulation. © 2021 Society of Chemical Industry.

Organic fertilizer activates soil beneficial microorganisms to promote strawberry growth and soil health after fumigation.

Soil fumigants aim to control soil-borne diseases below levels that affect economic crop production, but their use also reduces the abundance of beneficial microorganisms. Previous studies have shown that adding various types of fertilizers to soil after fumigation can reshape the soil microbial community and regulate crop growth. We fumigated soil with dazomet (DZ) that had been cropped continuously for more than 20 years. After fumigation we applied silicon fertilizer, potassium humate organic fertilizer, Bacillus microbial fertilizer or a mixture of the last two. We studied the effects of different fertilizers treatments on the soil's physicochemical properties, enzyme activities, key soil pathogens and beneficial microbes. We found that fertilizers applied after fumigation promoted soil beneficial microorganisms (such as Fimicutes, Chloroflexi, Bacillus and Actinomadura) restoration; increased Fusarium and Phytophthora pathogen mortality, the content of ammonium nitrogen, sucrase enzyme activity; and increased strawberry fruit yield. A significant increase in strawberry yield was positively correlated with increases in beneficial microorganisms such as Gemmatimonadota, Firmicutes, Bacillus and Flavisolibacter. We concluded that organic fertilizer applied after fumigation significantly increased the number of beneficial microorganisms, improved the physicochemical properties of the soil, increased soil enzyme activities, inhibited the growth of soil pathogens to increase strawberry fruit yield. In summary, organic fertilizer activated soil beneficial microorganisms after soil fumigation, promoted soil health, and increased strawberry fruit yield.

Controlled release of dinotefuran with temperature/pH-responsive chitosan-gelatin microspheres to reduce leaching risk during application.

Neonicotinoid-based pesticides are extensively used owing to their broad insecticidal spectrum and activity. We developed neonicotinoid dinotefuran (DIN)-loaded chitosan-gelatin microspheres using a spray-drying technology, resulting in a pH- and temperature-responsive controlled-release system. Upon introducing chitosan into the triple-helix structure of gelatin, the physically modified gelatin microspheres became smooth, round, and solid, improving their thermal storage stability. The spray-drying parameters were optimized using three-dimensional surface plots. When scaled up under optimal conditions, the corresponding loading content and encapsulation efficiency were 21.5% and 98.17%, respectively. Compared with commercial dinotefuran granules, our biodegradable composite carriers achieved the immobilization of dinotefuran to reduce pesticide leaching by 5.57-19.89% in soil, improved the soil half-life of DIN, and improved its cumulative absorption by plants. Therefore, the microspheres showed better efficacy against Trialeurodes vaporariorum. Our results confirm that this simple approach can improve the utilization efficiency of neonicotinoids, decrease leaching loss, and promote ecological safety.

Bio-based clothianidin-loaded solid dispersion using composite carriers to improve efficacy and reduce environmental toxicity.

BACKGROUND: Neonicotinoids comprise one of the most extensively used classes of pesticides worldwide owing to their broad insecticidal spectrum and excellent biological performance. However, their toxicity to honeybee (Apis mellifera Linnaeus) and silkworm (Bombyx Mori) limits their further application. To address this issue, clothianidin as a model neonicotinoid was developed into a novel controlled-release formulation employing advantaged solid dispersion (SD) technology using composite carriers. RESULTS: In this research, the clothianidin-loaded SD was characterized using integrated methods to elucidate its formation mechanism, showing that clothianidin was embedded into the carrier homogeneously in small crystalline entities. The composite carriers, which are both renewable and environmentally friendly, can significantly prolong the release of clothianidin from seven to 25 days, compared with that of PEG 8000 as a single carrier. Based on the excellent controlled release profiles, it reduced the acute toxicity to A. mellifera and B. mori by 57.68- and 85.32-fold (respectively) compared with that of the conventional formulation. Furthermore, the SD displayed favorable efficacy and persistency against Asian citrus psyllid (Hemiptera: Psyllidae). CONCLUSION: This novel strategy opens up a simple and powerful avenue for improving efficacy and promoting the environmental safety of neonicotinoid insecticides to be used in sustainable crop protection.

Chloropicrin alternated with dazomet improved the soil's physicochemical properties, changed microbial communities and increased strawberry yield.

Chloropicrin (Pic) and dazomet (DZ) are effective soil fumigants that are often used to reduce soil-borne pathogens that would otherwise reduce crop yield. As Pic is scheduled to be banned, we investigated whether its consumption could be halved by alternating it with DZ. We observed that Pic alternated with DZ increased the soil NH4+-N content by 28.74-47.07 times, increased available potassium content by 40.80%-46.81% and increased electrical conductivity by 39.23%-85.81%. It generally improved the soil's physicochemical properties. High-throughput DNA sequencing showed that Pic alternated with DZ changed the taxonomic diversity of bacteria and fungi by increasing the relative abundance of Bacillus and Firmicutes, and by decreasing Proteobacteria, Acidobacteria and Sphingomonas. Moreover, Pic alternated with DZ can inhibit key soil pathogens by more than 90% and significantly increased strawberry yield by 78.22%-116.12%. In terms of strawberry production, we recommend using DZ in the first year and Pic in the second year. Our results showed significant ecological benefit and yield benefit when Pic consumption was halved by alternating it with DZ.

2-Hydroxypropyl-ß-cyclodextrin encapsulates dimethyl disulfide producing a controlled release formulation.

Dimethyl disulfide (DMDS), a soil fumigant, is an effective, broad-spectrum compound that often replaces bromomethane (MB) in the prevention and treatment of soil-borne diseases. However, the disadvantages of DMDS include toxicity, volatility, pungent odor, risk of human exposure, and environmental pollution. Cyclodextrin (CD) has been widely used as a carrier of chemicals in many industries due to its functional advantages and safety. In this study, a DMDS-controlled release formulation was developed by encapsulating DMDS in the cavity of 2-hydroxypropyl-ß-cyclodextrin (HP-ß-CD). This formulation reduced DMDS usage and production costs. Orthogonal experimental design, Fourier transform infrared (FT-IR), Scanning electron microscopy (SEM), Thermal gravity analysis (TGA) characterization, efficacy comparison, safety, and other aspects of the evaluation showed that under the best preparation conditions, the encapsulation rate was 81.49%. The efficacy of DMDS@HP-ß-CD was similar to unformulated DMDS. The efficacy duration of the formulation was about two times longer than DMDS, and it was safer to use. This study reveals a cyclodextrin-DMDS formulation with reduced toxicity, longer duration, environmental safety and sustainability.

Bio-activation of soil with beneficial microbes after soil fumigation reduces soil-borne pathogens and increases tomato yield.

Soil-borne diseases have become increasingly problematic for farmers producing crops intensively under protected agriculture. Although soil fumigants are convenient and effective for minimizing the impact of soil-borne disease, they are most often detrimental to beneficial soil microorganisms. Previous research showed that bio-activation of soil using biological control agents present in biofertilizers or organic fertilizers offered promise as a strategy for controlling soil-borne pathogens when the soil was bio-activated after fumigation. Our research sought to determine how bio-activation can selectively inhibit pathogens while promoting the recovery of beneficial microbes. We monitored changes in the soil's physicochemical properties, its microbial community and reductions in soil-borne pathogens. We found that the population density of Fusarium and Phytophthora were significantly reduced and tomato yield was significantly increased when the soil was bio-activated. Soil pH and soil catalase activity were significantly increased, and the soil's microbial community structure was changed, which may have enhanced the soil's ability to reduce Fusarium and Phytophthora. Our results showed that soil microbial diversity and relative abundance of beneficial microorganisms (such as Sphingomonas, Bacillus, Mortierella and Trichoderma) increased shortly after bio-activation of the soil, and were significantly and positively correlated with pathogen suppression. The reduction in pathogens may have been due to a combination of fumigation-fertilizer that reduced pathogens directly, or the indirect effect of an optimized soil microbiome that improved the soil's non-biological factors (such as soil pH, fertility structure), enhanced the soil's functional properties and increased tomato yield.

Multi-Encapsulation Combination of O/W/O Emulsions with Polyurea Microcapsules for Controlled Release and Safe Application of Dimethyl Disulfide.

Dimethyl disulfide (DMDS), a promising alternative fumigant, has been highly desirable for excellent management of soil pests and diseases. However, high volatility and moderate toxicity of this sulfide limit its application. To address these issues, a novel controlled release formulation of DMDS was proposed employing multiple emulsions and polyurea microcapsules (DMDS@MEs-MCs). The successful combination of the two technologies was revealed by confocal laser scanning microscopy, scanning electron microscopy, thermogravimetric analysis, and Fourier transform infrared. According to the multiple encapsulation structure, the encapsulation efficiency decreased by only 3.13% after thermal storage, compared with a 15.21% decrease of microcapsules made with only a monolayer film. DMDS@MEs-MCs could effectively control the release of active ingredient, which increased applicator and environmental safety during application. Moreover, it could be facilely used by spraying and drip irrigation instead of a special fumigation device. The innovative formulation exhibited better control efficacy on soil pathogens (Fusarium spp. and Phytophthora spp.) and root-knot nematodes (Meloidogyne spp.) than DMDS technical concentration (DMDS TC). In addition, it did not inhibit seed germination after 10 days when the plastic film was removed from the fumigated soil. This method appears to be of broad interest for the development of safe and handy fumigant application.

Organic fertilizer improves soil fertility and restores the bacterial community after 1,3-dichloropropene fumigation.

Although fumigants can effectively control soil-borne diseases they are typically harmful to beneficial microorganisms unless methods are developed to encourage their survival after fumigation. The soil fumigant 1,3-dichloropropene (1,3-D) is widely used because of its effective management of pathogenic nematodes and weeds. After fumigation with 1,3-D, Bacillus subtilis and Trichoderma harzianum fertilizer (either singularly or together) or humic acid were added to soil that had been used to produce tomatoes under continuous production for >20 years. We evaluated changes to the soil's physicochemical properties and enzyme activity in response to these fertilizer treatments, and the effects of these changes on beneficial bacteria. Fertilizer applied after fumigation increased the content of ammonium nitrogen, nitrate nitrogen, available phosphorus, available potassium and organic matter, and it promoted an increase in pH and electrical conductivity. The activity of urease, sucrase and catalase enzymes in the soil increased after fumigation. Taxonomic identification of bacteria using genetic analysis techniques showed that fertilizer applied after fumigation increased the abundance of Actinobacteria and the relative abundance of the biological control genera Sphingomona, Pseudomonas, Bacillus and Lysobacter. The abundance of these beneficial bacteria increased significantly when B. subtilis and T. harzianum were applied together. These results showed that fertilizer applied after fumigation can increase the abundance of beneficial microorganisms in the soil within a short period of time, which improved the soil's fertility, ecological balance and potentially crop quality and yield.

Biochar mitigates the negative effect of chloropicrin fumigation on beneficial soil microorganisms.

Chloropicrin (CP) is the most commonly used soil fumigant worldwide. Although CP effectively controls soilborne pathogens, it is also detrimental to beneficial soil microorganisms unless measures can be put in place to protect them from the effects of fumigation. In this study, we evaluated the ability of biochar made from the invasive weed Eupatorium adenophorum to mitigate the effects of CP fumigation on beneficial species. Our results showed that the addition of biochar to the soil effectively reduced the detrimental effects of CP on beneficial species and their ecological functions. Biochar added to CP-fumigated soil shortened the time to 28-84 days for microbial diversity and nitrogen cycle functions to be restored to unfumigated levels. At the same time, the inorganic nitrogen (NH4+-N, NO3--N) content and N2O production potential level in CP-fumigated soil returned to unfumigated levels relatively quickly, which showed that nitrogen metabolism improved with the addition of biochar. The mitigation effect of biochar in CP-fumigated soil was more evident at higher biochar amendment rates. Our results suggest that the addition of biochar to CP-fumigated soil significantly reduced the impact of CP on beneficial species and their ecological functions, and significantly shortened the time for beneficial species to recover to pre-fumigation levels. Field research is required to determine biochar's ability to mitigate the impact of CP and other fumigants on beneficial species and to quantify its benefits on crop quality and yield.