Magnesium oxide nanoparticles reduce clubroot by regulating plant defense response and rhizosphere microbial community of tumorous stem mustard (Brassica juncea var. tumida).

Clubroot, caused by Plasmodiophora brassicae, is a major disease that significantly impairs the yield of cruciferous crops and causes significant economic losses across the globe. The prevention of clubroot, especially in tumorous stem mustard (without resistant varieties), are is limited and primarily relies on fungicides. Engineered nanoparticles have opened up new avenues for the management of plant diseases, but there is no report on their application in the prevention of clubroot. The results showed that the control efficacy of 500 mg/L MgO NPs against clubroot was 54.92%. However, when the concentration was increased to 1,500 and 2,500 mg/L, there was no significant change in the control effect. Compared with CK, the average fresh and dry weight of the aerial part of plants treated with MgO NPs increased by 392.83 and 240.81%, respectively. Compared with the F1000 treatment, increases were observed in the content of soil available phosphorus (+16.72%), potassium (+9.82%), exchangeable magnesium (+24.20%), and water-soluble magnesium (+20.64%) in the 1,500 mg/L MgO NPs treatment. The enzyme-linked immune sorbent assay (ELISA) results showed that the application of MgO NPs significantly increased soil peroxidase (POD, +52.69%), alkaline protease (AP, +41.21%), alkaline phosphatase (ALP, +79.26%), urease (+52.69%), and sucrase (+56.88%) activities; And also increased plant L-phenylalanine ammonla-lyase (PAL, +70.49%), polyphenol oxidase (PPO, +36.77%), POD (+38.30%), guaiacol peroxidase (POX, +55.46%) activities and salicylic acid (SA, +59.86%) content. However, soil and plant catalase (CAT, -27.22 and - 19.89%, respectively), and plant super oxidase dismutase (SOD, -36.33%) activities were significantly decreased after the application of MgO NPs. The metagenomic sequencing analysis showed that the MgO NPs treatments significantly improved the α-diversity of the rhizosphere soil microbial community. The relative abundance of beneficial bacteria genera in the rhizosphere soil, including Pseudomonas, Sphingopyxis, Acidovorax, Variovorax, and Bosea, was significantly increased. Soil metabolic functions, such as oxidative phosphorylation (ko00190), carbon fixation pathways in prokaryotes (ko00720), indole alkaloid biosynthesis (ko00901), and biosynthesis of various antibiotics (ko00998) were significantly enriched. These results suggested that MgO NPs might control clubroot by promoting the transformation and utilization of soil nutrients, stimulating plant defense responses, and enriching soil beneficial bacteria.

Toxic Effects of Copper Fungicides on the Development and Behavior of Zebrafish in Early-Life Stages.

Copper-based fungicides have been used to control various plant diseases for more than one hundred years and play very important roles in agriculture. Accumulation of copper in freshwater and environment pose severe threats to human health and the environment. The current study evaluated the developmental and behavioral toxicity of PEG@Cu NCs (copper nanoclusters), Kocide® 3000 (copper hydroxide), and Cu(CH3COO)2 (copper acetate) to zebrafish in early-life stages. The developmental toxicity was evaluated according to the parameters of mortality, hatching rate, autonomous movement and heartbeat of embryos, and body length of larvae. The 9 dpf (days postfertilization)-LC50 (50% lethal concentration) of embryonic mortality was 0.077, 0.174 or 0.088 mg/L, and the 9 dpf-EC50 (effective concentration of 50% embryos hatching) of hatching rate was 0.079 mg/L, 0.21 mg/L and 0.092 mg/L when the embryos were exposed to PEG@Cu NCs, Kocide® 3000 or Cu(CH3COO)2, respectively. Kocide® 3000 and Cu(CH3COO)2 obviously decreased the spontaneous movements, while PEG@Cu NCs had no adverse effects on that of embryos. The reduced heartbeat can return to normal after exposure to PEG@Cu NCs for 96 h, while it cannot recover from Kocide® 3000. In addition, Kocide® 3000 (≥0.2 mg/L), PEG@Cu NCs and Cu(CH3COO)2 with 0.05 mg/L or higher concentration exhibited obvious behavioral toxicity to zebrafish larvae according to the parameters of movement distance, average velocity, absolute sinuosity, absolute turn angle and absolute angular velocity.

Differential Analysis of Three Copper-Based Nanomaterials with Different Morphologies to Suppress Alternaria alternata and Safety Evaluation.

The overuse of copper-based fertilizers and pesticides over the last few decades has resulted in detrimental risks to our environment. Nano-enabled agrichemicals with a high effective utilization ratio have shown great potential for maintaining or minimizing environmental issues in agriculture. Copper-based nanomaterials (Cu-based NMs) serve as a promising alternative to fungicides. Three types of Cu-based NMs with different morphologies were analyzed for their different antifungal effects on Alternaria alternata in this current study. Compared to commercial copper hydroxide water power (Cu(OH)2 WP), all tested Cu-based NMs, including cuprous oxide nanoparticles (Cu2O NPs), copper nanorods (Cu NRs) and copper nanowires (Cu NWs), especially Cu2O NPs and Cu NWs, showed higher antifungal activity against Alternaria alternata. Its EC50 were 104.24 and 89.40 mg L-1, respectively, achieving comparable activity using a dose approximately 1.6 and 1.9-fold lower. Cu-based NMs could introduce the downregulation of melanin production and soluble protein content. In contrast to trends in antifungal activity, Cu2O NPs showed the strongest power in regulating melanin production and protein content and similarly exhibited the highest acute toxicity to adult zebrafish compared to other Cu-based NMs. These results demonstrate that Cu-based NMs could offer great potential in plant disease management strategies.

A pH- and enzymatic-responsive nanopesticide to control pea aphids and reduce toxicity for earthworms.

Thiacloprid is a new chlorinated nicotinoid insecticide against stinging-oral pests, such as aphids. It is less toxic to bees but more toxic to earthworms. In this study, a pH- and amylase-responsive MOF (ZIF-8) was constructed for site-specific delivery of thiacloprid to control pea aphids and more safety for earthworms. Thiacloprid from α-cyclodextrin@Thiacloprid@ZIF-8 (α-CD@T@ZIF-8) could be released quickly in pea aphids, which was ascribed to disintegration of ZIF-8 at low pH values in pea aphid intestines and degradation of α-CD under the action of α-amylase. The release results showed a significant pH dependence of α-CD@T@ZIF-8, with an approximately 65 % release amount at pH = 7 and a 95 % release amount at pH = 5 for 7 d. The results of the pot experiment and biosafety showed that for α-CD@T@ZIF-8, 88 % pea aphids could be killed compared with 32 % aphids for commercially available formulation on the 7th day after application. Meanwhile the LC50 of thiacloprid OD was 0.034 µg/cm2 and the LC50 of α-CD@T@ZIF-8 was 0.564 µg/cm2 on earthworms, and it was more safety for pea and lower acute toxicity and enrichment for the earthworms. α-CD@T@ZIF-8 could be used for intelligently controlled release of other insecticides against aphids.

Preparation and performance characteristics of spider venom peptide nanocapsules.

BACKGROUND: ω-hexatoxin-Hvn1b is an insecticidal toxin produced by the Tasmanian funnel-web spider (Hadronyche venenata), that can be exploited for development of novel bioinsecticides. Due to its larger size and low membrane permeability, this toxin usually has a slower mode of action compared to conventional small molecule insecticides. Nanoscale materials have unique optical, electrical, mechanical and biological properties, and show great application prospects for pesticide delivery. RESULTS: The physical and chemical properties of nanocapsules were characterized using transmission electron microscopy, laser particle size analysis, Fourier transform infrared spectroscopy, contact angle testing and with a fluorescence spectrophotometer. The results indicated that the nanocapsules were spherical, with an average particle size of 197.70 nm, the encapsulation efficiency rate was 75.82% and the Zeta potential was -32.90 mV. Penetration experiments showed that the nanocapsules could promote protein passage through the intestinal tract of Spodoptera litura and reach the body fluid. Then we expressed ω-hexatoxin-Hvn1b by prokaryotic expression. Bioassay results showed that the oral toxicity of ω-hexatoxin-Hvn1b nanocapsules to S. litura was higher than that of the ω-hexatoxin-Hvn1b. CONCLUSION: In this paper, we reported a construction method of spider venom peptide nanocapsules based on polylactic-co-glycolic acid by multiple emulsion for delivery of protein to improve the insecticidal effect and oral activity of ω-hexatoxin-Hv1a. © 2022 Society of Chemical Industry.

Synthesis of carbon dots@Fe3O4 and their photocatalytic degradation properties to hexaconazole.

The CD@Fe3O4 photocatalysts were synthesized via hydrothermal synthesis method. The CD@Fe3O4 particles were synthesized using Fe3O4 as the core and using citric acid and ethylenediamine as a raw material, which were heated to 200 °C for 4 h. The synthesized fluorescent CD@Fe3O4 was characterized by HR-TEM, IR and fluorescence spectrophotometer. The HR-TEM results showed CD and Fe3O4 nanoparticles were uniform, mono-dispersed sphere or hemisphere particles with an average size of approximately 3 nm, and particle size of CD@Fe3O4 were mainly in range of 20-30 nm. XRD results showed the nanoparticles mainly belonged to Fe3O4 and CD@Fe3O4, which made recycling our photocatalysts possible due to the magnetic performance. On daylight lamp, the half-life of hexaconazole in CD@Fe3O4 photocatalysts was about 4 days, and it is lower than half-life (over 100 days) of hexaconazole without CD@Fe3O4 photocatalysts.