Evaluation of fungicides enestroburin and SYP1620 on their inhibitory activities to fungi and oomycetes and systemic translocation in plants

Inhibitory activity to Fusarium spp. and control potential for wheat Fusarium crown rot of a novel succinate dehydrogenase inhibitor cyclobutrifluram

BACKGROUND

Wheat Fusarium crown rot (FCR) is a serious problem primarily caused by Fusarium pseudograminearum, a pathogenic agent known to produce mycotoxins, including deoxynivalenol (DON). Cyclobutrifluram, a novel succinate dehydrogenase inhibitor devised by Syngenta, has immense potential to control both nematodes and Fusarium diseases. However, its efficacy in combating Fusarium species, its ability to prevent and reverse the detrimental effects of FCR, and its impact on the production of DON by F. pseudograminearum are yet to be fully ascertained.

RESULTS

Cyclobutrifluram exhibited substantial inhibitory activity against Fusarium species, with half-maximal effective concentration values ranging from 0.0021-0.0647 μg mL-1 . It demonstrated significant inhibitory activity toward three developmental stages of F. pseudograminearum, F. graminearum and F. asiaticum. Furthermore, cyclobutrifluram showed both protective and curative activities against FCR and was rapidly absorbed by roots and transported to wheat stems and leaves. Cyclobutrifluram could also decrease DON production by F. pseudograminearum.

CONCLUSION

This investigation has revealed the potential of cyclobutrifluram as a formidable candidate fungicide, particularly in its ability to effectively combat FCR and other Fusarium-related ailments. This novel compound has exceptional pathogen-fighting capabilities, coupled with remarkable systemic translocation properties and a notable ability to reduce the production of DON. © 2023 Society of Chemical Industry.

Fabrication of ROS-responsive nanoparticles by modifying the interior pore-wall of mesoporous silica for smart delivery of azoxystrobin

The suboptimal efficiency in pesticide utilization may elevate residues, posing safety risks to human food and non-target organisms. To address this challenge, delivery systems, such as pathogen infection stimuli-responsive carriers, can be employed to augment the efficiency of fungicide utilization. The bursting of reactive oxygen species (ROS) is a common defense response of host plants to pathogenic infections. In this study, ROS-responsive mesoporous silica nanoparticles (MSN) modified with phenyl sulfide (PHS) as azoxystrobin (AZOX) carrier (MSN-PHS-AZOX) were fabricated. Results demonstrated that MSN-PHS-AZOX exhibited fungicide release kinetics dependent on ROS. In vitro inhibition experiments confirmed the fungicidal effect of MSN-PHS-AZOX on Botrytis cinerea, relying on external ROS. In vivo leaf experiments showcased the superior persistence of MSN-PHS-AZOX in compared to AZOX SC. Furthermore, MSN-PHS-AZOX exhibits favorable biosafety and lower toxicity to aquatic zebrafish compared to AZOX SC, with no adverse impact on cucumber leaf growth. These findings suggest the potential application of this ROS-responsive nano fungicide in managing plant disease in agricultural fields.

ABCC Transporter Gene MoABC-R1 Is Associated with Pyraclostrobin Tolerance in Magnaporthe oryzae

Rice blast is a worldwide fungal disease that poses a threat to food security. Fungicide treatment is one of the most effective methods to control rice blast disease. However, the emergence of fungicide tolerance hampers the control efforts against rice blast. ATP-binding cassette (ABC) transporters have been found to be crucial in multidrug tolerance in various phytopathogenic fungi. This study investigated the association between polymorphisms in 50 ABC transporters and pyraclostrobin sensitivity in 90 strains of rice blast fungus. As a result, we identified MoABC-R1, a gene associated with fungicide tolerance. MoABC-R1 belongs to the ABCC-type transporter families. Deletion mutants of MoABC-R1, abc-r1, exhibited high sensitivity to pyraclostrobin at the concentration of 0.01 μg/mL. Furthermore, the pathogenicity of abc-r1 was significantly diminished. These findings indicate that MoABC-R1 not only plays a pivotal role in fungicide tolerance but also regulates the pathogenicity of rice blast. Interestingly, the combination of MoABC-R1 deletion with fungicide treatment resulted in a three-fold increase in control efficiency against rice blast. This discovery highlights MoABC-R1 as a potential target gene for the management of rice blast.

Activity of the new OSBP inhibitor Y18501 against Pseudoperonospora cubensis and its application for the control of cucumber downy mildew

Y18501 is a new oxysterol-binding protein inhibitor (OSBPI) with a similar structure to oxathiapiprolin. Y18501 showed strong inhibitory activities against Phytophthora spp. and Pseudoperonospora cubensis, with EC50 ranging from 0.0005 to 0.0046 μg/mL. It also had good control efficacy on cucumber downy mildew (CDM) in the green house and in the field, and could effectively inhibit different development stages of P. cubensis, especially for sporangiophore production, sporangial production, mycelium extension, and elongation of germ tube. In addition, Y18501 showed excellent protective and curative activities against P. cubensis. It also had acropetal systemic mobility in the cucumber leaves, and could be taken up and translocated to the upper leaves more effectively from the lower leaves than from the roots. Y18501 had poorer permeability in cucumber leaves compared to oxathiapiprolin. The simultaneous application of Y18501 and chlorothalonil could significantly promote the inhibition of P. cubensis.

Uptake and Translocation of a Silica Nanocarrier and an Encapsulated Organic Pesticide Following Foliar Application in Tomato Plants

Pesticide nanoencapsulation and its foliar application are promising approaches for improving the efficiency of current pesticide application practices, whose losses can reach 99%. Here, we investigated the uptake and translocation of azoxystrobin, a systemic pesticide, encapsulated within porous hollow silica nanoparticles (PHSNs) of a mean diameter of 253 ± 73 nm, following foliar application on tomato plants. The PHSNs had 67% loading efficiency for azoxystrobin and enabled its controlled release over several days. Thus, the nanoencapsulated pesticide was taken up and distributed more slowly than the nonencapsulated pesticide. A total of 8.7 ± 1.3 μg of the azoxystrobin was quantified in different plant parts, 4 days after 20 μg of nanoencapsulated pesticide application on a single leaf of each plant. In parallel, the uptake and translocation of the PHSNs (as total Si and particulate SiO₂) in the plant were characterized. The total Si translocated after 4 days was 15.5 ± 1.6 μg, and the uptake rate and translocation patterns for PHSNs were different from their pesticide load. Notably, PHSNs were translocated throughout the plant, although they were much larger than known size-exclusion limits (reportedly below 50 nm) in plant tissues, which points to knowledge gaps in the translocation mechanisms of nanoparticles in plants. The translocation patterns of azoxystrobin vary significantly following foliar uptake of the nanosilica-encapsulated and nonencapsulated pesticide formulations.

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.

An Enantioselective Cpx Rh(III)-Catalyzed C-H Functionalization/Ring-Opening Route to Chiral Cyclopentenylamines

A chiral Cp^x Rh^III catalyst system in situ generated from a Cp^x Rh^I (cod) precatalyst and bis(o-toluoyl) peroxide as activating oxidant was developed for a C-H activation/ring-opening sequence between aryl ketoxime ethers and 2,3-diazabicyclo[2.2.1]hept-5-enes. This transformation provides access to densely functionalized chiral cyclopentenylamines in excellent yields and enantioselectivities of up to 97:3 er. The reported method is also well suitable for asymmetric alkenyl C-H functionalizations of α,β-unsaturated oxime ethers, furnishing skipped dienes with high levels of enantiocontrol.

High-Throughput Chemical Screening Identifies Compounds that Inhibit Different Stages of the Phytophthora agathidicida and Phytophthora cinnamomi Life Cycles

Oomycetes in the genus Phytophthora are among the most damaging plant pathogens worldwide. Two important species are Phytophthora cinnamomi, which causes root rot in thousands of native and agricultural plants, and Phytophthora agathidicida, which causes kauri dieback disease in New Zealand. As is the case for other Phytophthora species, management options for these two pathogens are limited. Here, we have screened over 100 compounds for their anti-oomycete activity, as a potential first step toward identifying new control strategies. Our screening identified eight compounds that showed activity against both Phytophthora species. These included five antibiotics, two copper compounds and a quaternary ammonium cation. These compounds were tested for their inhibitory action against three stages of the Phytophthora life cycle: mycelial growth, zoospore germination, and zoospore motility. The inhibitory effects of the compounds were broadly similar between the two Phytophthora species, but their effectiveness varied widely among life cycle stages. Mycelial growth was most successfully inhibited by the antibiotics chlortetracycline and paromomycin, and the quaternary ammonium salt benzethonium chloride. Copper chloride and copper sulfate were most effective at inhibiting zoospore germination and motility, whereas the five antibiotics showed relatively poor zoospore inhibition. Benzethonium chloride was identified as a promising antimicrobial, as it is effective across all three life cycle stages. While further testing is required to determine their efficacy and potential phytotoxicity in planta, we have provided new data on those agents that are, and those that are not, effective against P. agathidicida and P. cinnamomi. Additionally, we present here the first published protocol for producing zoospores from P. agathidicida, which will aid in the further study of this emerging pathogen.

Activity of the novel fungicide oxathiapiprolin against plant-pathogenic oomycetes

BACKGROUND

Oxathiapiprolin was the first of the piperidinyl thiazole isoxazoline class of fungicides to be discovered and developed by DuPont in 2007. Although oxathiapiprolin has been reported to have high activity against plant-pathogenic oomycetes, such as Peronospora belbahrii, Phytophthora nicotianae and Ph. capsici, little is known about its effectiveness against other plant-pathogenic oomycetes and its protective and curative properties.

RESULTS

Oxathiapiprolin exhibited substantial inhibitory activity against all of the plant-pathogenic oomycetes tested, with EC90 values ranging from 0.14 to 3.36 × 10(-3) µg mL(-1) , except the Pythium species Py. aphanidermatum and Py. deliense. Furthermore, doses as low as 10 µg mL(-1) were found to inhibit zoospore release and motility in Ph. capsici, while the mycelial development and sporangial production of Pseudoperonospora cubensis were restrained by an EC50 of 3.10 × 10(-4) and 5.17 × 10(-4) µg mL(-1) respectively. It was also found that oxathiapiprolin exhibited both protective and curative activity against the development of Ph. capsici infection in pepper plants under greenhouse conditions and in field tests.

CONCLUSION

The present study demonstrated that the novel fungicide oxathiapiprolin exhibits strong inhibitory activity against a range of agriculturally important plant-pathogenic oomycetes, including Phytophthora spp., Peronophythora litchii, Plasmopara viticola, Pe. parasitica, Ps. cubensis and Py. ultimum. © 2015 Society of Chemical Industry.

Resistance Mechanisms and Molecular Docking Studies of Four Novel QoI Fungicides in Peronophythora litchii

Peronophythora litchii is the causal agent of litchi downy blight. Enestroburin, SYP-1620, SYP-2815 and ZJ0712 are four novel QoI fungicides developed by China. Eight mutants of P. litchii resistant to these QoI fungicides and azoxystrobin (as a known QoI fungicide) were obtained in our preliminary work. In this study, the full length of the cytochrome b gene in P. litchii, which has a full length of 382 amino acids, was cloned from both sensitive isolates and resistant mutants, and single-site mutations G142A, G142S, Y131C, or F128S were found in resistant mutants. Molecular docking was used to predict how the mutations alter the binding of the five QoI fungicides to the Qo-binding pockets. The results have increased our understanding of QoI fungicide-resistance mechanisms and may help in the development of more potent inhibitors against plant diseases in the fields.