Effect of abamectin on root-knot nematodes and tomato yield

The combination of chemical fertilizer affected the control efficacy against root-knot nematode and environmental behavior of abamectin in soil

Chemical fertilizer and pesticide are necessary in agriculture, which have been frequently used, sometimes even at the same time or in combination. To understand the interactions of them could be of significance for better use of these agrochemicals. In this study, the influence of chemical fertilizers (urea, potassium sulfate, ammonium sulfate and superphosphate) on the control efficacy and environmental behavior of abamectin was investigated, which could be applied in soil for controlling nematodes. In laboratory assays, ammonium sulfate at 1 and 2 g/L decreased the LC50 values of abamectin to Meloidogyne incognita from 0.17 mg/L to 0.081 and 0.043 mg/L, indicating it could increase the contact toxicity. In greenhouse trial, ammonium sulfate at 1000 mg/kg increased the control efficacy of abamectin by 1.37 times. Meanwhile, the combination of abamectin with ammonium sulfate could also promote the tomato seedling growth as well as the defense-related enzyme activity under M. incognita stress. The persistence and mobility of abamectin in soil were significantly elevated by ammonium sulfate, which could prolong and promote the control efficacy against nematodes. These results could provide reference for reasonable use of abamectin and fertilizers so as to increase the control efficacy and minimize the environmental risks.

Biocontrol Efficacy of Bacillus methylotrophicus TA-1 Against Meloidogyne incognita in Tomato

Root-knot nematodes (RKNs) are harmful plant-parasitic nematodes of tomatoes which can cause significant yield losses. Therefore, there is increasing interest in exploring the application of bacterial nematicides. The bacterium Bacillus methylotrophicus TA-1 is a broad-spectrum biological control agent; however, its effect on RKNs control remains largely unclear. In this study, the toxicity of B. methylotrophicus TA-1 against Meloidogyne incognita was investigated in vitro, and the potential of B. methylotrophicus TA-1 to decrease infection of RKNs in tomato were evaluated in pot and field trials. Results showed that B. methylotrophicus TA-1 exhibited high nematicidal activity against second-stage juveniles (J2s) and eggs of M. incognita with 50% lethal concentration (LC50) values of 5.80 and 7.00 × 108 colony forming units (CFU)/ml, respectively. In the pot experiments and field trials conducted in 2020 and 2021, tomato plants treated with B. methylotrophicus TA-1 soil drench applied once at 3, 6, and 9 × 108 CFU/plant had significantly higher plant height and greater yield compared with the untreated control. Tomato yields of the treated plots with B. methylotrophicus TA-1 in 2 consecutive years' field trials were between 53.4 to 66.1 and 52.8 to 61.5 t/ha, while they were 49.7 and 48.2 t/ha in the untreated control for each year, respectively. The lowest population densities of M. incognita at 30 and 60 days after treatment were 119 and 135 J2s per 100 g soil in 2020 and 43 and 118 J2s in 2021 in TA-1-treated plots. The lowest gall index of 4.7 and 3.3 in 2020 and 2021, respectively, and the highest yield were all observed in the TA-1 at 9 × 108 CFU/plant treated plants, with no significant differences with the commercial control abamectin. These results provided a basis for further studies of B. methylotrophicus TA-1 formulations, application doses, frequencies, and mechanisms of action, which are necessary before it could be used as a component of integrated management programs to manage RKNs in tomato production.

Comparative biological activity of abamectin formulations on root-knot nematodes (Meloidogyne spp.) infecting cucumber plants: in vivo and in vitro

The root-knot nematodes (Meloidogyne spp.) are considered one of the most destructive diseases in the world. In Egypt, farmers primarily rely on chemical nematicides, which have become costly to control. Currently, abamectin is a bio-based pesticide used as an alternative tool against Meloidogyne spp. on cucumber plants (Cucumis sativus L.). During the current research, four tested abamectin formulations were DIVA (1.8% EW), RIOMECTIN (5% ME), AGRIMEC GOLD (8.4% SC) and ZORO (3.6% EC) compared with two reference nematicides namely, CROP NEMA (5% CS) and TERVIGO (2% SC). The main results showed that, in vitro study elucidated that the most effective formulations of abamectin as a larvicidal were EW with LC₅₀ value of 21.66 µg ml^-1. However, in the egg hatching test, the formulations of abamectin SC (2%) and EW were the most effective in reducing egg hatching, with LC₅₀ values of 12.83 and 13.57 µg ml^-1. The calculated relative potency values showed diversity depending on the two referenced nematicides. On the other hand, in vivo study, the results indicated that, all tested formulations of abamectin recorded general mean reductions in root galls (23.05-75.23%), egg masses (14.46-65.63%). Moreover, the total population density declined by 39.24-87.08%. Furthermore, the influence of abamectin formulations, in the presence of root-knot nematodes, on the growth of cucumber plants parameters, such as root dry weight, root length, root radius, root surface area, shoot dry weight and shoot height, as well as the content of macro-elements (N, P and K) exhibited varying levels of response.

Acute toxicity, biochemical and transcriptomic analysis of Procambarus clarkii exposed to avermectin

BACKGROUND

Pesticides are extensively applied globally. Pesticide residues induce calamitous effects on the environment and untargeted organisms. Public concerns for the safety of freshwater organisms and the challenges posed by aquatic contaminants remain high. In the present study, the acute toxicity of avermectins (AVMs) to the crayfish, Procambarus clarkii was evaluated. We also evaluated the potential effects of AVM on the biochemical and transcriptomic status of the hepatopancreas and gastrointestinal tract in P. clarkii.

RESULTS

The 24, 48, 72, 96 h median lethal concentrations (LC₅₀ ) of AVM on crayfish were 2.626, 1.162, 0.723, 0.566 mg L^-1 , respectively. The crayfish were then exposed to 0.65 mg L^-1 of AVM for 96 h. AVM significantly altered biochemical parameters including AChE and CAT activities in the hepatopancreas, and AChE, SOD and Na + -K + -ATPase activities in the gastrointestinal tract at several time points. Furthermore, transcriptomic analysis identified 953 and 1851 differentially-expressed genes (DEGs) in the hepatopancreas and gastrointestinal tract, respectively. KEGG enrichment showed that the gene expression profiles of the hepatopancreas and gastrointestinal tract were distinct from each other. The DEGs in the hepatopancreas were mostly enriched with stress-response pathways, while the majority of the DEGs in the gastrointestinal tract belonged to metabolism-related pathways.

CONCLUSION

We demonstrated that the AVM induced acute toxicity, oxidative stress, osmoregulation disturbance, neurotoxicity and transcriptome imbalance in crayfish. These findings unraveled the detrimental effects of AVMs exposure on crayfish. © 2022 Society of Chemical Industry.

Mixtures of fluopyram and abamectin for management of Meloidogyne incognita in tomato

The southern root-knot nematode (RKN), Meloidogyne incognita, causes significant damage to vegetable production and is a major problem in greenhouse tomatoes. The effect of a combination of fluopyram and abamectin, at a mass ratio of 1:5, was studied for RKN control. Pot trials showed that fluopyram, abamectin, and their combination at three dosages increased the height, stem diameter, root fresh weight, shoot fresh weight, and the root length of tomato plants. The RKN control efficacy of the 1:5 combination at 450 g a.i./ha was 74.06% at 30 days after transplanting (DAT), and the control efficacy of the combination at 337.5 and 450 g a.i./ha differed significantly from those of other treatments at 60 DAT. The root-galling index (RGI) control efficacy of the combination at 450 g a.i./ha and of fluopyram (41.7% SC) only at 450 g a.i./ha were better than the control efficacies of other treatments, and these two treatments significantly increased root activity. Field trial results showed that the soil nematode control efficacy was similar to that of the pot trials at 30 and 60 DAT. The RGI control efficacy of the combination at 337.5 and 450 g a.i./ha and of fluopyram (41.7% SC) only at 450 g a.i./ha differed significantly from those of the two other treatments. The tomato yields of the 1:5 combination at 450 g a.i./ha were increased by 24.07 and 23.22% compared to the control in field trials during two successive years. The combination of fluopyram and abamectin provides good nematode measure, and it can increase tomato yields. It provides an effective solution for the integrated management of southern RKN.

N-alkyl isatin derivatives: Synthesis, nematicidal evaluation and protein target identifications for their mode of action

Meloidogyne incognita is an economically dominant pathogen infesting a wide range of crops curbing their growth and productivity. Deregistration of frontline nematicides has necessitated exploration of innovative and novel class of structurally diverse nematicides with streamlined activity. In this context, N-alkylated derivatives of isatin known for their remarkable biological profile were synthesized, characterized and evaluated in vitro for their antinemic character followed by in silico studies for their mode of action and toxicological studies for their fitness as agrochemical. The antinemic evaluation was carried by egg hatch inhibition and juvenile mortality and its effect on egg hatching. Compounds 1 and 2a exhibited nematicidal potential and significantly decreased egg hatching and increased juvenile mortality. For egg hatch inhibition LC₅₀ and LC₉₅ values for 1 were found to be 0.125 and 1.380 mg/ml and for compound 2a, 0.457 and 8.511 mg/ml respectively. For juvenile mortality LC₅₀ and LC₉₅ values for 1 were found to be 0.109 and 0.776 mg/ml and for 2a, 0.190 and 1.380 mg/ml respectively. For insights into the mode of action of the synthesized molecules, in silico studies for the targeted effects were conducted which revealed novel interaction with pathogenic protein - Aspartyl protease. Computational studies on the drug-ability and potential toxicity of the selected compounds revealed they belonged to class IV and are safe. With good reasons, our compounds hold value for their exploration in agrochemical industry and thus, this study identifies a new scaffold with useful level of nematicidal activity for its use in agriculture industry.

Nematicidal Efficacy of Milbemectin against Root-Knot Nematodes

The nematicidal efficacy of milbemectin and its commercial formulate Milbeknock^® on (i) egg hatching, (ii) juvenile motility and (iii) infective capacity of root-knot nematodes was evaluated in vitro and in planta assays. Serial dilutions of pure milbemectin were tested against nematode eggs and juveniles and lethal concentrations LC50 and LC90 calculated. Exposure of egg masses to milbemectin at a concentration of 30 μg/mL for 72 h reduced egg hatching by 52%. The increase in exposure time to 240 h did not increase the egg hatching inhibition at the highest concentration 30 μg/mL (53%) but reduced egg hatching at 15 and 7 μg/mL by 35 and 24%, respectively, when compared to untreated controls. The inhibitory effect of milbemectin on juvenile motility ranged from 41 to 87% depending on its concentration, and this effect was persistent after rinsing the juveniles in water. The probabilistic dose–response model indicated that lethal concentrations of milbemectin for juvenile motility were LC50: 7.4 μg/mL and LC90: 29.9 μg/mL. The pre-plant application of Milbeknock^® to soils infested with the nematode reduced its infective capacity by 98–99% compared to untreated soils in pot experiments. Milbeknock^® reduced nematode soil population densities by 50–60% in natural infestations under field conditions. Milbemectin shows a high level of efficacy against root-knot nematodes as it reduces egg hatching, persistently immobilizes nematode juveniles, and reduces tomato root infection.

Tailored Lignocellulose-Based Biodegradable Matrices with Effective Cargo Delivery for Crop Protection

Controlled release and targeted delivery of agrochemicals are crucial for achieving effective crop protection with minimal damage to the environment. This work presents an innovative and cost-effective approach to fabricate lignocellulose-based biodegradable porous matrices capable of slow and sustained release of the loaded molecules for effective crop protection. The matrix exhibits tunable physicochemical properties which, when coupled with our unique "wrap-and-plant" concept, help to utilize it as a defense against soil-borne pests while providing controlled release of crop protection moieties. The tailored matrix is produced by mechanical treatment of the lignocellulosic fibers obtained from banana plants. The effect of different extents of mechanical treatments of the lignocellulosic fibers on the protective properties of the developed matrices is systematically investigated. While variation in mechanical treatment affects the morphology, strength, and porosity of the matrices, the specific composition and structure of the fibers are also capable of influencing their release profile. To corroborate this hypothesis, the effect of morphology and lignin content changes on the release of rhodamine B and abamectin as model cargos is investigated. These results, compared with those of the matrices developed from non-banana fibrous sources, reveal a unique release profile of the matrices developed from banana fibers, thereby making them strong candidates for crop protection applications.

Nematicidal activity of 5-iodoindole against root-knot nematodes

Multi-drug resistance in nematodes is a serious problem as lately several resistant phenotypes have emerged following the intermittent usage of synthetic nematicides. Contemporary research continues to focus on developing and/or repurposing small molecule inhibitors that are eco-friendly. Here, we describe the repurposing of the indole derivative, 5-iodoindole, as a nematicide for the root-knot nematode, Meloidogyne incognita. 5-Iodoindole effectively killed juveniles and freshly hatched juveniles by inducing multiple vacuole formation. Notably, at higher dosage (50 μg/mL), 5-iodoindole induced rapid juvenile death within 6 h. Microscopic analysis confirmed that the rapid death was due to the generation of reactive oxygen species (ROS). Computational docking attributed this ROS production to the antagonistic effect of 5-iodoindole on glutathione S-transferase (GST), which is known to play a critical role in the suppression of ROS in nematode models. Furthermore, 5-iodoindole also effectively reduced the gall formations and eggs masses of M. incognita on Solanum lycopersicum roots in pot experiments, and importantly it did not harm the physiological properties of the plant. Overall, the study provides valuable insights on the use of 5-iodoindole as an alternate measure to control root-knot nematodes. Overall, our findings suggest the efficacy of 5-iodoindole should be studied under field conditions.

Nematodes avoid and are killed by Bacillus mycoides-produced styrene

Root-knot nematodes are obligate parasites that feed on plant roots and cause serious crop losses worldwide. Bacillus species (Bacilliaceae) can produce nematicidal metabolites and have shown good potential for biological control of nematodes. In this study, Bacillus mycoides strain R2 isolated from rhizosphere soil of tomato plants exhibited high nematicidal activity against the free-living nematode Caenorhabditis elegans and the root-knot nematode Meloidogyne incognita. In a pot experiment, control efficiency of B. mycoides R2 on M. incognita was as high as 90.94%. The nematicidal compound was isolated and identified as styrene. The median lethal concentration of styrene against M. incognita was 4.55 μg/ml (m/v). The volatile styrene caused avoidance and killed nematodes primarily by the olfactory neuron and G protein signal pathway. C. elegans detected styrene with the AWB neuron; the signal was then transmitted to the downstream G protein coupled receptors CHE-3, DOP-3, and STR-2. Then signal activated G protein GPA-3 and GPA-7. The signal was then transmitted to ion channels (CNGs channel and TRPV channel), causing calcium ion internal flow and a stress response towards the increased concentration of intracellular calcium. Styrene should be registered as a nematode repellent and biocontrol agent for protection of crops against root-knot nematode attack.

Modifying the Formulation of Abamectin To Promote Its Efficacy on Southern Root-Knot Nematode (Meloidogyne incognita) under Blending-of-Soil and Root-Irrigation Conditions

The southern root-knot nematode (RKN), Meloidogyne incognita, is the most disastrous and prevalent nematode threat to the production of crops, especially vegetables. In the current study, second-stage juveniles (J2) of M. incognita were collected from five regions near Tai'an, China. The toxicity of abamectin to these J2 had insignificant differences, with LC₅₀ values of approximately 2 mg/L. Two pesticide application approaches (i.e., blending-of-soil and root-irrigation) were adopted in pot experiments; blending-of-soil was more beneficial for promoting the efficacy of abamectin on the RKN of tomatoes. Abamectin microcapsule suspension exhibited superiority to emulsifiable concentrate (EC) at dosages of 5 and 10 mg active ingredient per plant integrating efficacy, root length, plant height, the fresh weight of roots, and the fresh weight of stems + leaves. Adsorption, leaching, and mobility of abamectin in the soil also verified bioactivity test results. Modifying the formulation of abamectin can promote its efficacy on RKN under different application approaches.

Plant Virus-Based Nanoparticles for the Delivery of Agronomic Compounds as a Suspension Concentrate

Nanoparticle formulations of agrichemicals may enhance their performance while simultaneously mitigating any adverse environmental effects. Red clover necrotic mosaic virus (RCNMV) is a soil-transmitted plant virus with many inherent attributes that allow it to function as a plant virus-based nanoparticle (PVN) when loaded with biologically active ingredients. Here we describe how to formulate a PVN loaded with the nematicide abamectin (Abm) beginning with the propagation of the virus through the formulation, deactivation, and characterization of the finished product.

Effect of Abamectin on the Cereal Cyst Nematode (CCN, Heterodera avenae) and Wheat Yield

The cereal cyst nematode (CCN, Heterodera avenae) is a major pest in wheat and until now there is no pesticide registered to control this pest in China. Development of effective methods of controlling CCN is urgently needed. Abamectin is a biological pesticide that has a high nematicide activity. However, the efficacy of abamectin soil application to control CCN in wheat and its effect on yield in China remains unknown. Therefore, laboratory, greenhouse, and field tests were carried out to evaluate the potential of abamectin soil applications for CCN control and improvement of wheat yield. Laboratory tests showed that abamectin exhibited knockdown toxicity to CCN, with LC₅₀ and LC₉₀ values 9.8 and 59.4 mg liter^-1. Greenhouse experiment and field trials showed that soil applications of abamectin provided significant CCN control and higher straw dry weights and wheat grain yields. There was an 8.5 to 19.3% yield increase from the various abamectin treatments compared with the control. The results of this study demonstrated that abamectin exhibited a high nematicidal activity to H. avenae and adequate performance to enhance wheat crop yields.

Efficacy Evaluation of Seed-Coating Compounds Against Cereal Cyst Nematodes and Root Lesion Nematodes on Wheat

Cereal cyst nematodes (Heterodera avenae and H. filipjevi) and root lesion nematodes (Pratylenchus spp.) have been found to infect cereals in 16 provinces of China. To develop a nematicide that effectively controls nematodes, two novel chemical products, methylene bis thiocyanate (MBT) and MBT + thiamethoxam (MTT); four common pesticides, fipronil + chlorpyrifos (FIC), emamectin benzoate, imidacloprid, and Bacillus thuringiensis; and one fungicide, iprodione, were tested as seed coatings for the control of cereal cysts and root lesion nematodes from 2013 to 2015. Wheat seeds were treated with these seven seed coatings before sowing, and changes in the numbers of Heterodera spp. and Pratylenchus spp. were recorded during three different growth stages. Wheat yields were also compared after harvest. All treatments reduced the numbers of Pratylenchus in wheat and of cysts and eggs of Heterodera in the soil compared with the untreated control. Among the treatments, application of MTT or FIC was more effective than that of the other treatments for nematode control, and the other treatments had similar effects. The results of this study have demonstrated that MTT and FIC applied as seed treatments effectively reduce the number of cysts, inhibit the reproduction of Heterodera and Pratylenchus, and enhance wheat yields. MTT and FIC are thus suitable for controlling nematodes on wheat under natural field conditions.

Single basal application of thiacloprid for the integrated management of Meloidogyne incognita and Bemisia tabaci in tomato crops

Tomato growers commonly face heavy nematode (Meloidogyne incognita) and whitefly (B-biotype Bemisia tabaci) infestations, and previous studies demonstrated that thiacloprid could be used to control M. incognita and B. tabaci in cucumber. However, the efficacy of a single basal application of thiacloprid to control both pests and its effect on yield in tomato remains unknown. In this study, the potential of thiacloprid application to the soil for the integrated control of M. incognita and B. tabaci in tomato was evaluated in the laboratory and the field. Laboratory tests showed that thiacloprid was highly toxic to whitefly adults and eggs with an average lethal concentration 50 (LC50) of 14.7 and 62.2 mg ai L-1, respectively, and the LC50 of thiacloprid for nematode J2s and eggs averaged 36.2 and 70.4 mg ai L-1, respectively. In field trials, when thiacloprid was applied to the soil at 7.5, 15 and 30 kg ha-1 in two consecutive years, whitefly adults decreased by 37.8-75.4% within 60 days of treatment, and the root-galling index was reduced by 31.8-85.2%. Optimum tomato plant growth and maximum yields were observed in the 15 kg ha-1 treatment. The results indicated that a single basal application of thiacloprid could control M. incognita and B. tabaci and enhance tomato growth and yield.

Nematicidal Activity of trans-2-Hexenal against Southern Root-Knot Nematode (Meloidogyne incognita) on Tomato Plants

Botanical nematicides have recently received increasing interest because of the high risks of some traditional nematicides to human health and the environment. This study evaluated the nematicidal activity of a plant volatile, trans-2-hexenal, against Meloidogyne incognita. This compound exhibited higher activity in a fumigation experiment than in the aqueous phase in vitro. Both in pot tests and in field trials, trans-2-hexenal showed significant efficacy against M. incognita while maintaining excellent plant growth, especially at doses of 1000 and 500 L ha^-1, which were superior to that of abamectin at 180 g ha^-1 via hole application treatment but not significantly different from fumigation with 400 kg ha^-1 of dazomet. Furthermore, plants treated with 500 L ha^-1 trans-2-hexenal had fruit yields 20.2 and 45% greater than the control group. On this basis, trans-2-hexenal may be a potential alternative fumigation agent for controlling M. incognita on tomato crops.

Identification and characterization of microRNAs in the plant parasitic root-knot nematode Meloidogyne incognita using deep sequencing

The root-knot nematode Meloidogyne incognita is among the most damaging plant-parasitic pests of several crops including cotton (Gossypium hirsutum) and tomato (Lycopersicon escultentum). Recently, a genome has become available for M. incognita, which greatly facilitates investigation of the interactions between M. incognita and its plant hosts at the molecular level and enables formation of hypotheses concerning development at the cellular level. MicroRNAs (miRNAs) are a class of small RNA molecules that serve as endogenous gene regulators. They regulate many biological processes including reproduction, the sequencing of morphological development, and potentially of parasitism as well. Certain miRNAs regulate fundamental metabolism pathways and stress responses in M. incognita. Since a list of miRNAs has not been generated for M. incognita, we employed a bioinformatics tool called mirDeepFinder to identify miRNAs from the small RNA database of M. incognita (GSM611102) that was generated from deep sequencing. A total of 254 conserved miRNAs belonging to 161 miRNA families were identified, as were 35 novel miRNAs belonging to 31 families. The 16 most commonly found miRNAs in order of abundance were min-miR-100a, min-miR-124, min-miR-71a, min-miR-1, min-miR-228, min-miR-92, min-miR-72, min-miR-49b, min-miR-58, min-miR-252, min-miR-lin-4, min-miR-87, min-miR-2a, min-miR-34a, min-miR-50a, and min-miR-279a. The length of the pre-miRNAs varied greatly from 50 to 197 nt, with an average of 88 ± 39 nt. The average minimal folding free energy (MFE) and MFE index (MFEI) of the identified miRNAs were -30.3 Kcal/mol and 0.92, respectively, indicating that these miRNAs can readily fold into a typical hairpin secondary structure.

Effect of Emamectin Benzoate on Root-Knot Nematodes and Tomato Yield

Southern root-knot nematode (Meloidogyne incognita) is an obligate, sedentary endoparasite of more than 3000 plant species, that causes heavy economic losses and limit the development of protected agriculture of China. As a biological pesticide, emamectin benzoate has effectively prevented lepidopteran pests; however, its efficacy to control M. incognita remains unknown. The purpose of the present study was to test soil application of emamectin benzoate for management of M. incognita in laboratory, greenhouse and field trials. Laboratory results showed that emamectin benzoate exhibited high toxicity to M. incognita, with LC50 and LC90 values 3.59 and 18.20 mg L(-1), respectively. In greenhouse tests, emamectin benzoate soil application offered good efficacy against M. incognita while maintaining excellent plant growth. In field trials, emamectin benzoate provided control efficacy against M. incognita and resulted in increased tomato yields. Compared with the untreated control, there was a 36.5% to 81.3% yield increase obtained from all treatments and the highest yield was received from the highest rate of emamectin benzoate. The results confirmed that emamectin benzoate has enormous potential for the control of M. incognita in tomato production in China.