Toxicity of phenolic compounds to entomopathogenic nematodes: A case study with Heterorhabditis bacteriophora exposed to lentisk (Pistacia lentiscus) extracts and their chemical components

Nematocidal Potential of Phenolic Acids: A Phytochemical Seed-Coating Approach to Soybean Cyst Nematode Management

Soybeans, one of the most valuable crops worldwide, are annually decimated by the soybean cyst nematode (SCN), Heterodera glycines, resulting in massive losses in soybean yields and economic revenue. Conventional agricultural pesticides are generally effective in the short term; however, they pose growing threats to human and environmental health; therefore, alternative SCN management strategies are urgently needed. Preliminary findings show that phenolic acids are significantly induced during SCN infection and exhibit effective nematocidal activities in vitro. However, it is unclear whether these effects occur in planta or elicit any negative effects on plant growth traits. Here, we employed a phytochemical-based seed coating application on soybean seeds using phenolic acid derivatives (4HBD; 2,3DHBA) at variable concentrations and examined SCN inhibition against two SCN types. Moreover, we also examined plant growth traits under non-infected or SCN infected conditions. Notably, 2,3DHBA significantly inhibited SCN abundance in Race 2-infected plants with increasingly higher chemical doses. Interestingly, neither compound negatively affected soybean growth traits in control or SCN-infected plants. Our findings suggest that a phytochemical-based approach could offer an effective, more environmentally friendly solution to facilitate current SCN management strategies and fast-track the development of biopesticides to sustainably manage devastating pests such as SCN.

Effects of Coumarinyl Schiff Bases against Phytopathogenic Fungi, the Soil-Beneficial Bacteria and Entomopathogenic Nematodes: Deeper Insight into the Mechanism of Action

Coumarin derivatives have been reported as strong antifungal agents against various phytopathogenic fungi. In this study, inhibitory effects of nine coumarinyl Schiff bases were evaluated against the plant pathogenic fungi (Fusarium oxysporum f. sp. lycopersici, Fusarium culmorum, Macrophomina phaseolina and Sclerotinia sclerotiourum). The compounds were demonstrated to be efficient antifungal agents against Macrophomina phaseolina. The results of molecular docking on the six enzymes related to the antifungal activity suggested that the tested compounds act against plant pathogenic fungi, inhibiting plant cell-wall-degrading enzymes such as endoglucanase I and pectinase. Neither compound exhibited inhibitory effects against two beneficial bacteria (Bacillus mycoides and Bradyrhizobium japonicum) and two entomopathogenic nematodes. However, compound 9 was lethal (46.25%) for nematode Heterorhabditis bacteriophora and showed an inhibitory effect against acetylcholinesterase (AChE) (31.45%), confirming the relationship between these two activities. Calculated toxicity and the pesticide-likeness study showed that compound 9 was the least lipophilic compound with the highest aquatic toxicity. A molecular docking study showed that compounds 9 and 8 bind directly to the active site of AChE. Coumarinyl Schiff bases are promising active components of plant protection products, safe for the environment, human health, and nontarget organisms.

Phenolic Compounds Regulating the Susceptibility of Adult Pine Species to Bursaphelenchus xylophilus

Pine wilt disease (PWD), caused by the pinewood nematode (PWN) Bursaphelenchus xylophilus, is one of the most destructive diseases in trees of the genus Pinus and is responsible for significant environmental and economic losses in North America, Eastern Asia, and Western Europe. However, pine species are not equally affected, with some being tolerant/resistant while others are susceptible to nematode infection for reasons still unclear. The present study aims to investigate differential chemical responses of susceptible and tolerant/resistant pine species shortly after nematode infection by characterizing the phenolic profiles of adult Pinus sylvestris, Pinus pinaster, Pinus pinea, and Pinus halepensis. HPLC and LC-MS were used to identify and quantify the pine´s phenolic compounds: gallic acid, ferulic acid, taxifolin, rutin, resveratrol, (+)-secoisolariciresinol, (−)-epicatechin, protocatechuic acid hexoside, gallic acid hexoside, ferulic acid glucoside, quercetin hexoside, and two unidentified compounds (#A and #B). Prior to infection, we could not differentiate between nematode-tolerant/resistant and susceptible adult pine species based on their constitutive phenolic compounds. In the presence of the PWN, the phenolic profile allowed for a noticeable separation of the PWN-tolerant/resistant P. halepensis from the susceptible P. sylvestris, contrasting with a more homogenous response from P. pinea and P. pinaster. Observations on P. halepensis suggest that taxifolin, resveratrol, and rutin may have an active role in protecting against B. xylophilus, possibly in conjugation with other biochemical and anatomical characters. We emphasize the importance of studying pine tolerant/resistance on adult trees, and not on excised branches, saplings, or seedlings to accurately simulate the nematode–pine host interactions occurring under natural conditions.

Comparison of Biological Activity of Field Isolates of Steinernema feltiae with a Commercial S. feltiae Biopesticide Product

Insect trap studies were carried out to determine the presence of entomopathogenic nematodes (EPN) from the family Steinernematidae in the soils of Poland and to compare the biological activities of field nematode isolates with nematodes from commercial biopesticide. The fauna of these organisms in central Poland is poorly studied in both taxonomic and biological terms. Tilled soils representative of this region were sampled from cultivated fields. EPN were isolated from soil samples under laboratory conditions and identified using a key for species identification and molecular analysis. Basic morphometric parameters of infective juveniles and adult males of the first generation were determined. The research showed that males and infective juveniles Steinernema feltiae from Łoniów were the largest. The smallest infective juveniles were found in the isolate from Oblasy, and the smallest males in the isolate from Danków. In Poland, new field isolates showed close genetic similarity to other S. feltiae isolates. The research showed that the field isolates from Poland had greater infectivity and rate of reproduction compared with nematodes from the commercial biopesticide. The findings indicate the potential use of field S. feltiae isolates from Poland (iso1Lon, iso1Dan and iso1Obl) to develop new biopesticide products.

Biological Activities Related to Plant Protection and Environmental Effects of Coumarin Derivatives: QSAR and Molecular Docking Studies

The aim was to study the inhibitory effects of coumarin derivatives on the plant pathogenic fungi, as well as beneficial bacteria and nematodes. The antifungal assay was performed on four cultures of phytopathogenic fungi by measuring the radial growth of the fungal colonies. Antibacterial activity was determined by the broth microdilution method performed on two beneficial soil organisms. Nematicidal activity was tested on two entomopathogenic nematodes. The quantitative structure-activity relationship (QSAR) model was generated by genetic algorithm, and toxicity was estimated by T.E.S.T. software. The mode of inhibition of enzymes related to the antifungal activity is elucidated by molecular docking. Coumarin derivatives were most effective against Macrophomina phaseolina and Sclerotinia sclerotiorum, but were not harmful against beneficial nematodes and bacteria. A predictive QSAR model was obtained for the activity against M. phaseolina (R²_tr = 0.78; R²_ext = 0.67; Q²_loo = 0.67). A QSAR study showed that multiple electron-withdrawal groups, especially at position C-3, enhanced activities against M. phaseolina, while the hydrophobic benzoyl group at the pyrone ring, and –Br, –OH, –OCH₃, at the benzene ring, may increase inhibition of S. sclerotiourum. Tested compounds possibly act inhibitory against plant wall-degrading enzymes, proteinase K. Coumarin derivatives are the potentially active ingredient of environmentally friendly plant-protection products.

Aqueous Leaf Extract of Pistacia lentiscus Improves Acute Acetic Acid-Induced Colitis in Rats by Reducing Inflammation and Oxidative Stress

We investigate the antioxidant activity and protective effects of the aqueous leaf extract of Pistacia lentiscus (AELPL) against ulcerative colitis induced by acetic acid infusion through the rectum in Wistar rats. Phytochemical analyses allowed the identification of numerous phenolic compounds in P. lentiscus leaves such as flavonoids (isoquercetin and luterolin), flavonols (catechin, rutin, and kaempferol), phenolic acids (ellagic and dicaffeoylquinic), and tanins. Acetic acid exposure induced macroscopic colonic mucosal lesions with hemorrhage, congestion, edema, and the development of an expected oxidative stress state revealed by an increase in lipoperoxidation and carbonylation of proteins and a decrease in sulfhydryl (SH) group levels and antioxidant enzyme activities such as superoxide dismutase, catalase, glutathione-S-peroxidase, and glutathione transferase, as well as an increase in the inflammatory cytokine, interleukin-6, in the colon and plasma. Administration of acetic acid also increased plasma and tissue levels of hydrogen peroxide and rates of iron and free calcium, whereas AELPL significantly and dose-dependently attenuated all the previous biochemical alterations and intracellular mediator perturbations. In conclusion, the AELPL exhibited a potent cytoprotective effect against acetic acid-induced colitis in rats, mainly through its antioxidant and anti-inflammatory activities.

Evaluation of different sponge types on the survival and infectivity of stored entomopathogenic nematodes

Sponges are one of the cheapest and most suitable substrates used to formulate and/or store the infective juveniles (IJs) of entomopathogenic nematodes (EPNs). Our study investigated the survival and infectivity of the IJs on five different sponges compared to that in an aqueous suspension (control). The sponges were Oasis® floral, Nanosponge, Scotchbrite^TM, or Lysol® and natural sea sponge. EPN species tested were Heterorhabditis bacteriophora, Steinernema carpocapsae and S. feltiae. The recovery efficiency of the IJs from sponges was initially assessed. Subsequently, IJs were stored in the sponges and placed in plastic bags or Falcon tubes and incubated at 10° or 27 °C for 8 months or 11 weeks, respectively. IJ survival and infectivity were monitored monthly for the 10 °C and weekly for 27 °C in these sponge types. The IJs were recovered from the sponges, and their survival was based on observing their movement under a dissecting microscope, and infectivity was based on larval mortality in Galleria mellonella. Recovery efficiency of IJs was best for the Oasis floral sponge for all nematode species ranging between 83 and 91%. The survival and infectivity of stored IJs in all sponge types and control for both 10° and 27 °C gradually decreased over time. IJs stored in Scotchbrite, Lysol, and Nanosponge had the best survival and infectivity, whereas Oasis floral and natural sea sponges showed the poorest results. After 8 months at 10 °C in plastic bags, the survival ratio of all IJs in these three sponges (Scotchbrite, Lysol, and Nanosponge) was approximately 55%. IJs in Scotchbrite and Nanosponge were also able to survive and retain their infectivity at 27 °C for 3 months. IJs stored in Falcon tubes had survival that ranged from 26 to 53% at 27 °C and 55 to 77% at 10 °C. H. bacteriophora IJs lost their infectivity when stored at 27 °C after 10 weeks. However, S. carpocapsae and S. feltiae exhibited 85% infectivity when stored in Scotchbrite and 50% in Nanosponge, respectively. Overall, sponges made from polyurethane (Scotchbrite) followed by melamine (Nanosponge) and cellulose (Lysol) are recommended for long-term nematode storage and transportation of nematode samples. However, Oasis floral sponge may be preferred for short-term IJ formulation for field applications because of easier recovery of IJs.

Can an entomopathogenic nematode serve, as proxy for strongyles, in assessing the anthelmintic effects of phenolic compounds?

As gastro-intestinal nematodes (GINs) become increasingly resistant to chemical anthelmintics, and because consumers scrutinize chemical residues in animal products, the use of herbal anthelmintics and in particular, phenolic compounds, has become attractive. Most life stages of GINs cannot be grown in the lab as they are obligatory parasites, which limits our understanding of the effects of phenolic compounds on their parasitic stages of life. We hypothesized that a species phylogenetically close to GINs and grown in vitro, the insect-parasitic nematode Heterorhabditis bacteriophora (Rhabditida; Heterorhabditiade), when fed with Photorhabdus luminescens exposed to plant phenolics, can serve, as proxy for strongyles, in assessing the anthelmintic effects of phenolic compounds. We compared the development of H. bacteriophora infective juveniles (IJ) and the exsheathment rate of L3 larvae of the strongyle Teladorsagia circumcincta and Trichostrongylus colubriformis when exposed to catechin, rutin, chlorogenic and gallic acids, and myricetin. Gallic acid had the highest impact in terms of IJ mortality but the highest impairment of IJ development to adulthood was imposed by myricetin. The studied compounds were not lethal to GINs stricto sensu but we consider that the practical implications of total exsheathment inhibition and mortality on GIN populations are similar. Catechin and rutin had similar effects on rhabditid and strongyles: they imposed ca. 90% lethality of IJs at concentrations higher than 1200 ppm and the remaining live IJs did not develop further, and they also totally inhibited strongyle L3 exsheathment in a dose-response fashion. Gallic acid was 100% lethal to IJs exposed above 300 ppm and chlorogenic acid caused 87% mortality above 1200 ppm, with no development for the surviving IJs but for all lower concentrations, all the IJs developed to adult stages. Likewise, gallic and chlorogenic acids did not affect the exsheatment of GIN L3 larvae. Therefore, a discrepancy between the effects of gallic and chlorogenic acids on the development of rhabditid IJs and exsheathment of GIN L3 larvae was found only when they were exposed to high concentrations. A dose-response of IJ lethality to myricetin was found, with no IJ development between 150 and 2400 ppm; but contrary to the other compounds, myricetin also impaired IJ development of IJs above 10 ppm in a dose-response manner and showed dose-responses in the L3 exsheathment. Apart for the high rates of lethality imposed on IJs by gallic and chlorogenic acids at high concentration, these results suggest that H. bacteriophora fed P. luminescens exposed to phenolics shows potential to serve as model in studies of the anthelmintic effects of phenolics in GIN.