Nematicidal activity of essential oils: a review

Sosa M.E., Lancelle H.G., Tonn C.E., Andres M.F., Gonzalez-Coloma A.

The defensive properties against insects and plant–parasites nematodes (antifeedant action against the aphids Myzus persicae and Ropalosiphum padi and the nematicidal effects on the root-knot nematode Meloidogyne javanica ) of essential oils from Argentinean semi-arid plants have been studied in relation with their chemical composition. The major components of Baccharis salicifolia essential oils obtained from samples collected from two locations (A and B) in San Luis (Argentina) were ( Z )-β-ocimene, germacrene D, muuroladiene and β-cubebene, with the addition of α-thujene and α-phellandrene, in location A and isoledene in location B. The essential oils of the Eupatorium species ( Eupatorium buniifolium , Eupatorium inulaefolium , Eupatorium arnotii , and Eupatorium viscidum ) have been previously described. M. persicae was strongly affected by these oils except for E. buniifolium and E. arnotii . Additionally, the essential oil from B. salicifolia (location A) had post-ingestive toxicity to Spodoptera littoralis larvae without antifeedant effects. Among these oils, E. viscidum showed a strong nematicidal effect.

Park I., Seo S., Kim J.

AbstractCommercial essential oils from 29 plant species were tested for their nematicidal activity against the pine wood nematode, Bursaphelenchus xylophilus. Good nematicidal activity against B. xylophilus was achieved with essential oils of Gaultheria fragrantissima and Zanthoxylum alatum. GC-MS analysis of the corresponding oils led to the identification of two and ten major compounds, respectively. Four compounds, methyl salicylate, ethyl salicylate, methyl trans-cinnamate and ethyl trans-cinnamate, were tested individually for their nematicidal activities against the pine wood nematode. Methyl and ethyl salicylates showed strong nematicidal activity at concentration of 2.0 mg ml–1. Concentrations of 1.0 mg ml–1, as well as lower concentrations showed only minor effects. Another compound, methyl trans-cinnamate, showed 100% activity at concentrations of 0.0625-2.0 mg ml–1. With ethyl trans-cinnamate, 100% mortality was observed at concentrations of 0.25-2.0 mg ml–1. The essential oils and their components described herein merit further study as potential nematicides against the pine wood nematode.

Bai C.Q., Liu Z.L., Liu Q.Z.

Essential oil of Chinese medicinal herb,Chenopodium ambrosioidesaerial parts was found to possess nematicidal activity against the root-knot nematodes,Meloidogyne incognita. The essential oil ofC. ambrosioideswas obtained by hydrodistillation and analyzed by gas chromatography-mass spectrometry (GC-MS). A total of 27 components of the essential oil were identified. The principal compounds inC. ambrosioidesessential oil were (Z)-ascaridole (27.27%),ρ-cymene (19.05%), isoascaridole (14.75%),α-pinene (6.33%) andα-terpinene (5.12%). Bioactivity-guided chromatographic separation of the essential oil on repeated silica gel columns led to isolate three volatile components ((Z)-ascaridole,ρ-cymene and isoascaridole) from the essential oil. The essential oil and (Z)-ascaridole exhibited strong nematicidal activity againstM. incognitawith LC50values of 49.55 μg/mL and 32.79 μg/mL, respectively.ρ-Cymene and isoascaridole also possessed nematicidal activity againstM. incognitawith LC50values of 435.89 μg/mL and 1323.51 μg/mL, respectively but weaker than the crude essential oil.

Gupta A., Sharma S., Naik S.N.

The biopesticidal potential of six plant-derived essential oils (mint [ Mentha arvensis ], ajwain [ Carum capticum ], lemongrass [ Cymbopogon citrates ], clove [ Eugenia caryophyllata ], cedarwood [ Cedrus deodara ], and eucalyptus [ Eucalyptus globulas ]) was evaluated against Odontotermes obesus (termites), Fusarium oxysporum (plant pathogenic fungi), and Meloidogyne incognita (nematodes). In the case of termites, a “no-choice” bioassay revealed that the mint oil gave the best results (100% mortality in 30 min with 10% oil and in 10 h with 0.12% oil) followed by the lemongrass and ajwain oils. The disc diffusion method was adopted to test the anti-fungal activity of the essential oils and it was found that the clove oil gave the maximum inhibition measured in terms of the average inhibition zone diameter (5.3 ± 0.2 cm with 10% oil and 6.6 ± 0.9 cm with 20% oil), followed by the ajwain oil. To check the anti-nematicidal activity of the essential oil, in-vitro growth chamber experiments revealed that eucalyptus oil was the most efficient (100% mortality in 6 h with 1000 μl l −1 oil and in 30 h with 125 μl l −1 oil), followed by the ajwain oil. The use of the crude oils at low concentrations provided satisfactory results at the laboratory level against these pathogens, and needs further evaluation in field trials.

Kaur S., Rana S., Singh H.P., Batish D.R., Kohli R.K.

Ntalli N.G., Ferrari F., Giannakou I., Menkissoglu-Spiroudi U.

Varona S., Kareth S., Martín Á., Cocero M.J.

Essential oils, and in particular lavandin (lavandula hybrida) essential oil, can be used as natural biocides as an alternative to synthetic chemical biocides. For this purpose, agrochemical formulations of the essential oils should be physically stable in the long term and should enhance the biological performance of the agrochemical. In this work, such a formulation of lavandin essential oil obtained by encapsulation of the oil in a biodegradable polymer has been studied. Two high-pressure precipitation techniques, particles from gas saturated solutions (PGSS) and PGSS-drying, have been applied to perform the encapsulation. The PGSS process has been used to encapsulate the oil in polyethylene glycol (PEG). With PGSS-drying the oil has been encapsulated in n-octenyl succinic (OSA)-modified starches, by removing the water form an oil-in-water emulsion stabilized using the OSA-starches as surfactants. Operating conditions were selected in order to reduce oil losses due to its dissolution in supercritical CO2 or due to emulsion destabilization. A comparison between the characteristics of the particles obtained by encapsulation in PEG with PGSS and by encapsulation in OSA-starches with PGSS-drying was done. Results revealed that encapsulation efficiencies of lavandin oil were higher in PEG microcapsules obtained by PGSS (14–66% of initial oil encapsulated). Particles show a spherical morphology and a narrow particle size distribution, which is favourable for a controlled release of lavandin essential oil.

Ntalli N.G., Ferrari F., Giannakou I., Menkissoglu-Spiroudi U.

Eight essential oils (EOs) as well as 13 single terpenes were studied for their nematicidal activity against Meloidogyne incognita , for three immersion periods (24, 48, and 96 h). The EOs were isolated from eight Greek Lamiaceae species: Melissa officinalis , Sideritis clandestina , Origanum dictamnus , Ocimum basilicum , Mentha pulegium , Origanum vulgare , Vitex agnus castus , and Salvia officinalis . The EOs nematicidal activity was correlated to their chemical composition as well as to the pure terpenes' activity tested individually. Clear dose and time response relationships were established. The EOs of O. vulgare, O. dictamnus, M. pulegium, and M. officinalis exhibited high nematicidal activity against M. incognita, and the EC(50) values (96 h) were calculated at 1.55, 1.72, 3.15, and 6.15 muL/mL, respectively. The activity of the nematicidal terpenes was found to decrease in the order l-carvone, pulegone, trans-anethole, geraniol, eugenol, carvacrol, thymol, terpinen-4-ol, and the respective EC(50) values (24 h) were calculated in the range of 115-392 mug/mL. Terpenes tested individually were more active than as components in EO, implementing antagonistic action.

Martin A., Varona S., Navarrete A., Cocero M.J.

Lei J., Leser M., Enan E.

In vitro cultures of two nematodes (Caenorhabditis elegans and Ascaris suum) were established to study the nematicidal activity of three monoterpenoids (thymol, carvacrol and p-cymene). Toxicity of thymol and carvacrol was found for the two nematodes tested. The study was then aimed to address whether nematode tyramine receptor (TyrR) could interact with the two compounds by using HEK293 mammalian cells transfected with a C. elegans TyrR (ser-2) sequence, in hope of developing a high-throughput cell-based platform for future screening of new antihelminthic compounds. SER-2 expression and functionality in the transfected cells was first confirmed by green fluorescent protein tagging, competitive receptor binding, intracellular cyclic AMP, and intracellular calcium [Ca(2+)](i) mobilization assays. Thymol and carvacrol were then tested and demonstrated to interact with TyrR in desensitizing SER-2 for tyramine activation in [Ca(2+)](i) mobilization assay, and in translocating SER-2 from membrane to cytoplasm in receptor internalization assay. Receptor internalization activity of thymol and carvacrol was significantly blocked in cells expressing mutant SER-2 with the S210A/S214A double mutations, thus confirming specificity of the interactions. In summary, the current study showed that the nematicidal activity of thymol and carvacrol might be mediated through TyrR as the two compounds could trigger the signaling cascade downstream from the receptor in cells expressing wild-type but not a mutant SER-2. The TyrR-expressing cell system may prove to be a good screening platform for developing new antihelmintic compounds that may overcome parasite drug resistance, especially when such chemicals are used in combination with commercial drugs.

Isman M.B., Miresmailli S., Machial C.

In spite of intensive research on plant natural products and insect-plant chemical interactions over the past three decades, only two new types of botanical insecticides have been commercialized with any success in the past 15 years, those based on neem seed extracts (azadirachtin), and those based on plant essential oils. Certain plant essential oils, obtained through steam distillation and rich in mono- and sesquiterpenes and related phenols, are widely used in the flavouring and fragrance industries and in aromatherapy. Some aromatic plants have traditionally been used for stored product protection, but the potential for development of pesticides from plant essential oils for use in a wide range of pest management applications has only recently been realized. Many plant essential oils and their major terpenoid constituents are neurotoxic to insects and mites and behaviourally active at sublethal concentrations. Most plant essential oils are complex mixtures. In our laboratory we have demonstrated that individual constituents of oils rarely account for a major share of the respective oil’s toxicity. Further, our results suggest synergy among constituents, including among those that appear non-toxic in isolation. Repellent effects may be particularly useful in applications against public health and domestic pests, but may be useful in specific agricultural applications as well. In all of these applications, there is a premium on human and animal safety that takes priority over absolute efficacy. In agriculture, the main market niche for essential oil-based pesticides is in organic food production, at least in developed countries, where there are fewer competing pest management products. There is also scope for mixing these oils with conventional insecticides and for enhancing their efficacy with natural synergists. Some examples of field efficacy against agricultural pests are discussed.

Douda O., Zouhar M., Mazáková J., Nováková E., Pavela R.

The northern root-knot nematode (Meloidogyne hapla) is a prominent root vegetable pest in the Czech Republic. Effects of several plant essences for M. hapla management on carrot (Daucus carota) were tested. The tested compounds included commercially available plant essences from Ocimum basilicum (sweet basil), Mentha arvensis (field mint), Tagetes erecta (Mexican marigold), and commercial product of neem seed (Azadirachta indica). Two further essences from Eugenia caryophyllata (clove) and Origanum majorana (marjoram) were obtained by distillation. Tests were conducted on container-grown carrots maintained under field conditions. The delivery method involved absorbing the tested essences in perlite particles placed in a substrate. The results showed a negative correlation between gall numbers of the carrots and treatment concentrations, especially for clove and majoram. Similar results were achieved when considering M. hapla egg numbers. Furthermore, the same treatments showed significant differences (P ≥ 0.05) in fresh and dry root weights. Based on these results the management of M. hapla using plant essences seems to be possible, however, further research is desirable to determine the appropriate dosage needed for efficient and most appropriate delivery method of these substances under field conditions.

Echeverrigaray S., Zacaria J., Beltrão R.

Nematicidal activity of 22 monoterpenoids were evaluated in vitro and in pot experiments. Twenty of the twenty-two monoterpenoids significantly reduced hatching, and 11 reduced J2 mobility of the root-knot nematode Meloidogyne incognita at a concentration of 250 mg/liter. In general, compounds with hydroxyl and carbonyl groups exhibited higher nematicidal activity than other terpenoids. Borneol, carveol, citral, geraniol, and α-terpineol showed the highest nematicidal activity among the in vitro tested monoterpenoids. These compounds exhibited a dose dependent effect, and drastically reduced eggs hatching and J2 viability at low concentrations. These monoterpenoids, at 100 and 250 mg/kg concentration, diminished root galling of tomato plants in pot experiments. The results suggest that the selected monoterpenoids, and essential oils with high concentration of these compounds, are potential nematicides against Meloidogyne.

Nyczepir A.P., Thomas S.H.

Bird D.M., Williamson V.M., Abad P., McCarter J., Danchin E.G., Castagnone-Sereno P., Opperman C.H.

Plant-parasitic nematodes are the most destructive group of plant pathogens worldwide and are extremely challenging to control. The recent completion of two root-knot nematode genomes opens the way for a comparative genomics approach to elucidate the success of these parasites. Sequencing revealed that Meloidogyne hapla, a diploid that reproduces by facultative, meiotic parthenogenesis, encodes approximately 14,200 genes in a compact, 54 Mpb genome. Indeed, this is the smallest metazoan genome completed to date. By contrast, the 86 Mbp Meloidogyne incognita genome encodes approximately 19,200 genes. This species reproduces by obligate mitotic parthenogenesis and exhibits a complex pattern of aneuploidy. The genome includes triplicated regions and contains allelic pairs with exceptionally high degrees of sequence divergence, presumably reflecting adaptations to the strictly asexual reproductive mode. Both root-knot nematode genomes have compacted gene families compared with the free-living nematode Caenorhabditis elegans, and both encode large suites of enzymes that uniquely target the host plant. Acquisition of these genes, apparently via horizontal gene transfer, and their subsequent expansion and diversification point to the evolutionary history of these parasites. It also suggests new routes to their control.

Haris M., Laasli S., Taoussi M., Hussain T., Khan F., Khan A., Shariq M., Ansari M.S., Khan A.A., Lahlali R.

Elkhiat Z.K., Aly A.F., Fahmy H.H., Raddy H.M.

Díaz-González S., Andrés M.F., González-Sanz C., Sacristán S., González-Coloma A.

Abstract Endophytic fungi produce a diverse range of bioactive secondary metabolites with potential applications in biopesticide development. This study investigates the nematicidal and antifeedant properties of ethyl acetate extracts from endophytic fungi isolated from wild Arabidopsis thaliana populations in Spain. The extracts were tested against the plant-parasitic nematode Meloidogyne javanica, and two common insect pests, Myzus persicae and Spodoptera littoralis. Nine of the 13 extracts demonstrated significant nematicidal and/or antifeedant activity, indicating their potential as biopesticides. The active extracts were derived from six genera: Alternaria (3 isolates), Dydimella (1), Dothiora (1), Pleiochaeta (1), Penicillium (1), and Fusarium (2). Five extracts exhibited nematicidal activity above 90%, with three reducing the total number of M. javanica second-stage juveniles hatched from egg masses by 22–37%. Four extracts showed strong settling inhibition (> 70%) against M. persicae, and three exhibited feeding inhibition against S. littoralis. Chemical analysis by GC-MS and LC-MS revealed a wide array of unique secondary metabolites in the active extracts, reflecting substantial chemical diversity, regardless of the fungal origin. This study highlights the potential of fungal endophytes from A. thaliana as sources of novel biopesticides, paving the way for future research focused on harnessing these fungi for biopesticide development.

KP J., Favas V A., Sherin S., Waqar S.

Root-knot nematodes (RKN) are a serious threat to sustainable agroecosystems. They attack a wide range of crops all over the world and lead to significant yield losses. This chapter explores the use of bio-organic management strategies instead of harmful chemical control measures. We evaluate the possibilities of decreasing the RKN population by effectively using cropping practices such as crop rotation, resistant cultivars, and soil solarization. Most importantly, the chapter discusses about biological control agents (BCA) such as nematode-trapping fungi, endoparasitic fungi, Bacillus pumilus, Pasteuria penetrans, and other useful microorganisms to suppress the nematode population. Finally, we conclude by discussing the use of soil amendments such as botanicals, plant extracts, oil cakes, and other organic materials like manure and vermicompost to inhibit the RKN population and enhance soil health. This chapter provides us with valuable information on how to control nematode populations effectively and promote sustainable and environmentally friendly agricultural practices.

Kumar R., Dutta T.K., Mandal A., Saha S., Dutta A., Kundu A.

Belaid S., Gonzalez-Coloma A., Andres M.F., Elfalleh W., Idoudi S., Romdhane M., Saadaoui E.

ABSTRACTLeaf essential oils (EOs) of seven Eucalyptus species planted in Southern Tunisia (E. gracilis, E. lesouefii, E. salmonophloia, E. sargentii, E. flocktoniae, E. oleosa, and E. salubris) were screened for their antifeedant, nematicidal, and phytotoxic effects as well as their chemical compositions. The yield of EOs of these species varied from 1.32% ± 0.38% to 4.92%±0.37%. Using gas chromatography mass spectrometry (GC–MS) analysis, 22 compounds were identified, representing 87.16%–96.83% of the total oil content. The main components found in all EOs were 1,8‐cineole (38.71%–70.44%), α‐pinene (4.40%–8.88%), p‐cymene (0.95%–14.99%), pinocarvone (0.17%–3.22%), trans‐pinocarveol (1.53%–13.48%), spathulenol (0.18%–5.39%), and globulol (0.22%–6.47%). The insect antifeedant, nematicidal, and phytotoxic effects of these oils against insect pests (Spodoptera littoralis, Myzus persicae, and Rhopalosiphum padi), the root‐knot nematode (Meloidogyne javanica), and two plant models (Lolium perenne and Lactuca sativa) were examined. Despite the moderate insect antifeedant activity, the EOs of E. salubris, E. salmonophloia, E. lesouefii, and E. sargentii were the most effective against M. persicae. Significant nematicidal effects were observed for both E. salmonophloia and E. oleosa EOs. Moreover, all Eucalyptus EOs significantly suppressed the root and leaf growth of L. perenne than the root length of L. sativa, indicating that EOs from Eucalyptus possessed an excellent phytotoxic potential.

Lyssaios F.A., González-Coloma A., Andrés M.F., Díaz C.E.

Endolichenic fungi represent an important ecological group of microorganisms that form associations with photobionts in the lichen thallus. These endofungi that live in and coevolve with lichens are known for synthesizing secondary metabolites with novel structures and diverse chemical skeletons making them an unexplored microbial community of great interest. As part of our search for new phytoprotectants, in this work, we studied the endolichenic fungus Xylaria sp. isolated from the lichen Hypogymnia tubulosa, which grows as an epiphyte on the bark of the endemic Canarian tree Pinus canariensis. From the extract of the liquid fermentation, we isolated two unreported piliformic derivatives, (+)-9-hydroxypiliformic acid (1) and (+)-8-hydroxypiliformic acid (2), along with four previously reported compounds, (+)-piliformic acid (3), hexylaconitic acid A anhydride (4), 2-hydroxyphenylacetic acid (5), and 4-hydroxyphenylacetic acid (6). Their structures were elucidated based on NMR and HRESIMS data. The extract and the isolated compounds were tested for their insect antifeedant (Myzus persicae, Rhopalosiphum padi, and Spodoptera littoralis), antifungal (Alternaria alternata, Botrytis cinerea, and Fusarium oxysporum), nematicidal (Meloidogyne javanica), and phytotoxic effects on mono- and dicotyledonous plant models (Lolium perenne and Lactuca sativa). Compounds 4, 5, and 6 were effective antifeedants against M. persicae and 4 was also active against R. padi. Moreover, 3 and 4 showed antifungal activity against B. cinerea and 4 was the only nematicidal. The extract had a strong phytotoxic effect on L. sativa and L. perenne growth, with compounds 3, 4, and 5 identified as the phytotoxic agents, while at low concentrations compounds 3 and 4 stimulated L. sativa root growth.

Bojórquez Quintal E., Machuca Chávez P., Téllez A.V.

Rawat A., Prakash O., Kumar R., Kumar S., Srivastava R.M., Latwal M., Pandey G.

Kabdal T., prakash O., Kumar R., Arya S., Rawat D.S., Kumar S.

AbstractThis study investigates the phytochemical profiles and pesticidal activities of various Elsholtzia species, including E. ciliata, E. flava, E. fruticosa, and E. eriostachya, to discover their bioactive potential for sustainable pest management. Through comparative phytochemical analysis using GC‐MS technique, key compounds in the essential oils were identified. The major components were thymoquinone (44.97 %) in E. ciliata, shisofuran (28.66 %) in E. flava, perillene (50.88 %) in E. fruticosa, and pinocarvone (42.41 %) in E. eriostachya. Despite variability in chemical composition, all species primarily contained oxygenated monoterpenes. The bioactivity of the oils was evaluated for their nematicidal and herbicidal bioassays. E. ciliata showed the highest egg hatching inhibition and juvenile mortality of M. incognita, while E. flava exhibited the lowest activity. For herbicidal activity, E. eriostachya achieved 96.70 % seed germination inhibition, 100 % root growth inhibition, and 95.56 % shoot growth inhibition. E. flava showed the lowest inhibition in germination, root length, and shoot length at 66.70 %, 81.56 %, and 85.28 %, respectively. The findings revealed significant variations in phytochemical composition and pesticidal efficacy, emphasizing the importance of species selection for pest management. This research highlights the bioactive potential of Elsholtzia species in sustainable pest management strategies.

Beesa N., Kuncharoen N., Dethoup T., Jindapunnapat K., Sasnarukkit A., Chinnasri B.

Hirschmanniella mucronata and Meloidogyne graminicola are the main plant-parasitic nematodes found in paddy fields in Thailand causing significant rice production yield losses. Although these nematodes are found widely in fields, an effective management method has not been documented. Here, we examined the nematicidal effects of different cavalcade leaf ages (1-, 2- and 3-month-old), used as aqueous extracts and soil amendments, on H. mucronata and M. graminicola. In vitro tests evidenced maximum mortality of H. mucronata (55.6–60.0%) in 50 mg ml−1 extract from all leaf ages, while mortality (65.9%) and hatchability (67.0%) of M. graminicola second-stage juveniles were observed in 50 mg ml−1 extract from 1-month-old leaves only. Moreover, aqueous extracts of cavalcade showed a repellent effect on both nematodes. Similarly, greenhouse experiments showed a significant reduction of H. mucronata population densities and reproduction of M. graminicola in soil amended with 0.5 and 1.0% (w/w) from each leaf age. LC-QTOF-MS analysis determined that three bioactive compounds, including quercetin, rutin, and kaempferol, are associated with the nematicidal activity of cavalcade against H. mucronata and M. graminicola. The information derived from this study indicates that the leaves of cavalcade are a source of promising phytonematicidals. This is the first study to assess and document its potential for nematicidal activity against H. mucronata and M. graminicola in Thailand. However, further research is needed to evaluate their efficacy under paddy field conditions.

Khan A., Mfarrej M.F., Husain F.M., Zia Q., Adil M., Arshad M., Umar K., Jha N.K., Malan P., Pandit S., Ahmad F.

Mondal P.C., Kumar V., Kaushik P., Shakil N.A., Pankaj, Rana V.S.

Meloidogyne incognita (root-knot nematode) is one of the most destructive pests of crops worldwide. Injudicious use of synthetic nematicides has led to environmental toxicity, development of resistance, and disruption of ecological balance, necessitating the need for safer and effective alternatives. Essential oil from Mentha spicata (Spearmint) has been reported to have nematicidal activity but the activity of its polar constituents is unexplored against the nematodes, infesting agricultural crops. Six compounds, stigmasterol (1), β-sitosterol-3-O-β-D-glucoside (2), 3β,13β-dihydroxy-urs-11-en-28-oic acid (3), 5,6-dihydroxy-7,8,4′-trimethoxyflavone (4), 5,6,4′-trihydroxy-7,8,3′-trimethoxyflavone (5), and 5,6,4′-trihydroxy-7,8-dimethoxyflavone (6), were isolated from methanolic extract of Mentha spicata (spearmint) and identified by NMR (1D & 2D) spectral analysis. Compound 3 was identified for the first time from genus Mentha. In vitro nematicidal activity of pure compounds (2 and 4–6) was carried out against Meloidogyne incognita, and results showed significant mortality (LC50 values ranging between 62.64 and 74.19 ppm after 96 h). Molecular docking study revealed the favourable binding of the test compounds with acetylcholinesterase enzyme, facilitated by H-bond, electrostatic interactions, and hydrophobic interactions. The binding energy of the tested compounds with the target protein was found highest in 5 (− 10.0 kcal/mol) and 6(− 9.9 kcal/mol) followed by 2 (− 9.2 kcal/mol) and 4 (− 8.9 kcal/mol). The minimum binding energy was recorded in carbofuran (−7.5 kcal/mol), a positive control, and was also corroborated with in vitro nematicidal activity. This study showed the potent nematicidal activity of compounds (2 and 4–6), which can be further used for the development of nematicides against M. incognita in agriculture.

Faria J.M., Barbosa P.

Traditional pesticides are based on toxic compounds that can reduce biodiversity, degrade the environment, and contribute to less healthy living. Plant allelochemicals can provide more environmentally friendly and sustainable alternatives. Essential oils (EOs) are complex mixtures of plant secondary metabolites that show strong biological activities. In the present study, the EOs of Cymbopogon citratus were screened for activity against the pinewood nematode (PWN), the causal agent of pine wilt disease. To understand their nematicidal properties, EOs were fractioned into hydrocarbon molecules and oxygen-containing compounds, and their main compounds were acquired and tested separately against the PWN. The EO oxygen-containing molecules fraction was highly active against the PWN (EC50 = 0.279 µL/mL), with citral and geraniol showing higher activities (EC50 = 0.266 and 0.341 µL/mL, respectively) than emamectin benzoate (EC50 = 0.364 µL/mL), a traditional nematicide used against the PWN. These compounds were additionally reported to be less toxic to non-target organisms (fish, invertebrates, and algae) and safer to human health (with higher reported toxicity thresholds) and predicted to exert fewer environmental impacts than traditional nematicides. Resorting to approved natural compounds can quickly leverage the development of sustainable alternatives to traditional nematicides.

Faria J.M., Rusinque L., Inácio M.L.

The rice root-knot nematode (RRKN), Meloidogyne graminicola Golden and Birchfield 1965, is a dangerous crop pest that affects rice production on a global scale. The largest rice-producing countries struggle with the impacts of RRKN infestation, namely, underdeveloped plants and a reduction in rice grain that can reach up to 70% of crop yield. In addition, the shift to strategies of sustainable pest management is leading to a withdrawal of some of the most effective pesticides, given the dangers they pose to the environment and human health. Volatile metabolites produced by plants can offer safer alternatives. The present study characterized the nematicidal activity of volatile phytochemicals against the RRKN and compared the most active with commercial nematicides concerning their safety to the environment and human health. Rice plants were used to grow large numbers of RRKNs for direct-contact bioassays. Mortality induced by the volatiles was followed for four days on RRKN second-stage juveniles. Of the 18 volatiles tested, carvacrol, eugenol, geraniol, and methyl salicylate showed the highest mortalities (100%) and were compared to traditional nematicides using (eco)toxicological parameters reported on freely available databases. While methyl salicylate had a faster activity, carvacrol had more lasting effects. When compared to synthetic nematicides, these volatile phytochemicals were reported to have higher thresholds of toxicity and beneficial ecotoxicological parameters. Ultimately, finding safer alternatives to traditional pesticides can lower the use of damaging chemicals in farming and leverage the transition to agricultural practices with a lower impact on biodiversity.