Chemical Characterization of Plant Extracts and Evaluation of their Nematicidal and Phytotoxic Potential

Biochemical Defence of Plants against Parasitic Nematodes

Plant parasitic nematodes (PPNs), such as Meloidogyne spp., Heterodera spp. and Pratylenchus spp., are obligate parasites on a wide range of crops, causing significant agricultural production losses worldwide. These PPNs mainly feed on and within roots, impairing both the below-ground and the above-ground parts, resulting in reduced plant performance. Plants have developed a multi-component defence mechanism against diverse pathogens, including PPNs. Several natural molecules, ranging from cell wall components to secondary metabolites, have been found to protect plants from PPN attack by conferring nematode-specific resistance. Recent advances in omics analytical tools have encouraged researchers to shed light on nematode detection and the biochemical defence mechanisms of plants during nematode infection. Here, we discuss the recent progress on revealing the nematode-associated molecular patterns (NAMPs) and their receptors in plants. The biochemical defence responses of plants, comprising cell wall reinforcement; reactive oxygen species burst; receptor-like cytoplasmic kinases; mitogen-activated protein kinases; antioxidant activities; phytohormone biosynthesis and signalling; transcription factor activation; and the production of anti-PPN phytochemicals are also described. Finally, we also examine the role of epigenetics in regulating the transcriptional response to nematode attack. Understanding the plant defence mechanism against PPN attack is of paramount importance in developing new, effective and sustainable control strategies.

Hydroalcoholic Extracts from Pleurotus ostreatus Spent Substrate with Nematocidal Activity against Nacobbus aberrans Phytonematode and the Non-Target Species Panagrellus redivivus

Pleurotus ostreatus, an edible mushroom widely consumed worldwide, generates a by-product known as spent mushroom substrate (SMS). This material has demonstrated biological activity against agricultural crop pathogens. In this study, we evaluated the nematocidal effectiveness of hydroalcoholic extracts (T5, T2, AT5, and AT2) derived from SMS of P. ostreatus against (J2) of the phytonematode Nacobbus aberrans and assessed their potential toxicity towards the non-target nematode Panagrellus redivivus. Among these extracts, AT5 exhibited the highest efficacy against N. aberrans and was the least toxic against P. redivivus. Liquid-liquid partitioning yielded the AQU fraction, which showed significant nematocidal activity against J2 (75.69% ± 8.99 mortality), comparable to chitosan. The GC-MS analysis revealed the presence of several compounds, including palmitic acid, linoleic acid, and 2,4-Di-tert-butylphenol. These findings are consistent with studies confirming the antagonistic effectiveness of these compounds against phytonematodes. Additionally, all extracts exhibited toxicity against P. redivivus, with T2 being the most toxic. Our findings demonstrate that while the AT5 extract displays antagonistic effectiveness against both N. aberrans and P. redivivus, it was the least toxic among the extracts tested. Thus, SMS of P. ostreatus holds potential as a source of nematocidal compounds, which could offer significant benefits for agricultural pest control.

Assessing the In Vitro Individual and Combined Effect of Arthrobotrys oligospora and A. musiformis (Orbiliales) Liquid Culture Filtrates against Infective Larvae of the Sheep Blood-Feeding Nematode Haemonchus contortus (Trichostrongylidae)

BACKGROUND

Arthrobotrys species are nematophagous fungi that secrete extracellular nematocidal products (ECP). The individual and combined effects of ECP from Arthrobotrys oligospora (Ao) and A. musiformis (Am) growth in liquid media against Haemonchus contortus L3 (HcL3) were assessed.

METHODS

The isolation, morphological (MI) and molecular identification (Mol-I), assessment of nematocidal activity (NA) of fungal liquid culture filtrates (LCF) in two liquid media alone and in combination and the myco-compound profile identification (MCP) were performed.

RESULTS

The MI suggested that the fungi corresponded to the species Ao and Am. This result was confirmed by PCR analysis followed by sequencing, alignment and a phylogenetic analysis. Likewise, the highest Hc mortalities were 91.4% with individual LCF of Am and 86.2% with those of Ao at the highest concentration (100 mg/mL) in Czapek-Dox Broth. The combination of both LCF resulted in a similarly high larval mortality with no statistical differences in relation to individual activity (p > 0.05). The MCP showed the presence of alkaloids in both fungi. Coumarins, sterols and saponins were found only in Ao.

MAIN CONCLUSIONS

Both fungi produced ECP with a high NA that could be identified and assessed in future studies as potential natural anthelmintic compounds.

Evaluation of Solanum linnaeanum and S. sisymbriifolium extracts for the management of Meloidogynechitwoodi

Meloidogyne chitwoodi causes significant yield losses in many crops and the chemical control measures currently used are less effective for this nematode. The activity of aqueous extracts (0.8 mg/mL) of one-month-old (R1M) and two-months-old roots and immature fruits (F) of Solanum linnaeanum (Sl) and S. sisymbriifolium cv. Sis 6001 (Ss) were tested on hatching, mortality, infectivity and reproduction of M. chitwoodi. The extracts selected reduced the hatching of second-stage juveniles (J2) (cumulative hatching of 40% for Sl R1M and 24% for Ss F) but did not affect J2 mortality. However, infectivity of J2 exposed to the selected extracts, during 4 and 7 days, was lower (3% and 0% for Sl R1M and 0% and 0% for Ss F) compared to the control (23% and 3%). Reproduction was affected only after 7 days of exposure (reproduction factor (RF) was 7 for Sl R1M and 3 for Ss F) compared to the control (RF = 11). The results suggest that the selected Solanum extracts are effective and can be a useful tool in sustainable M. chitwoodi management. This is the first report on the efficacy of S. linnaeanum and S. sisymbriifolium extracts against root-knot nematodes.

Natural nematicidal metabolites and advances in their biocontrol capacity on plant parasitic nematodes

Covering: 2010 to 2021Natural nematicidal metabolites are important sources of nematode control. This review covers the isolation and structural determination of nematicidal metabolites from 2010 to 2021. We summarise chemical structures, bioactivity, metabolic regulation and biosynthesis of potential nematocides, and structure-activity relationship and application potentiality of natural metabolites in plant parasitic nematodes' biocontrol. In doing so, we aim to provide a comprehensive overview of the potential roles that natural metabolites can play in anti-nematode strategies.

Phytochemical Screening and Evaluation of Pesticidal Efficacy in the Oleoresins of Globba sessiliflora Sims and In Silico Study

Globba sessiliflora Sims is an aromatic rhizomatous herb of family Zingiberaceae which is endemic to Peninsular India. This study first reports the phytochemical profile and pesticidal potential of oleoresins obtained from the aerial and rhizome parts of Globba sessiliflora Sims. The oleoresins were prepared by the cold percolation method and were analyzed by a gas chromatography-mass spectrometry (GC-MS) method. Both the oleoresins varied greatly in composition, the major compounds identified in aerial part oleoresin (GSAO) were methyl linoleate, methyl palmitate, and phytol, while the major compounds present in rhizome part oleoresin (GSRO) were γ-sitosterol, 8 (17),12-labdadiene-15, 16-dial, methyl linoleate, and methyl palmitate. In order to evaluate the biological activities, the oleoresins were tested under laboratory conditions for nematicidal action and inhibition of egg hatching potential against root knot nematode, where GSRO was more effective. Insecticidal activity was performed against mustard aphid, Lipaphis erysimi and castor hairy caterpillar, Selepa celtis. In case of mustard aphid, GSRO (LC₅₀ = 154.8 ppm) was more effective than GSAO (LC₅₀ = 263.0 ppm), while GSAO (LC₅₀ = 346.7.0 ppm) was more effective against castor hairy caterpillar than GSRO (LC₅₀ = 398.1 ppm). The herbicidal activity was performed in the receptor species Raphanus raphanistrum subsp. sativus, and the oleoresins showed different intensities for seed germination inhibition and coleoptile and radical length inhibition. Molecular docking studies were conducted to screen the in vitro activities and through molecular docking, it was found that the major oleoresins components were able to interact with the binding pocket of HPPD and AChE with γ-sitosterol showing the best binding affinity.

Sustainable strategies for management of the "false root-knot nematode" Nacobbus spp

The genus Nacobbus, known as the false root-knot nematode, is native to the American continent and comprises polyphagous species adapted to a wide range of climatic conditions. Alone or in combination with other biotic and abiotic factors, Nacobbus spp. can cause significant economic yield losses on main food crops such as potato, sugar beet, tomato, pepper and bean, in South and North America. Although the genus distribution is restricted to the American continent, it has quarantine importance and is subject to international legislation to prevent its spread to other regions, such as the European Union. The management of Nacobbus spp. remains unsatisfactory due to the lack of information related to different aspects of its life cycle, survival stages in the soil and in plant material, a rapid and reliable diagnostic method for its detection and the insufficient source of resistant plant genotypes. Due to the high toxicity of chemical nematicides, the search for alternatives has been intensified. Therefore, this review reports findings on the application of environmentally benign treatments to manage Nacobbus spp. Biological control strategies, such as the use of different organisms (mainly bacteria, fungi and entomopathogenic nematodes) and other eco-compatible approaches (such as metabolites, essential oils, plant extracts, phytohormones and amendments), either alone or as part of a combined control strategy, are discussed. Knowledge of potential sources of resistance for genetic improvement for crops susceptible to Nacobbus spp. are also reported. The sustainable strategies outlined here offer immediate benefits, not only to counter the pathogen, but also as good alternatives to improve crop health and growth.

Chemical profile, antimicrobial activity, and leaf anatomy of Adenophyllum porophyllum var. cancellatum

Adenophyllum porophyllum var. cancellatum, known as “árnica del monte” in Mexico, is an aromatic annual plant belonging to the Asteraceae family that grows from southern Arizona to central Mexico. The aerial parts of the plant are used in traditional medicine to treat skin diseases such as irritations, infections, and wounds. In this study, the essential oil of this plant was characterized, and its antimicrobial activity was evaluated. This species has large glands in its leaves; therefore, for quality control purposes, an anatomical study of the leaves was performed. The essential oil was isolated from the aerial parts of the plant through hydro-distillation and analyzed using a gas chromatography/mass spectrometry (GC/MS) system. Its anti-yeast activity was evaluated against three Candida species and ten bacterial strains using the disk diffusion technique. The minimum inhibitory concentration (MIC), minimum fungicidal concentration (MFC), and minimum bactericidal concentration (MBC) were determined using broth microdilution. Anatomical study was performed on the middle part of the leaf. A yield of 0.5% of the essential oil was obtained from the herb, and Eighteen compounds in the essential oil were identified, within them trans pinocamphone (29.5%), limonene (24.7%), pinocarvone (21.8%), and cis pinocamphone (8.0%) were the main components. The inhibition zones were between 10 mm and 20 mm, and the MIC and MFC against the three Candida species ranged from 60 to 500 μg/ml. The leaf anatomy showed anisocytic stomata, simple and glandular trichomes of different types, and large and elliptical-shaped lysigenous glands, which can be used for taxonomic identification. The A. porophyllum var. cancellatum essential oil can serve as an alternative source of natural antimicrobial agents as an affordable approach to control infectious diseases. This is the first study that reports the chemical composition and antimicrobial activity of the essential oil, as well as the leaf anatomy of this species.

Review of nematode interactions with hemp (Cannabis sativa)

The many decades during which the cultivation of Cannabis sativa (hemp) was strongly restricted by law resulted in little research on potential pathogenic nematodes of this increasingly important crop. The primary literature was searched for hemp-nematode papers, resulting in citations from 1890 through 2021. Reports were grouped into two categories: (i) nematodes as phytoparasites of hemp, and (ii) hemp and hemp products and extracts for managing nematode pests. Those genera with the most citations as phytoparasites were Meloidogyne (root-knot nematodes, 20 papers), Pratylenchus (lesion nematodes, 7) and Ditylenchus (stem nematodes, 7). Several Meloidogyne spp. were shown to reproduce on hemp and some field damage has been reported. Experiments with Heterodera humuli (hop cyst nematode) were contradictory. Twenty-three papers have been published on the effects of hemp and hemp products on plant-parasitic, animal-parasitic and microbivorous species. The effects of hemp tissue soil incorporation were studied in five papers; laboratory or glasshouse experiments with aqueous or ethanol extracts of hemp leaves accounted for most of the remainder. Many of these treatments had promising results but no evidence was found of large-scale implementation. The primary literature was also searched for chemistry of C. sativa roots. The most abundant chemicals were classified as phytosterols and triterpenoids. Cannabinoid concentration was frequently reported due to the interest in medicinal C. sativa. Literature on the impact of root-associated chemicals on plant parasitic nematodes was also searched; in cases where there were no reports, impacts on free-living or animal parasitic nematodes were discussed.

Plant Parasitic Nematodes: A Review on Their Behaviour, Host Interaction, Management Approaches and Their Occurrence in Two Sites in the Republic of Ireland

Plant parasitic nematodes are a major problem for growers worldwide, causing severe crop losses. Several conventional strategies, such as chemical nematicides and biofumigation, have been employed in the past to manage their infection in plants and spread in soils. However, the search for the most sustainable and environmentally safe practices is still ongoing. This review summarises information on plant parasitic nematodes, their distribution, and their interaction with their host plants, along with various approaches to manage their infestations. It also focuses on the application of microbial and fermentation-based bionematicides that have not only been successful in controlling nematode infection but have also led to plant growth promotion and proven to be environmentally safe. Studies with new information on the relative abundance of plant parasitic nematodes in two agricultural sites in the Republic of Ireland are also reported. This review, with the information it provides, will help to generate an up-to-date knowledge base on plant parasitic nematodes and their management practices.