Plant-parasitic Nematodes Research Articles

Evaluation of nematophagous and biocontrol efficacy of Dactylellina phymatopaga against Meloidogyne graminicola on rice (Oryza sativa L.)

Dactylellina phymatopaga is a nematode-trapping fungus which traps, kills and parasitizes nematodes. The rice root-knot nematode, Meloidogyne graminicola, is an important plant-parasitic nematode that threatens rice production worldwide. Therefore, it is most important to find new substitute for chemical control of M. graminicola. The present study aimed to investigate the in vitro trapping, germination and nematophagous ability in soil and fungus efficacy to reduce the number and biomass of developing stages of M. graminicola in rice roots. Isolates of D. phymatopaga were found to produced sessile adhesive knobs on growing hypahe to trap and paralyze M. graminicola J2 up to 98.8 % within 120 h of inoculation, in in-vitro conditions. Test for germination and nematophagous activities in various soils showed that spores of D. phymatopaga frequently germinate in soil with formation of adhesive sessile knobs on their germ lings, capturing and parasitizing nearby free living nematodes. Application of D. phymatopaga in M. graminicola-infested soil at the time and prior to rice sowing showed significant reduction in the number of root galls, number and biomass of developing stages of M. graminicola in rice roots (62.65–80.73 %) increasing plant health as compared to plants grown in nematode infested soil. Application of D. phymatopaga 7 days before sowing showed the highest biocontrol ability by decreasing in the nematode biomass in the associated rice roots per plant and the expended nematode-to-root biomass ratio (NB:RB). The results showed that the nematode-trapping behavior of D. phymatopaga yields a bio-management potential in reducing the number of developing stages of M. graminicola and their biomass in rice roots.

A variant of the venom allergen-like protein, DdVAP2, is required for the migratory endoparasitic plant nematode Ditylenchus destructor parasitism of plants.

The potato rot nematode, Ditylenchus destructor, poses a serious threat to numerous root and tuber crops, yet the functional characterization of effectors from this migratory endoparasitic plant nematode remains limited. Despite inhabiting distinct habitats, sedentary and migratory plant parasitic nematodes share the structurally conserved effectors, such as venom allergen-like proteins (VAPs). In this study, a variant of DdVAP2 was cloned from D. destructor. The transcription profile analysis revealed that DdVAP2 was higher expressed in D. destructor feeding on either potato or sweet potato compared to on fungus via qRT-PCR. And DdVAP2 was highly expressed at all life stages feeding on sweet potato, except for eggs. DdVAP2 was confirmed to be specifically expressed in the subventral esophageal glands of D. destructor through in situ hybridization assays. Combined with functional validation of the signal peptide of DdVAP2, it suggested that DdVAP2 could be secreted from nematode into host. Heterologous expression of DdVAP2 in Nicotiana benthamiana revealed that the protein localized in both cytosol and nuclei of plant cells. Knocking down DdVAP2 by RNAi in D. destructor resulted in infection and reproduction defects on plants. All the results suggest that DdVAP2 plays a crucial role in the interaction between D. destructor and plants by facilitating the nematode infection.

Response of nutrient elements to Nemarioc-AL® phytonematicide in Swiss chard under greenhouse conditions

ABSTRACT Swiss chard (Beta vulgaris L. var. cicla) is susceptible to the root-knot nematodes (Meloidogyne spp.) since registered nematicides for this vegetable are not readily available. As a result, the noble product Nemarioc-AL® phytonematicide is currently used to manage plant parasitic nematodes on various crops. The product consistently suppressed nematode numbers. The efficacy of the product on nematode suppression was comparable to synthetic chemical nematicides. However, there is a lack of information on how the product will affect accumulation of nutrients in Swiss chard. Leaves of Swiss chard are an excellent source for Na and Mg; stems contain high K contents. The study was conducted to investigate how selected nutrient elements in Swiss chard would respond to concentrations of Nemarioc-AL® phytonematicide. Treatments ranging from 0% to 64% were applied weekly for 8 weeks. Potassium (K), Ca, Mg, Fe and Zn versus Nemarioc-AL® phytonematicide exhibited positive quadratic relations, with models explained by 96%, 79%, 64%, 78% and 77% associations, respectively. Increasing concentration of Nemarioc-AL® phytonematicide increased accumulation of selected nutrient elements in leaf tissues of Swiss chard.

Associate plant parasitic nematodes to weed species in some newly reclaimed lands

Plant-parasitic nematodes (PPNs) are vital soil organisms well-known to damage and reduce crop yield worldwide. Surveys were attempts to determine the impact of weed species on the communities and composition of nematodes in barley, wheat, quinoa, eggplant, and tomato crops in Alexandria and Ismailia regions of Egypt. During the surveys, eight occurring genera of nematodes were found namely; Meloidogyne spp, Pratylenchus spp, Helicotylenchus spp, Rotylenchulus spp, Xiphinema spp, Criconemoides spp, Ditylenchus spp, and Longidorus spp associated with the soil’s rhizosphere of 28 weed species belonging to 12 families. Among these weeds, Hordeum marinum and Sonchus oleraceus were good hosts to nematode species. Both wheat and barley had higher nematode diversity than quinoa in the winter season. Pratylenchus spp, Meloidogyne spp and Rotylenchulus spp can be considered vital potential PPNs with economic importance. Nematode abundances and structural indices varied greatly based on the host weed species, crop types and soil characteristics. A positive correlation was monitored among weeds, nematode frequencies and relative abundances as well as their crops. Finally, weed species are critical components in nematode communities that may increase the incidence and severity of nematode risks based on crop type and soil characteristics. Therefore weeds should be managed properly to diminish reservoir sites when developing nematode management options.

Relationship between plant parasitic nematodes population and soil moisture and temperature

Relationship between plant parasitic nematodes population and soil moisture and temperature

The Biofumigation Potential of Wild Radish (Raphanus Raphanustrum) and Field Mustard (Sinapis Arvensis) in Controlling Some Phytoparisitic Nematodes

Biofumigation is the process of introducing plants and their residues into the soil to release volatile compounds. Among these plants, those belonging to the Brassicaceae family are the most commonly used ones for biofumigation purposes. These plants are rich in glucosinolates, which upon enzymatic hydrolysis produce compounds such as isothiocyanates, which are approved as nematicides. Raphanus, Sinapis, and Eruca species genera are the most frequently used plants in the Brassicaceae family for biofumigation. This technique is becoming increasingly popular as a sustainable alternative to restricting fumigants in agriculture production. Dry plants (at vegetative and flowering stages) of Raphanus raphanustrum and Sinapis arvensis are incorporated into the soil and evaluated for their biofumigation effects on some phytoparasitic nematodes in comparison to a synthetic nematicide (tefluthrin 1.5%) and untreated control. Thirty days post-incorporation, soil samples were collected for nematode extraction and counting, and subsequently identified at the genus level. We identified four phytoparasitic nematodes that are most harmful to cultivated plants (Tylenchorhynchus, Pratylenchus, Paratylenchus, and Tylenchus). Each treatment decreased nematode population densities from 67% to 92%. Sinapis arvensis biofumigation was the most effective, reducing nematode densities by up to 92%. Conversely, Raphanus raphanustrum and Tefluthrin 1.5% treatments generally resulted in increased nematode densities (up to 74% and 67% respectively). The results of this study have given valuable information and suggest that Sinapis arvensis could be used to manage plant-parasitic nematodes, particularly the Tylenchorhynchus population. Biofumigation is a promising strategy that can be used especially by subsistence farmers for the sustainable production of crops in the presence of lower nematode pest densities.

Molecular and functional characterization of chemosensory genes from the root-knot nematode Meloidogyne graminicola

BackgroundRoot-knot nematode Meloidogyne graminicola has emerged as a major threat in rice agroecosystems owing to climate change-induced changes in cultivation practices. Synthetic nematicides are continually being withdrawn from the nematode management toolbox because of their ill effects on the environment. A sustainable strategy would be to develop novel nematicides or resistant plants that would target nematode sensory perception, which is a key step in the host finding biology of plant-parasitic nematodes (PPNs). However, compared to the extensive literature on the free-living nematode Caenorhabditis elegans, negligible research has been performed on PPN chemosensory biology.ResultsThe present study characterizes the five chemosensory genes (Mg-odr-7, Mg-tax-4, Mg-tax-4.1, Mg-osm-9, and Mg-ocr-2) from M. graminicola that are putatively associated with nematode host-finding biology. All the genes were highly transcribed in the early life stages, and RNA interference (RNAi)-induced downregulation of each candidate gene perturbed the normal behavioural phenotypes of M. graminicola, as determined by examining the tracking pattern of juveniles on Pluronic gel medium, attraction to and penetration in rice root tip, and developmental progression in rice root. In addition, a detrimental effect on nematode chemotaxis towards different volatile and nonvolatile organic compounds and host root exudates was documented.ConclusionOur findings enrich the existing literature on PPN chemosensory biology and can supplement future research aimed at identifying a comprehensive chemosensory signal transduction pathway in PPNs.

Whole mount multiplexed visualization of DNA, mRNA, and protein in plant-parasitic nematodes

BackgroundPlant-parasitic nematodes compromise the agriculture of a wide variety of the most common crops worldwide. Obtaining information on the fundamental biology of these organisms and how they infect the plant has been restricted by the ability to visualize intact nematodes using small molecule stains, antibodies, or in situ hybridization. Consequently, there is limited information available about the internal composition of the nematodes or the biology of the effector molecules they use to reprogram their host plant.ResultsWe present the Sperling prep - a whole mount method for nematode preparation that enables staining with small molecules, antibodies, or in situ hybridization chain reaction. This method does not require specialized apparatus and utilizes typical laboratory equipment and materials. By dissociating the strong cuticle and interior muscle layers, we enabled entry of the small molecule stains into the tissue. After permeabilization, small molecule stains can be used to visualize the nuclei with the DNA stain DAPI and the internal structures of the digestive tract and longitudinal musculature with the filamentous actin stain phalloidin. The permeabilization even allows entry of larger antibodies, albeit with lower efficiency. Finally, this method works exceptionally well with in situ HCR. Using this method, we have visualized effector transcripts specific to the dorsal gland and the subventral grand of the sugar beet cyst nematode, Heterodera schachtii, multiplexed in the same nematode.ConclusionWe were able to visualize the internal structures of the nematode as well as key effector transcripts that are used during plant infection and parasitism. Therefore, this method provides an important toolkit for studying the biology of plant-parasitic nematodes.

A full-length SSU rRNA-based workflow for high-resolution monitoring of nematode communities reveals direct and indirect responses to plant-based manipulations

Agricultural intensification has resulted in a decline in soil biodiversity, and concerns about the deterioration of the biological condition of soils prompted the development of measures to restore soil life. Due to the overwhelming biodiversity of soils, evaluation of such measures is not straightforward, and proxies are used to assess soil health. Because of their trophic diversity, high abundance, and relatively well-characterized ecologies, nematodes are often used as soil health indicators. However, the scarcity of informative morphological characters hampers the upscaling of this proxy. Here we present a community analysis approach that uses nanopore sequencing to generate full-length sequences of small subunit ribosomal DNAs (SSU rDNA). Cover cropping is a common agricultural practice that stimulates soil life, and we mapped the effects of ten cover crop treatments on nematode communities in a field experiment. These analyses included the monitoring of a high-impact plant-parasite, Meloidogyne chitwoodi. In total, 132 nematode samples were analyzed, and 65 nematode taxa were detected, mostly at the species level, including representatives of all trophic groups. As a validation, all samples were analyzed microscopically for M. chitwoodi, and a comparison of count and DNA read data revealed highly similar results. Treatments did not only affect plant-parasitic nematodes but also free-living nematodes in a cover crop-specific manner. Free-living nematodes from the same trophic group, and even congeneric species, responded differentially to plant-mediated manipulations of the soil microbiome. Hence, nanopore-based SSU rDNA sequencing could facilitate a substantial refinement of the use of nematodes as indicators for soil health.

Effects of Silver, Gold, and Platinum Nanoparticles on Selected Nematode Trophic Groups

Abstract As trophic organisms, nematodes play an essential role in the soil environment: they mineralize nutrients into plant-available forms, are a food source for other soil organisms, and feed on pathogenic organisms and plant pests, therefore regulating populations of soil microorganisms. The plant-parasitic nematodes are important pests of crops. Nanoparticles (NP) are increasingly used in agriculture and other production sectors. They are present in the soil, not necessarily in trace amounts, and can affect various soil organisms, including nematodes. In this article, the effects of silver (Ag), gold (Au), and platinum (Pt) nanoparticles on the mortality and reproduction activity of selected nematode species from two trophic groups: entomopathogenic nematodes (EPN) (Heterorhabditis bacteriophora and Steinernema feltiae) and plant parasitic nematodes (PPN) (Xiphinema diversicaudatum, Ditylenchus dipsaci, Heterodera schachtii) were studied under laboratory conditions. All nanoparticles decreased the nematode population to an extent depending on the nematode species, nanoparticle type, and exposure time. AgNP had the greatest nematicidal effect, except for AuNP, which reduced the population of H. schachtii the most. The greatest sensitivity to AgNP was observed in X. diversicaudatum (100% mortality), D. dipsaci (90% mortality), and 37 to 13% mortality in other species. Effect of AuNP and PtNP on entomopathogenic nematodes was comparable to the control, not treated with nanoparticles. AuNP and PtNP similarly influenced nematode mortality. However, the effect of nanoparticles on new generations of entomopathogenic nematodes developing in host larvae Galleria mellonella was inconclusive. All nanoparticles decreased the number of larvae of S. feltiae and increased the number of H. bacteriophora migrating outside the cadavers compared to the control.

Response of soybean and tomato plants under dual inoculation with Glomus sp. and root-knot nematode Meloidogyne incognita

The arbuscular mycorrhiza fungus Glomus can increase plant’s water and nutrient uptake and provide protection against plant parasitic nematodes. This study aimed to determine the response of soybean and tomato plants under inoculation with Glomus sp. and root-knot nematode Meloidogyne incognita at different application times in pot experiments. On soybean, Glomus sp. alone or in combination with M. incognita significantly increased plant height, while simultaneous inoculation of both microorganisms significantly increased the root dry weight. The total leaf P content of soybean however, significantly decreased in response to all inoculation methods. On tomato plants, Glomus alone significantly increased tomato shoot dry weight, total plant dry weight, and the total leaf P content. The final nematode population, the number of nematodes penetrating the root, and the root gall scores were not significantly impacted by either Glomus or M. incognita inoculation The inconsistent effect of Glomus inoculation on plant growth and total leaf P content as well as the inability of Glomus to reduce M. incognita infestation may be contributed by the extent of root colonization by Glomus and variability in the species of Glomus.

Using Brassica Cover Crops as Living Mulch in a Vineyard, Changes over One Growing Season

Farmers hoping to manage cropping systems sustainably are turning to cover crops to help mitigate plant pathogens. Plants with biofumigant properties are used to control soil-borne pathogens in agricultural settings, especially in till systems, where the brassicas are incorporated into the soil as green manure or seed meal. The effect of these crops is not well studied in no-till systems; thus, it is hard to know if they are as effective as green manure. Whether or not these cover crops can effect changes during a single growth season has not yet been studied. This study compared the response of the soil microbial community to four different brassica cover crops, two of which are commonly used in vineyards (Sinapis alba L. (white mustard) and Raphanus sativus (L.) Domin (tillage radish)) as well as two brassicas that are native or naturalized to the Okanagan (Capsella bursa-pastoris (L.) Medik. (Shepherd’s purse) and Boechera holboelli (Hornem.) Á. Löve and D. Löve (Holbøll’s rockcress)). Cover crops did not affect fungal species richness, but B. holboelli recover crops were associated with increased evenness among fungal taxa. Both C. bursa-pastoris and S. alba had lower levels of plant parasitic nematodes compared to non-brassica controls. These results were apparent only after a single growing season, which indicates growers could use this approach as needed, minimizing long-term exposure to biofumigants for beneficial soil microbes.

Efficacy of Biologically Synthesized Nanoparticles on Suppression Plant-Parasitic Nematodes: A review

Efficacy of Biologically Synthesized Nanoparticles on Suppression Plant-Parasitic Nematodes: A review

The Plant Parasitic Nematodes Database: A Comprehensive Genomic Data Platform for Plant Parasitic Nematode Research

Plant parasitic nematodes are important phytopathogens that greatly affect the growth of agricultural and forestry plants. Scientists have conducted several studies to prevent and treat the diseases they cause. With the advent of the genomics era, the genome sequencing of plant parasitic nematodes has been considerably accelerated, and a large amount of data has been generated. This study developed the Plant Parasitic Nematodes Database (PPND), a platform to combine these data. The PPND contains genomic, transcriptomic, protein, and functional annotation data, allowing users to conduct BLAST searches and genome browser analyses and download bioinformatics data for in-depth research. PPND will be continuously updated, and new data will be integrated. PPND is anticipated to become a comprehensive genomics data platform for plant parasitic nematode research.

Syncytium Induced by Plant-Parasitic Nematodes.

Plant-parasitic nematodes from the genera Globodera, Heterodera (cyst-forming nematodes), and Meloidogyne (root-knot nematodes) are notorious and serious pests of crops. They cause tremendous economic losses between US $80 and 358 billion a year. Nematodes infect the roots of plants and induce the formation of specialised feeding structures (syncytium and giant cells, respectively) that nourish juveniles and adults of the nematodes. The specialised secretory glands enable nematodes to synthesise and secrete effectors that facilitate migration through root tissues and alter the morphogenetic programme of host cells. The formation of feeding sites is associated with the suppression of plant defence responses and deep reprogramming of the development and metabolism of plant cells.In this chapter, we focus on syncytia induced by the sedentary cyst-forming nematodes and provide an overview of ultrastructural changes that occur in the host roots during syncytium formation in conjunction with the most important molecular changes during compatible and incompatible plant responses to infection with nematodes.

Loss-of-function of an α-SNAP gene confers resistance to soybean cyst nematode

Plant-parasitic nematodes are one of the most economically impactful pests in agriculture resulting in billions of dollars in realized annual losses worldwide. Soybean cyst nematode (SCN) is the number one biotic constraint on soybean production making it a priority for the discovery, validation and functional characterization of native plant resistance genes and genetic modes of action that can be deployed to improve soybean yield across the globe. Here, we present the discovery and functional characterization of a soybean resistance gene, GmSNAP02. We use unique bi-parental populations to fine-map the precise genomic location, and a combination of whole genome resequencing and gene fragment PCR amplifications to identify and confirm causal haplotypes. Lastly, we validate our candidate gene using CRISPR-Cas9 genome editing and observe a gain of resistance in edited plants. This demonstrates that the GmSNAP02 gene confers a unique mode of resistance to SCN through loss-of-function mutations that implicate GmSNAP02 as a nematode virulence target. We highlight the immediate impact of utilizing GmSNAP02 as a genome-editing-amenable target to diversify nematode resistance in commercially available cultivars.

Isolation, Identification, and Evaluation of the Predatory Activity of Chinese Arthrobotrys Species towards Economically Important Plant-Parasitic Nematodes.

The current investigation aimed to isolate and identify predatory fungal strains and evaluate their efficacy in mitigating the effects of plant-parasitic nematodes. We successfully isolated three distinct nematophagous fungal strains from soil samples, identified as Arthrobotrys megalosporus, A. oligospora, and A. sinensis, using conventional and molecular identification methodologies. In vitro trials illustrated the high capture efficiency of these fungi against plant-parasitic nematodes. Over an exposure period of 48 h to Aphelenchoides besseyi, Bursaphelenchus xylophilus, and Ditylenchus destructor, A. megalosporus (GUCC220044) displayed predation rates of 99.7%, 83.0%, and 21.1%, respectively. A. oligospora (GUCC220045) demonstrated predation rates of 97.3%, 97.3%, and 54.6%, and A. sinensis (GUCC220046) showed rates of 85.1%, 68.3%, and 19.0% against the same cohort of nematodes. The experimental outcomes substantiate that all three identified fungal strains demonstrate predatory activity against the tested nematodes, albeit with varying efficiencies.

Cover crop functional types alter soil nematode community composition and structure in dryland crop-fallow rotations

Increasing dryland cropping intensity by integrating cover crops into crop-fallow rotations can add diversity and alter soil ecosystem functions, including improvements in soil nutrient and water retention and cycling, and suppression of soil-borne pests. However, the use of cover crops can also carry the risk of increasing the abundance of plant-parasitic nematodes that could undermine system productivity. Here, we examined how the integration of diverse cover crops of different functional groups: Poaceae [forage oat (Avena sativa L.)]; Brassicaceae [forage rape (Brassica napus L.)]; and Fabaceae [common vetch (Vicia sativa subsp. sativa L. and fababean (Vicia faba L.) in monocultures and mixtures into a dryland crop-fallow rotation altered soil nematode community composition and structure relative to conventional fallows. We found that cover crop mixtures had greater diversity and complexity of free-living nematodes, indicating enhanced cycling of energy and nutrients (enrichment index >50 %) compared to monocultures. Furthermore, using a structural equation modelling approach, we showed the abundance of free-living nematodes is driven primarily by cover crop residue quality (C:N ratio, and cellulose content) and marginally by cover crop quantity (biomass). The grass-legume mixture had the highest abundance of plant-parasitic nematodes (Pratylenchus neglectus and Merlinius brevidens) but also fostered robust soil food webs with complex soil nematode trophic interactions, indicating promotion of soil ecosystem functions related to N and C cycling and overall improvement in soil health. The results indicate bottom-up effects of cover crops on soil nematode communities are modulated by cover crop functional type and mixture composition. Consequently, cover crops with appropriate traits must be selected if soil health is to be improved via suppression of plant-parasitic nematodes, promotion of free-living nematodes, and enhancement of soil food web complexity.

Evaluating the Influence of Water Scarcity on the Host Response of Garlic to the Stem and Bulb Nematode Ditylenchus dipsaci.

Ditylenchus dipsaci is a plant-parasitic nematode with a great economic impact on bulbous crops, including garlic (Allium sativum L.), and is distributed worldwide, particularly in the Mediterranean region. Traditionally, garlic was a rainfed crop in Spain, but irrigated areas have increased during the last few decades. However, the expected climatic conditions, with longer and more intense droughts, will make it necessary to reduce the water supply to garlic crops. This poses the urgent need to select garlic cultivars more tolerant to water scarcity and that are also more resistant to plant pathogenic organisms. The aim of this work was to analyze the influence of water stress on the host response of garlic plants to D. dipsaci. The specific objectives were to evaluate the level of nematode infestation in plants from four garlic genotypes treated with a reduced irrigation regime and compare them with those of control plants not subjected to water stress. The observed results were correlated with changes in the bulb and root development, as well as in the physiological parameters (total chlorophyll concentration and proline accumulation). The effects were different depending on whether the plants were subjected to water stress before or after nematode inoculation, as well as whether the water stress was continuous or discontinuous. Garlic inter-cultivar variability also affected the obtained results.

Plant-parasitic nematodes associated with bush tea (Athrixia phylicoides) in South Africa and their relationship with physico-chemical soil properties

Summary Bush tea (Athrixia phylicoides) is an aromatic, perennial, leafy shrub that is endemic to the northeastern mountain ranges of South Africa and has a high potential for commercialisation as an alternative to caffeine-containing tea. During the summer and winter of 2018-2019, a survey was carried out at nine localities in the northeastern regions of South Africa to study the diversity of nematodes associated with bush tea and, in terms of frequency of occurrence and abundance, identify the dominant plant-parasitic nematodes. Twenty-one plant-parasitic nematode species belonging to 14 genera were identified in 90 rhizosphere soil and root samples. Meloidogyne and Helicotylenchus were the dominant plant-parasitic nematode genera. Meloidogyne javanica and Scutellonema brachyurus were found at all localities, followed by M. enterolobii, Pratylenchus brachyurus, Rotylenchulus parvus, H. martini and S. truncatum (found at 7-8 localities). Other species identified included Criconema corbetii, C. sphaerocephalus, C. xenoplax, Criconemoides ihlathum, C. parvus, Discocriconemella glabrannulata, H. dihystera, H. erythrinae, H. paraplatyurus, Hemicycliophora typica, M. hapla, M. incognita, Rotylenchulus unisexus and R. clavicaudatus. Individuals of Crossonema, Paratylenchus, Ogma, the Xiphinema americanum-group and X. americanum sensu lato could not be identified to species level due to the low number of specimens present in the samples. Comparison of the two methods used to identify the Meloidogyne populations to species level shows that morphological identification (particularly perineal pattern morphology) provided a more complete picture of the Meloidogyne species present in the samples compared with the molecular SCAR-PCR technique. High levels of Cu, K and pH were associated with the highest relative population densities (RPD% = average population density of a nematode genus/total nematode population density × 100) of Meloidogyne, whilst high levels of Al and soil resistivity were associated with the lowest RPD% of Meloidogyne. By contrast, high levels of K and pH were associated with the lowest RPD% of Helicotylenchus, whilst high levels of Al and soil resistivity were associated with the highest RPD% of Helicotylenchus.