Plant-parasitic Nematodes Research Articles

Fusarium oxysporum and soil nutrient amendments provide short-term inhibition of Cosmopolites sordidus raising questions on biopesticide and plant nutrition potentials in tissue culture banana

Endophytic Fusarium oxysporum strain V5w2 has been suggested to offer the ecosystem service of suppressing Cosmopolites sordidus and other pests that attack tissue culture banana plants in agroecosystems. The effects of endophytic F. oxysporum V5w2 and nutrient supply on C. sordidus in potted tissue culture banana plants were investigated. In the screenhouse, rhizome damage by C. sordidus larvae was lower in F. oxysporum V5w2-inoculated plants than in non-inoculated ones. Banana plants inoculated with F. oxysporum V5w2 were larger and suffered less rhizome damage but with low chlorophyll content. Weights of C. sordidus larvae were not different between those reared on F. oxysporum V5w2-inoculated banana plants and the non-inoculated ones. Larval C. sordidus from nutrient-treated plants had lower weight than those that fed on plants that did not receive nutrients. In the field, fewer adult C. sordidus were found on F. oxysporum V5w2-inoculated banana plants than on non-inoculated plants 12 h after insect release. The number of adult C. sordidus and their eggs did not vary between F. oxysporum V5w2-inoculated banana plants and controls at the end of the experiment. Adult C. sordidus did not discriminate between nutrient-treated banana plants and those without nutrient treatment. However, non-beneficial interactions between F. oxysporum V5w2 and plant-parasitic nematodes negate the chances of its application as an endophytic biological control agent. In conclusion, while F. oxysporum V5w2 is not quite viable for application as an endophytic biological control agent for C. sordidus and other banana pests, this fungus may still have some potential to offer alternative ecosystem services through the provisioning of pest-inhibitive organic compounds.

Application of Entomopathogenic nematodes Suppresses the Root Knot Nematodes, Agrotis ipsilon, Spodoptera litura in Tobacco

Application of Entomopathogenic nematodes (EPNs) is an efficient and novel alternative for management of plant-parasitic nematode and other insects to improve the productivity of tobacco and to protect the tobacco from the disturbing of underground and leaf chewing insects. In the present work, laboratory and field trials were conducted to control root-knot nematode (M. javanica) by using EPNs and the symbiotic bacterial, and the effect of the application was evaluated in tobacco plant. Approximately after inoculation of sixty days, egg masses and galls on tobacco root and agronomic characters of tobacco were calculated. Results showed that both EPNs and the symbiotic bacterium affected the reproduction of M. javanica population and the gall, egg masses and the root-knot nematodes in the tobacco root were significant reduced. EPNs also showed suppressive effect on S. litura larvae, and Agrotis ipsilon larvae as well. It might be the first study about the use of EPNs in the control of M. javanica in tobacco plant.

Role of CLE peptide signaling in root-knot nematode parasitism of plants.

We summarize recent findings that have provided new insights into the mechanisms underlying CLE signaling systems in the regulation of plant development and phytonematode interactions. CLAVATA3/EMBRYO SURROUNDING REGION-RELATED (CLE) peptides are short sequences consisting of 12 or 13 amino acids characterized by hydroxylated proline residues, and their presence has been demonstrated in various plant species and phytonematodes across multiple paralogous genes. Here, we review recently conducted research to understanding the signaling pathway of CLE peptide during plant development and infection caused by phytonematodes. Cell-to-cell communication is important for the coherent functioning of living organisms. CLE peptides combined with their specific transmembrane receptors to induce downstream intracellular signaling pathways shows divergent modes of action in many developmental processes in variable species. Moreover, CLE peptide was also involved in plant disease mechanism caused by various plant parasitic nematodes.

Efficacy of banana fibre paper for the management of the root-knot nematode, Meloidogyne incognita, on potato (Solanum tuberosum) in Kenya

Summary Globally, potato (Solanum tuberosum) is a key staple food crop. In Kenya, it is the second most important food crop after maize. Among the various constraints to potato production are plant-parasitic nematodes. In particular, root-knot nematodes (Meloidogyne spp.) are a significant impediment to potato production, suppressing yield and reducing the quality of harvested tubers. The current study was undertaken to evaluate the efficacy of a lignocellulose fibre matrix (banana paper) either impregnated with a chemical or drenched with a biologically-based nematicide for the management of root-knot nematodes on potatoes, in Kenya. The experiment was conducted in both field and pot trials over two consecutive cropping seasons. Wrapping seed potatoes in banana paper impregnated with abamectin or drenched with Trichoderma asperellum (Real Trichoderma®) led to suppression of soil Meloidogyne incognita densities by 87% and 68% in the field, and 86% and 40% in pots, respectively, which led to a 3.3- and 3.7-fold increase in yield in the field. This novel technology, also referred to as ‘Wrap & Plant’, presents a practical option for nematode management in potato under the resource-limited conditions of sub-Saharan Africa and offers potential for the targeted management of other soil-borne diseases.

Allelopathic effects of sorghum/sorghum-sudangrass hybrids against Rotylenchulus reniformis.

Reniform nematode (Rotylenchulus reniformis) is a damaging and difficult-to-manage pest on many agricultural crops. Sorghum and sorghum-sudangrass hybrids (SSgH) have shown potential in managing plant-parasitic nematodes by releasing toxic hydrogen cyanide gas through the hydrolysis of dhurrin, a cyanogenic glucoside found in leaf epidermal cells. The objectives of this study were to evaluate the effect of different SSgH varieties and their age on the suppression of R. reniformis and to quantify their dhurrin contents. Shoot biomass of seven SSgH varieties was harvested at 1, 2, and 3 months of growth and used as a soil amendment in two greenhouse cowpea bioassay trials. Dhurrin concentration was analyzed using high-performance liquid chromatography (HPLC) from 2-month-old tissues. The results indicated that energy sorghum 'NX-D-61' and SSgH 'Latte' exhibited the highest dhurrin concentrations (P ≤ 0.05) and suppressed R. reniformis development in cowpea roots (P ≤ 0.05). In Trial I, 2-month-old amendments showed the greatest suppression, while in Trial II, 1-month-old amendments were more suppressive (P ≤ 0.05). Potential effect of environmental stress on dhurrin concentration in SSgH tissue was discussed. Nonetheless, dhurrin concentrations were negatively related to the number of R. reniformis infecting cowpea roots (r2 =0.69; P = 0.02). These findings suggest that high dhurrin SSgH varieties can be integrated into reniform nematode management plans as a cover crop and terminated no more than 2 months after planting.

First Report of the cyst nematode Heterodera koreana parasitizing bamboo (Phyllostachys reticulata) in Georgia, USA.

Soil and root samples were collected from two plots (5.5 x 6 m) cultivated with bamboo Phyllostachys reticulata (syn. P. bambusoides) at the USDA Southeastern Fruit and Tree Nut Research Station in Byron, Georgia, USA, in November 2021, December 2022, and December 2023. Each soil sample consisted of five randomly collected subsamples, which were analyzed for the presence of plant-parasitic nematodes as part of regular monitoring. No aboveground symptoms were seen in the field plots, but roots showed discoloration and stunted growth (Fig. 1A). An average population density of 160, 36, and 188 second-stage juveniles (J2) of cyst nematodes (Heterodera spp.) per 100 cm3 of soil was detected in 2021, 2022, and 2023, respectively. To confirm the cyst nematode parasitism, three healthy P. reticulata plants were transplanted into 10 cm diameter pots filled with nematode-infested soil and grown in a greenhouse at 25-28°C. After three months, young cysts containing eggs protruding from the bamboo roots were seen, confirming nematode parasitism (Fig. 1B and C). Morphological and molecular analyses were conducted to identify the nematode species. The J2 body shape was cylindrical with three incisures in lateral field and well-developed rounded stylet knobs. Measurements of J2 (n = 10) included the length (range = 406.0-518.1 μm, mean = 458.2 ± 16.1 μm) and width (16.0-17.2 μm, 16.6 ± 0.5 μm) of body, labial region height (3.0-3.6 μm, 3.2 ± 0.2 μm), stylet (17.2-18.9 μm, 18.02 ± 0.6 μm), tail (61.1-65.9 μm, 63.1 ± 5.8 μm), body width at anus (9.7-12.4 μm, 10.8 ± 0.3 μm), and hyaline tail terminus (35.4-53.0 μm, 44.0 ± 3.8 μm). The cysts (n = 5) were relatively lemon-shaped, light to dark brown in color with projected neck and vulval cone that lacked fenestration, bullae, and underbridge. Morphometrics were body length including neck (420.5-745.0 μm, 550.4 ± 72 μm), body width (345.0-544.1 μm, 430.1 ± 59 μm), and L/W ratio (1.0-1.4 μm, 1.1 ± 0.1 μm). The morphometric of vulval cone included fenestral length (48 to 69 µm, 60.2 ± 4.0 µm), fenestral width (43 to 51 µm, 48.9 ± 4.0 µm) and vulval slit (47 to 58 µm, 49.1 ± 2.6 µm). Morphology and morphometric measurements of the cysts and J2 (Fig. 2A-C) were comparable to previous reports of Korean cyst nematode, H. koreana from other Asian countries (Mundo-Ocampo et al., 2008; Wang et al., 2012; Tanha Maafi and Taheri, 2015; Sekimoto et al., 2017). For molecular diagnosis, DNA was extracted from single cysts (n= 3) using DNeasy Blood and Tissue Kit, and 28S rRNA and partial cytochrome oxidase I (COI) gene fragments were amplified using D2A/D3B and Het-coxiF/Het-coxiR primer sets, respectively according to Subbotin et al. (2015) and Hajihassani et al. (2018). PCR products were then purified by a DNA Clean & Concentrator kit (Zymo Research, CA, USA) and sequenced at Genewiz (South Plainfield, NJ, USA). The resulting sequences were deposited into the GenBank database and subjected to BLASTn searches. Sequence analysis of the 28S rRNA gene (GenBank accession number OL812726) showed that the H. koreana isolate from Georgia was 100% identical (692/692 bp) with H. koreana populations from Japan and South Korea. Analysis of the H. koreana isolate from Georgia based on the COI sequence (OL813218 and OL813219) revealed 100% similarity (421/422 bp) with a population of H. koreana from Japan and 98% similarity (409/409 bp) with a population from South Korea. To our knowledge, this is the first report of H. koreana parasitizing P. reticulata in Georgia as the second state in the USA. This nematode was first reported in Florida infecting fish pole bamboo (P. aurea) propagated from plant material from the Far East (Inserra et al. 1999). This report expands the information on the geographical distribution of H. koreana. Given the significant potential for damage to bamboo, precautions should be taken to prevent the nematode's spread to unaffected regions.

A comparison of extraction methods for preparation of glucosinolate-containing extracts from Brassica juncea antagonistic toward Ditylenchus dipsaci

Summary The stem and bulb nematode, a globally distributed pest, primarily affects onions and garlic, causing significant yield losses. Chemical treatments are a practical and effective method for controlling plant-parasitic nematodes to protect high-value crops. However, to minimise environmental damage, chemicals of natural origin need to be investigated. Brown mustard (Brassica juncea) plant is an annual plant in the Brassicaceae family, which is rich in bioactive compounds called glucosinolates. These bioactive compounds play a major role in the defence of Brassica plants against biotic stress factors in nature. Based on this point, efforts to develop plant protection products from the brown mustard plant are ongoing. In this study, the most suitable pre-extraction and extraction conditions were determined to ensure the maximum preservation of glucosinolate content and biological activity, to process brown mustard on an industrial scale. For this purpose, steam treatment was applied before extraction at 3 bar (=3 × 105 Pa) pressure for 1 and 3 min. Four different temperatures (room temperature, 40, 55 and 70°C) and two different methanol concentrations (70% and 80%) were tested to optimise glucosinolates extraction from brown mustard. It was found that sinigrin was the most abundant glucosinolate, with extraction yields 1184.4 ± 14.4 mg kg−1 at 55°C for 3 min, and 2624.2 ± 98.5 mg kg−1 at 70°C/70% MeOH for 1 min. However, nematode immobility was higher at 55°C/70% MeOH for 3 min. It was determined that the application of hot steam for 3 min at 3 bar pressure as a pre-extraction process provided optimal conditions for methanolic extraction. The results may contribute significantly to the development of potential plant protection products with further studies.

Hemicycliophora potteri n. sp. (Tylenchida: Hemicycliophoridae) infesting highbush blueberry (Vaccinium corymbosum) in Ontario, Canada

Summary Highbush blueberry is a blueberry species native to North America and is a food crop of significant economic importance for Canada. Plant-parasitic nematodes are known to infest this crop. Species of Hemicycliophora, commonly known as sheath nematodes, are obligatory plant-parasites, and some cause diseases on a wide range of crops. A population of Hemicycliophora of high number was found in highbush blueberry fields in Norfolk and Middlesex counties of southwestern Ontario. Following through morphological and molecular studies, this population was determined a new species as Hemicycliophora potteri n. sp. This species is characterised by its outer sheath adpressed fitting to the body, lateral fields with diagonal connections of transverse striae, amphid apertures covered by lateral plates, lip region slightly set-off with four annuli; excretory pore anterior to the base of the pharynx, stylet knob cavity moderate, vulva lips modified, tail tapering gradually and more abruptly towards the last one-third, and no males were found. Molecularly, the 18S, and 28S ribosomal DNA sequences are most similar to those of H. thienemanni, H. similis, H. gracilis, and a few unidentified species. A dichotomous key for the diagnostic of the species of Hemicycliophora in Canada was presented. To the best of our knowledge, Hemicycliophora potteri n. sp. is the first recorded species of the genus to be named and fully described from highbush blueberry.

Soil biological health assessment based on nematode communities under maize and peanut intercropping

BackgroundCereal/legume intercropping can enhance crop productivity and improve soil health in dryland farming. However, little is known about soil biological health under maize/peanut intercropping. The aim of this study was to assess soil biological health based on nematode communities in a maize/peanut intercropping system.MethodsWe conducted a field experiment with different planting patterns, including monoculture maize (M), monoculture peanut (P), and maize intercropped with peanut (IM, intercropped maize; IP, intercropped peanut) to determine the influence on soil biological health. We measured soil physicochemical properties and nematode communities, and employed exploratory factor analysis combined with cumulative normal distribution curve scoring to identify potential soil biological health traits.ResultsThe intercropped maize gave the highest plant parasitic nematode abundance, trophic diversity index, evenness index, and structure index. The monoculture peanut gave the highest enrichment index and least plant parasitic nematode abundance, trophic diversity index, Shannon diversity index, evenness index, structure index, and channel index. We identified four soil biological health traits, including basic nutrients and biodiversity, food web complexity, slow energy channel, and fast energy channel, mainly represented by soil ammonium nitrogen and Shannon diversity index, structural index and omnivore-predator nematode abundance, fungivorous nematode abundance and plant parasitic nematode abundance, microbial biomass carbon and bacterivorous nematode abundance, respectively. The intercropping systems improved the comprehensive score of soil biological health, especially maize intercropping soil. Intercropping maize and intercropping peanut significantly improved oil biological health traits representing the food web complexity compared with the corresponding monoculture soils.ConclusionsOur results indicate that soil nematode and physicochemical indicators reflect different soil biological health traits. Among those traits, the improvement of basic nutrients and biodiversity and the complexity of the food web were the main reasons for improving soil biological health through the intercropping system.

Reactions of different gerbera varieties to Aphelenchoides besseyi

In this study, the aim of determining the reactions of different gerbera cultivars (Gerbera jamesonii L.) to the plant-parasitic nematode Aphelenchoides besseyi was investigated. The reactions of three different gerbera cultivars, Rosellin, Done, and Mor, which were infected in two different trials, were compared. Based on 100 plants, it was found that the mortality rates of the gerbera were 40%, 30%, and 20% for Rosellin, Done, and Mor respectively. The lowest mortality against Aphelenchoides besseyi was observed in the Mor variety cultivar.

Prevalence and abundance of plant-parasitic nematodes in New Zealand maize fields: effects of territory, soil orders, crop stage, and sampling time

ABSTRACT Plant-parasitic nematodes (PPNs) are significant agricultural pests that can reduce maize yields. This study examines the prevalence, abundance, and diversity of PPNs in New Zealand maize fields, focusing on the effects of territory, soil orders, crop stages, and sampling times. Seven PPN genera were identified: Pratylenchus spp. (root-lesion), Helicotylenchus spp. (spiral), Meloidogyne spp. (root-knot), Heterodera spp. (cyst), Paratylenchus spp. (pin), Criconemella spp. (ring), and Tylenchus spp. PPNs were present in 98% of the samples, with Pratylenchus spp. being the most prevalent (91%), followed by Helicotylenchus spp. (38%). Compared to Waikato and Manawatu-Whanganui, Canterbury had the highest nematode populations, particularly of Pratylenchus spp. and Helicotylenchus spp. Brown and pallic soils supported higher PPN abundances. Sampling during the maize harvesting stage and late autumn resulted in the highest nematode populations and diversity indices. Pratylenchus spp. populations often exceeded the economic threshold of 500 Pratylenchus kg−1 of soil, suggesting a significant threat to maize yield in New Zealand. The findings highlight the need for further research to assess the impact of Pratylenchus spp. on maize yield and to develop effective management practices for maize cultivation in the country.

Effects of Perennial Alfalfa on the Structure and Function of Soil Micro-Food Webs in the Loess Plateau.

The Loess Plateau is one of the most vulnerable areas in the world. Numerous studies have been conducted to investigate alfalfa fields with different planting years. Soil microorganisms and nematodes are vital in ecosystem functionality and nutrient cycling. Therefore, comprehending their response to alfalfa fields with varying years of planting is essential for predicting the direction and trajectory of degradation. Alfalfa fields with different planting years (2 years, 9 years, and 18 years) were used as the research object, and farmland was used as the control (CK). High-throughput sequencing and morphological methods determined the community composition of microorganisms and nematodes. Carbon metabolic footprints, correlation networks, and structural equations were used to study soil microorganisms and nematode interactions. Principal component analysis (PCA) results showed that alfalfa fields with different planting years significantly impacted soil microorganisms and nematode community structures. Planting alfalfa significantly increased the nematode channel ratio (NCR) and Wasilewska index (WI), but significantly reduced the soil nematode PPI/MI and dominance (λ). The correlation network results indicated that, for the 2-year and 18-year treatments, the total number of links and positive links are higher than other treatments. Conversely, the 9-year treatment had fewer positive links and more negative links compared to other treatments. Additionally, the keystone species within each network varied based on the treatment years. Structural equation results show that alfalfa planting years directly impact soil fungal community structure and plant-parasitic nematodes' carbon metabolism omnivorous-predatory nematodes. Furthermore, the carbon metabolism of omnivorous-predatory nematodes directly influences soil organic carbon fixation. Moreover, as the duration of alfalfa planting increases, the metabolic footprint of plant-parasitic nematodes decreases while that of omnivorous-predatory nematodes rises. Among treatments varying in alfalfa planting durations, the 9-year treatment exhibited the most incredible energy conversion and utilization efficiency within the soil food web, demonstrating the most stable structure. This study reveals optimal alfalfa planting duration for soil ecosystem stability in the Loess Plateau. Future research should explore sustainable crop rotations and alfalfa-soil-climate interactions for improved agricultural management.

Occurrence of plant-parasitic nematodes on rice (Oryza sativa) in Kenya with a focus on Hirschmanniella oryzae

Summary Rice ranks as the third most important staple cereal food crop in Kenya, following maize and wheat. The demand for rice has been increasing at a faster rate than most cereals, occasionally requiring imports to meet local needs. In response, the Kenyan government has been implementing a programme to increase rice production by expanding irrigated lowland rice schemes from 32 988 to 171 676 ha, while increasing rain-fed upland production areas four-fold to 42 000 ha by 2030. However, with continued rice monocropping in irrigated lowland fields and intensification in rain-fed upland ecosystems, there is a growing concern that plant-parasitic nematodes may emerge as a significant problem across rice ecosystems. This study characterised the nematode genera associated with rice in Kenya and assessed their diversity and distribution across rice ecosystems, with a focus on Hirschmanniella species. Eleven nematode genera were identified in both ecosystems, indicating a relatively high diversity. These genera, ranked by prominence, included Hirschmanniella, Hoplolaimus, Pratylenchus, Helicotylenchus, Meloidogyne, Ditylenchus, Trichodorus, Xiphinema, Rotylenchus, Longidorus and Paratylenchus. The family Tylenchidae was also found to be an important component of the nematofauna. Both morphological and molecular analyses confirmed the presence of Hirschmanniella oryzae in irrigated lowland and rain-fed upland rice, which represents the first documented report for Kenya. A notably large molecular variation was also observed for these Kenyan populations on the 18S region, with intraspecific variation up to 10 bp difference. Understanding the diversity, distribution, and species composition of nematodes in rice ecosystems is important for raising awareness among plant protection services, farmers, cooperatives and extension agents about plant-parasitic nematodes and their challenges in rice production. Future research should build on this knowledge to support extensive studies on population dynamics and damage threshold, focusing on local rice cultivars to develop effective management strategies, including breeding programmes and other cultural practices.

Naturally-occurring nematicides of plant origin: two decades of novel chemistries.

Plant-parasitic nematodes are among the most destructive plant pathogens, resulting in a global annual economic loss of about 358 billion dollars. Using synthetic nematicides to control plant-parasitic nematodes has resulted in broad-spectrum toxicity to the environment. Plant-derived secondary metabolites have recently emerged as viable options that provide effective, greener, and renewable routes for managing plant-parasitic nematodes in various cropping systems. However, limited comprehensive information on plant-derived secondary metabolites sources, chemical structures, and nematicidal activities is available. This study aims to compile and analyze data on plant-based secondary metabolites with nematicidal properties collected over the last two decades. In this review, we identified 262 plant-based metabolites with nematicidal activities that were isolated from 35 plant families and 65 plant species. Alkaloids, terpenoids, saponins, flavonoids, coumarins, thiophenes, and annonaceous acetogenins were among the most studied compounds. In addition to the structure-activity relation for specific metabolites with nematicidal potency, various techniques for their extraction and isolation from plant material are discussed. Our findings demonstrate the potential of plants as a feedstock for sourcing nematicidal compounds and discovering new chemistries that could potentially be used for developing the next generation of nematicides. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Soil biodiversity and microbial antagonism for suppression of plant-parasitic nematodes

Abstract Plant parasitic nematodes (PPN) cause significant economic losses in agriculture and the use of nematicides is the most common management practice applied today. However, due to the impact of such chemicals, more sustainable methods are needed. Current trends consider the exploitation of indigenous soil microbial communities. In this review we discuss some concepts required for the conservation and management of soil microorganisms, considered as a fundamental natural resource. Co-evolution and co-speciation are basic evolutionary processes of soil taxa involved in soil ecosystem services such as nematode regulation. The microorganisms showing a host-parasite co-evolution hold potential for the insurgence or re-construction of a natural equilibrium in soil, aiming at nematode regulation. The impact on soil microbial diversity of farming intensification and PPN management through nematicides is also discussed. Some examples of soil microbial resources and their impact including antagonists like nematophagous fungi (NF), aquatic parasites and bacteria are also briefly reviewed.

Purification and Identification of the Nematicidal Activity of S1 Family Trypsin-Like Serine Protease (PRA1) from Trichoderma longibrachiatum T6 Through Prokaryotic Expression and Biological Function Assays.

Heterodera avenae is a highly significant plant-parasitic nematode, causing severe economic losses to global crop production each year. Trichoderma species have been found to parasitize nematodes and control them by producing enzymes that degrade eggshells. The T. longibrachiatum T6 (T6) strain has been demonstrated the parasitic and lethal effects on H. avenae cysts and eggs, associated with the increased serine protease activity and trypsin-like serine protease gene (PRA1) expression. Our present study aimed to purify the recombinant PRA1 protease through a prokaryotic expression system and identify its nematicidal activity. The recombinant PRA1 protease was identified as S1 family trypsin-like serine protease, with a molecular weight of 43.16 kDa. The purified soluble protease exhibited the optimal activity at 35 °C and pH 8.0, and also demonstrating higher hydrolytic ability toward casein and skimmed milk. Meanwhile, the Ca2+ and Mg2+ enhanced its activity, while the inhibitor PMSF significantly reduced it. The contents of H. avenae eggs leaked out after treatment with the recombinant PRA1 protease, with egg hatching inhibition and relative hatching inhibition rates at 70.60% and 66.58%, respectively. In contrast, there was no sign of content dissolution, and embryos developed normally in the control group. Our present study revealed that the PRA1 protease of T6 strain has a lethal effect on H. avenae eggs, which providing a theoretical basis for developing biocontrol agents to control nematodes.

Sensitivity of Meloidogyne incognita and Rotylenchulus reniformis to Cyclobutrifluram.

Cyclobutrifluram, a succinate dehydrogenase inhibitor fungicide, is being evaluated as a seed-applied nematicide in cotton and soybean to manage plant-parasitic nematodes. Currently, there is no information on the toxicity, ovicidal activity, nematode recovery, or effects on nematode infection for Meloidogyne incognita or Rotylenchulus reniformis after exposure to low concentrations of cyclobutrifluram. Nematode toxicity assays were performed in aqueous solutions of cyclobutrifluram, and root infection assays were conducted on tomato. Nematode paralysis was observed after 2 h of exposure to 0.5 μg/ml cyclobutrifluram for both nematode species. Based on an assay of nematode motility, the 2-h effective concentration of fungicide required for 50% growth inhibition (EC50) value for M. incognita and R. reniformis was 0.48 and 1.07 μg/ml, respectively. In a comparable assay with a similar nematicide, continuous exposure to 0.5 μg/ml cyclobutrifluram for 24 h resulted in at least 45% more immotile nematodes for both species compared with those treated with 0.5 μg/ml fluopyram. Continuous exposure to concentrations greater than 1.0 μg/ml suppressed hatching for both species compared with the water control. Nematode recovery from paralysis was greater than 80% for M. incognita and R. reniformis 24 h after nematodes were rinsed and removed from a 1-h treatment to their respective 2-h EC50 concentrations. Nematode infection of tomato roots was reduced following a 1-h treatment with aqueous solutions of cyclobutrifluram, ranging from 0.12 to 0.48 μg/ml for M. incognita and 0.27 to 1.07 μg/ml for R. reniformis. Overall, the toxicity of cyclobutrifluram to these nematode species was greater than that of fluopyram, and although the effects of cyclobutrifluram were reversible, low concentrations were effective at reducing the ability of both nematodes to infect tomato roots.

Changes in the population and diversity of plant parasitic nematodes and their effects on sugarcane growth at Wonji‐Shoa Sugar Estate, Ethiopia

AbstractIn Wonji‐Shoa Sugar Estate (WSSE), sugarcane (Saccharum spp. hybrid) yields have declined by about 48% over the last 70 years. One of the causes for the decline is assumed to be the long‐term monoculture production system that results in the buildup of plant parasitic nematodes (PPNs). Therefore, the population and diversity of PPNs were investigated by conducting soil sampling using a biosequential method (simultaneous sampling of the soils of adjacent cultivated land [CL] and uncultivated land [UL]) and a chronosequential method (taking soil samples at different times from the same site). The samples were subjected to analysis using standard procedures to determine the change in the population, and identify the genera of PPNs. Additionally, a pot experiment that involved fumigation was conducted on top soils sampled from the CL and UL of the plantation. The results revealed that about 10 genera of PPNs (Meloidogyne, Helicotylenchus, Hoplolaimus, Rotylenchulus, Hemicycliophora, Discriconemella, Xhiphinema, Pratylenchus, Tylenchorhynchus, and Scutellonema) were detected, of which the first four were newly identified. The population density and the number of genera of PPNs found in the CL were 36‐fold and 4.5‐fold higher than those found in the UL, respectively. Furthermore, fumigation reduced the population of the PPNs by 61% and increased production of cane biomass by 63%. It is concluded that the soils of the WSSE are infested by PPNs, which consequently have detrimental effects on sugarcane growth. While amending soil fertility is crucial, reversing the decline in sugarcane yields also necessitates implementing an integrated soil management system that includes PPNs.

Plant-Parasitic and Free-Living Nematode Community Associated with Oak Tree of Magoebaskloof Mountains, Limpopo Province, South Africa

A study was conducted in the mountains of Magoebaskloof, Limpopo Province, where oak trees grow along the banks of the Broederstroom River. This study revealed that 22 nematode genera were associated with oak trees (Quercus robur). The most frequently occurring nematodes were Aphelenchus sp. (100%) and Plectus sp. (100%), followed by Helicotylenchus sp. (90%). This study examined the relationship between nematodes and the physicochemical properties of the soil using Pearson correlation. It uncovered that the organic matter content (OMC) had a negative correlation with the number of Panagrolaimus sp. (r = −0.770) and Hemicycliophora sp. (r = −0.674). Conversely, the sand percentage positively correlated (r = 0.695) with the number of Hemicycliophora sp. The clay content of the soil showed a positive correlation (r = 0.617) with the number of Ditylenchus. Soil pH demonstrated a significant negative correlation with Acrobeloides sp. (r = −0.877). The canonical correspondence analysis (CCA) explained 63.3% of the relationship between nematodes and soil physicochemical properties. The CCA results indicated that Ditylenchus exhibited a positive correlation with OMC, while the Panagrolaimus and Hemicycliophora species showed a negative correlation with OMC. The results indicated that none of the soil sample sites were under stress. The soil food web analysis revealed that most soil samples were nutrient-enriched with a low C/N ratio. In conclusion, this study revealed that oak trees harbor a high diversity of plant-parasitic and free-living nematodes. The results suggest that soil nematodes, particularly free-living bacterivores, such as Panagrolaimus, can indicate organic matter content in the soil.

Emerging Trends and Technologies Used for the Identification, Detection, and Characterisation of Plant-Parasitic Nematode Infestation in Crops.

Accurate identification and estimation of the population densities of microscopic, soil-dwelling plant-parasitic nematodes (PPNs) are essential, as PPNs cause significant economic losses in agricultural production systems worldwide. This study presents a comprehensive review of emerging techniques used for the identification of PPNs, including morphological identification, molecular diagnostics such as polymerase chain reaction (PCR), high-throughput sequencing, meta barcoding, remote sensing, hyperspectral analysis, and image processing. Classical morphological methods require a microscope and nematode taxonomist to identify species, which is laborious and time-consuming. Alternatively, quantitative polymerase chain reaction (qPCR) has emerged as a reliable and efficient approach for PPN identification and quantification; however, the cost associated with the reagents, instrumentation, and careful optimisation of reaction conditions can be prohibitive. High-throughput sequencing and meta-barcoding are used to study the biodiversity of all tropical groups of nematodes, not just PPNs, and are useful for describing changes in soil ecology. Convolutional neural network (CNN) methods are necessary to automate the detection and counting of PPNs from microscopic images, including complex cases like tangled nematodes. Remote sensing and hyperspectral methods offer non-invasive approaches to estimate nematode infestations and facilitate early diagnosis of plant stress caused by nematodes and rapid management of PPNs. This review provides a valuable resource for researchers, practitioners, and policymakers involved in nematology and plant protection. It highlights the importance of fast, efficient, and robust identification protocols and decision-support tools in mitigating the impact of PPNs on global agriculture and food security.