Plant-parasitic Nematodes Research Articles

Walnut growers want rootstocks that can resist diseases

Abstract: English walnuts are the walnut species of choice for nut production. In the United States, edible English walnuts are almost exclusively produced in California, using soil and water resources on more than 370,000 acres. Scion cultivars of English walnuts are grafted onto rootstocks. Traditional rootstocks are seedling populations of so-called Paradox hybrids generated from crosses of black walnut with English walnut. These rootstocks are susceptible to soil-borne diseases, including crown gall, Phytophthora root and crown rot, and plant-parasitic nematodes. Strategies to respond to these diseases include the use of newly developed clonal walnut rootstocks with genetic resistance. In a survey conducted during 2020 through 2021, walnut growers revealed their willingness to pay higher prices for clonal walnut rootstocks with some disease resistance. The survey showed that they were most concerned with crown gall and nematodes, and were willing to pay significant price premiums for rootstocks that are resistant to these pathogens.

Characterisation of Paratylenchus cacao n. sp. from Ghana, and P. enigmaticus (Nematoda: Paratylenchinae) from Belgium

Summary Paratylenchus cacao n. sp., a pin nematode associated with cocoa (Theobroma cacao L.) from Ghana, is described herein based on morphology, morphometrics and phylogenetic relationships with other species. Morphologically, P. cacao n. sp. is characterised by a female body length of 174-265 μm, body assuming a ‘C’ or ‘J’ shape after heat relaxation, a flat head, slightly set off lip region, a truncated anterior end, a rigid stylet of 24-31 μm, four lateral lines, vulval region with distinct vulval flaps, and a finely rounded tail with a mucron-like terminus. The findings of the phylogenetic analyses utilising the D2-D3 expansion segments of 28S, ITS of rDNA, and COI of mitochondrial DNA sequences indicate that P. cacao n. sp. is a species closely related to P. leptos. Additionally, based on butterhead lettuce and leek populations from Belgium, the first description of a male, SEM pictures and COI sequences of P. enigmaticus are presented. Both studies exemplify how even potentially important plant-parasitic nematode species can remain unnoticed for a long time. This suggests the need to conduct more nematode diversity studies and underscores the significance of correct nematode identification through the utilisation of tools such as integrative taxonomy.

CHEMOTAXIS RESPONSE OF PHASMARHABDITIS CALIFORNICA (FAMILY: RHABDITIDAE) AND PRISTIONCHUS ENTOMOPHAGUS (FAMILY: NEODIPLOGASTERIDAE) TO THE MUCUS OF FOUR SLUG SPECIES.

The chemotaxis responses of soil nematodes have been well studied in bacteriophagic nematodes, plant-parasitic nematodes, entomopathogenic nematodes, and to a lesser extent malacopathogenic nematodes. Free-living stages of parasitic nematodes often use chemotaxis to locate hosts. In this study, we compared the chemotaxis profile of 2 slug-associated nematodes with overlapping host ranges. Phasmarhabditis californica is a facultative parasite that has been shown to express strain-dependent variation in chemoattraction profile. We tested 4 slug species to determine the attraction index of a Canadian strain of Ph. californica and a sympatric necromenic nematode, Pristionchus entomophagus. When tested against a control (distilled water), Ph. californica showed a clear (positive) attraction towards the mucus of slugs Ambigolimax valentianus, Arion rufus, and Arion fasciatus, but not Deroceras reticulatum. However, when given a choice between the mucus of D. reticulatum and Ar. fasciatus in a pairwise test, Ph. californica was strongly attracted to the former. Other pairwise comparisons did not reveal a clear preference for either slug species in the following pairs: D. reticulatum-Ar. rufus, Am. valentianus-Ar. rufus, D. reticulatum-Am. valentianus. The chemotaxis assay for Pr. entomophagus showed an attraction toward D. reticulatum and Ar. fasciatus (tested against controls); the attraction index for Am. valentianus was positive, but this was not statistically significant. In contrast, the attraction index for Ar. rufus was negative, suggesting possible repulsion to the mucus of this slug species. Given that Pr. entomophagus and Ph. californica occupy overlapping habitats, utilize similar hosts, and exhibit similar chemotaxis profiles, there is a potential for direct interaction between these 2 nematodes. Like other members of the genus Pristionchus, Pr. entomophagus may be able to prey upon the co-occurring Ph. californica, such antagonistic interactions could have important implications for the coexistence of these 2 species and Ph. californica in particular as a biocontrol agent against pestiferous slugs.

Plant-parasitic nematodes associated with Panicum maximum and Mimosa hirsutissima in a pasture field

Pastures and weed plants can host plant-parasitic nematodes of economic importance, with the limited yield of pastures representing a continuous challenge for agriculture, especially in the lower Jequitinhonha Valley in southeastern Brazil, where dairy and beef cattle play a crucial role in the local economy. From this perspective, this study aimed to provide information on the population density of plant-parasitic nematodes associated with Panicum maximum cv. Mombaça and Mimosa hirsutissima, weed species commonly found in pasture areas cropped with this grass in the municipality of Almenara, MG, in the Jequitinhonha Valley region of southeastern Brazil. Soil and root samples were collected from the field and placed in plastic bags, which were labeled and taken to the laboratory for nematode extraction. Nematode population densities were estimated in a Peters counting slide under a light microscope, and genera identification was based on morphological traits. In rhizosphere soil (100 g) of P. maximum cv. Mombaça, the highest population densities were observed for Helicotylenchus sp. (3,999), followed by Tylenchus sp. (1,191), Meloidogyne spp. (939), and Pratylenchus sp. (544). In roots (1 g), on the other hand, the highest values corresponded to Pratylenchus sp. (19.6) and Meloidogyne spp. (15.5). However, in rhizosphere soil of M. hirsutissima, the highest population densities were recorded for Tylenchus sp. (2,072), Helicotylenchus sp. (1,883), Pratylenchus sp. (751), and Meloidogyne spp. (307). In contrast, in the roots, the highest values were observed for Meloidogyne spp. (6.9), Tylenchus sp. (4.4), and Pratylenchus sp. (2.7). These findings are essential to take decisions on the management of plant-parasitic nematodes.

Influence of Seasonal Variations on Population Dynamics of Phyto-Parasitic Nematodes in Soil and Roots of Bell Pepper (Capsicum annuum L.) in Otari, Rivers State, Nigeria

Weather instability affects nematode proliferation in soil, affecting plant growth. Identifying endemic species and favourable seasons can guide farmers in cultivating crops during specific seasons, minimizing infections and improving yield. A survey to evaluate the influence of seasonal disparity on plant parasitic nematodes population in soil and roots of bell pepper (Capsicum annuum L.) was carried out during dry and rainy seasons in Otari, Abua/Odual Local Government Area of Rivers State, Nigeria. Five bell pepper cultivated fields were randomly selected and a total of 300 soil samples were collected and assayed for soil nematodes. The soil samples were collected using a soil auger at 0-15 cm depth, and roots were collected by the use of sterilized kitchen knife simultaneously for the isolation of nematode. The modified sieve plate method was employed for the extraction of nematodes. Nematode identification was carried out using a pictorial key. A total of 2,220 nematodes from 11 genera were reported in this study, among which 1,290 (58.1%) were recovered during the rainy season while the dry season showed 930 (41.9%) nematodes. Nematode population vary significantly between seasons in soil (P = .13) and roots of bell pepper (P = 3.90), with Heterodera species having higher density (1.44 and 1.03) during the rainy and dry seasons respectively in the soil. High density of Meloidogyne (0.97) was recorded during the rainy season and Radopholus spp (1.40) during the dry season in the root of bell pepper plant. The study showed that seasonal variations impacted on nematode population abundance in fields, establishing that nematodes are responsive to every unsteady condition of the soil environment resulting from seasonal disparity, and only species who adapt rapidly survive. Farmers should increase crop cultivation during the rainy season to boost yield, as nematodes population decline as rainfall increases.

Modulation of the Host Defence System by Nematophagous Fungi and Chitosan

Nematophagous fungi (NFs), which are responsible for soil suppression of plant-parasitic nematodes, are multitrophic biocontrol agents. This raises the question of the transition between lifestyles (e.g., endophytism vs. egg parasitism). The NF Pochonia chlamydosporia colonises food crops and promotes their growth and yield. When colonising the plant, P. chlamydosporia induces the plant immunity (PI). However, it also evades the PI. To do this, both endophytic NF and pathogenic fungi (PF) secrete LysM effectors (LysM-effs). LysM effectors have been shown to have diverse functions in different organisms, including the protection of fungal chitin from plant chitinases. P. chlamydosporia is resistant to chitosan, which modulates gene expression in fungi and plants and has antimicrobial properties. P. chlamydosporia chitin deacetylases (CDA) and chitosanases (CSN) also help P. chlamydosporia evade plant immunity, resist exogenous chitosan, and are induced during fungal infection of nematode eggs. NF-chitosan formulations are new biomanagement tools against plant parasitic nematodes, fungal wilt pathogens and insect pests that currently threaten food security crops. Furthermore, omics techniques are useful tools to elucidate the role of CDAs, CSNs, LysM-effs, adhesion proteins and carbohydrate-active enzymes in pathogen–BCA–plant interactions, adhesion and infection to nematode eggs and their modulation by chitosan.

Resistance to both aphids and nematodes in tobacco plants expressing a Bacillus thuringiensis crystal protein.

Bacillus thuringiensis (Bt) and its crystal toxin or δ-endotoxins (Cry) offer great potential for the efficient control of crop pests. A vast number of pests can potentially infect the same host plant, either simultaneously or sequentially. However, no effective Bt-Cry protein has been reported to control both aphids and plant parasitic nematodes due to its highly specific activity. Our study indicated that the Cry5Ba2 protein was toxic to the green peach aphid Myzus persicae, which had a median lethal concentration (LC50) of 9.7 ng μL-1 and fiducial limits of 3.1-34.6 ng μL-1. Immunohistochemical localization of Cry5Ba2 revealed that it could bind to the apical tip of microvilli in midgut regions. Moreover, transgenic tobacco plants expressing Cry5Ba2 exhibited significant resistance to Myzus persicae, as evidenced by reduced insect survival and impaired fecundity, and also intoxicated the Meloidogyne incognita as indicated by a decrease in galls and progeny reproduction. In sum, we identified a new aphicidal Bt toxin resource that could simultaneously control both aboveground and belowground pests, thus extending the application range of Bt-based strategy for crop protection. © 2024 Society of Chemical Industry.

Characterization of regulatory genes Plhffp and Plpif1 involved in conidiation regulation in Purpureocillium lavendulum.

Purpureocillium lavendulum is an important biocontrol agent against plant-parasitic nematodes, primarily infecting them with conidia. However, research on the regulatory genes and pathways involved in its conidiation is still limited. In this study, we employed Agrobacterium tumefaciens-mediated genetic transformation to generate 4,870 random T-DNA insertion mutants of P. lavendulum. Among these mutants, 131 strains exhibited abnormal conidiation, and further in-depth investigations were conducted on two strains (designated as #5-197 and #5-119) that showed significantly reduced conidiation. Through whole-genome re-sequencing and genome walking, we identified the T-DNA insertion sites in these strains and determined the corresponding genes affected by the insertions, namely Plhffp and Plpif1. Both genes were knocked out through homologous recombination, and phenotypic analysis revealed a significant difference in conidiation between the knockout strains and the wild-type strain (ku80). Upon complementation of the ΔPlpif1 strain with the corresponding wildtype allele, conidiation was restored to a level comparable to ku80, providing further evidence of the involvement of this gene in conidiation regulation in P. lavendulum. The knockout of Plhffp or Plpif1 reduced the antioxidant capacity of P. lavendulum, and the absence of Plhffp also resulted in decreased resistance to SDS, suggesting that this gene may be involved in the integrity of the cell wall. RT-qPCR showed that knockout of Plhffp or Plpif1 altered expression levels of several known genes associated with conidiation. Additionally, the analysis of nematode infection assays with Caenorhabditis elegans indicated that the knockout of Plhffp and Plpif1 indirectly reduced the pathogenicity of P. lavendulum towards the nematodes. The results demonstrate that Agrobacterium tumefaciens - mediated T-DNA insertion mutagenesis, gene knockout, and complementation can be highly effective for identifying functionally important genes in P. lavendulum.

Evolution of parasitism genes in the plant parasitic nematodes

The plant-parasitic nematodes are considered as one of the most destructive pests, from which the migratory and sedentary endoparasitic plant parasitic nematodes infect more than 4000 plant species and cause over $100 billion crop losses annually worldwide. These nematodes use multiple strategies to infect their host and to establish a successful parasitism inside the host such as cell-wall degradation enzymes, inhibition of host defense proteins, and molecular mimicry. In the present study, the main parasitism-associated gene families were identified and compared between the migratory and sedentary endoparasitic nematodes. The results showed that the migratory and sedentary endoparasitic nematodes share a core conserved parasitism mechanism established throughout the evolution of parasitism. However, genes involved in pectin degradation and hydrolase activity are rapidly evolving in the migratory endoparasitic nematodes. Additionally, cell-wall degrading enzymes such as GH45 cellulases and pectate lyase and peptidase and peptidase inhibitors were expanded in the migratory endoparasitic nematodes. The molecular mimicry mechanism was another key finding that differs between the endoparasitic and sedentary parasitic nematodes. The PL22 gene family, which is believed to play a significant role in the molecular mechanisms of nematode parasitism, has been found to be present exclusively in migratory endoparasitic nematodes. Phylogenetic analysis has suggested that it was de novo born in these nematodes. This discovery sheds new light on the molecular evolution of these parasites and has significant implications for our understanding of their biology and pathogenicity. This study contributes to our understanding of core parasitism mechanisms conserved throughout the nematodes and provides unique clues on the evolution of parasitism and the direction shaped by the host.

Long-term benefit contribution of chemical and biological nematicide in coffee nematode management in soil microbial diversity and crop yield perspectives

The plant-parasitic root-knot nematode Meloidogyne exigua causes significant damage and is an important threat in Coffea arabica plantations. The utilization of plant-beneficial microbes as biological control agents against sedentary endoparasitic nematodes has been a longstanding strategy. However, their application in field conditions to control root-knot nematodes and their interaction with the rhizospheric microbiota of coffee plants remain largely unexplored. This study aimed to investigate the effects of biological control agent-based bioproducts and a chemical nematicide, used in various combinations, on the control of root-knot nematodes and the profiling of the coffee plant rhizomicrobiome in a field trial. The commercially available biological products, including Trichoderma asperellum URM 5911 (Quality), Bacillus subtilis UFPEDA 764 (Rizos), Bacillus methylotrophicus UFPEDA 20 (Onix), and nematicide Cadusafos (Rugby), were applied to adult coffee plants. The population of second-stage juveniles (J2) and eggs, as well as plant yield, were evaluated over three consecutive years. However, no significant differences were observed between the control group and the groups treated with bioproducts and the nematicide. Furthermore, the diversity and community composition of bacteria, fungi, and eukaryotes in the rhizosphere soil of bioproduct-treated plants were evaluated. The dominant phyla identified in the 16 S, ITS2, and 18 S communities included Proteobacteria, Acidobacteria, Actinobacteria, Ascomycota, Mortierellomycota, and Cercozoa in both consecutive years. There were no significant differences detected in the Shannon diversity of 16 S, ITS2, and 18 S communities between the years of data. The application of a combination of T. asperellum, B. subtilis, and B. methylotrophicus, as well as the use of Cadusafos alone and in combination with T. asperellum, B. subtilis, and B. methylotrophicus, resulted in a significant reduction (26.08%, 39.13%, and 21.73%, respectively) in the relative abundance of Fusarium spp. Moreover, the relative abundance of Trichoderma spp. significantly increased by 500%, 200%, and 100% at the genus level, respectively, compared to the control treatment. By constructing a co-occurrence network, we discovered a complex network structure among the species in all the bioproduct-treated groups. However, our findings indicate that the introduction of exogenous beneficial microbes into field conditions was unable to modulate the existing microbiota significantly. These findings suggest that the applied bioproducts had no significant impact on the reshaping of the overall microbial diversity in the rhizosphere microbiome but rather recruited selected microrganisms and assured net return to the grower. The results underscore the intricate nature of the rhizosphere microbiome and suggest the necessity for alternate biocontrol strategies and a re-evaluation of agricultural practices to improve nematode control by aligning with the complex ecological interactions in the rhizosphere.

Unzipped genome assemblies of polyploid root-knot nematodes reveal unusual and clade-specific telomeric repeats

Using long-read sequencing, we assembled and unzipped the polyploid genomes of Meloidogyne incognita, M. javanica and M. arenaria, three of the most devastating plant-parasitic nematodes. We found the canonical nematode telomeric repeat to be missing in these and other Meloidogyne genomes. In addition, we find no evidence for the enzyme telomerase or for orthologs of C. elegans telomere-associated proteins, suggesting alternative lengthening of telomeres. Instead, analyzing our assembled genomes, we identify species-specific composite repeats enriched mostly at one extremity of contigs. These repeats are G-rich, oriented, and transcribed, similarly to canonical telomeric repeats. We confirm them as telomeric using fluorescent in situ hybridization. These repeats are mostly found at one single end of chromosomes in these species. The discovery of unusual and specific complex telomeric repeats opens a plethora of perspectives and highlights the evolutionary diversity of telomeres despite their central roles in senescence, aging, and chromosome integrity.

Biosynthesis of Cry5B-Loaded Sulfur Nanoparticles using Arthrobotrys oligospora Filtrate: Effects on Nematicidal Activity, Thermal Stability, and Pathogenicity against Caenorhabditis elegans.

Cry5B, a crystal protein produced by Bacillus thuringiensis (Bt), is a bionematicide with potent nematicidal activity against various plant-parasitic and free-living nematodes. This protein, however, is susceptible to destruction by ultraviolet light, proteolytic enzymes, and high temperatures. This study aims to produce Cry5B protein for bionematicidal use and improve its stability and nematicidal efficacy by loading it intoArthrobotrys oligospora-mediated sulfur nanoparticles (AO-SNPs). Based on the mortality assay, the Cry5B protein exhibited dose-dependent nematicidal activity against the model organismCaenorhabditis elegans. The nematicidal activity, thermal stability, and pathogenic effects of Cry5B-loaded AO-SNPs (Cry5B-SNPs) were compared to those of free Cry5B. After 3 h of exposure to heat at 60 °C, Cry5B-SNPs had greater nematicidal activity than free Cry5B protein, indicating the effective formulation of Cry5B-SNPs that could be used as an alternative to current nematicide delivery strategies.

A Critical Appraisal of DNA Transfer from Plants to Parasitic Cyst Nematodes.

Plant-parasitic nematodes are one of the most economically important pests of crops. It is widely accepted that horizontal gene transfer-the natural acquisition of foreign genes in parasitic nematodes-contributes to parasitism. However, an apparent paradox has emerged from horizontal gene transfer analyses: On the one hand, distantly related organisms with very dissimilar genetic structures (i.e. bacteria), and only transient interactions with nematodes as far as we know, dominate the list of putative donors, while on the other hand, considerably more closely related organisms (i.e. the host plant), with similar genetic structure (i.e. introns) and documented long-term associations with nematodes, are rare among the list of putative donors. Given that these nematodes ingest cytoplasm from a living plant cell for several weeks, there seems to be a conspicuous absence of plant-derived cases. Here, we used comparative genomic approaches to evaluate possible plant-derived horizontal gene transfer events in plant parasitic nematodes. Our evidence supports a cautionary message for plant-derived horizontal gene transfer cases in the sugar beet cyst nematode, Heterodera schachtii. We propose a 4-step model for horizontal gene transfer from plant to parasite in order to evaluate why the absence of plant-derived horizontal gene transfer cases is observed. We find that the plant genome is mobilized by the nematode during infection, but that uptake of the said "mobilome" is the first major barrier to horizontal gene transfer from host to nematode. These results provide new insight into our understanding of the prevalence/role of nucleic acid exchange in the arms race between plants and plant parasites.

Effect of Fluopyram on Pratylenchus penetrans on Corn in the Field and In Vitro.

The effects of a fluopyram seed treatment on lesion nematodes (Pratylenchus spp.) and other plant-parasitic nematodes (PPNs) were evaluated on corn in multiple field locations in 2020 and 2021. The highest rate of fluopyram seed treatment (0.15 mg seed-1) reduced early season population density of lesion nematodes compared with the base treatment control in 2020 only. However, fluopyram did not affect late season lesion nematode population density and corn yields. Fluopyram seed treatment also had minimal or nonsignificant effects on other PPN species. Based on these results, the effects of fluopyram were tested in vitro on Pratylenchus penetrans. Results demonstrated that fluopyram severely affected motility in P. penetrans. The sensitivity of P. penetrans second-stage juveniles (J2s) to fluopyram was significantly higher than at J4 and adult, suggesting that sensitivity to fluopyram is dependent on developmental stage. In addition, the effects of fluopyram were reversible at an EC50 but were irreversible at the maximum concentration (25 μg/ml). Overall, our results indicate that fluopyram has potential for controlling P. penetrans, but its efficacy is variable depending on nematode developmental stage and chemical concentration. Further research is needed to determine if these impacts can translate to field scenarios.

Functional Characterization of ShK Domain-Containing Protein in the Plant-Parasitic Nematode Bursaphelenchus xylophilus

ShK domain-containing proteins are peptides found in different parasitic and venomous organisms. From a previous transcriptomic dataset from Bursaphelenchus xylophilus, a plant-parasitic nematode that infects forest tree species, we identified 96 transcripts potentially as ShK domain-containing proteins with unknown function in the nematode genome. This study aimed to characterize and explore the functional role of genes encoding ShK domain-containing proteins in B. xylophilus biology. We selected and functionally analyzed nine candidate genes that are putatively specific to B. xylophilus. In situ hybridization revealed expression of one B. xylophilus ShK in the pharyngeal gland cells, suggesting their delivery into host cells. Most of the transcripts are highly expressed during infection and showed a significant upregulation in response to peroxide products compared to the nematode catalase enzymes. We reported, for the first time, the potential involvement of ShK domain genes in oxidative stress, suggesting that these proteins may have an important role in protecting or modulating the reactive oxygen species (ROS) activity of the host plant during parasitism.

Testing the viability of poultry droppings as an option in the management of soil nematodes on <i>Capsicum annuum</i> plant

A survey to evaluate the viability of poultry droppings as a management option for the control of plant parasitic nematodes was tested on Capsicum annuum. Bell pepper monoculture farms cultivated conventionally and another with poultry droppings as fertilizer were surveyed. Soil samples were collected using a hand trowel while roots were collected by means of kitchen knife. Plant parasitic nematodes extraction was done by using sieve plate method. Nematodes were identified using the light microscope of x4 and x10 objectives, and identification was done using a pictorial key. Roots assay from the conventional far revealed a total of 175 endophytic nematodes from 10 genera while 56 nematodes from 6 genera were extracted from the farm with poultry droppings. Nematode dynamics in diversity was observed such that certain nematode genera such as Meliodogyne, Radopholus, Pratylenchus, Ditylenchus, Hoplolaimus, Rhaditis were reported in both plots. Phyto-parasitic species were predominant at the conventional farm plot whereas nematodes predatory species recorded higher populations in the farm plot with poultry droppings, an observation which depict that parasitic nematodes could be inhibited by the presence of free living species. This observation further suggests that poultry droppings can adequately fit in as a management of nematodes management if properly harmonised.

Morphological and molecular characterisation of Helicotylenchus zengchengensis n. sp. (Nematoda: Hoplolaimidae) from China, with a review on Helicotylenchus species in China

Helicotylenchus comprises a significant group of plant-parasitic nematodes that primarily feed on plant roots. This study focuses on the description of a newly discovered species, Helicotylenchus zenchengensis n. sp., from China. The distinguishing characteristic of this species, as observed under a microscope, is the absence of head annulation. The stylet, measuring between 23.8 and 29.3 μm, exhibits anteriorly flattened or indented stylet knobs. The elongated tail has a c value ranging from 15.8 to 22.6 and a c’ value between 1.9 and 2.4. It bears 15 to 18 tail annuli, presenting a conical shape with projections. The phasmids are located at the 4th to 10th body annulations posterior to the anus, while no males were observed. Three phylogenetic trees were constructed to determine the evolutionary relationships using the 18S rRNA, ITS, and 28S D2-D3 expansion segments of the newly discovered species and related Helicotylenchus sequences obtained from the database. Based on the ITS sequences, a phylogenetic tree revealed that H. zenchengensis n. sp. clustered with H. cuspicaudatus. However, it was distinguished from H. cuspicaudatus when examining the 18S and 28S rRNA sequences and morphological characteristics. Additionally, comprehensive and diagnostic tables for all known species of Helicotylenchus in China are provided for reference.

Unravelling cryptic diversity in the Paratrichodorus allius-group species complex to resolve eight new species of the genus and new insights on the molecular phylogeny (Nematoda: Trichodoridae)

Abstract The stubby-root nematode genus Paratrichodorus comprises species of plant polyphagous ectoparasitic nematodes distributed worldwide and a few of them are plant virus-vectors (tobravirus). This is one of the most difficult nematode genera in terms of species identification, since it is phenotypically conserved with closely related species and is highly sensitive to the specimen fixation and preservation processes. Using an integrative and multidisciplinary taxonomy framework, we determined species boundaries among the Paratrichodorus populations from a P. allius species-complex sampled in cultivated and natural ecosystems across Spain. We support the hypothesis that nematode diversity of the P. allius species-complex remains underestimated and describe here a total of eight new species on the basis of detailed morphological and molecular characterization of 16 Paratrichodorus populations: Paratrichodorus asidonaensis sp. nov., Paratrichodorus benalupensis sp. nov., Paratrichodorus hinogerus sp. nov., Paratrichodorus litoralis sp. nov., Paratrichodorus paraallius sp. nov., Paratrichodorus rocianerus sp. nov., Paratrichodorus tarifaensis sp. nov., and Paratrichodorus uliaensis sp. nov. This study emphasizes the importance of properly applying a broad taxonomic framework in plant-parasitic nematodes. It is also relevant for plant health, since it correctly delimits species morphologically closed to the virus vector nematode, P. allius, and gives proper molecular markers for its unequivocal identification.

Rapid identification of Meloidogyne hapla by KASP assay

Meloidogyne hapla causes significant economic damage to many cultivated plants including especially vegetables, fruit trees and potatoes. Due to the high number of hosts of this species, it limits the variety of crops to be planted in infested areas. In order to make quarantine measures and management strategies timely against M. hapla, the species need to be identified accurately and quickly. In this study, Kompetitive Allele-Specific PCR (KASP) genotyping assays were developed to identify M. hapla. Two forward primers and one reverse primer were designed as well and performed in the KASP protocols. The designed KASP assays were able to successfully distinguish M. hapla isolates from other root-knot nematodes (RKNs) and plant-parasitic nematodes (PPNs) species. The results showed that even DNA isolated from only one juvenile of M. hapla can be sufficient for molecular identification, and the sensitivity of the assay was very high. The developed KASP assays can be used for accurate and rapid identification of M. hapla.

Differentiation of Root-knot and Cyst Nematodes from Nitrogen-fixing Nodules in Grain Legumes: A Mini-review

The review paper aims to provide insight into the plant parasitic nematodes affecting grain legumes, specifically focusing on Root-knot and Cyst nematodes. These nematodes have a significant impact on legume crops, and their signs can bring confusion, making it difficult for farmers to make informed farm management decisions. The review summarizes the key points and findings of the literature on the differentiation of root-knot and cyst nematodes from nitrogen-fixing nodules in grain legumes. The scope of the review is to provide an overview of the current knowledge on the differentiation of these nematodes, which can help farmers make informed decisions. The literature search for this review focused primarily on peer-reviewed articles available on Google Scholar and published between 2000 and 2023. The review found that the differentiation of root-knot and cyst nematodes from nitrogen-fixing nodules can be challenging, and various methods have been proposed, including on-farm identification and microscopic examination. The review concludes that a combination of these methods can be more effective in accurately differentiating nematodes galls from nitrogen-fixing nodules in legumes. Keywords: Root-knot, Cyst, Legume, Nematode, Nitrogen-fixing nodules