Rathayibacter tanaceti sp. nov., a Novel Actinobacterium from Tanacetum vulgare Infested by Foliar Nematode Aphelenchoides sp

Two novel yellow-pigmented, rod-shaped and non-motile coryneform actinobacteria, strains VKM Ac-2596T and VKM Ac-2761, were isolated from a plant Tanacetum vulgare (Asteraceae) infested by foliar nematode Aphelenchoides sp. The strains exhibited the highest 16S rRNA gene sequence similarities to Rathayibacter agropyri CA4T (99.71%), Rathayibacter rathayi DSM 7485T (99.65%) and Rathayibacter iranicus VKM Ac-1602T (99.65%). The pairwise average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between VKM Ac-2596T and VKM Ac-2671 towards the type strains of Rathayibacter species did not exceed 85.24% and 29.40%, respectively, that are well below the thresholds for species delineation. The target strains had key chemotaxonomic properties typical of the genus Rathayibacter, namely, the DAB-based peptidoglycan, rhamnose and mannose as the predominant sugars and a rhamnomannan in the cell, the major menaquinone MK-10 and fatty acids of iso-anteiso type, with a large proportion of anteiso-15:0. The strains showed clear differences from the recognized Rathayibacter species in several phenotypic characteristics, including the difference in the composition of cell wall glycopolymers. Based on the results obtained in this study and the data published previously, we provide a description of a new species, Rathayibacter tanaceti sp. nov., with DL-642T (= VKM Ac-2596T = LMG 33114T) as the type strain.

Discovery and Mechanism of a Nematicide Candidate (): A Novel Amide Compound Containing a Cyclopropyl Moiety

To find novel nematicides, we screened the nematicidal activity of compounds in our laboratory compound library. Interestingly, the compound N-((1R,2R)-2-(2-fluoro-4-(trifluoromethyl)phenyl)cyclopropyl)-2-(trifluoromethyl)benzamide (W3) showed a broad spectrum and excellent nematicidal activity. The LC50 values of compound W3 against second-stage juveniles of Bursaphelenchus xylophilus (B. xylophilus), Aphelenchoides besseyi, and Ditylenchus destructor are 1.30, 1.63, and 0.72 mg/L, respectively. Nematicidal activities of compound W3 against second-stage juveniles of Meloidogyne incognita were 87.66% at 100 mg/L. Meanwhile, compound W3 can not only observably inhibit the feeding, reproduction, and egg hatching of B. xylophilus but can also effectively promote the oxidative stress adverse reactions of nematodes and cause intestinal damage. Compound W3 can promote the production of MDA and inhibit the activities of defense enzymes SOD and GST in B. xylophilus. Compound W3 can affect the transcription of genes involved in regulating the tricarboxylic acid cycle in nematodes, resulting in weakened nematode respiration and reduced nematode activity and even death. In addition, compound W3 had good inhibitory activity against five pathogenic fungi. Among them, the EC50 of compound W3 against Fusarium graminearum was 8.4 mg/L. In the future, we will devote ourselves to the toxicological and structural optimization research of the candidate nematicide W3.

Unveiling the Diversity: Plant Parasitic Nematode Effectors and Their Plant Interaction Partners

Root-knot and cyst nematodes are two groups of plant parasitic nematodes that cause the majority of crop losses in agriculture. As a result, these nematodes are the focus of most nematode effector research. Root-knot and cyst nematode effectors are defined as secreted molecules, typically proteins, with crucial roles in nematode parasitism. There are likely hundreds of secreted effector molecules exuded through the nematode stylet into the plant. The current research has shown that nematode effectors can target a variety of host proteins and have impacts that include the suppression of plant immune responses and the manipulation of host hormone signaling. The discovery of effectors that localize to the nucleus indicates that the nematodes can directly modulate host gene expression for cellular reprogramming during feeding site formation. In addition, plant peptide mimicry by some nematode effectors highlights the sophisticated strategies the nematodes employ to manipulate host processes. Here we describe research on the interactions between nematode effectors and host proteins that will provide insights into the molecular mechanisms underpinning plant-nematode interactions. By identifying the host proteins and pathways that are targeted by root-knot and cyst nematode effectors, scientists can gain a better understanding of how nematodes establish feeding sites and subvert plant immune responses. Such information will be invaluable for future engineering of nematode-resistant crops, ultimately fostering advancements in agricultural practices and crop protection. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2024.

Characterization and Effect of a Nematophagous Fungus Talaromyces cystophila sp. nov. for the Biological Control of Corn Cyst Nematode

The dynamic of plant-parasitic nematode populations in soil is closely related to soil microorganisms. Fungi from Heterodera zeae cysts were isolated to explore the phenomenon of decline in the H. zeae population in the soil. Phylogenetic study of partial ITS, BenA, CaM, and RPB2 gene sequences, in addition to morphological investigations, was utilized to identify a nematode-destroying fungus. The nematicidal activity of a novel strain GX1 against H. zeae was assessed in vitro and in the greenhouse. Our findings revealed that strain GX1 is a new species of Talaromyces, named Talaromyces cystophila. It has a strong parasitic and lethal effect on H. zeae cysts, with 91.11% parasitism on cysts at 3 days after treatment. The contents of second-stage juveniles (J2s) and eggs inside the cysts were degraded and formed dense vacuoles, and the damaged eggs could not hatch normally. The spore suspension exhibited high nematophagous activity against nematodes, and fermentation filtrate exhibited marked inhibition of egg hatching and nematicidal activities on J2s. The hatching inhibition rates of eggs exposed to 1 × 108 CFU/ml spore suspensions or 20% 1-week fermentation filtrate (1-WF) for 15 days were 98.56 and 100%, respectively. The mortality of J2s exposed to 1 × 108 CFU/ml spore suspension reached 100% at 24 h; exposure to 50% 2-WF was 98.65 and 100% at 24 and 48 h, respectively. Greenhouse experiments revealed that the spore suspension and fermentation broth considerably decreased H. zeae reproduction by 56.17 to 78.76%. T. cystophila is a potential biocontrol strain with nematophagous and nematicidal activity that deserves attention and application.

Evaluation of Soybean Genotypes (Glycine max and G. soja) for Resistance to the Root-Knot Nematode, Meloidogyne enterolobii

Potential resistance to the root-knot nematode (RKN) Meloidogyne enterolobii in 72 Glycine soja and 44 G. max soybean genotypes was evaluated in greenhouse experiments. Approximately 2,500 eggs of M. enterolobii were inoculated on each soybean genotype grown in a steam sterilized 1:1 sand to soil mixture. Sixty days postinoculation, plants were destructively harvested to determine the host status. The host status of each soybean genotype was determined by assessing root galling severity and calculating the final eggs per root system divided by the initial inoculum, or the reproduction factor (Rf). Five G. soja soybean genotypes were identified as resistant (Rf < 1) to M. enterolobii: '407202', '407239', '424083', '507618', and '639621'. None of the tested G. max soybean genotypes were identified as resistant to M. enterolobii. Some of the G. max genotypes determined to be susceptible to M. enterolobii include 'Hagood', 'Avery', 'Rhodes', 'Santee', and 'Bryan'. The genotype 'Bryan' had the lowest Rf values among the group at 5.06 and 6.67 in two independent trials, respectively, which represents a five- to sixfold increase in reproduction of M. enterolobii. Plant genotypes resistant to RKNs are effective in managing the disease and preserving yield, cost-efficient, and environmentally sustainable, and host resistance is often regarded as the most robust management tactic for controlling plant-parasitic nematodes. Resistance to RKNs in soybean genotypes has been identified for other Meloidogyne species, yet there is currently limited data regarding soybean host status to the highly aggressive nematode M. enterolobii. This study adds to the knowledge of potential native resistance to M. enterolobii in wild and cultivated soybean.

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.

Pine wilt disease: what do we know from proteomics?

Pine wilt disease (PWD) is a devastating forest disease caused by the pinewood nematode (PWN), Bursaphelenchus xylophilus, a migratory endoparasite that infects several coniferous species. During the last 20 years, advances have been made for understanding the molecular bases of PWN-host trees interactions. Major advances emerged from transcriptomic and genomic studies, which revealed some unique features related to PWN pathogenicity and constituted fundamental data that allowed the development of postgenomic studies. Here we review the proteomic approaches that were applied to study PWD and integrated the current knowledge on the molecular basis of the PWN pathogenicity. Proteomics has been useful for understanding cellular activities and protein functions involved in PWN-host trees interactions, shedding light into the mechanisms associated with PWN pathogenicity and being promising tools to better clarify host trees PWN resistance/susceptibility.

Design, Synthesis, Nematicidal, and Fungicidal Activities of Novel Azo and Azoxy Compounds

Bursaphelenchus xylophilus (B. xylophilus) and Meloidogyne are parasitic nematodes that have caused severe ecological and economic damage in pinewood and crops, respectively. Jietacins (jietacin A and B) were found to have excellent biological activity against B. xylophilus. Based on our tremendous demand for chemicals against B. xylophilus, a novel scaffold based on the azo and azoxy groups was designed, and a series of compounds were synthesized. In the bioassay, Ia, IIa, IIc, IId, and IVa exhibited higher activity against B. xylophilus in vitro than avermectin (LC50 = 2.43 μg·mL-1) with LC50 values of 1.37, 1.12, 0.889, 1.56, and 1.10 μg·mL-1, respectively. Meanwhile, Ib, Ic, IIc, and IVa showed good inhibition effects against Meloidogyne in vivo at the concentrations of 80 and 40 μg·mL-1 with inhibition rates of 89.0% and 81.6%, 95.6% and 75.7%, 96.3% and 41.2%, and 86.8% and 78.7%, respectively. In fungicidal activity in vitro, IIb and IVa exhibited excellent effect against Botryosphaeria dothidea with the inhibition of 82.59% and 85.32% at the concentration of 10 μg·mL-1, while the inhibition of Ia was 83.16% against Rhizoctonia solani at the concentration of 12.5 μg·mL-1. Referring to the biological activity against B. xylophilus, a 3D-QASR model was built in which the electron-donating group and small group at the 4-phenylhydrazine were favorable for the activity. In general, the novel azoxy compounds, especially IIc possess great potential for application in the prevention of B. xylophilus.

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.

Characteristics of pine wood nematode disease in Nankang District, Ganzhou, Jiangxi Province, China

Pine wood nematode (PWN) disease is one of the major disasters in forests of southern China, causing substantial forest resources and ecological and economic losses. Based on field surveys and WFV image data from the GF-1 satellite, we constructed a spatial identification model of PWN disease with the random forest model to explore the relative influences of topography, human activities and stand factors on the occurrence of diseases and predict their spatial distribution. We then used the spatial autocorrelation analysis to assess the distribution characteristics of PWN disease at the regional scale. The results showed that the random forest model constructed in this study was effective in identifying pine nematode diseases (AUC value=0.99, overall accuracy=0.96). The norma-lized difference greenness index (NDGI), the distance to the highway, and normalized vegetation index (NDVI) were important factors in explaining the spatial variations of PWN disease occurrence. There was a positive spatial correlation in the occurrence of PWN disease (not randomly distributed but with obvious spatial aggregation characteristics). The high occurrence areas of pine wood nematode disease concentrated in Chitu Township, Zhufang Township and Shibatang Township, low occurrence areas concentrated in the vicinity of Rongjiang Street. The areas far away from the highway, low in elevation, and close to county roads were suffered to PWN disease. The results could serve the regional monitoring of pine nematode disease occurrence and provide practical guidance for PWN disease management.

The essential role of arginine biosynthetic genes in lunate conidia formation, conidiation, mycelial growth, and virulence of nematophagous fungus, Esteya vermicola CBS115803

BACKGROUND

The pinewood nematode (Bursaphelenchus xylophilus) causes severe damage to pine trees. The nematophagous fungus, Esteya vermicola, exhibits considerable promise in the biological control of Bursaphelenchus xylophilus due to its infectivity. Notably, the lunate conidia produced by E. vermicola can infect Bursaphelenchus xylophilus. In the study, we aim to investigate the genes involved in the formation of the lunate conidia of E. vermicola CBS115803.

RESULTS

Esteya vermicola CBS115803 yielded 95% lunate conidia on the complete medium (CM) and 86% bacilloid conidia on the minimal medium (MM). Transcriptomic analysis of conidia from both media revealed a significant enrichment of differentially expressed genes in the pathway related to 'cellular amino acid biosynthesis and metabolism'. Functional assessment showed that the knockout of two arginine biosynthesis genes (EV232 and EV289) resulted in defects in conidia germination, mycelial growth, lunate conidia formation, and virulence of E. vermicola CBS115803 in Bursaphelenchus xylophilus. Remarkably, the addition of arginine to the MM improved mycelial growth, conidiation and lunate conidia formation in the mutants and notably increased conidia yield and the lunate conidia ratio in the wild-type E. vermicola CBS115803.

CONCLUSION

This investigation confirms the essential role of two arginine biosynthesis genes in lunate conidia formation in E. vermicola CBS115803. The findings also suggest that the supplementation of arginine to the culture medium can enhance the lunate conidia yield. These insights contribute significantly to the application of E. vermicola CBS115803 in managing Bursaphelenchus xylophilus infections. © 2023 Society of Chemical Industry.

Discovery of Trifluorobutene Amide Derivatives as Potential Nematicides: Design, Synthesis, Nematicidal Activity Evaluation, SAR, and Mode of Action Study

Plant-parasitic nematodes are one of the major threats to crop protection. However, only limited nematicides are currently available and are confronted with a growing resistance problem, which necessitates the development of novel nematicides. In this study, a series of trifluorobutene amide derivatives was synthesized through the strategy of amide bond reversal, and their nematicidal activity against Meloidogyne incognita was evaluated. The bioassay showed that compounds C2, C10, and C18 and some analogues thereof exhibited good nematicidal activity. Among them, the derivatives of compound C2 containing a benzene ring [C26 (R = 2-CH3) and C33 (R = 2-Cl)] exhibited excellent bioactivity against M. incognita in vitro. The LC50/72h values reached 14.13 and 14.71 mg·L-1, respectively. Moreover, analogues of compounds C10 and C18 containing a thiophene ring [C43 (R = 5-CH3), C44 (R = 4-CH3), and C50 (R = 5-Cl)] exhibited significant bioactivity against M. incognita in vivo with inhibition rates of 68.8, 65.5, and 69.8% at 2.5 mg·L-1 in a matrix, respectively. Meanwhile, C44 and C50 also showed excellent control effects against M. incognita in both cups and microplots. The structure-activity relationship (SAR) of synthesized compounds was discussed in detail. Comparative molecular field analysis (CoMFA) was also conducted to develop the SAR profile. The preliminary mode of action investigation showed that compound C33 exhibited strong inhibition on egg hatching, motility, feeding behavior, and growth of Caenorhabditis elegans. At the same time, the impact of active compounds on biochemical indicators related to oxidative stress showed that compound C33 influenced the production of ROS (reactive oxygen species), and the accumulation of lipofuscin and lipids on C. elegans.

Design, Synthesis, Nematicidal Activity, and Mechanism of Novel Amide Derivatives Containing an 1,2,4-Oxadiazole Moiety

To discover new nematicides, a series of novel amide derivatives containing 1,2,4-oxadiazole were designed and synthesized. Several compounds showed excellent nematicidal activity. The LC50 values of compounds A7, A18, and A20-A22 against pine wood nematode (Bursaphelenchus xylophilus), rice stem nematode (Aphelenchoides besseyi), and sweet potato stem nematode (Ditylenchus destructor) were 1.39-3.09 mg/L, which were significantly better than the control nematicide tioxazafen (106, 49.0, and 75.0 mg/L, respectively). Compound A7 had an outstanding inhibitory effect on nematode feeding, reproductive ability, and egg hatching. Compound A7 effectively promoted the oxidative stress of nematodes and caused intestinal damage to nematodes. Compound A7 significantly inhibited the activity of succinate dehydrogenase (SDH) in nematodes, leading to blockage of electron transfer in the respiratory chain and thereby hindering the synthesis of adenosine triphosphate (ATP), which consequently affects the entire oxidative phosphorylation process to finally cause nematode death. Therefore, compound A7 can be used as a potential SDH inhibitor in nematicide applications.

Rearing and Conservation of Nematode Populations Under Greenhouse or Axenic Conditions

Once a nematode has been identified, to conduct studies for screening programs or pathogenicity tests, it is necessary a supply of large numbers of nematodes from field crops or reproduced and stored to be used in periods of the year when they are not available from fields. Therefore, nematodes must be reared in greenhouse or under in vitro conditions and stored for future needs. In this chapter, suggestions are given on how to obtain nematodes from fields and reproduce most of them on host plants in greenhouse (mainly Meloidogyne spp. and Globodera spp.) or in vitro. Reproductions in vitro include: On suitable callus of host plants (Pratylenchus spp., Ditylenchus spp.) On fungal cultures mainly of Botrytis cinerea or Alternaria spp. for Aphelenchoides spp. and other aphelenchids, including Bursaphelenchus xylophilus. On carrot disks for Pratylenchus spp. and Ditylenchus spp. Other specific media, such as garlic, potato, and sweet potato for D. destructor, and cocoyam disks for Radopholus similis. Guidelines are also given to store different nematodes for rather long times, including in vitro methods and in infected seeds, hay, and other plant parts. No information is given on how to prepare and store fixed materials.

Detection of the Effects of Root Exudates (Diffusates) on Nematode Hatching and Attraction

Plant-parasitic nematodes have enormous economic and social impacts. The majority of plant-parasitic nematodes are soil dwelling and feed on plant roots. Exudates from actively growing roots initiate hatch of some nematode species, thus ensuring infective juveniles emerge in close proximity to host plant roots. Several gradients of volatile and non-volatile compounds are established around plant roots, at least some of which are used by nematodes to orientate toward the roots. Plant-parasitic nematodes are microscopic in size (less than 1 mm in length and between 15 and 20 μm in diameter), so investigations into behavior are challenging. Various in vitro techniques have been used to evaluate the effects of root exudates. The techniques can also be used to evaluate the comparative attractiveness of different plants or cultivars of the same plant species. This chapter describes some examples of different types of basic in vitro assays.

Detection of Resistance, Susceptibility, Tolerance, and Virulence in Plant-Nematode Interactions: Part II: Migratory and Semi-endoparasitic Nematodes

This chapter is a continuation of Chap. 3 . Initially, protocols for the screening of several host plants to their major migratory and semi-endoparasitic nematodes are presented. Then the problems related to assessment of tolerance to these nematodes are described, followed by the determination of nematode races. The main plant-nematode interactions considered are annuals and perennials to Pratylenchus spp.; banana to Radopholus similis; potato to Nacobbus aberrans; several crop plants, including onion, alfalfa, clovers, and potato, to Ditylenchus dipsaci; broad bean to D. giga; potato and sweet potato to D. destructor; peanut to D. africanus; rice to D. angustus and Aphelenchoides besseyi; wheat to Anguina tritici; different plants to Rotylenchulus reniformis; and citrus to Tylenchulus semipenetrans. Schemes to identify races or biotypes are only presented for D. dipsaci and T. semipenetrans. The occurrence of pathotypes in other nematode species is also discussed. Finally, comments are made on ectoparasitic nematodes.

Sampling and Extraction of Plant Parasitic Nematodes

The study of nematodes requires availability of nematode specimens and their population densities in plants and soil. This can be achieved using adequate sampling schemes and extraction methods. In this chapter, the most common and suitable sampling and extraction procedures and equipment are described. These include the use of Baermann's funnels, Cobb's decanting and sieving, floating methods such as the Oostenbrink method and Fenwick can, elutriators such as Seinhorst methods, centrifugation methods including that of Coolen, and mechanical and enzymatic maceration. The combination of different methods for cleaning the nematode suspensions is described, such as Cobb's sieving with Baermann's funnels or centrifugation, and for cysts combining Seinhorst's elutriator or Fenwick can with the alcohol methods. Methods for extraction of eggs and/or juveniles of cyst and egg mass forming nematodes, to be used as inoculum or to ascertain egg viability, are also described. Only little information is also noted on the use of molecular tools to identify and quantify nematode populations in soil and roots.

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.

Description of Aphelenchoides persicus sp. n. (Nematoda: Aphelenchoididae) from Iran

During a survey on the soil nematodes, a population of the genus Aphelenchoides was collected around the rhizosphere of persimmon in Guilan Province, Iran. The morphological and molecular characters confirmed the new species, namely A. persicus sp. n. The new species is characterized by a female body length (699-1068 μm), lip region offset from the rest of the body by a slight constriction, lateral fields with six incisures, stylet 12-13.5 μm long, with a clear basal swelling, excretory pore ca 1.5 metacorpal length posterior to base of the metacorpus, post uterine sac elongate, about 4-7 times than the vulval body diameter; conical female tail with a single centrally located mucron with tiny projection close to the tail tip, male body length (663-908 μm), and spicule well developed with rounded condylus, blunt conical rostrum, and a hook-like tip of dorsal limb. The new species belongs to the Group 2 category of Aphelenchoides species and was similar to seven known species with six lateral field incisures, including A. allius, A. chinensis, A. meghalayensis, A. nechaleos, A. paranechaleos, A. parasexlineatus, and A. sexlineatus. The molecular phylogeny based on 28S rDNA revealed that the new species stands close to A. hamospiculatus (MN931591; MN931592) and two unidentified Aphelenchoides (KY769057; LC583315). The measurements, line illustrations, LM photographs, and phylogenetic analysis are given for the new species.

Occurrence of Root-Knot Nematode (Meloidogyne spp.) on Peppers in Hainan, China, and M. enterolobii and M. incognita Resistance of Common Cultivars

Root-knot nematodes (Meloidogyne spp.) are the most economically damaging group of plant-parasitic nematodes. They are considered to be a major constraint of pepper (Capsicum annuum L.) crops worldwide. In China, Hainan Island is the main producer of pepper, where the climatic conditions and cropping patterns are favorable for infection by Meloidogyne spp. In this study, we conducted a detailed investigation of the occurrence, severity, and population distribution of root-knot nematodes infesting pepper throughout Hainan Island. We also tested the level of resistance to M. enterolobii and M. incognita of the common pepper cultivars in Hainan. Our results showed that root-knot nematodes belonging to M. enterolobii, M. incognita, and M. javanica were found in Hainan, and the dominant population was M. enterolobii, which is the predominant species in the tropical area. Notably, all the pepper cultivars in this study were highly susceptible to M. enterolobii, which is probably a reason for its rapid spread throughout Hainan. The pepper cultivars exhibited different levels of resistance to M. incognita. This study promotes the comprehensive understanding of the root-knot nematode distribution and host resistance level of Meloidogyne in Hainan, which will guide the effective control of root-knot nematodes.

Integrated Nematode Management in a World in Transition: Constraints, Policy, Processes, and Technologies for the Future

Plant-parasitic nematodes are one of the most insidious pests limiting agricultural production, parasitizing mostly belowground and occasionally aboveground plant parts. They are an important and underestimated component of the estimated 30% yield loss inflicted on crops globally by biotic constraints. Nematode damage is intensified by interactions with biotic and abiotic factors constraints: soilborne pathogens, soil fertility degradation, reduced soil biodiversity, climate variability, and policies influencing the development of improved management options. This review focuses on the following topics: (a) biotic and abiotic constraints, (b) modification of production systems, (c) agricultural policies, (d) the microbiome, (e) genetic solutions, and (f) remote sensing. Improving integrated nematode management (INM) across all scales of agricultural production and along the Global North-Global South divide, where inequalities influence access to technology, is discussed. The importance of the integration of technological development in INM is critical to improving food security and human well-being in the future.

Nematode-Suppressive Potential of Digestates to Meloidogyne incognita and Heterodera schachtii

Management of plant-parasitic nematodes uses host plant resistance, crop rotation, cultural methods, and nematicide applications. Host plant resistance is tedious to develop, and crop rotation and cultural methods are challenging to use. Environmental and human health concerns render sole reliance on chemical nematode suppression nonsustainable. Previously, digestate from anaerobically fermented maize silage suppressed Heterodera schachtii in Beta vulgaris crops. Here, seven digestates were investigated for nematode suppressive potential: liquid dairy manure digestate (LDMD), liquid dairy manure digestate with ammonia removed (LDMDA-), food waste digestate (FWD), liquid food waste digestate with ammonia removed (LFWDA-), liquid food waste digestate (LFWD), food waste hydrolysate from the Renewable Energy Anaerobic Digester (HREAD), and food waste hydrolysate from the South Area Transfer Station in Sacramento (HSATS). In a red radish (Raphanus sativus) bioassay with H. schachtii, digestates were amended at rates of 0.02, 0.11, 0.57, and 2.86 ml per 100 cm3 of soil. At a rate of 2.86 ml, all amendments except LDMDA- and LFWDA- significantly reduced juvenile root penetration compared with the infested control. In a greenhouse watermelon (Citrullus lanatus) bioassay with Meloidogyne incognita, amendments FWD, LFWD, HREAD, and HSATS as well as LDMD (less effectively) at 2.86 and 5.76 ml per 100 cm3 of soil significantly reduced egg masses per root system compared with the nontreated, nematode-infested control. In a microplot experiment with M. incognita and red radish, in the treatment amended with LFWD at 2.37 ml per 100 cm3 of soil, marketable yields were improved by approximately 50% over the nontreated control and were comparable with those in the treatment with the nematicide Reklemel. In a second microplot experiment with M. incognita and watermelon, treatments that contained LFWD at rates of 3.55 ml per 100 cm3 of soil had transient numerical effects of initial nematode suppression that were not maintained throughout the 3-month growth period. The results of these studies demonstrated that digestates FWD and LFWD consistently expressed some nematode-suppressive capacity.

Identification, Diversity, and Distribution of Meloidogyne spp. in Vegetable Fields of South Georgia, U.S.A

Root-knot nematode (RKN; Meloidogyne spp.) is the most prevalent plant-parasitic nematode in vegetable fields of Georgia, with an incidence of 67.3%. Because aggressive RKN species are reported in the southeastern United States, molecular-based identification of RKN species was conducted on soil samples taken from a nematode surveillance study in 2018 from 292 RKN-infested vegetable fields in southern Georgia. The RKN-infested soil was potted with tomato cultivar Rutgers, and individual nematode females were isolated from galled roots and subjected to species-specific PCR and mitochondrial haplotype-based RKN species identification. The incidence (%), mean, and maximum relative abundance (second-stage juveniles per 100 cm3 of soil) of the five RKN species identified consisted of M. incognita (91.9, 486, 14,144), M. arenaria (36.0, 707, 14,144), M. floridensis (2.2, 909, 5,264), M. javanica (5.5, 352, 1,488), and M. haplanaria (0.7, 8, 14). A large proportion of fields (29%) had mixed populations of M. incognita and M. arenaria, which may reflect the region's long history of cotton and peanut cultivation. For unknown reasons, mixed populations of M. incognita and M. arenaria were associated with higher population densities. M. incognita is the most important RKN species in vegetable fields, followed by M. arenaria; therefore, pure or mixed populations of these species should be addressed in nematode management programs. Although at a lower incidence, the newly detected species, M. floridensis and M. haplanaria, have the potential to become a major threat since they reproduce on vegetables with Mi-resistant genes.

Discovery of 1,2,4-Oxadiazole Derivatives Containing Haloalkyl as Potential Acetylcholine Receptor Nematicides

Plant-parasitic nematodes pose a serious threat to crops and cause substantial financial losses due to control difficulties. Tioxazafen (3-phenyl-5-thiophen-2-yl-1,2,4-oxadiazole) is a novel broad-spectrum nematicide developed by the Monsanto Company, which shows good prevention effects on many kinds of nematodes. To discover compounds with high nematocidal activities, 48 derivatives of 1,2,4-oxadiazole were obtained by introducing haloalkyl at the 5-position of tioxazafen, and their nematocidal activities were systematically evaluated. The bioassays revealed that most of 1,2,4-oxadiazole derivatives showed remarkable nematocidal activities against Bursaphelenchus xylophilus, Aphelenchoides besseyi, and Ditylenchus dipsaci. Notably, compound A1 showed excellent nematocidal activity against B. xylophilus with LC50 values of 2.4 μg/mL, which was superior to that of avermectin (335.5 μg/mL), tioxazafen (>300 μg/mL), and fosthiazate (436.9 μg/mL). The transcriptome and enzyme activity results indicate that the nematocidal activity of compound A1 was mainly related to the compound which affected the acetylcholine receptor of B. xylophilus.

Two Novel Bursaphelenchus xylophilus Kunitz Effector Proteins Using Different Infection and Survival Strategies to Suppress Immunity in Pine

Pine wilt disease, caused by Bursaphelenchus xylophilus, results in tremendous economic loss in conifer production every year. To disturb the host immune responses, plant pathogens secrete a mass of effector proteins that facilitate the infection process. Although several effectors of B. xylophilus have been identified, detailed mechanisms of their functions remain largely unexplored. Here, we reveal two novel B. xylophilus Kunitz effectors, named BxKU1 and BxKU2, using different infection strategies to suppress immunity in Pinus thunbergii. We found that both BxKU1 and BxKU2 could suppress PsXEG1-triggered cell death and were present in the nucleus and cytoplasm in Nicotiana benthamiana. However, they had different three-dimensional structures and various expression patterns in B. xylophilus infection. In situ hybridization experiments showed that BxKU2 was expressed in the esophageal glands and ovaries, whereas BxKU1 was only expressed in the esophageal glands of females. We further confirmed that the morbidity was significantly decreased in P. thunbergii infected with B. xylophilus when BxKU1 and BxKU2 were silenced. The silenced BxKU2I, but not BxKU1, affected the reproduction and feeding rate of B. xylophilus. Moreover, BxKU1 and BxKU2 targeted to different proteins in P. thunbergii, but they all interacted with thaumatin-like protein 4 (TLP4) according to yeast two-hybrid screening. Collectively, our study showed that B. xylophilus could incorporate two Kunitz effectors in a multilayer strategy to counter immune response in P. thunbergii, which could help us better understand the interaction between plant and B. xylophilus.

Discovery of quinazoline compound as a novel nematicidal scaffold

With the aim of discovering novel nematicidal scaffolds, the nematicidal activities of a series of quinazoline compounds were tested, with some compounds showing excellent results. Among them, the LC₅₀ values of compound K11 against Bursaphelenchus xylophilus, Aphelenchoides besseyi, and Ditylenchus destructor were 7.33, 6.09, and 10.95 mg/L, respectively. In addition, the nematicidal activity of compound K11 against Meloidogyne incognita was 98.77% at 100 mg/L. Compound K11 not only increased the production of reactive oxygen species and the accumulation of lipofuscin and lipids in nematodes, but it also attenuated nematode pathogenicity by reducing the nematodes' antioxidant capacity. Transcriptomic analysis showed that compound K11 had significant effects on fatty acid degradation, metabolic pathways, and the differentially expressed genes related to redox processes in nematodes. Furthermore, the expression levels of the corresponding differentially expressed genes were verified using real-time quantitative polymerase chain reaction. Quinazoline can be used as a new nematicidal scaffold, and it is expected that more work will be done on the discovery of novel nematicides based on the lead compound K11 in the future.

Silicon Mediated Plant Immunity against Nematodes: Summarizing the Underline Defence Mechanisms in Plant Nematodes Interaction

Silicon (Si) is known to stimulate plant resistance against different phytopathogens, i.e., bacteria, fungi, and nematodes. It is an efficient plant growth regulator under various biotic and abiotic stresses. Silicon-containing compounds, including silicon dioxide, SiO₂ nanoparticles (NPs), nano-chelated silicon fertilizer (NCSF), sodium siliconate, and sodium metasilicate, are effective in damaging various nematodes that reduce their reproduction, galling, and disease severity. The defence mechanisms in plant-nematodes interaction may involve a physical barrier, plant defence-associated enzyme activity, synthesis of antimicrobial compounds, and transcriptional regulation of defence-related genes. In the current review, we focused on silicon and its compounds in controlling plant nematodes and regulating different defence mechanisms involved in plant-nematodes interaction. Furthermore, the review aims to evaluate the potential role of Si application in improving plant resistance against nematodes and highlight its need for efficient plant-nematodes disease management.

Elucidation of the nematicidal mode of action of grammicin on Caenorhabditis elegans

Grammicin (Gra) is derived from the endophytic fungus Xylaria grammica EL000614 and shows nematicidal activity against the devastating root-knot nematode Meloidogyne incognita in-vitro, in planta, and in-field experiments. However, the mechanism of the nematicidal action of Gra remains unclear. In this study, Gra exposure to the model genetic organism Caenorhabditis elegans affected its L1, L2/3, L4, and young adult stages. In addition, Gra treatment increased the intracellular reactive oxygen species (ROS) levels of C. elegans and M. incognita. Molecular docking interaction analysis indicated that Gra could bind and interact with GCS-1, GST-4, and DAF-16a in order of low binding energy, followed by SOD-3, SKN-1, and DAF-16b. This implies that the anthelmintic action of Gra is related to the oxidative stress response. To validate this mechanism, we examined the expression of the genes involved in the oxidative stress responses following treatment with Gra using transgenic C. elegans strains such as the TJ356 strain zIs356 [daf-16p::daf-16a/b::GFP + rol-6 (su1006)], LD1 ldIs7 [skn-1p::skn-1b/c::GFP + rol-6 (su1006)], LD1171 ldIs3 [gcs-1p::GFP + rol-6 (su1006)], CL2166 dvIs19 [(pAF15) gst-4p::GFP::NLS], and CF1553 strain muIs84 [(pAD76) sod-3p::GFP + rol-6 (su1006)]. Gra treatment caused nuclear translocation of DAF-16/FoxO and enhanced gst-4::GFP expression, but it had no change in sod-3::GFP expression. These results indicate that Gra induces oxidative stress response via phase II detoxification without reduced cellular redox machinery. Gra treatment also inhibited the nuclear localization of SKN-1::GFP in the intestine, which may lead to a condition in which oxidative stress tolerance is insufficient to protect C. elegans by the inactivation of SKN-1, thus inducing nematode lethality. Furthermore, Gra caused the mortality of two mutant strains of C. elegans, CB113 and DA1316, which are resistant to aldicarb and ivermectin, respectively. This indicates that the mode of action of Gra is different from the traditional nematicides currently in use, suggesting that it could help develop novel approaches to control plant-parasitic nematodes.

The α2δ Calcium Channel Subunit Accessorily and Independently Affects the Biological Function of Ditylenchus destructor

The α2δ subunit is a high-voltage activated (HVA) calcium channel (Cav1 and Cav2) auxiliary subunit that increases the density and function of HVA calcium channels in the plasma membrane of mammals. However, its function in plant parasitic nematodes remains unknown. In this study, we cloned the full-length cDNA sequence of the voltage-gated calcium channel (VGCC) α2δ subunit (named DdCavα2δ) in Ditylenchus destructor. We found that DdCavα2δ tends to be expressed in the egg stage, followed by the J3 stage. RNA-DIG in situ hybridization experiments showed that the DdCavα2δ subunit was expressed in the body wall, esophageal gland, uterus, post uterine, and spicules of D. destructor. The in vitro application of RNA interference (RNAi) affected the motility, reproduction, chemotaxis, stylet thrusting, and protein secretion of D. destructor to different degrees by targeting DdCα1D, DdCα1A, and DdCavα2δ in J3 stages, respectively. Based on the results of RNAi experiments, it was hypothesized that L-type VGCC may affect the motility, chemotaxis, and stylet thrusting of D. destructor. Non-L-type VGCC may affect the protein secretion and reproduction of D. destructor. The DdCavα2δ subunit gene also affected the motility, chemotaxis, and reproduction of D. destructor. These findings reveal the independent function of the VGCC α2δ subunit in D. destructor as well as give a theoretical foundation for future research on plant parasitic nematode VGCC.

Distribution, Ecological Factors, Molecular Diversity, and Specific PCR for Major Species of Pin Nematodes (Paratylenchus spp.) in Prunus Plantations in Spain

This study aimed to evaluate the prevalence and distribution of Paratylenchus species in the main areas of Prunus spp. production in Spain, their ecological constraints, and new molecular tools for the specific identification of major species. Pin nematodes are recognized as plant-parasitic nematodes with a wide host range and global distribution. Therefore, understanding the environmental and agronomic factors involved in their distribution is critical to design environmental and sustainable management strategies to reduce plant damage. A total of 219 sampling sites were surveyed and 12 Paratylenchus species were identified based on an integrative taxonomic approach (P. baldaccii, P. enigmaticus, P. goodeyi, P. hamatus, P. holdemani, P. indalus, P. israelensis, P. pedrami, P. tateae, P. tenuicaudatus, P. veruculatus, and P. zurgenerus). The most common pin nematode was P. hamatus, followed by P. tenuicaudatus. Nematode abundance was influenced by climatic characteristics, soil chemical properties, and agronomic management practices. Nine explanatory variables were selected as the most strongly associated with Paratylenchus distribution. Specifically, P. tenuicaudatus was significantly correlated with soil chemical characteristics, such as pH and carbon, sulfur, and sodium content, whereas P. goodeyi was closely related to fields with <10 years of almond cultivation. Species-specific PCRs were developed for P. hamatus and P. tenuicaudatus and their validity was evaluated studying the molecular variability of these species and against other Paratylenchus species.

Feeding Selectivity of Aphelenchoides besseyi and A. pseudogoodeyi on Fungi Associated with Florida Strawberry

Aphelenchoides besseyi and A. pseudogoodeyi are foliar nematodes associated with commercial strawberry production in Florida, United States. The reproductive and feeding habits of these two nematode species were assessed on Florida isolates of the fungi Botrytis cinerea, Colletotrichum gloeosporioides, Macrophomina phaseolina, and Neopestalotiopsis rosae, which are pathogenic to strawberry, and nonpathogenic isolates of Fusarium oxysporum and Monilinia fructicola grown on potato dextrose agar in Petri dishes. Each culture was inoculated with six specimens of mixed life stages of A. besseyi or A. pseudogoodeyi and incubated at 24°C under axenic and nonaxenic conditions 23 and 31 days after inoculation, respectively. A. besseyi reproduction rates were greater on strawberry-pathogenic isolates of B. cinerea, C. gloeosporioides, and N. rosae than on the nonpathogenic isolates of F. oxysporum and M. fructicola. In contrast, reproductive rates of A. pseudogoodeyi did not vary among fungi cultures. For both nematode species, M. phaseolina was a poor host because it did not produce mycelium on the media used. Our findings indicate that A. besseyi is more selective in its fungal-feeding preference than A. pseudogoodeyi. Additionally, A. pseudogoodeyi eggs and juveniles were significantly more numerous than adults. Yet, for A. besseyi, adult stages were more abundant. Fungi aid in the maintenance of soil-dwelling populations of these two nematode species. Removing fungus-infected strawberry plant residues is both a desirable and effective management practice to limit A. besseyi in central Florida commercial strawberry fields.

Aphelenchoides besseyi Parasitizing Cowpea (Vigna unguiculata) in Brazil

Several species of nematodes are known to cause losses to cowpea (Vigna unguiculata) throughout the world. In Brazil, Aphelenchoides besseyi was described as causing damage on soybean, cotton, and common bean, but no report was found about the parasitism of this nematode in cowpea. This study aimed to verify the host reaction of cowpea cultivars to A. besseyi. The experiment was conducted under greenhouse conditions, using two A. besseyi populations as inocula, obtained from symptomatic soybean and cotton plants collected in naturally infested fields. Cultivars Imponente, Aracê, Guariba, Tumucumaque, Nova Era, and Tracuateua were inoculated with 500 A. besseyi of each population, separately, into soil, and after 30 days from the inoculation nematodes were extracted from shoot systems. Both populations were able to parasitize all the cowpea cultivars. Independently of the cultivar, cowpea plants exhibited symptoms of leaf deformation similar to those described for soybean, cotton, and common bean and, in addition, severe brooming was observed, with the interior of the stems being porous and necrotic. To our knowledge, this is the first report of parasitism by A. besseyi of cowpea in Brazil, under greenhouse conditions, increasing the list of hosts of this nematode.

Diversity of plant parasitic nematodes characterized from fields of the French national monitoring programme for the Columbia root-knot nematode

Plant parasitic nematodes are highly abundant in all agrosystems and some species can have a major impact on crop yields. To avoid the use of chemical agents and to find alternative methods to manage these pests, research studies have mainly focused on plant resistance genes and biocontrol methods involving host plants or natural enemies. A specific alternative method may consist in supporting non-damaging indigenous species that could compete with damaging introduced species to decrease and keep their abundance at low level. For this purpose, knowledge about the biodiversity, structure and functioning of these indigenous communities is needed in order to carry out better risk assessments and to develop possible future management strategies. Here, we investigated 35 root crop fields in eight regions over two consecutive years. The aims were to describe plant parasitic nematode diversity and to assess the potential effects of cultivation practices and environmental variables on communities. Community biodiversity included 10 taxa of plant parasitic nematodes. Despite no significant abundance variations between the two sampling years, structures of communities varied among the different regions. Metadata collected for the past six years, characterizing the cultural practices and soils properties, made it possible to evaluate the impact of these variables both on the whole community and on each taxon separately. Our results suggest that, at a large scale, many variables drive the structuration of the communities. Soil variables, but also rainfall, explain the population density variations among the geographical areas. The effect of the variables differed among the taxa, but fields with few herbicide applications and being pH neutral with low heavy metal and nitrogen concentrations had the highest plant parasitic nematode densities. We discuss how these variables can affect nematode communities either directly or indirectly. These types of studies can help to better understand the variables driving the nematode communities structuration in order to support the abundance of indigenous non-damaging communities that could compete with the invasive species.

A Bursaphelenchus xylophilus pathogenic protein Bx-FAR-1, as potential control target, mediates the jasmonic acid pathway in pines

BACKGROUND

The pine wilt disease (PWD) caused by Bursaphelenchus xylophilus is a devastating forest disease and its pathogenesis remains unclear. Secreted enzymes and proteins are important pathogenicity determinants and Bx-FAR-1 is an important pathogenic protein involved in the interaction between pine and B. xylophilus. However, the function of the Bx-FAR-1 protein in monitoring and prevention PWD remains unknown.

RESULTS

We found a small peptide of B. xylophilus effector Bx-FAR-1 is sufficient for immunosuppression function in Nicotiana benthamiana. Transient expression of Bx-FAR-1 in N. benthamiana revealed that nuclear localization is required for its function. The results of the ligand binding test showed that Bx-FAR-1 protein had the ability to bind fatty acid and retinol. We demonstrated that Bx-FAR-1 targeted to the nuclei of Pinus thunbergii using the polyclonal antibody by immunologic approach. The content of jasmonic acid (JA) was significantly increased in P. thunbergii infected with B. xylophilus when Bx-FAR-1 was silenced. We identified an F-box protein as the host target of Bx-FAR-1 by yeast two-hybrid and co-immunoprecipitation. Moreover, we found that Pt-F-box-1 was up-regulated during B. xylophilus infection and the expression of Pt-F-box-1 was increased in Bx-FAR-1 double-stranded RNA (dsRNA)-treated host pines.

CONCLUSION

This study illustrated that Bx-FAR-1 might mediate the JA pathway to destroy the immune system of P. thunbergii, indicating that PWN likely secretes effectors to facilitate parasitism and promote infection, which could better reveal the pathogenesis mechanisms of B. xylophilus and would be beneficial for developing disease control strategies.

The Bursaphelenchus xylophilus effector BxML1 targets the cyclophilin protein (CyP) to promote parasitism and virulence in pine

BACKGROUND

Bursaphelenchus xylophilus is the causal agent of pine wilt disease (PWD) that has caused enormous ecological and economic losses in China. The mechanism in the interaction between nematodes and pine remains unclear. Plant parasitic nematodes (PPNs) secrete effectors into host plant tissues. However, it is poorly studied that role of effector in the infection of pine wood nematode (PWN).

RESULTS

We cloned, characterized and functionally validated the B. xylophilus effector BxML1, containing an MD-2-related lipid-recognition (ML) domain. This protein inhibits immune responses triggered by the molecular pattern BxCDP1 of B. xylophilus. An insitu hybridization assay demonstrated that BxML1 was expressed mainly in the dorsal glands and intestine of B. xylophilus. Subcellular localization analysis showed the presence of BxML1 in the cytoplasm and nucleus. Furthermore, number of B. xylophilus and morbidity of pine were significantly reduced in Pinus thunbergii infected with B. xylophilus when BxML was silenced. Using yeast two-hybrid (Y2H) and coimmunoprecipitation (CoIP) assays, we found that the BxML1 interacts with cyclophilin protein PtCyP1 in P. thunbergii.

CONCLUSIONS

This study illustrated that BxML1 plays a critical role in the B. xylophilus-plant interaction and virulence of B. xylophilus.

Observations on the Population Genetic Structure of the Leaf Galling Nematode, Ditylenchus gallaeformans

Ditylenchus gallaeformans is a plant parasitic nematode that induces galls on aboveground parts of Melastomataceae plants. It differs from most gall-inducing nematodes in that it is not an endoparasite and has been considered as a possible biological control agent against invasive species of Miconia. Little is known about D. gallaeformans biology, genetic differences among populations, and host preferences. This study examined the genetic differences among D. gallaeformans populations from different locations and host species and the phylogenetic relationships among them. Nematodes were collected from galls in plants from Costa Rica, Dominica, and Trinidad. The Cytochrome c oxidase 1 (cox1) region was sequenced from a total of 33 individual nematodes isolated from 33 different plant individuals, representing 21 species of Melastomataceae. Phylogenetic reconstructions, haplotype networks, and analysis of molecular variance showed that the species is monophyletic and has three major clades, which were mostly consistent with geographic location but not with host species. The first clade was composed by two subclades, one with individuals from Costa Rica and one with individuals from Dominica. The second and third clades comprised nematodes only from Trinidad. Overall, there is no evidence of host-species specialization in D. gallaeformans. Biocontrol efforts using the nematode against invasive Miconia could focus on geographical location matching but likely will not need to match host species.

Toward Chemical Ecology of Plant-Parasitic Nematodes: Kairomones, Pheromones, and Other Behaviorally Active Chemical Compounds

An overview of natural chemical compounds involved in plant-parasitic nematode (PPN) behavior is presented and classified following a system accepted by chemoecologists. Kairomonal and other egg-hatching stimulants, as well as attractants for juveniles, are presented. Sex, aggregation, egg-hatching, and putative diapause PPN pheromones are analyzed and grouped into clusters of primers and releasers. The role of over 500 chemical compounds, both organic and inorganic, involved in PPN behavior is reviewed, with the most widely analyzed and least studied fields of PPN chemical ecology indicated. Knowledge on PPN chemical ecology facilitates environmentally friendly integrated pest management. This could be achieved by disrupting biointeractions between nematodes and their host plants and/or between nematodes. Data on biologically active chemicals reveals targets for resistant plant selection, including through application of gene silencing techniques.

Development of chitosan-coated nanoemulsions of two sulfides present in onion (Allium cepa) essential oil and their nematicidal activities against the pine wood nematode, Bursaphelenchus xylophilus

Pine wood nematode, Bursaphelenchus xylophilus, is a plant parasitic nematode which causes severe damage to several Pinus species. Two natural compounds, dipropyl trisulfide (DPTS) and methyl propyl trisulfide (MPTS), showed strong nematicidal activity against the pine wood nematode, presenting 4.24 and 17.81 μg/mL LC₅₀ values, respectively. However, hydrophobicity and low stability have limited their practical use in the field as nematicides. To overcome these problems, chitosan-coated nanoemulsions of DPTS and MPTS were developed. The optimum chitosan concentration for the delivery system of the two sulfides was 0.5%. Optimized chitosan-coated nanoemulsions of sulfides have a uniform size distribution (mean diameter = 203.7 and 207.7 nm, mean polydispersity index = 0.176 and 0.178) with sufficient colloidal stability (mean zeta potential = +40 and +45 mV). The LC₅₀ values of DPTS and MPTS nanoemulsions coated with 0.5% chitosan against the pine wood nematode were 5.01 and 16.60 μg/mL, respectively. In addition, chitosan coating improved the long-term storage stability and persistence of nematicidal activity of the nanoemulsions. This study indicates that the chitosan-coated nanoemulsion is a suitable formulation for sulfides as novel nematicides against the pine wood nematode for field application.

A novel pine wood nematode effector, BxSCD1, suppresses plant immunity and interacts with an ethylene-forming enzyme in pine

The plant-parasitic nematode Bursaphelenchus xylophilus, the causal agent of pine wilt disease (PWD), causes enormous economic loss every year. Currently, little is known about the pathogenic mechanisms of PWD. Several effectors have been identified in B. xylophilus, but their functions and host targets have yet to be elucidated. Here, we demonstrated that BxSCD1 suppresses cell death and inhibits B. xylophilus PAMP BxCDP1-triggered immunity in Nicotiana benthamiana and Pinus thunbergii. BxSCD1 was transcriptionally upregulated in the early stage of B. xylophilus infection. In situ hybridization experiments showed that BxSCD1 was specifically expressed in the dorsal glands and intestine. Cysteine residues are essential for the function of BxSCD1. Transient expression of BxSCD1 in N. benthamiana revealed that it was primarily targeted to the cytoplasm and nucleus. The morbidity was significantly reduced in P. thunbergii infected with B. xylophilus when BxSCD1 was silenced. We identified 1-aminocyclopropane-1-carboxylate oxidase 1, the actual ethylene-forming enzyme, as a host target of BxSCD1 by yeast two-hybrid and coimmunoprecipitation. Overall, this study illustrated that BxSCD1 played a critical role in the B. xylophilus-plant interaction.

Nematicidal activity of teleocidin B4 isolated from Streptomyces sp. against pine wood nematode, Bursaphelenchus xylophilus

BACKGROUND

Pine wilt disease (PWD) is a plant disease that causes serious damage to pine trees. PWD occurs when the host plant is infected with pinewood nematode (PWN), Bursaphelenchus xylophilus. In this study, a compound with nematicidal activity was isolated from actinomycetes and its efficacy was investigated in vitro.

RESULT

We screened and selected Streptomyces sp. 680560, which had nematicidal activity against B. xylophilus. Based on 16S rRNA sequence analysis, it showed 99.93% similarity with Streptomyces blastmyceticus NRRB-5480^T . Furthermore, the active compound was isolated and identified as teleocidin B4. Teleocidin B4 at concentrations ranging from 6.25 to 100 μM had low nematicidal activity after 24 and 36 h against adult and stage juveniles (J2) of B. xylophilus, but after 48 h nematicidal activity exceeded 95%. The rate of inhibition of egg hatching for Teleocidin B4 6.25, 12.5, 25, 50, and 100 μM was confirmed to be dose-dependently inhibited after 48 h of treatment. Teleocidin B4 is not only toxic to hatched B. xylophilus, but also affects egg hatching.

CONCLUSION

This study was carried out to isolate actinomycete metabolites from pine tree endophytes from various natural environments for control of PWD. A compound with nematicidal activity was isolated from a selected strain and its structure was identified as teleocidin B4. The nematicidal effect of the isolated active substance, teleocidin B4, was confirmed. This is the first report of the effect of teleocidin B4 on B. xylophilus, suggesting its possibility as a PWD control agent. © 2020 Society of Chemical Industry.

Aphelenchoides besseyi Parasitizing Common Bean in Brazil

Aphelenchoides besseyi is the causal agent of soybean green stem and foliar retention syndrome known as "Soja Louca II." This nematode has recently been reported parasitizing cotton in Brazil. In Costa Rica, it causes the symptoms known as "amachamiento" and false angular spots in common bean (Phaseolus vulgaris). Due to the great importance of beans to Brazilian agriculture, the objective of this research was to study the pathogenicity of A. besseyi in common bean under greenhouse conditions, including its endoparasitic relationships by staining root and shoot system tissues with fuchsin acid. In addition, A. besseyi was collected and quantified from shoot systems 30 days after inoculation by washing the tissue in water and blender centrifugal flotation. We observed the symptoms of amachamiento, leaf and vein deformation in the expanded trifoliate leaves, and also leaves with necrotic, brown to reddish and angular lesions, characteristics from false angular spot, and deformed stems characterized by enlargement of nodes, retortions, and necrotic lesions. High numbers of nematodes were found inside common bean plants. This is the first report of the pathogenicity and symptoms caused by A. besseyi in common bean in Brazil. These findings are important for development of management strategies to avoid losses on bean cropped in infested areas.

Nematotoxicity of a Cyt-like protein toxin from Conidiobolus obscurus (Entomophthoromycotina) on the pine wood nematode Bursaphelenchus xylophilus

BACKGROUND

The pine wood nematode Bursaphelenchus xylophilus is a destructive pest on Pinus trees and lacks effective control measures. The present study identified a novel nematotoxic cytolytic (Cyt)-like protein originating from the entomopathogenic fungus Conidiobolus obscurus.

RESULTS

The protein was successfully purified using heterologous expression in Escherichia coli and affinity chromatography. N-hydroxysuccinimide-rhodamine-labeled Cyt-like protein was used to establish the route of toxin uptake, and revealed that the toxin can enter the nematode via the stylet. In bioassays, the purified protein had high nematicide activity against B. xylophilus, with a median lethal concentration at 24 h of 15.8 and 29.4 μg mL^-1 for juveniles and adults, respectively. Compared with the deionized water control, fecundity, thrashing, and egg hatching were significantly reduced by 97%, 98%, and 83%, respectively, with 40 μg mL^-1 Cyt-like protein at 24-36 h. Staining with Oil-Red-O showed a decrease in large lipid droplet formation in the protein-treated adult nematodes.

CONCLUSION

The Cyt-like protein toxin possesses high nematicide activity against B. xylophilus with effects on nematode vitality and fecundity. The potential exists to use the Cyt-like protein for the control of B. xylophilus.

Esteya floridanum sp. nov.: An Ophiostomatalean Nematophagous Fungus and Its Potential to Control the Pine Wood Nematode

The nematophagous fungal genus Esteya is reported as a natural enemy of the pine wood nematode Bursaphelenchus xylophilus, which causes pine wilt in Asia and Europe. During a survey of fungi associated with ambrosia beetles in Florida, an undescribed Esteya species was found. A phylogenetic analysis based on nuclear large subunit and β-tubulin DNA sequences supported this isolate as a new species, E. floridanum. Morphological and phylogenetic characteristics and a species description are provided here. The fungus was observed to kill the pine wood nematode in vitro. To evaluate the ability of E. floridanum to protect trees against the pine wood nematode in vivo, the effect of prophylactic inoculation was tested on Pinus koraiensis and Larix olgensis in Liaoning, China. The results suggest that the fungus is not a plant pathogen and that it delays wilt and postpones death of two conifer trees. This presents a potential new avenue for research on biocontrol of pine wilt disease and stresses the value of research on pest organisms in their native regions.

Chia: Host Status for Meloidogyne incognita and Activity of Plant Extracts

Chia (Salvia hispanica L.) seeds are used for food, drinks, oil, and animal feed, and all plant parts are employed in traditional medicine. The growing demand for the seed has created a need for improved disease management. Plant-parasitic nematodes have been found on other Salvia spp., but none have been reported from S. hispanica. Chia has also not been tested for production of compounds active against these nematodes. Therefore, aqueous extracts from shoots and roots of six chia lines, Brad's Organic, Cono, E2, G3, G5, and W13.1, were tested in laboratory assays. Some concentrations of all extracts were nematotoxic, killing about one-third of Meloidogyne incognita (Kofoid & White) Chitwood second-stage juveniles (J2s) in shoot extracts and up to nearly half of J2s in root extracts. Hatch was generally not affected by the extracts. In greenhouse trials, all six chia lines were hosts of M. incognita. Chia line G3 had approximately two times or more eggs per gram of root than Brad's Organic or Cono. When cucumber seedlings were transplanted into soil amended with chopped chia shoots (2.3 or 2.5% weight of fresh shoots/weight of dry soil), galling and egg production on cucumber roots were not suppressed. To our knowledge, this is the first report that chia is a host to M. incognita (or any phytoparasitic nematode) and that chia shoots and roots produce compounds active against a nematode.

Autophagy contributes to resistance to the oxidative stress induced by pine reactive oxygen species metabolism, promoting infection by Bursaphelenchus xylophilus

BACKGROUND

Autophagy plays an important role in eukaryotes. We investigated its role in the pine wood nematode (PWN), Bursaphelenchus xylophilus, the causative agent of pine wilt disease (PWD), to find promising control strategies against PWD.

RESULTS

We analysed the expression levels of PtRBOH1 and PtRBOH2, which regulate reactive oxygen species (ROS) metabolism, in Pinus thunbergii and the expression of three autophagy genes, BxATG5, BxATG9 and BxATG16, in PWN by quantitative reverse transcription-polymerase chain reaction (qRT-PCR), and measured the content of H₂ O₂ , the main product of ROS metabolism, in pine stem. There was a correlation between the expression of autophagy genes in PWN and pine ROS metabolism during early infection. We also found that oxidative stress induces autophagy in PWN according to qRT-PCR, transmission electron microscopy and Western blot analyses. Inhibition of autophagy by 3-methyladenine or silencing of the autophagy genes BxATG9 and BxATG16 in PWN showed that autophagy is essential for feeding, fecundity, egg hatching and survival of PWN under oxidative stress, confirming the importance of autophagy in the antioxidant defences of PWN. Similarly, we demonstrated that autophagy contributes to the virulence of PWN. Moreover, PWN likely ameliorates oxidative damage by enhancing the activities of the peroxidase and catalase antioxidant pathways when autophagy is inhibited.

CONCLUSION

Autophagy contributes to resistance to the oxidative stress induced by pine ROS metabolism, thus promoting infection by PWN. Our findings clarify the defence mechanisms of PWN and the pathogenesis of PWD, and provide promising hints for control of PWD by blocking autophagy. © 2020 Society of Chemical Industry.

Directed energy system technology for the control of soilborne fungal pathogens and plant-parasitic nematodes

BACKGROUND

It is challenging to manage soilborne pathogens and plant-parasitic nematodes using sustainable practices. Here, we evaluated a novel energy application system, Directed Energy System (DES). This system generates pulses of energy capable of impacting selected biological organisms. The oomycete Phytophthora cinnamomi, the fungus Verticillium dahliae, and the plant-parasitic nematodes Meloidogyne hapla and Globodera ellingtonae were added to soil. Then DES-generated energy was applied to soil and impacts on target organisms were determined.

RESULTS

DES applied at 20, 40 and 70 J cm^-3 to P. cinnamomi and V. dahliae resulted in ≥50% and 92% reductions (respectively) of propagules per gram of soil in comparison to the untreated control. There was a significant reduction of M. hapla eggs per gram of host tomato root between the untreated control, and 2.2, 13 and 25 J cm^-3 DES dosages applied pre- or post-planting. Additionally, an 84% reduction in hatch from G. ellingtonae encysted eggs after treatment with 70 J cm^-3 DES was observed. The dosages ranged from 40 or 80V mm^-1 for nematodes to 200 V mm^-1 for fungi.

CONCLUSION

DES-generated energy reduced survival of the soilborne pathogens P. cinnamomi and V. dahlia, and the plant-parasitic nematodes M. hapla and G. ellingtonae. The application of this technology to a field setting remains to be considered. Published 2020. This article is a U.S. Government work and is in the public domain in the USA. Pest Management Science published by Wiley Periodicals, Inc. on behalf of © 2020 Society of Chemical Industry.

Transcriptomic profiling of effects of emamectin benzoate on the pine wood nematode Bursaphelenchus xylophilus

BACKGROUND

Emamectin benzoate (EB) has recently been successfully applied as a trunk injection for preventative control of the pine wilt disease (PWD) caused by Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle. Here, a whole-organism transcriptomic analysis provides comprehensive insights into the adverse effects of EB on B. xylophilus.

RESULTS

A large set of differentially expressed genes (DEGs) were found, demonstrating the antagonistic effects of EB on B. xylophilus embryonic and larval development, reproduction, nervous and motor systems, and pathogenesis. In toxicity assays with EB, the number of eggs laid, hatching rate, thrashing frequency, and developmental rate of B. xylophilus were significantly suppressed at low concentrations (0.1 μg mL^-1 ). Moreover, the transcriptional changes validated by real-time quantitative PCR showed downregulated transcript levels of the genes encoding pectate lyases, β-1,4-endoglucanases, and upregulated the genes encoding glutamate-gated chloride channel, γ-aminobutyric acid type β receptor, uridine 5'-diphospho-glucuronosyl transferase, ATP-binding cassette transporter. The potential responses of B. xylophilus to EB included the upregulation of several genes putatively contributing to oocyte protection, stem cell renewal, and xenobiotic degradation, implying the potential for drug resistance to develop.

CONCLUSION

Our findings further our understanding of the effects of EB for managing the PWD and may help to improve the pesticide-use strategies for controlling B. xylophilus. © 2019 Society of Chemical Industry.

Spot drip application of dimethyl disulfide as a post-plant treatment for the control of plant parasitic nematodes and soilborne pathogens in grape production

BACKGROUND

Plant parasitic nematodes and soilborne pathogens can reduce the overall productivity in grape production. Not all grape growers apply soil fumigants before planting, and there is no single rootstock resistant to all nematode species. The aim of this investigation was to evaluate the effect of dimethyl disulfide (DMDS) applied at 112, 224, 448 and 897 kg ha(-1) as a post-plant treatment against soilborne plant parasitic nematodes and pathogens on the grape yield in established grapevines.

RESULTS

In microplot and field trials, post-plant fumigation with DMDS controlled citrus (Tylenchulus semipenetrans), root-knot (Meloidogyne spp.), pin (Paratylenchus spp.) and ring (Mesocriconema xenoplax) nematodes in established Thomson Seedless grapevines. However, DMDS did not control the soilborne pathogens Pythium ultimum and Fusarium oxysporum. No indications of phytotoxicity were detected after post-plant fumigation with DMDS. In the field trial, grape yield was significantly higher with the lowest DMDS rate, but no difference among other rates was observed in comparison with the untreated control.

CONCLUSION

Post-plant fumigation with DMDS controlled plant parasitic nematodes in established grapevines but was less efficacious against soilborne pathogens. Low rates of DMDS were sufficient for nematode control and increased the grape yield, probably without affecting beneficial soil organisms. Further research on evaluating the potential effect of DMDS against beneficial soil organisms is needed.

Searching for resistance genes to Bursaphelenchus xylophilus using high throughput screening

BACKGROUND

Pine wilt disease (PWD), caused by the pinewood nematode (PWN; Bursaphelenchus xylophilus), damages and kills pine trees and is causing serious economic damage worldwide. Although the ecological mechanism of infestation is well described, the plant's molecular response to the pathogen is not well known. This is due mainly to the lack of genomic information and the complexity of the disease. High throughput sequencing is now an efficient approach for detecting the expression of genes in non-model organisms, thus providing valuable information in spite of the lack of the genome sequence. In an attempt to unravel genes potentially involved in the pine defense against the pathogen, we hereby report the high throughput comparative sequence analysis of infested and non-infested stems of Pinus pinaster (very susceptible to PWN) and Pinus pinea (less susceptible to PWN).

RESULTS

Four cDNA libraries from infested and non-infested stems of P. pinaster and P. pinea were sequenced in a full 454 GS FLX run, producing a total of 2,083,698 reads. The putative amino acid sequences encoded by the assembled transcripts were annotated according to Gene Ontology, to assign Pinus contigs into Biological Processes, Cellular Components and Molecular Functions categories. Most of the annotated transcripts corresponded to Picea genes-25.4-39.7%, whereas a smaller percentage, matched Pinus genes, 1.8-12.8%, probably a consequence of more public genomic information available for Picea than for Pinus. The comparative transcriptome analysis showed that when P. pinaster was infested with PWN, the genes malate dehydrogenase, ABA, water deficit stress related genes and PAR1 were highly expressed, while in PWN-infested P. pinea, the highly expressed genes were ricin B-related lectin, and genes belonging to the SNARE and high mobility group families. Quantitative PCR experiments confirmed the differential gene expression between the two pine species.

CONCLUSIONS

Defense-related genes triggered by nematode infestation were detected in both P. pinaster and P. pinea transcriptomes utilizing 454 pyrosequencing technology. P. pinaster showed higher abundance of genes related to transcriptional regulation, terpenoid secondary metabolism (including some with nematicidal activity) and pathogen attack. P. pinea showed higher abundance of genes related to oxidative stress and higher levels of expression in general of stress responsive genes. This study provides essential information about the molecular defense mechanisms utilized by P. pinaster and P. pinea against PWN infestation and contributes to a better understanding of PWD.

Taxonomy, life cycle, development, and habits of two new species of Allantonematidae (Nematoda) parasitic in drosophilid flies

1. Two species of Allantonematidae were found parasitizing five of twelve species of Drosophila collected at Rothamsted Experimental Station, Harpenden, Herts, England.

2. H. aoronymphium sp.nov. was found in 20·8 % of D. phalerata and 4·3 % of D. kuntzei examined. Parasitylenchus diplogenus sp.nov. was found in about 5 % of D. subobscura, D. obscura, and D. silvestris examined.

3. The type species and taxonomy of the genus Parasitylenchus are discussed.

4. The life history of H. aoronymphium is typical of most allantonematids except that the female is fertilized when she is a fourth-stage larva. P. diplogenus has two sexual generations per cycle.

5. Both nematodes have a precocious development of the male and a retarded development of the female genital system. Both destroy host gonads.

6. The specificity of the nematodes is not a result of dissimilar ovipositing habits of the hosts, but shows a similarity to the taxonomic assignment of the hosts to subgenera.