Root-knot Nematode Meloidogyne Research Articles

Morphological and Molecular Identification of Root-knot Nematode, Meloidogyne incognita Infecting Pomegranate (Punica granatum L.) in Jodhpur, Rajasthan, India

Root-knot nematodes (Meloidogyne spp.) pose a major threat to pomegranate (Punica granatum L.) cultivation in India, leading to significant yield losses. In this study, galled roots of pomegranate were collected from orchards in Jodhpur, Rajasthan and nematode infestation was confirmed through root staining. The perineal pattern of females displayed the typical characteristics of the Meloidogyne incognita. To further confirm the species, DNA was extracted and a polymerase chain reaction (PCR) assay using species-specific SCAR (sequence-characterized amplified region) primers was conducted. The M. incognita- species specific primers, MincF1/MincR1, yielded the expected 150 bp product, verifying the presence of M. incognita. This study marks the first molecular confirmation of M. incognita infecting pomegranate orchards in this region, demonstrating the efficacy of SCAR markers in complementing traditional morphological identification as well.

Effect of Bio-Agents on Enzymatic Activity and Nematode Management in Tomato Plants Infected with Meloidogyne javanica

The tomato (Solanum esculentum Mill.) is one of the most widely cultivated vegetable crops worldwide. It serves as a favorable host for plant-parasitic nematodes, particularly the root-knot nematode (Meloidogyne javanica). Investigations were carried out to determine the effectiveness of bio-agents against root-knot nematodes in pot conditions. The bio-agents included Metarhizium anisopliae, Bacillus subtilis, Verticillium lecanii, Trichoderma harzianum and, Trichoderma asperellum) against root-knot nematode in pot condition. Effect of bio-agents was also estimated for accumulation of PPO and PAL and Root-knot nematode-infected tomato roots containing phenol. The results of the experiment showed that all the bio-agents significantly increased the levels of PPO, PAL, and phenol in tomato roots, improved plant growth parameters, and reduced nematode reproduction compared to the untreated control. The best treatment with the highest PPO, PAL, and phenol activity among the investigated bio-agents was determined to be Trichoderma harzianum at 3 gm/kg soil, followed by Bacillus subtilis and Metarhizium anisopliae. It improves the plant growth parameter and lowers the number of nematodes in the pot.

Prevalence and Distribution of Rice Root Knot Nematode in Rice Nurseries in Chitwan and Lamjung Districts of Nepal

To determine the natural infection of the rice root-knot nematode (Meloidogyne graminicola Golden & Brichfield) in rice nurseries, a survey was carried out in Chitwan and Lamjung in June and July of 2022. Rice nurseries were randomly selected based on geographical location, agro-ecological region, land type, cropping practice, and soil type. Forty rice nurseries were surveyed i.e. twenty from each district and 100 seedlings from each nursery as the sample for the study using the simple random method of sampling were evaluated. Field survey revealed that M. graminicola was widely distributed in most rice growing areas of Chitwan and Lamjung districts. Most of the rice nurseries in Lamjung district were found to be infested with M. graminicola as compared to that of the Chitwan district. Disease severity was reported up to 23.26% in Lamjung and 20.2% in Chitwan district. Additionally, the study showed that dry bed conditions were more likely to be affected by rice root-knot disease than wet bed conditions. The majority of farmers planted seedlings on upland (dry) soil, where second-stage juvenile (J2) populations and rice root-knot disease were more common. Most farmers (87.5%) have limited knowledge about rice root knot nematodes and their control methods. This suggested a significant loss in rice output and a high danger of nematode multiplication. This information will provide knowledge about the prevalence of nematode and enabling rice growers in this region to design and implement an appropriate control strategy for managing M. graminicola.

Exploring Nonanol from Bacillus velezensis (YEBBR6) for Root-Knot Nematode Management in Bananas: Integrating Experimental and Computational Approaches

Nematode infestations pose a severe threat to global banana production, leading to substantial yield losses and economic damage. Among these, the root-knot nematode Meloidogyne incognita is particularly detrimental, causing root galls that severely impair water and nutrient uptake, leading to stunted growth, reduced fruit quality, and significant economic losses for farmers. In the face of increasing agricultural challenges, bacterial endophytes have emerged as essential tools for sustainable agriculture, offering ecofriendly solutions to enhance plant health and manage pests. The present study aims to identify and characterise biomolecules from bacterial endophyte Bacillus velezensis (YEBBR6) with potential nematicidal properties against root-knot nematode Meloidogyne incognita infecting banana. The analysis of volatile and non-volatile organic compounds (VOCs/NVOCs) from the inhibition zone during the ditrophic interaction between B. velezensis (YEBBR6) and Fusarium oxysporum f.sp. cubense (Foc) revealed the presence of several distinctive biomolecules with antifungal and antimicrobial properties. These compounds included linoelaedic acid, nonanol, acetylvaleryl, 5–hydroxyl methyl furfural, clindamycin, allobarbital, 3-thiazolidine carboxamide, azulene, aminomorpholine, procyclidine, campholic acid, 3 amino-4 hydroxy phenyl sulfone, 3–deoxy mannoic lactone, hexadecanoic acid, oleic acid, and dihydroacridine. The in-silico analysis revealed that nonanol, exhibited strong binding efficacy against M. incognita protein targets, including cytochrome C oxidase subunit 1, calreticulin, neuropeptide G-protein coupled receptor, chorismate mutase 1, venom allergen-like proteins, and β-1,4-endoglucanase. Notably, nonanol proved more effective than the commercially used nematicide carbofuran 3G. Molecular dynamics studies further supported the potential of nonanol, and its nematicidal properties were validated through in vitro and pot culture studies. Moreover, nonanol was found to induce the expression of defense-related genes, such as MAPK10, WRKY22, ascorbate peroxidase, catalase, and NADPH oxidase, in banana seedlings, thus enhancing the plant's immune response. These findings highlight the potential of nonanol, derived from B. velezensis (YEBBR6), as a potent and environmentally friendly alternative for controlling nematode infestations in banana cultivation.

Nematicidal and Insecticidal Compounds from the Laurel Forest Endophytic Fungus Phyllosticta sp.

The search for natural product-based biopesticides from endophytic fungi is an effective tool to find new solutions. In this study, we studied a pre-selected fungal endophyte, isolate YCC4, from the paleoendemism Persea indica, along with compounds present in the extract and the identification of the insect antifeedant and nematicidal ones. The endophyte YCC4 was identified as Phyllosticta sp. by molecular analysis. The insect antifeedant activity was tested by choice bioassays against Spodoptera littoralis, Myzus persicae, and Rhopalosiphum padi, and the in vitro and in vivo mortality was tested against the root-knot nematode Meloidogyne javanica. Since the extract was an effective insect antifeedant, a strong nematicidal, and lacked phytotoxicity on tomato plants, a comprehensive chemical study was carried out. Two new metabolites, metguignardic acid (4) and (-)-epi-guignardone I (14), were identified along the known dioxolanones guignardic acid (1), ethyl guignardate (3), guignardianones A (5), C (2), D (7), and E (6), phenguignardic acid methyl ester (8), the meroterpenes guignardone A (9) and B (10), guignarenone B (11) and C (12), (-)-guignardone I (13), and phyllomeroterpenoid B (15). Among these compounds, 1 and 4 were effective antifeedants against S. littoralis and M. persicae, while 2 was only active on the aphid M. persicae. The nematicidal compounds were 4, 7, and 8. This is the first report on the insect antifeedant or nematicidal effects of these dioxolanone-type compounds. Since the insect antifeedant and nematicidal activity of the Phyllosticta sp. extract depend on the presence of dioxolanone components, future fermentation optimizations are needed to promote the biosynthesis of these compounds instead of meroterpenes.

Evolutionary Systems Biology Identifies Genetic Trade-offs In Rice Defense Against Above- and Belowground Attackers.

Like other plants, wild and domesticated rice species (Oryza nivara, O. rufipogon, and O. sativa) evolve in environments with various biotic and abiotic stresses that fluctuate in intensity through space and time. Microbial pathogens and invertebrate herbivores such as plant-parasitic nematodes and caterpillars show geographical and temporal variation in activity patterns and may respond differently to certain plant defensive mechanisms. As such, plant interactions with multiple community members may result in conflicting selection pressures on genetic polymorphisms. Here, through assays with different above- and belowground herbivores, the fall armyworm (Spodoptera frugiperda) and the southern root-knot nematode (Meloidogyne incognita), respectively, and comparison with rice responses to microbial pathogens, we identify potential genetic trade-offs at the KSL8 and MG1 loci on chromosome 11. KSL8 encodes the first committed step towards biosynthesis of either stemarane- or stemodane-type diterpenoids through the japonica (KSL8-jap) or indica (KSL8-ind) allele. Knocking out KSL8-jap and CPS4, encoding an enzyme that acts upstream in diterpenoid synthesis, in japonica rice cultivars increased resistance to S. frugiperda and decreased resistance to M. incognita. Furthermore, MG1 resides in a haplotype that provided resistance to M. incognita, while alternative haplotypes are involved in mediating resistance to the rice blast fungus Magnaporthe oryzae and other pests and pathogens. Finally, KSL8 and MG1 alleles are located within trans-species haplotypes and may be evolving under long-term balancing selection. Our data are consistent with a hypothesis that polymorphisms at KSL8 and MG1 may be maintained through complex and diffuse community interactions.

Streptomyces avermitilis MICNEMA2022: a new biorational strain for producing abamectin as an integrated nematode management agent

BackgroundAbamectin (ABA) is considered a powerful insecticidal and anthelmintic agent. It is an intracellular product of Streptomyces avermitilis; is synthesized through complicated pathways and can then be extracted from mycelial by methanol extraction. ABA serves as a biological control substance against the root-knot nematode Meloidogyne incognita. This investigation is intended to reach a new strain of S. avermitilis capable of producing ABA effectively.ResultsAmong the sixty actinobacterial isolates, Streptomyces St.53 isolate was chosen for its superior nematicidal effectiveness. The mycelial-methanol extract of isolate St.53 exhibited a maximum in vitro mortality of 100% in one day. In the greenhouse experiment, the mycelial-methanol extract demonstrated, for the second-stage juveniles (J2s), 75.69% nematode reduction and 0.84 reproduction rate (Rr) while for the second-stage juveniles (J2s), the culture suspension demonstrated 75.38% nematode reduction and 0.80 reproduction rate (Rr). Molecular identification for St.53 was performed using 16 S rRNA gene analysis and recorded in NCBI Genbank as S. avermitilis MICNEMA2022 with accession number (OP108264.1). LC-MS was utilized to detect and identify abamectin in extracts while HPLC analysis was carried out for quantitative determination. Both abamectin B1a and abamectin B1b were produced and detected at retention times of 4.572 and 3.890 min respectively.ConclusionStreptomyces avermitilis MICNEMA2022 proved to be an effective source for producing abamectin as a biorational agent for integrated nematode management.

Pepper root exudate alleviates cucumber root-knot nematode infection by recruiting a rhizobacterium

Root-knot nematodes (Meloidogyne spp.) have garnered significant attention from researchers due to their substantial damage to crops and worldwide distribution. However, controlling this nematode disease is challenging which results from limited chemical pesticides and biocontrol agents effective against them. Here, we demonstrate that pepper-rotation markedly reduces Meloidogyne incognita infection in cucumber and diminishes the presence of p-hydroxybenzoic acid in the soil, a compound known to exacerbate M. incognita infection. Pepper-rotation also structures the rhizobacterial community, leading to the colonization of two Pseudarthrobacter oxydans strains (RH60 and RH97) in the cucumber rhizosphere, facilitated by palmitic acid enrichment in pepper root exudates. Furthermore, both strains exhibit high nematocidal activity against M. incognita, and possess the ability to biosynthesize indoleacetic acid and biodegrade p-hydroxybenzoic acid. RH60 and RH97 additionally induce systemic resistance in cucumber plants and promote their growth. These data suggest that pepper root-exudate palmitic acid alleviates M. incognita infection by recruiting beneficial P. oxydans in the cucumber rhizosphere. Our analyses identify a novel chemical component in root exudates and uncover its pivotal role in crop rotation for disease attenuation, providing intriguing insights into the keystone function of root exudates in plant protection against root-knot nematode infection.

Wild mungbean resistance to the nematode Meloidogyne enterolobii involves the induction of phenylpropanoid metabolism and lignification.

Root-knot nematodes (Meloidogyne spp.) are plant parasites causing annual economic losses amounting to several billion US dollars worldwide. One of the most aggressive species is M. enterolobii, a growing threat to agriculture due to its broad host range and ability to overcome many known resistance genes. Mungbean, a nutritionally and economically valuable crop, is particularly vulnerable to nematodes and pathogens. However, research focusing on mungbean resistance to M. enterolobii is scarce, and the corresponding defense mechanisms are poorly understood. Here, we screened mungbean accessions and identified an accession strongly resistant to M. enterolobii. Transcriptome analysis revealed 2730 differentially expressed genes (DEGs) in this resistant accession (CPI106939) compared to 1777 in the susceptible accession (Crystal) 7 days after nematode inoculation. The gene ontology (GO) upregulated in CPI106939 with functions related to plant-pathogen interactions, plant hormone signaling, oxidative stress, and plant immunity. Plant defense-related genes (WRKY, PAL, MAPK, POD and PR) were also significantly induced in CPI106939. Metabolome analysis showed that four secondary metabolites related to phenylpropanoid metabolism and lignification were significantly enriched in CPI106939. The induced immune response and secondary metabolites may underpin the enhanced resistance to M. enterolobii, providing insight into the resistance mechanisms in accession CPI106939 as well as candidate genes controlling the interaction between mungbean and its nematode parasite. Our study therefore provides foundations for the breeding of new varieties with intrinsic M. enterolobii resistance.

Dual nematode infection in Brassica nigra affects shoot metabolome and aphid survival in distinct contrast to single-species infection.

Previous studies showed that aphid performance was compromised on Brassica nigra infected by root-lesion nematodes (Pratylenchus penetrans, Pp), but less, or positively influenced by root-knot nematode (Meloidogyne spp., Mi) infection. These experiments were on single-nematode infections, while naturally, roots are infected with several nematode species simultaneously. We performed greenhouse assays to assess the effects of single (Mi, Pp) and concurrent (MP)-nematode infections on aphid performance. Using targeted and untargeted profiling of leaf and phloem metabolomes, we examined how single- and concurrent-nematode infections affect shoot metabolomes, and elucidated the possible consequences on aphid performance. We found that the metabolic response towards double-infection is different from single-species infections. Moreover, Mi- and Pp-infections triggered discrete changes in B. nigra leaf and phloem metabolic profiles. Both Pp and MP-infections reduced aphid survival, suggesting that the biological effect could primarily be dominated by Pp-induced changes. This concurred with increased indole glucosinolates and hydroxycinnamic acid levels in the leaves, in particular the putative involvement of salicylic acid-2-O-β-D-glucoside. This study provides evidence that concurrent infection by different nematode species, as is common in natural environments, is associated with distinct changes in aboveground plant metabolomes, which are linked to differences in the survival of an aboveground herbivore.

Genetic variations underlying root-knot nematode resistance in sweetpotato

Root-knot nematode (Meloidogyne incognita) causes severe crop damage and large economic losses worldwide. Several cultivars of sweetpotato [Ipomoea batatas (L.) Lam)] have been developed with root-knot nematode-resistant traits; however, many of these cultivars do not have favorable agronomic characteristics. To understand the genetic traits underlying M. incognita resistance in sweetpotato, whole genome resequencing was conducted on three RKN-susceptible (Dahomi, Shinhwangmi, and Yulmi) and three RKN-resistant (Danjami, Pungwonmi, and Juhwangmi) sweetpotato cultivars. Three SNPs (single nucleotide polymorphisms) in promotor sequences were shared in RKN-resistant cultivars and were correlated with disease resistance. One of these SNPs was located in G6617|TU10904, which encoded a homolog of RIBOSOMAL PROTEIN EL15Z, and was associated with reduced expression in RKN-resistant cultivars only. Alongside SNP analysis, mRNA-seq data were analyzed for the same cultivars with and without nematode infection, and 18 nematode-sensitive genes were identified that responded in a cultivar-specific manner. Of these genes, expression of G8735|TU14367 was lower in sensitive cultivars than in RKN-resistant cultivars. Overall, this study identified two genes that potentially have key roles in the regulation of nematode resistance and will be useful targets for nematode resistance breeding programs.

Host status of cover crops for the management of Meloidogyne izalcoensis in coffee orchards infested with root-knot nematodes

Summary The root-knot nematode Meloidogyne izalcoensis was described parasitising coffee trees and causing damage in the Izalco volcano region, Sonsonate, El Salvador. In Brazil, it was detected in coffee roots in the municipality of Indianópolis, Minas Gerais state (MG). Intercropping cover crops is a traditional practice in Brazilian coffee orchards, and the use of plants that are non-hosts or antagonistic to the nematodes is a very promising strategy for coffee in infested areas. Due to the scarce information on the host status of M. izalcoensis, the aim of this study was to evaluate 24 plants of different species of cover crops and select the non-hosts or poor hosts. Two assays were conducted at different times, and all plants were inoculated with 10 000 eggs. After 90 days, the following parameters were determined: fresh root weight, reproduction factor (RF) and final reaction. Plants with RF < 1.0 were classified as non-hosts (NH), those with RF > 1.0 were classified as hosts and using statistical analyses as: good host (GH), intermediate host (IH) and poor host (PH). Most of the botanical species tested were classified as NH or PH to M. izalcoensis: cotton, rice, white oat, black oat, ryegrass, corn, three species of grass, two cultivars of millet, two wheat cultivars, Crotalaria breviflora, C. ochroleuca, C. spectabilis, jack bean, gray mucuna bean and two species of rice grass. Only tomato and bean were classified as GH, and C. juncea and soybean were classified as IH. The plants identified as non-hosts or poor hosts can be recommended for intercropping or for crop rotation in Brazilian coffee orchards in regions infested by M. izalcoensis.

Optimization andutilization ofemerging waste (fly ash) for growth performance of chickpea (Cicer arietinum L.) plant and mitigation of root-knot nematode (Meloidogyne incognita) stress.

The sustainable management of large amounts of fly ash (FA) is a concern for researchers, and we aim to determine the FA application in plant development and nematicidal activity in the current study. A pot study is therefore performed to assess the effects of adding different, FA-concentrations to soil (w/w) on the infection of chickpea plants with the root-knot nematode Meloidogyne incognita. Sequence characteristic amplified region (SCAR) and internal transcribed spacer (ITS) region-based-markers were used to molecularly confirm M. incognita. With better plant growth and chickpea yield performance, FA enhanced the nutritious components of the soil. When compared with untreated, uninoculated control (UUC) plants, the inoculation of M. incognita dramatically reduced chickpea plant growth, yield biomass, and metabolism. The findings showed that the potential of FA to lessen the root-knot nematode illness in respect of galls, egg-masses, and reproductive attributes may be used to explain the mitigating effect of FA. Fascinatingly, compared with the untreated, inoculated control (UIC) plants, the FA treatment, primarily at 20%, considerably (p ≤ 0.05) boosted plant growth, yield biomass, and pigment content. Additionally, when the amounts of FA rose, the activity of antioxidants like superoxide dismutase-SOD, catalase-CAT, and peroxidase-POX as well as osmo-protectants like proline gradually increased. Therefore, our findings imply that 20% FA can be successfully applied as a potential strategy to increase biomass yield and plant growth while simultaneously reducing M. incognita infection in chickpea plants.

Effect of Temperature on the Embryogenesis of Three Geographically Distinct Populations of Meloidogyne incognita Is Driven by Intrinsic Thermal Acclimation Reaction.

Research interest in the mechanisms enabling plant-parasitic nematodes to adjust their physiological performance and cope with changing temperatures has intensified in light of global warming. Here, we show that geographically distinct populations of the root-knot nematode Meloidogyne incognita, which is prevalent in the three main pepper-growing regions in Israel-Carmel Valley (Carmel), Jordan Valley (JV), and Arava Rift (Arava)-possess persistent differences in their thermal acclimation capacity, which affect pre- and postembryonic development. The optimal temperature for embryonic growth completion was 25°C for the Carmel population; 25 and 30°C for the JV population; and 30°C for the Arava population. Cumulative hatching percentages showed variations among populations; relative to hatching at 25°C, the Carmel population experienced hatching reduction at the higher studied temperatures 30 and 33°C, while the JV and Arava populations exhibited an increase in hatching at 30 and 33°C, respectively. Juvenile survival indicates that at the lowest temperature (20°C), the Carmel population gained the highest survival rates throughout the experimental duration, while at the same duration at 33°C, the Arava population gained the highest survival rate. Infective juveniles of the Carmel population demonstrated increased penetration of tomato roots at 25°C compared to the JV and Arava populations. Inversely, at 33°C, increased penetration was observed for the Arava compared to the Carmel and JV populations. Altogether, the Arava population's performance at 33°C might incur distinct fitness costs, resulting in consistent attenuation compared to the Carmel population at 25°C. Precisely defining a population's thermal acclimation response might provide essential information for models that predict the impact of future climate change on these populations.

Metabolomics and histopathological analysis of two tomato cultivars after co-infection with soil-borne pathogens (Southern root-knot nematode and Fusarium wilt fungus)

Southern root-knot nematode (Meloidogyne incognita) and Fusarium wilt fungus (Fusarium oxysporum) are one of the most predominant pathogens responsible for substantial agricultural yield reduction of tomato. The current study planned to assess the effects of M. incognita (Mi) and F. oxysporum (Fo) and their co-infection on two tomato cultivars, Zhongza 09 (ZZ09) and Gailing Maofen 802 (GLM802). The present study examined the effects of co-infection on leaf morphology, chlorophyll content, leaf area, and histopathology. The present study used metabolomics to evaluate plant-pathogen interactions. The outcomes of the current study revealed that chlorophyll content and leaf area decreased more in GLM802 during co-infection. In co-infection (Fo + Mi), the chlorophyll content reduction in ZZ09 was 11%, while in GLM802 the reduction reached up to 31% as compared to control. Moreover, the reduction in leaf are in ZZ09 was 31%, however, in the GLM802 reduction was observed 54% as compared to control plants. Similarly, GLM802 stems exhibited larger brown patches on their vascular bundles than ZZ09 stems. The rate of browning of GLM802 stems was 247% more than ZZ09, during co-infection. Moreover, GLM802 roots exhibited a higher abundance of hyphae and larger galls than ZZ09 roots. In metabolic studies, glutathione, succinic acid, and 2-isopropylmalic acid decreased, whereas spermine and fumaric acid increased in GLM802 co-infected stems. It indicates that GLM802 is weakly resistant; therefore, F. oxysporum and other pathogens readily damage tissue. In the co-infected stem of ZZ09, L-asparagine and shikimic acid increased, but pipecolic acid, L-saccharine, and 2-isopropylmalic acid declined. L-asparagine was crucial in preserving the stability of nitrogen metabolism, chlorophyll synthesis, and leaf growth in ZZ09. Shikimic acid's substantial accumulation could explain the limited extent of browning observed in the vascular bundles of ZZ09. Thus, the present study provides insight into M. incognita and F. oxysporum co-infection in two tomato cultivars, which may aid breeding efforts to generate commercially viable resistant cultivars. However, further research on the relationship between M. incognita and F. oxysporum in different host plants is required in the future.

Distinct changes in tomato-associated multi-kingdom microbiomes during Meloidogyne incognita parasitism

BackgroundThe interplay between root-knot nematode (RKN) parasitism and the complex web of host-associated microbiota has been recognized as pivotal for effective management of the pest. However, studies assessing this relationship have focussed on the bacterial and fungal communities, neglecting the unicellular eukaryotic members. Here, we employed amplicon sequencing analysis of the bacterial 16S rRNA, fungal ITS and eukaryotic 18S rRNA genes, and comprehensively examined how the microbiome composition, diversity and networking developed with time in the rhizospheres and roots of RKN-inoculated and non-inoculated tomato plants.ResultsAs expected, infection with the RKN Meloidogyne incognita decreased plant growth. At individual timepoints, we found distinct bacterial, fungal and eukaryote community structures in the RKN-inoculated and non-inoculated rhizospheres and roots, and RKN inoculation affected several taxa in the root-associated microbiome differentially. Correlation analysis revealed several bacterial and fungal and few protist taxa that correlated negatively or positively with M. incognita. Moreover, network analysis using bacterial, fungal and eukaryotic data revealed more dynamic networks with higher robustness to disturbances in the RKN-inoculated than in the non-inoculated rhizospheres/roots. Hub taxa displayed a noticeable successional pattern that coincided with different phases of M. incognita parasitism. We found that fungal hubs had strong negative correlations with bacteria and eukaryotes, while positive correlations characterized hub members within individual kingdoms.ConclusionOur results reveal dynamic tomato-associated microbiomes that develop along different trajectories in plants suffering M. incognita infestation and non-infested plants. Overall, the results identify stronger associations between RKN and bacterial and fungal taxa than between eukaryotic taxa and RKN, suggesting that fungal and bacterial communities could play a larger role in the regulation of RKN. The study identifies several putative RKN-antagonistic bacterial and fungal taxa and confirms the antagonistic potential previously identified in other taxa.

Local and systemic transcriptome and spliceome reprogramming induced by the root-knot nematode Meloidogyne incognita in tomato.

Root-knot nematodes (Meloidogyne spp.) are widely spread root parasites that infect thousands of vascular plant species. These highly polyphagous nematodes engage in sophisticated interactions with host plants that results in the formation of knot-like structures known as galls whose ontogeny remains largely unknown. Here, we determined transcriptome changes and alternative splicing variants induced by Megalaima incognita in galls and neighboring root cells at two distinct infective stages. M. incognita induced substantial transcriptome changes in tomato roots both locally in galls and systemically in neighboring cells. A considerable parallel regulation of gene expression in galls and neighboring cells were detected, indicative of effective intercellular communications exemplified by suppression of basal defense responses particularly during the early stage of infection. The transcriptome analysis also revealed that M. incognita exerts a tight control over the cell cycle process as a whole that results in an increase of ploidy levels in the feeding sites and accelerated mitotic activity of the gall cells. Alternative splicing analysis indicated that M. incognita significantly modulates pre-mRNA splicing as a total of 9064 differentially spliced events from 2898 genes were identified where intron retention and exon skipping events were largely suppressed. Furthermore, a number of differentially spliced events were functionally validated using transgenic hairy root system and found to impact gall formation and nematode egg mass production. Together, our data provide unprecedented insights into the transcriptome and spliceome reprogramming induced by M. incognita in tomato with respect to gall ontogeny and nematode parasitism.

Utilizing endophytic plant growth-promoting bacteria and the nematophagous fungus Purpureocillium lilacinum as biocontrol agents against the root-knot nematode (Meloidogyne incognita) on tomato plants

AbstractThe present investigation was designed to assess how administering biocontrol agents (BCAs) made from the nematophagous endophytic fungus MR20 (Purpureocillium lilacinum) or a mixture of endophytic plant growth-promoting bacteria MR12 (Pseudomonas fluorescens), and MR25 (Serratia marcescens), could enhance tomato growth and resistance to Meloidogyne incognita under in vivo conditions. The three strains’ cell-free culture filtrates showed a strong nematocidal impact (P < 0.05) on M. incognita infective second-stage juveniles (J2s). The highest mortality rates by the three BCAs were at concentrations of 80%, followed by 60%, 40%, and 20%. The in vitro hatching of free eggs was found to be considerably (P < 0.05) reduced as the concentrations of the endophytic bacteria MR12, and MR25 were increased in the order 1 × 105, 1 × 106, 1 × 107, 0.5 × 108, to 1 × 108 colony forming units (CFU)/mL, and the maximum nematicidal activity in killing M. incognita free eggs occurred at 1 × 108 CFU/mL. A statistically significant (P < 0.05) reduction in the percentage of M. incognita-free eggs retrieved was seen in vitro when various concentrations of the endophytic fungus MR20 were applied compared to the negative control (distilled water). The endophytic fungus MR20 had the highest nematicidal activity against M. incognita free eggs at a concentration of 3 × 106 CFU/mL. The application of P. lilacinum or a combination of P. fluorescens and S. marcescens to tomato plants in the presence of M. incognita under greenhouse conditions resulted in a significant increase (P < 0.05) in root and shoot fresh weight, number of leaves, weight of leaves, and stem diameter when compared to the positive control treatment that contained only M. incognita. Treatment with P. lilacinum was more effective (P < 0.05) than P. fluorescens and S. marcescens in reducing egg masses per root, J2s per 100 g of soil, egg masses per 100 g of soil, J2s + eggs of M. incognita per 100 g of soil, reproduction factor, and reduction percentage after 60 days under greenhouse conditions. Nevertheless, the reduction of M. incognita gall size categorization (> 4 mm, 2–4 mm, and < 2 mm) was more effectively achieved by treatment with P. fluorescens and S. marcescens than by treatment with P. lilacinum. Under in vivo conditions, the tested P. lilacinum or a mixture of P. fluorescens and S. marcescens effectively controlled nematode population densities below the economic threshold.

Integrated Analysis of the lncRNA-miRNA-mRNA Expression Profiles in Response to Meloidogyne incognita in Radish (Raphanus sativus L.)

Radish is an important root vegetable that is widely grown in Asia. The root-knot nematode (RKN) Meloidogyne incognita seriously affects the growth and development of radish root and causes poor appearance quality. However, the molecular mechanism of radish response to RKNs remains poorly understood. In this study, a total of 220 lncRNAs, 1144 mRNAs, 20 miRNAs and 153 proteins were differential expressed between the RKN-infected and WT samples. Correlation analysis of all DEPs compared with all DGEs showed that 8 mRNAs-DEPs showed a changed abundance. The results showed that 18 DEmiRNAs have 167 target DEGs in 220 miRNA-target modules and 29 DElncRNAs were predicted as putative targets of 16 DEmiRNAs in 37 miRNA-target modules. In all, 6 DGEs in the ABA pathway and 2 DGEs in the JA pathway were identified under RKN infection, respectively. The four regulatory networks of lncRNA-miRNA-mRNA were constructed in response to RKN infection. qRT-PCR analysis found that the expression pattern of 6 DElncRNAs, 6 DEmRNAs, 6 DEmiRNAs and 6 DEPs were consistent with sequencing results. These results provide a theoretical basis for studying the molecular mechanism of radish in response to M. incognita and breeding resistant varieties to this nematode.

Botanicals as Phyto-nematicides Against Root-knot Disease Caused by the Root-knot Nematode (Meloidogyne incognita) via Promoting growth, Yield, and Biochemical Performance of Cabbage Crop

Botanicals as Phyto-nematicides Against Root-knot Disease Caused by the Root-knot Nematode (Meloidogyne incognita) via Promoting growth, Yield, and Biochemical Performance of Cabbage Crop