Incognita Infection Research Articles

Aqueous, Ethanolic and Nanoparticles of Two Plant Extracts Compared to Abamectin on Tomato Plant as Affected by Meloidogyne incognita and Rotylenchulus reniformis Infection

Aqueous, Ethanolic and Nanoparticles of Two Plant Extracts Compared to Abamectin on Tomato Plant as Affected by Meloidogyne incognita and Rotylenchulus reniformis Infection

Integrated stress responses in okra plants (cv. ‘’Meya’]: unravelling the mechanisms underlying drought and nematode co-occurrence

BackgroundClimate change threatens sub-Saharan Africa’s agricultural production, causing abiotic and biotic stressors. The study of plant responses to joint stressors is crucial for understanding molecular processes and identifying resilient crops for global food security. This study aimed to explore the shared and tailored responses of okra plants (cv. ‘’Meya’), at the biochemical and molecular levels, subjected to combined stresses of drought and Meloidogyne incognita infection.DesignThe study involved 240 okra plants in a completely randomized design, with six treatments replicated 20 times. Okra plants were adequately irrigated at the end of every 10-days water deficit that lasted for 66 days (D). Also, the plants were infected with M. incognita for 66 days and irrigated at 2-days intervals (R). The stresses were done independently, in sequential combination (D before R and R before D) and concurrently (R and D). All biochemical and antioxidant enzyme assays were carried out following standard procedures.ResultsSignificant reductions in leaf relative water content were recorded in all stressed plants, especially in leaves of plants under individual drought stress (D) (41.6%) and plants stressed with root-knot nematode infection before drought stress (RBD) (41.4%). Malondialdehyde contents in leaf tissues from plants in D, nematode-only stress (RKN), drought stress before root-knot nematode infection (DBR), RBD, and concurrent drought-nematode stress (RAD) significantly increased by 320.2%, 152.9%, 186.5%, 283.7%, and 109.6%, respectively. Plants in D exhibited the highest superoxide dismutase activities in leaf (147.1% increase) and root (105.8% increase) tissues. Catalase (CAT) activities were significantly increased only in leaves of plants in D (90.8%) and RBD (88.9%), while only roots of plants in D exhibited a substantially higher CAT activity (139.3% increase) in comparison to controlled plants. Okra plants over-expressed NCED3 and under-expressed Me3 genes in leaf tissues. The NCED3 gene was overexpressed in roots from all treatments, while CYP707A3 was under-expressed only in roots of plants in RBD and RKN. CYP707A3 and NCED3 were grouped as closely related genes, while members of the Me3 genes were clustered into a separate group.ConclusionThe biochemical and molecular responses observed in okra plants (cv. ‘’Meya’) subjected to combined stresses of drought and Meloidogyne incognita infection provide valuable insights into enhancing crop resilience under multifaceted stress conditions, particularly relevant for agricultural practices in sub-Saharan Africa facing increasing climatic challenges.

Metabolic engineering of a 1,8-cineole synthase from Nicotiana suaveolens, confers enhanced resistance to Meloidogyne incognita by synergistic blend of root volatiles

Root-knot nematodes (RKNs) pose a significant threat to global crop production. Given the detrimental effects of fumigants and conventional chemical nematicides, there is a growing interest in exploring biological nematicides as a promising alternative for pest control. In this study, we present data demonstrating the role of root volatiles in enhancing resistance against Meloidogyne incognita (M. incognita) in tobacco plants overexpressing NsCINS (NsCINS-OE). The NsCINS gene, derived from Nicotiana suaveolens, encodes a 1,8-cineole synthase induced by M. incognita infection and predominantly localized to the chloroplast. The roots of NsCINS-OE plants exhibited deterrent properties to infective second-stage juveniles (J2s) of M. incognita. Moreover, NsCINS-OE plants showed enhanced resistance against M. incognita, as evidenced by reduced gall numbers and egg mass counts compared to wild type (WT) plants. Notably, the emission of root volatiles from NsCINS-OE plants, including 1,8-cineole, α-terpineol, terpinene-4-ol, and furfural, was significantly higher than that of WT. In vitro assays confirmed that a mixture of commercially available volatile organic compounds (VOCs) had a deterrent effect on infective J2s. Furthermore, the natural root volatiles emitted by NsCINS-OE plants effectively enhanced tobacco's resistance against M. incognita. Our findings provide valuable insights into the role of NsCINS in volatile-based defense and highlight the potential of metabolic engineering of monoterpene synthase genes to control M. incognita by enhancing root volatile emissions.

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

Root-knot nematodes (Meloidogyne spp.) have garnered significant attention from researchers owing to the substantial damage they cause to crops and their worldwide distribution. However, controlling these nematodes is challenging because a limited number of chemical pesticides and biocontrol agents are 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 restructures the rhizobacterial community, leading to the colonization of the cucumber rhizosphere by two Pseudarthrobacter oxydans strains (RH60 and RH97), facilitated by enrichment of palmitic acid in pepper root exudates. Both strains exhibit high nematocidal activity against M. incognita and have the ability to biosynthesize indoleacetic acid and biodegrade p-hydroxybenzoic acid. RH60 and RH97 also induce systemic resistance in cucumber plants and promote their growth. These data suggest that the pepper root exudate palmitic acid alleviates M. incognita infection by recruiting beneficial P. oxydans to the cucumber rhizosphere. Our analyses identify a novel chemical component in root exudates and reveal its pivotal role in crop rotation for disease control, providing intriguing insights into the keystone function of root exudates in plant protection against root-knot nematode infection.

First Report of the Root‐Knot Nematode Meloidogyne incognita Infecting Ficus tikoua in China

ABSTRACTFicus tikoua can be used as resources for fruit and herbal medicine inspiring large‐scale planting in China. Nodular galls were found on the roots of the planted F. tikoua individuals in 2022. The mature females and egg masses of nematodes were extracted from the nodular galls, and microscopic examination suggested Meloidogyne infection. Molecular identification based on ITS, 18S rRNA sequences assigned the infecting species to Meloidogyne incognita, which was further demonstrated by the successful application of specific SCAR marker M. incognita in all samples. The pathogenicity of M. incognita was conducted on F. tikoua cutting seedlings based on Koch's postulates. This is the first report of M. incognita infection in F. tikoua in China.

Protective role of native root-associated bacterial consortium against root-knot nematode infection in susceptible plants

Root-knot nematodes (RKNs) are a global menace to agricultural crop production. The role of root-associated microbes (RAMs) in plant protection against RKN infection remains unclear. Here we observe that cucumber (highly susceptible to Meloidogyne incognita) exhibits a consistently lower susceptibility to M. incognita in the presence of native RAMs in three distinct soils. Nematode infection alters the assembly of bacterial RAMs along the life cycle of M. incognita. Particularly, the loss of bacterial diversity of RAMs exacerbates plant susceptibility to M. incognita. A diverse range of native bacterial strains isolated from M. incognita-infected roots has nematode-antagonistic activity. Increasing the number of native bacterial strains causes decreasing nematode infection, which is lowest when six or more bacterial strains are present. Multiple simplified synthetic communities consisting of six bacterial strains show pronounced inhibitory effects on M. incognita infection in plants. These inhibitory effects are underpinned via multiple mechanisms including direct inhibition of infection, secretion of anti-nematode substances, and regulation of plant defense responses. This study highlights the role of native bacterial RAMs in plant resistance against RKNs and provides a useful insight into the development of a sustainable way to protect susceptible plants.

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.

The root-knot nematode effector MiEFF12 targets the host ER quality control system to suppress immune responses and allow parasitism.

Root-knot nematodes (RKNs) are microscopic parasitic worms able to infest the roots of thousands of plant species, causing massive crop yield losses worldwide. They evade the plant's immune system and manipulate plant cell physiology and metabolism to transform a few root cells into giant cells, which serve as feeding sites for the nematode. RKN parasitism is facilitated by the secretion in planta of effector molecules, mostly proteins that hijack host cellular processes. We describe here a conserved RKN-specific effector, effector 12 (EFF12), that is synthesized exclusively in the oesophageal glands of the nematode, and we demonstrate its function in parasitism. In the plant, MiEFF12 localizes to the endoplasmic reticulum (ER). A combination of RNA-sequencing analysis and immunity-suppression bioassays revealed the contribution of MiEFF12 to the modulation of host immunity. Yeast two-hybrid, split luciferase and co-immunoprecipitation approaches identified an essential component of the ER quality control system, the Solanum lycopersicum plant bap-like (PBL), and basic leucine zipper 60 (BZIP60) proteins as host targets of MiEFF12. Finally, silencing the PBL genes in Nicotiana benthamiana decreased susceptibility to Meloidogyne incognita infection. Our results suggest that EFF12 manipulates PBL function to modify plant immune responses to allow parasitism.

Pomegranate (Punica granatum L.) growth and biochemical alterations in response to meloidogyne incognita infection, minerals, and nano-fertilizers

The effects of four inoculum levels (500, 1,000, 2,000, or 4,000 second-stage juveniles (J2) per plant) of the root-knot nematode, Meloidogyne incognita, on two pomegranate cultivars (‘Manfalouty’ and ‘Wonderful’) were investigated under greenhouse conditions in response to plant inorganic and organic chemical concentrations. Furthermore, the effects of six commercial chemical fertilizers (inorganic fertilizers and nano-fertilizers) on plant growth and nematode reproduction were also studied. Both cultivars recorded the highest gall formation, embedded stages, and final nematode population at the inoculum dosage of 2,000 J2/plant. The highest reproductive rate was achieved with 500 J2/plant, while the lowest rate was observed with 4,000 J2/plant on both cultivars. ‘Wonderful’, at all M. incognita inoculum levels, was more sensitive to nematode infestation than ‘Manfalouty’. ‘Wonderful’ showed a greater reduction in fresh and dry plant weights than ‘Manfalouty’ at 2,000 and 4,000 J2/plant. In both cultivars, the concentrations of N, P, and K decreased with increasing nematode inoculum levels. This decline was more pronounced in ‘Manfalouty’ than in ‘Wonderful’. The nano-fertilizers, Hyper Feed®, and Hyper Feed Solo® reduced all nematode parameters but only in ‘Wonderful’. Treatment with Hyper Feed® resulted in the highest percentage increases in all plant growth parameters in ‘Wonderful’. Total carbohydrate concentration was increased in ‘Manfalouty’ treated with the nano-fertilizers, especially with Hyper Feed®. Also, concentrations of total phenols and tannins increased in ‘Wonderful’ when treated with either nano-fertilizer. Generally, both nano-fertilizers showed an increase in plant N levels. We recommend using nano-fertilizers in integrated pest management (IPM) programs on pomegranate where they improved plant growth parameters and reduced nematode multiplication parameters more markedly than inorganic fertilizers.

Joint Impacts of Meloidogyne incognita and Soil Nutrition on Solanum lycopersicum var. cerasiforme.

Strategies for plant nutrient resource allocation under Meloidogyne spp. infection and different soil nutrient conditions are not well established. In response, the objectives of this research are to determine if increased vegetative growth of Solanum lycopersicon var. cerasiforme (cherry tomato) under high nutrition enhances resistance to M. incognita and whether adaptive strategies for growth, reproduction, and nutrient uptake by cherry tomato infected with M. incognita alter nutrient availability. The study was conducted under greenhouse conditions using high, medium, and low soil nutrient regimes. The research results indicate that the total biomass of cherry tomato was less in the presence of M. incognita infection under all three nutrient conditions, compared with plants grown in the absence of this nematode. However, the increase in the root/shoot ratio indicates that cherry tomato allocated more resources to belowground organs. Under the combined impacts of M. incognita infection and low or medium soil nutrition, the nitrogen content in root system tissues and the phosphorus content in shoot system tissues were increased to meet the nutrient requirements of galled root tissue and plant fruit production. It is suggested that plants increase the allocation of reproductive resources to fruits by improving phosphorus transportation to the aboveground reproductive tissues under low and medium nutrient conditions. Overall, the study highlights a significant impact of soil nutrient levels on the growth and resource allocation associated with M. incognita-infected cherry tomato. In response, soil nutrient management is another practice for reducing the impacts of plant-parasitic nematodes on crop production.

Antioxidant Responses and Growth Impairment in Cucurbita moschata Infected by Meloidogyne incognita.

Pumpkins (Cucurbita moschata), valued for their nutritional, medicinal, and economic significance, face threats from Meloidogyne incognita, a critical plant-parasitic nematode. This study extensively examines the impact of M. incognita on the growth, physiological, and biochemical responses of C. moschata. We demonstrate that M. incognita infection leads to significant growth impairment in C. moschata, evidenced by reduced plant height and biomass, along with the significant development of nematode-induced galls. Concurrently, a pronounced oxidative stress response was observed, characterized by elevated levels of hydrogen peroxide and a significant increase in antioxidant defense mechanisms, including the upregulation of key antioxidative enzymes (superoxide dismutase, glutathione reductase, catalase, and peroxidase) and the accumulation of glutathione. These responses highlight a dynamic interaction between the plant and the nematode, wherein C. moschata activates a robust antioxidant defense to mitigate the oxidative stress induced by nematode infection. Despite these defenses, the persistence of growth impairment underscores the challenge posed by M. incognita to the agricultural production of C. moschata. Our findings contribute to the understanding of plant-nematode interactions, paving the way for the development of strategies aimed at enhancing resistance in Cucurbitaceae crops against nematode pests, thus supporting sustainable agricultural practices.

Biological Control of a Root-Knot Nematode Meloidogyne incognita Infection of Tomato (Solanum lycopersicum L.) by the Oomycete Biocontrol Agent Pythium oligandrum.

The biocontrol agent Pythium oligandrum, which is a member of the phylum Oomycota, can control diseases caused by a taxonomically wide range of plant pathogens, including fungi, bacteria, and oomycetes. However, whether P. oligandrum could control diseases caused by plant root-knot nematodes (RKNs) was unknown. We investigated a recently isolated P. oligandrum strain GAQ1, and the P. oligandrum strain CBS530.74, for the control of an RKN Meloidogyne incognita infection of tomato (Solanum lycopersicum L.). Initially, P. oligandrum culture filtrates were found to be lethal to M. incognita second-stage juveniles (J2s) with up to 84% mortality 24 h after treatment compared to 14% in the control group. Consistent with the lethality to M. incognita J2s, tomato roots treated with P. oligandrum culture filtrates reduced their attraction of nematodes, and the number of nematodes penetrating the roots was reduced by up to 78%. In a greenhouse pot trial, the P. oligandrum GAQ1 inoculation of tomato plants significantly reduced the gall number by 58% in plants infected with M. incognita. Notably, the P. oligandrum GAQ1 mycelial treatment significantly increased tomato plant height (by 36%), weight (by 27%), and root weight (by 48%). A transcriptome analysis of tomato seedling roots inoculated with the P. oligandrum GAQ1 strain identified ~2500 differentially expressed genes. The enriched GO terms and annotations in the up-regulated genes suggested a modulation of the plant hormone-signaling and defense-related pathways in response to P. oligandrum. In conclusion, our results support that P. oligandrum GAQ1 can serve as a potential biocontrol agent for M. incognita control in tomato. Multiple mechanisms appear to contribute to the biocontrol effect, including the direct inhibition of M. incognita, the potential priming of tomato plant defenses, and plant growth promotion.

Green fabrication of titanium dioxide nanoparticles via Syzygium cumini leaves extract: characterizations, photocatalytic activity and nematicidal evaluation

ABSTRACT The most significant plant parasitic nematode in terms of economic impact is root-knot nematode (Meloidogyne incognita), which severely harms essential crops used for agriculture. This study investigated green fabrication of titanium dioxide nanoparticles (TiO2 NPs) utilizing Syzygium cumini (SC) leaf extract and evaluated its nematotoxic activity against M. incognita in vitro and in pots. During experiments, second-stage juveniles (J2s) and egg masses of M. incognita were treated with different concentrations (125, 250, 375 and 500 ppm) of SC-TiO2 NPs. After 48 h and five days of exposure, respectively, lowest J2s mortality and per cent inhibition in egg hatching was discovered at 125 ppm, and highest J2s mortality and maximum per cent inhibition in egg hatching determined at 500 ppm. The treatment of SC TiO2 NPs considerably reduced M. incognita infection and enhanced carrot plants' growth and physiological characteristics. The characterization of green synthesized SC-TiO2 NPs made by X-ray diffraction, Photoluminescence, FTIR, SEM, UV-Visible Diffuse Reflectance Spectrophotometer, TEM, and photocatalytic activity also examined. In conclusion, it can be said that SC-TiO2 NPs possess nematode-toxic potential against M. incognita and are used as substitutes for high-risk chemical nematicides without causing any phytotoxicity.

Rhizosphere-Associated Microbiota Strengthen the Pathogenicity of Meloidogyne incognita on Arabidopsis thaliana

Microorganisms associated with nematodes or enriched in galls have been reported previously to aid plant-parasitic nematodes (PPNs) in infecting and establishing parasitism in the host plants. However, the rhizosphere-associated microbiota, which strengthens the pathogenicity of PPNs, remains largely unknown. This study illustrated rhizosphere bacteria enhancing Meloidogyne incognita infection on Arabidopsis thaliana by comparing the gall numbers of the treatments between natural soil and the sterile soil or soils drenched with antibiotics. By culture-dependent and pot testing methods, sixteen bacterial combinations from rhizosphere soils of A. thaliana were demonstrated to enhance M. incognita pathogenicity, including the most effective Nocardioides. Single-strain inoculation from the Nocardioides combination significantly resulted in M. incognita forming more galls on roots than the control, in which N. nematodiphilus R-N-C8 was the most effective strain. Strain R-N-C8 could substantially facilitate the M. incognita second-stage juveniles (J2s) moving towards the roots of A. thaliana and infecting the roots by releasing chemoattractant to attract J2s. The chemoattractant from strain R-N-C8 was determined to be L-lysine. This study furnishes vital insights for understanding the infection of root-knot nematodes associated with rhizosphere microbes.

Divergent colonization traits, convergent benefits: different species of arbuscular mycorrhizal fungi alleviate Meloidogyne incognita damage in tomato

Arbuscular mycorrhizal fungi (AMF) can increase plant tolerance and/or resistance to pests such as the root-knot nematode Meloidogyne incognita. However, the ameliorative effects may depend on AMF species. The aim of this work was therefore to evaluate whether four AMF species differentially affect plant performance in response to M. incognita infection. Tomato plants grown in greenhouse conditions were inoculated with four different AMF isolates (Claroideoglomus claroideum, Funneliformis mosseae, Gigaspora margarita, and Rhizophagus intraradices) and infected with 100 second stage juveniles of M. incognita at two different times: simultaneously or 2 weeks after the inoculation with AMF. After 60 days, the number of galls, egg masses, and reproduction factor of the nematodes were assessed along with plant biomass, phosphorus (P), and nitrogen concentrations in roots and shoots and root colonization by AMF. Only the simultaneous nematode inoculation without AMF caused a large reduction in plant shoot biomass, while all AMF species were able to ameliorate this effect and improve plant P uptake. The AMF isolates responded differently to the interaction with nematodes, either increasing the frequency of vesicles (C. claroideum) or reducing the number of arbuscules (F. mosseae and Gi. margarita). AMF inoculation did not decrease galls; however, it reduced the number of egg masses per gall in nematode simultaneous inoculation, except for C. claroideum. This work shows the importance of biotic stress alleviation associated with an improvement in P uptake and mediated by four different AMF species, irrespective of their fungal root colonization levels and specific interactions with the parasite.

Biocontrol Efficacy and Induced Resistance of Paenibacillus polymyxa J2-4 Against Meloidogyne incognita Infection in Cucumber.

Meloidogyne incognita is one of the most destructive agricultural pathogens around the world, resulting in severe damage to yield and quality in agricultural production. Biological control promises to be a great potential alternative to chemical agents against M. incognita. Paenibacillus polymyxa J2-4, isolated from ginger plants injured by M. incognita, has shown excellent biocontrol efficacy against M. incognita in cucumber. In vitro experiments with the strain J2-4 resulted in a correct mortality rate of 88.79% (24 h) and 98.57% (48 h) for second-stage juveniles (J2s) of M.incognita. Strain J2-4 significantly suppressed nematode infection on potted plants, with a 65.94% reduction in galls and a 51.64% reduction in eggs compared with the control. The split-root assay demonstrated that strain J2-4 not only reduced J2s' invasion but also inhibited nematode development through the dependence on salicylic acid and jasmonic acid signaling of strain J2-4 induction of plant resistance in local and systemic roots of cucumbers. Genomic analysis of strain J2-4 indicated biosynthetic gene clusters encoding polymyxin, fusaricidin B, paenilan, and tridecaptin. In addition, genetic analysis showed that none of the genes encoding virulence factors were detected in the genome of J2-4 compared with the pathogenic Bacillus species. Taking all the data together, we conclude that P. polymyxa J2-4 has potential as a biological control agent against M. incognita on cucumbers and can be considered biologically safe when used in agriculture.

Effectiveness of various nematode-trapping fungi for biocontrol of the Meloidogyne incognita in tomato (Lycopersicion esculentum Mill.)

The nine promising species of nematode-trapping fungi namely Dr. dactyloides, Dr. brochopaga, Da. gephyropaga, Da. phymatopaga, A. eudermata, A. oligospora, A. conoides, A. thaumasia and A. musiformis were isolated from the root-knots rhizosphere to compare their, in vitro nematode trapping ability against Meloidogyne incognita, ability to form conidial traps close to nematode infested soils and their effectiveness in reducing on M. incognita infection indices on tomato. The laboratory assays of nematophagous efficacy of nine nematode-trapping fungi against M. incognita revealed that Dr. dactyloides, Dr. brochopaga, D. gephyropaga and Da. phymatopaga seemed to be the most effective, with 73.2–99.8% trapping and killing of juveniles within 5 days of nematode and fungal interface. Conidial trap forming ability of different species of nematode-trapping fungi showed that Dr. dactyloides, Dr. brochopaga formed frequent formation of conidial traps without intermediate germ tubes whereas Da. phymatopaga and Da. gephyropaga formed adhesive traps on spore germ tubes in close vicinity of root-knot nematode infested soils and killed the nematode present on the agar discs. A. eudermata, A. oligospora, A. conoides, A. thaumasia and A. musiformis frequently germinated by germ tubes in soil and occasionally formed fewer traps. The pot experiment results showed that Dr. brochopaga and Dr. dactyloides, which dominantly formed conidial traps without an intermediate mycelial phase caused the highest decrease in the number of roots-knots (67.2–70.4%), females (80.5–85.8%) and eggs and juveniles (84.9–88.8%) of M. incognita followed by Da. gephyropaga and Da. phymatopaga which formed traps on conidial germ lings and mycelium. A. eudermata, A. oligospora, A. conoides, A. thaumasia and A. musiformis which formed poor conidial traps caused a moderate decrease in the number of root-knots (45.3–53.4%), females (55.5–61.1%), eggs and juveniles (52.9–60.1%) of M. incognita in comparison to control. This paper analyses the effective biocontrol of M. incognita by using different nematode-trapping fungi, especially conidial traps forming fungi and the fate of application of these species in the RKN-infested soil for management of M. ingocnita.

Eco-friendly management of Meloidogyne incognita in cadmium-contaminated soil by using nematophagous fungus Purpureocillium lavendulum YMF1.683: Efficacy and mechanism

Root-knot nematodes (RKNs) are distributed globally, including in agricultural fields contaminated by heavy metals (HM), and can cause serious crop damages. Having a method that could control RKNs in HM-contaminated soil while limit HM accumulation in crops could provide significant benefits to both farmers and consumers. In this study, we showed that the nematophagous fungus Purpureocillium lavendulum YMF1.683 exhibited a high nematocidal activity against the RKN Meloidogyne incognita and a high tolerance to CdCl2. Comparing to the P. lavendulum YMF1.838 which showed low tolerance to Cd2+, strain YMF1.683 effectively suppressed M. incognita infection and significantly reduced the Cd2+ uptake in tomato root and fruit in soils contaminated by 100 mg/kg Cd2+. Transcriptome analyses and validation of gene expression by RT-PCR revealed that the mechanisms contributed to high Cd-resistance in YMF1.683 mainly included activating autophagy pathway, increasing exosome secretion of Cd2+, and activating antioxidation systems. The exosomal secretory inhibitor GW4869 reduced the tolerance of YMF1.683 to Cd2+, which firstly demonstrated that fungal exosome was involved in HM tolerance. The up-regulation of glutathione synthesis pathway, increasing enzyme activities of both catalase and superoxide dismutase also played important roles in Cd2+ tolerance of YMF1.683. In Cd2+-contaminated soil, YMF1.683 limited Cd2+-uptake in tomato by up-regulating the genes of ABCC family in favor of HM sequestration in plant, and down-regulating the genes of ZIP, HMA, NRAMP, YSL families associated with HM absorption, transport, and uptake in plant. Our results demonstrated that YMF1.683 could be a promising bio-agent in eco-friendly management of M. incognita in Cd2+ contaminated soils.

Transcriptome-Based Comparative Expression Profiling of Sweet Potato during a Compatible Response with Root-Knot Nematode Meloidogyne incognita Infection.

M. incognita, a root-knot nematode (RKN), infects the roots of several important food crops, including sweet potato (Ipomoea batatas Lam.), and severely reduces yields. However, the molecular mechanisms underlying infection remain unclear. Previously, we investigated differential responses to RKN invasion in susceptible and resistant sweet potato cultivars through RNA-seq-based transcriptome analysis. In this study, gene expression similarities and differences were examined in RKN-susceptible sweet potato cultivars during the compatible response to RKN infection. Three susceptible cultivars investigated in previous research were used: Dahomi (DHM), Shinhwangmi (SHM), and Yulmi (YM). Of the three cultivars, YM had the highest number of genes with altered expression in response to infection. YM was also the cultivar with the highest susceptibility to RKN. Comparisons among cultivars identified genes that were regulated in more than one cultivar upon infection. Pairwise comparisons revealed that YM and DHM shared the most regulated genes, whereas YM and SHM shared the lowest number of regulated genes. Five genes were up-regulated, and two were down-regulated, in all three cultivars. Among these, four genes were highly up-regulated in all cultivars: germin-like protein, anthranilate synthase α subunit, isocitrate lyase, and uncharacterized protein. Genes were also identified that were uniquely regulated in each cultivar in response to infection, suggesting that susceptible cultivars respond to infection through shared and cultivar-specific pathways. Our findings expand the understanding of the compatible response to RKN invasion in sweet potato roots and provide useful information for further research on RKN defense mechanisms.

Bioassay to characterise the effects of nematicidal compounds on Meloidogyne species

Summary A bioassay was developed to characterise the effects of nematicidal compounds and tested using low concentrations (0.125 and 0.25 mg l−1) of three nematicides: fluensulfone, fluopyram and fluazaindolizine. Germinating lettuce seeds with ca 2-3 mm roots were planted in a 5.5-cm-diam. Petri dish on agar containing the nematicides. Second-stage juveniles (J2) of Meloidogyne javanica and M. incognita were introduced to the agar plate immediately after planting. Alternatively, lettuce seeds were planted 48 h after introducing J2 to the plate. The number of J2 attracted to a root tip and J2 mobility were recorded 19 h after inoculation or planting, and infection rate and root length were recorded 5 days after planting. The three nematicides showed different effects on J2 of the Meloidogyne species. Fluensulfone did not inhibit infection by either species if the lettuce was planted immediately after inoculation, but their infection rates, and especially those of M. incognita, were reduced when lettuce seeds were planted 2 days later. Fluopyram reduced infection with M. javanica J2 at higher rates (>83.3%) than for M. incognita J2 (<58.4%) compared to the control, even without 48 h exposure before planting. Fluazaindolizine reduced M. incognita infection at high rates (>83.3%), although the J2 were attracted to the lettuce roots. Root lengths also showed differences in infection severity. This assay distinguished the effects of the three nematicides on the two Meloidogyne species and can also serve to screen compounds that inhibit nematode infection without killing Meloidogyne J2.