Nematode-infected Plants Research Articles

Evaluation of the lethal effect of hydrogen peroxide on the root-knot nematode, Meloidogyne javanica, and the disruption in the activity of enzymes related to its biosynthesis

Summary In this study, the accumulation of hydrogen peroxide (H2O2) in different parts (healthy root, gall, root attached to gall, aerial parts) of healthy tomato plants and plants infected by the root-knot nematode, Meloidogyne javanica, was investigated after treating the roots with β-aminobutyric acid (BABA). In addition, the effects of different concentrations of H2O2 (0-2 mM) on mortality, body structures and the digestive system of second-stage juveniles (J2) were also investigated in in vitro experiments. Results showed that exposure to concentrations of more than 1 mM H2O2 is lethal for J2, while the digestive system is not able to tolerate concentrations of more than 0.2 mM. Evaluating the activity level of enzymes related to biosynthesis and removing H2O2 in treated plants also showed that the nematode has significant suppressive effects on the biosynthesis enzymes of this compound, and this effect is greater in the site of nematode activity than in other parts of the plant. By contrast, the activity of catalase enzyme, as one of the H2O2-removing enzymes, shows a significant increase in all parts of nematode infected plants (especially in galls).

Dicer-like 3a mediates intergenerational resistance against root-knot nematodes in rice via hormone responses.

In a continuously changing and challenging environment, passing down the memory of encountered stress factors to offspring could provide an evolutionary advantage. In this study, we demonstrate the existence of 'intergenerational acquired resistance' in the progeny of rice (Oryza sativa) plants attacked by the belowground parasitic nematode Meloidogyne graminicola. Transcriptome analyses revealed that genes involved in defense pathways are generally downregulated in progeny of nematode-infected plants under uninfected conditions but show a stronger induction upon nematode infection. This phenomenon was termed "spring loading" and depends on initial downregulation by the 24nt siRNA biogenesis gene dicer-like 3a (dcl3a) involved in the RNA-directed DNA methylation pathway. Knock-down of dcl3a led to increased nematode susceptibility and abolished intergenerational acquired resistance, as well as jasmonic acid/ethylene spring loading in the offspring of infected plants. The importance of ethylene signaling in intergenerational resistance was confirmed by experiments on a knock-down line of ethylene insensitive 2 (ein2b), which lacks intergenerational acquired resistance. Taken together, these data indicate a role for DCL3a in regulating plant defense pathways during both within-generation and intergenerational resistance against nematodes in rice.

Alleviation of Meloidogyne incognita induced biotic stress in Daucus carota by nitrogen: Insights into cellular viability and reactive oxygen species of the host

Developing innovative nematode management solutions is becoming more important since ecologically hazardous nematicides are being phased out of the global markets. As a result, alternative measures that are less harmful to the environment are preferred for dealing with the root-knot nematodes which cause huge economic losses to farmers. This investigation was therefore, entailed to find the optimum nitrogen fertilizer rate to maximize plant growth promotion and upsurge nematicidal activity, while minimizing the harmful effects on environment. Among the various nitrogen fertilizer treatments from 50 kg/ha to 200 kg/ha, the most effective concentration was found to be 150 kg/ha N (U150Mi) at which significant (P ≤ 0.05) improvements in growth, yield, photosynthetic pigments, nitrate reductase activity (NRA), protein, and carbohydrate content of carrot were observed as compared to the nematode inoculated untreated plants. Scanning electron microscopy showed that compared to the untreated inoculated control, the stomatal characteristics of carrot improved significantly at U150Mi (150 kg/ha N). Laser confocal microscopy illustrated that nitrogen fertilizer markedly improved the cellular viability of carrot at U150Mi (150 kg/ha N) in comparison to nematode infected plants. Histochemical analysis revealed that the reactive oxygen species (ROS) marker, superoxide anion radicals were significantly scavenged by the enhanced antioxidant defense system of carrot at U150Mi (150 kg/ha N). In vitro studies demonstrate that nitrogen fertilizer has nematicidal properties that were dose dependent. Gall/egg mass indices and reproduction factor were dramatically reduced when U150Mi (150 kg/ha N) was applied to carrot plants inoculated with Meloidogyne incognita.

Comparative Effectiveness of Filamentous Fungi in Biocontrol of Meloidogyne javanica and Activated Defense Mechanisms on Tomato.

The nematicidal potential of five filamentous fungi as biological control agents (BCAs) against the root-knot nematode (RKN), Meloidogyne javanica, infecting tomato was assessed in vitro and in pot experiments. The five promising native taxa, namely Trichoderma longibrachiatum, T. harzainum, T. asperellum, Lecanicillium spp., and Metacordyceps chlamydosporia, were selected to compare their effectiveness against both chemical (Mocap, 10% ethoprophos) and biological (abamectin) nematicides on M. javanica reproduction indices and plant growth parameters. The stimulation of defense mechanisms was assessed by monitoring changes in the enzymatic activities of the polyphenol oxidase (PPO), peroxidase (POD), ascorbate peroxidase (APX), catalase (CAT), lipid peroxidation (MDA), phenols, and proteins content of tomato roots. The laboratory assays revealed that T. longibrachiatum, M. chlamydoporia, and Lecanicillium spp. seemed to be the most effective under laboratory conditions, with more than 60% of juvenile mortality. The egg infection rate was above 62%, and the egg hatching rate was below 32%. The direct parasitism by the five taxa was confirmed by scanning electron microscope observation. The results of this study found a similar parasitism mechanism for T. longibrachiatum, T. harzianum, and M. chlamydosporia, where their hyphae and spores adhered to the M. javanica juveniles cuticle layer and formed trapping rings around them. The pot experiment results showed that T. harzianum and Lecanicillium spp. enhanced the plant growth parameters. Trichoderma longibrachiatum, abamectin, and the ethoprophos-based nematicides effectively decreased the reproduction rates of the nematode. The Trichoderma species and M. chlamydosporia significantly reduced the gall index and female fecundity of RKN. The treatment with BCAs and chemical nematicides involved a significant increase in the antioxidant activities of nematode-infected plants. The ethoprophos and fungal treatments decreased the MDA and total phenols content compared with the nematode-infested seedlings. This paper analyzes the advancements made towards the effective and efficient biocontrol of M. javanica using different fungal taxa, especially T. longibrachiatum and M. chlamydosporia, and the implications of these advancements for sustainable agriculture and food security.

Modulation of Various Phytoconstituents in Tomato Seedling Growth and Meloidogyne incognita–Induced Stress Alleviation By Vermicompost Application

In addition to chemical pesticides and fertilizers, the use of vermicompost can help in the management of root-knot nematodes (RKN) while also augmenting plant growth. The present study is carried out to determine the role of neem-based vermicompost on plant growth during stress produced by Meloidogyne incognita. Vermicompost (Vcom) and soil were mixed in various proportions (0, 20, 40, 60, 80, and 100%) and used to treat tomato plants against nematode infestation. After 10 days of inoculation of second-stage juveniles of M. incognita, several morphological parameters such as root length, shoot length, root weight, shoot weight, number of galls, and number of leaves were evaluated to investigate the plant growth. Various photosynthetic pigments (chlorophyll a and b, total chlorophyll, and carotenoid content) and gaseous exchange parameters (photosynthesis rate, intercellular carbon dioxide intensity, stomatal conductance, and transpiration rate) were also investigated in order to better understand plant respiration and response to nematode stress. In biochemical studies, the protein content and unit activity of antioxidative enzymes such as catalase, superoxide dismutase, guaiacol peroxidase, glutathione-s-transferase, ascorbate peroxidase, and polyphenol oxidase were investigated. The analyses of malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents were also performed to examine the stress caused by nematodes and the effect of vermicompost in overcoming that stress. Aside from that, the influence of vermicompost on several bioactive components of plants was investigated by quantifying non-antioxidative enzymes (ascorbic acid, glutathione, and tocopherol levels) and secondary metabolites (total phenolic, total flavonoid, and anthocyanin contents). The results of the foregoing experiments reveal a significant increase in all morphological, biochemical, and photosynthetic parameters except MDA and H2O2, which tend to decrease with increasing vermicompost concentration as compared to untreated and nematode-infected plants. The current study reveals that vermicompost has a high potential for lowering the nematode stress and enhancing plant growth and development through the augmentation of different bioactive components in plants.

Kök lezyon nematodlarının (Pratylenchus thornei) nohut bitkisinin rhizobium bakterileri üzerinde etkisi

Chickpea (Cicer arietinum) is one of the most significant legume crops and supply high-quality protein for human nutrition. legume crops such as chickpea are important agriculturally because of their symbiotic ability to nitrogen fixation with specific soil bacteria. Legumes like chickpea depend on nitrogen provided by the activity to grow, but these rhizobium bacteria are affected by plant-parasitic nematodes that cause less activity and decrease the number of nodules in the chickpea plant. The root-lesion nematodes (Pratylenchus thornei) are common and economically important pests described as one of the major limiting factors in agriculture and the growing chickpea field in the world. In this study, the effects of this nematode on the number of rhizobia (nodules) and rhizobium bacteria activity were assessed in both wild and domesticated accession of Cicer species under laboratory conditions. We inoculated all Cicer accession with the Mesorhizobium bacteria and with one species of the genus Pratylenchus (P. thornei). The result showed that P. thornei has a negative impact on the number of nodules and the activity of rhizobium bacteria. Nematode infection on chickpea caused decreased nodulation. Where, nematode infected plant formed 4-8 nodules/root and less nodule number than an uninfected plant.

Phenol and antioxidant enzymatic activity in root knot nematode, Meloidogyne incognita infected tomato plants treated with chitosan nanoparticles

Root knot nematode, Meloidogyne spp. causes severe yield losses in vegetable crops. Chitosan is one of the most abundant biopolymer available worldwide next to cellulose. It is known to have anti-nemic, anti-fungal and anti- bacterial properties. Application of chitosan induces systemic resistance in tomato plants against pathogens by increasing phenolic content and antioxidant enzymes viz., Polyphenol oxidase, Superoxide dismutase and phytoalexins. A study was conducted to study the phenol content and activity of antioxidant enzymes, polyphenol oxidase and peroxidase activities in root knot nematode infected tomato plants treated with chiotsan nanoparticles. The antioxidant enzymatic activities were recorded after 25th day of nematode inoculation. It was observed that the phenolic content increased due to the application of chitosan nanoparticle in nematode infected plants (174.32 µg/g of root) compared to 160.37 µg/g of root in untreated plants. Similarly the peroxidase and polyphenol oxidase activity also increased in chitosan nanoparticle treated nematode infected plants. The study revealed that chitosan nano particles protect plants from root knot nematode infection by increasing the phenol content, peroxidase and polyphenol oxidase activity and induce systemic resistance against nemayodes.

Current Utility of Arbuscular Mycorrhizal Fungi and Hydroxyapatite Nanoparticles in Suppression of Tomato Root-Knot Nematode

Effective biosafe management strategies are used to decrease world crop damage produced by plant-parasitic nematodes. This study evaluated the efficiency of hydroxyapatite nanoparticles (n-HAP) and mycorrhizal fungi to control the Meloidogyne incognita infecting tomato plants. Application of n-HAP significantly increased the juveniles’ mortality (195.67%) and egg hatching inhibition percentage (80.71%) compared to the untreated control, in vitro. Mycorrhizal and/or n-HAP treatments increased the plant growth parameters (root and shoot length, dry weight, and leaf area) and reduced the negative consequence of nematode infection. This may be due to indirect mechanisms through increasing plant nutrient uptake efficiency and increasing the internal plant resistance against nematode infection. In dual-treated plants, phosphorus, nitrogen, and calcium content recorded the highest value in the nematode-infected plants. Whereas the dual inoculation significantly increased mineral contents in tomato plants compared with control, this may induce the strength of the cell wall of the epidermal layer and cortex and consequently increase the plant resistance against nematode infection. Our results revealed that the application of the plant resistance-stimulants enhanced the plant growth parameters and internal nutrient content and reduced the nematode’s criteria. Consequently, the internal plant resistance against nematode infection was induced.

A Semi-supervised approach to cluster symptomatic and asymptomatic leaves in root lesion nematode infected walnut trees

• Pratylenchus vulnus infection in walnut detectable with hyperspectral data. • Agglomerative clustering with spectral angle mapper can isolate symptomatic leaves. • MDPA between control and infected histograms allows high-throughput phenotyping. • Rootstocks ranked least to most impacted by P. vulnus : VX211, MS1 122, MS1 127. Breeding strategies for many crops require quantitative evaluations of many genotypes from within as large of a diverse breeding pool as possible. In selecting pathogen tolerant genotypes, accurate and fast phenotyping to investigate genetic responses to pathogen infection and reproduction is crucial. Analyzing leaf tissues with spectral tools along with ground truth data offers potentially large gains in screening efficiency. However, ground truth labels per plant may not capture the effects of asymptomatic leaves and heterogeneous canopy responses to stress. We explored a semi-supervised clustering-based technique in which spectral patterns unique to and common among leaves from nematode infected plants are distinguished from patterns with no relationship to infection; we utilize these spectral patterns in ranking genotype tolerances to infection as a secondary objective. Proximal hyperspectral leaf scans (360 nm–1700 nm) of three walnut rootstock genotypes (MS1 122, VX211, MS1 127) were used in an agglomerative clustering procedure based on spectral angle mapper (SAM) distances to choose a spectral endmember representing the root lesion nematode, Pratylenchus vulnus , stress symptom on leaf per genotype. The histogram of SAM distances between control samples and the endmember was calculated. Next, the histogram of SAM distances between infected samples and the endmember was calculated. The shift between these histograms was then found using the minimum difference of pair assignments (MDPA) measure. The MDPA measures were 4.88, 3.14, and 5.48 for MS1 122, VX211, and MS1 127, respectively. This meant a genotype ranking in the order VX211, MS1 122 and, MS1 127 from the least affected by nematode infection to most impacted, which agreed with classification by nematological examinations of the plants. Clustering leaves based on their spectral response has the potential to overcome the limitation of heterogeneous canopy responses to stress in high-throughput phenotyping and other applications.

Pre-inoculation with arbuscular mycorrhizal fungi affects essential oil quality and the reproduction of root lesion nematode in Cymbopogon citratus.

Cymbopogon citratus (lemongrass) is an important medicinal and aromatic plant containing citral-rich essential oil, of which the quality and quantity may be affected by nematode infection. Research has shown that arbuscular mycorrhizal fungi (AMF) may act as nematode biocontrol agents and improve the chemical composition of plants. Three experiments were conducted to assess the effects of AMF inoculation on vegetative growth, essential oil composition, induction of defense-related proteins, and control of Pratylenchus brachyurus in C. citratus. Seedlings were transplanted into pots inoculated with one of two AMF species (Rhizophagus clarus or Claroideoglomus etunicatum). At 30days after AMF inoculation, plants were inoculated with P. brachyurus. Evaluations were performed at 75days after nematode inoculation. Although both AMF treatments led to effective root colonization (> 84%), fungus inoculation was not effective in reducing P. brachyurus population density. Nevertheless, C. etunicatum promoted an increase in shoot weight, and AMF treatments contributed to preserving essential oil composition in nematode-infected plants. In addition, both AMF treatments enhanced polyphenol oxidase activity and R. clarus increased peroxidase activity after nematode inoculation.

Influence of Meloidogyne javanica parasitism on soybean development and chemical composition

BackgroundSoybean is a major economic crop worldwide, but its yield and quality are greatly affected by root-knot nematode infection. This study aimed to assess the effects of Meloidogyne javanica parasitism on soybean growth, yield, and quality. Soybean plants were inoculated with 0, 1000, 2000, or 4000 eggs + second-stage juveniles (J2) of M. javanica and evaluated for vegetative and nematode parameters. Grains from each treatment were analyzed for yield, proximate composition, total phenolic content, total flavonoid content, isoflavone profile, and antioxidant capacity.ResultsPlants free of nematodes had lower vegetative growth and higher yield than nematode-infected plants. The maximum estimated reproduction factor was 34.85, achieved by inoculation of 2433 eggs + J2. Moisture, fiber, and protein contents decreased with increasing inoculum levels. Lipid content increased with inoculum level until reaching 22.59 g 100 g−1 of sample. Total phenolic and flavonoid contents decreased with increasing inoculum level up to about 2000 eggs + J2 and then increased until reaching 219.20 mg gallic acid equivalents 100 g−1 of sample and 121.67 mg quercetin equivalent 100 g−1 of sample, respectively, at 4000 eggs + J2. A similar behavior was observed for antioxidant capacity determined by the 2,2-diphenyl-1-picrylhydrazyl radical scavenging, superoxide radical scavenging, and ferric reducing antioxidant power assays. The highest contents of malonylgenistin (539 mmol g−1), acetylglycitin (106 mmol g−1), and genistin (87 mmol g−1) were found in grains from plants inoculated with 4000 eggs + J2.ConclusionsM. javanica inoculum level affected soybean development, grain production, yield, composition, and antioxidant capacity.

Belowground plant-plant signaling of root infection by nematodes

Communication between plants mediated by herbivore-induced volatile organic compounds has been extensively studied aboveground. However, the role of root herbivory in belowground plant-plant communication is much less understood. We here investigated whether root herbivores can trigger plant roots to emit warning signals to neighbouring plants that are not yet in direct contact with them.We used a split-root system and infected half of the roots of Agrostis stolonifera plants with root-knot nematodes (Meloidogyne minor) and left the other half uninfected. As a control, we grew plants without nematodes in separate pots. Leachates from each split-root soil compartment and from soils with control plants were applied to separate pots with A. stolonifera plants, of which biomass allocation and morphological traits were measured one month after leachate addition.Plants receiving leachates from the soil with the nematode-free roots of the nematode-infected plants showed a significantly larger total biomass, more root branches, and deeper rooting than plants receiving leachates from the soil with the nematode-infected roots or from soil with control plants. Plants were taller and the root/shoot ratio was higher in plants receiving leachates from soil with the nematode-free roots than in plants receiving leachates from soil with nematode-infected roots. Shoot tiller number was higher in plants receiving leachates from either root compartment of the nematode-infected plants than in plants receiving control leachates.Our results suggest that an overcompensation response was triggered by systemically induced root-derived compounds from nematode-free roots of a plant locally infected with root-feeding nematodes. Signals from directly attacked roots of the same nematode-infected plant only caused receiver plants to develop more shoot tillers, possibly for future stolon development to grow away from the infected area. This may indicate an anticipatory tolerance response to root feeders that are still distant and an additional generalized escape response to root feeding.

Phytochemistry-mediated disruption of ant-aphid interactions by root-feeding nematodes.

Plants link interactions between aboveground and belowground organisms. Herbivore-induced changes in plant chemistry are hypothesized to impact entire food webs by changing the strength of trophic cascades. Yet, few studies have explored how belowground herbivores affect the behaviors of generalist predators, nor how such changes may act through diverse changes to the plant metabolome. Using a factorial experiment, we tested whether herbivory by root-knot nematodes (Meloidogyne incognita) affected the aboveground interaction among milkweed plants (Asclepias fascicularis or Asclepias speciosa), oleander aphids (Aphis nerii), and aphid-tending ants (Linepithema humile). We quantified the behaviors of aphid-tending ants, and we measured the effects of herbivore treatments on aphid densities and on phytochemistry. Unexpectedly, ants tended aphids primarily on the leaves of uninfected plants, whereas ants tended aphids primarily at the base of the stem of nematode-infected plants. In nematode-infected plants, aphids excreted more sugar per capita in their ant-attracting honeydew. Additionally, although plant chemistry was species-specific, nematode infection generally decreased the richness of plant secondary metabolites while acting as a protein sink in the roots. Path analysis indicated that the ants' behavioral change was driven in part by indirect effects of nematodes acting through changes in plant chemistry. We conclude that belowground herbivores can affect the behaviors of aboveground generalist ant predators by multiple paths, including changes in phytochemistry, which may affect the attractiveness of aphid honeydew rewards.

The impact of Spodoptera exigua herbivory on Meloidogyne incognita-induced root responses depends on the nematodes' life cycle stages.

Induced responses to above-ground and below-ground herbivores may interact via systemic signalling in plants. We investigated whether the impact of above-ground herbivory on root-knot nematode-induced responses depends on the nematode’s life cycle stages. Tomato plants were infected with the nematode (Meloidogyne incognita) for 5, 15 or 30 days before receiving Spodoptera exigua caterpillars above-ground. We collected root materials after 24 h of caterpillar feeding. We investigated phytohormones and α-tomatine levels, and the expression of defence and glycoalkaloid metabolism (GAME) marker genes in tomato roots. Nematode infection alone increased the endogenous root levels of jasmonic acid (JA), salicylic acid (SA), abscisic acid (ABA), α-tomatine and the expression of the GLYCOALKALOID METABOLISM 1 (GAME1) gene mostly at 30 days post-nematode inoculation. Caterpillar feeding alone upregulated Lipoxygenase D and downregulated Basic-β-1-glucanase and GAME1 expression in roots. On nematode-infected plants, caterpillar feeding decreased JA levels, but it increased the expression of Leucine aminopeptidase A. The induction patterns of ABA and SA suggest that caterpillars cause cross-talk between the JA-signalling pathway and the SA and ABA pathways. Our results show that caterpillar feeding attenuated the induction of the JA pathway triggered by nematodes, mostly in the nematodes’ reproduction stage. These results generate a better understanding of the molecular and chemical mechanisms underlying frequent nematode–plant–caterpillar interactions in natural and agricultural ecosystems.

Combined of salicylic acid and Pseudomonas fluorescens CHA0 on the expression of PR1 gene and control of Meloidogyne javanica in tomato

Root-knot nematodes (Meloidogyne spp.) are among the most dangerous herbal parasites which destroy 8.8 to 14.6 percent of agricultural products annually. This study examined inducing resistance to tomato against Meloidogyne javanica, as well as time-dependent changes in the expression of PR1 gene, after applying salicylic acid (SA) and Pseudomonas fluorescens CHA0 (Pf) in the leaf tissue of healthy and infected tomatoes. Combined application of SA and Pf improved the plant growth and reduced root-galling, the number of eggs and egg-masses and reproduction factor. The results of the experiment of gene expression revealed that in all of the treatments, the expression of PR1 gene changed at different time points. The expression of PR1 gene in infected plants, 24 h after inoculation with nematode, was 98% higher than that of the control plants and 48 h after nematode inoculation, was about 58% less than that of control plants. The maximum expression of PR1 gene in nematode infected plants treated with Pf + SA was observed eight days after soil drench application of Pf that was 48 h after treatment with SA and 24 h after nematode inoculation and nine days after application of Pf, downregulation of the PR1 gene occurred. This study revealed that SA and Pf improved the plant growth indices and reduced the infection of Meloidogyne javanica in tomato plants and also it was observed that the expression of PR1 gene was significantly reduced in treatments with Pf and SA, as compared to their combination.

Impact of Plant Growth Promoting Rhizobacteria in the Orchestration of Lycopersicon esculentum Mill. Resistance to Plant Parasitic Nematodes: A Metabolomic Approach to Evaluate Defense Responses Under Field Conditions.

The present study deals with biological control of Meloidogyne incognita in 45-days old Lycopersicon esculentum, inoculated with Pseudomonas aeruginosa(M1) and Burkholderia gladioli (M2). The improved plant growth and biomass of nematode infested Plant growth promoting rhizobacteria (PGPR) inoculated plants was observed. Remarkable reduction in the numbers of second stage juvenile (J2s), root galls was recorded after treatment of microbes relative to experimental controls. Moreover, the lowered activities of oxidative stress markers (H2O2 (hydrogen peroxide), O2− (superoxide anion), malondialdehyde (MDA)) was estimated in plants after rhizobacterial supplementation. Higher activities of enzymatic (SOD (Superoxide dismutase), POD (Guaiacol peroxidase), CAT (Catalase), GPOX (Glutathione peroxidase), APOX (Ascorbate peroxidase), GST (Glutathione-S-transferase), GR (Glutathione reductase), DHAR (Dehydroascorbate reductase), PPO (Polyphenol oxidase)) and non-enzymatic (glutathione, ascorbic acid, tocopherol) antioxidants were further determined in nematode infected plants following the addition of bacterial strains. The upregulation of photosynthetic activities were depicted by evaluating plant pigments and gas exchange attributes. An increase in the levels of phenolic compounds (total phenols, flavonoids, anthocyanins), osmoprotectants (total osmolytes, carbohydrates, reducing sugars, trehalose, proline, glycine betaine, free amino acids) and organic acids (fumaric, succinic, citric, malic acid) were reflected in infected plants, showing further enhancement after application of biocontrol agents. The study revealed the understanding of plant metabolism, along with the initiative to commercially exploit the biocontrol agents as an alternative to chemical nematicides in infected fields for sustainable agriculture.

Evaluation of the role of Rhizobacteria in controlling root knot nematode (RKN) infection in Lycopersicon esculentum plants by modulation in the secondary metabolite profiles

Abstract Environmental stress imposes negative impacts on the growth and development of the crop plants. The present study was designed to assess the effect of PGPR (Pseudomonas aeruginosa and Burkholderia gladioli) on plant pigments and phenolic compounds in 10-days-old root knot nematode (RKN)-infected Lycopersiconesculentum seedlings. The levels of different osmoprotectants and organic acids were also evaluated in nematode-infected L. esculentum seedlings. Our results revealed that nematode-infected seedlings had reduced levels of plant pigments(chlorophyll (70.5%), carotenoids (64.8%), and xanthophylls (34.3%)) and enhanced levels of phenolic compounds(total phenols (40.3%), flavonoids (80.9%), anthocyanins (28.9%), and polyphenols (366.1%)), osmoprotectants(total osmolytes (15.3%), total carbohydrates (54.9%), reducing sugars (45.3%), trehalose (94.5%), glycine betaine (59.01%) and proline (69.6%) and (citric acid (28.4%), fumaric acid (18.16%), succinic acid (179.9%), and malic acid (21.7%)). The levels of these metabolites increased after inoculation with P. aeruginosa and B. gladioli. The expression of genes encoding different enzymes pertaining to phenols and organic acid metabolism were also studied. The expression of genes was elevated in nematode-infected plants i.e. CHS (chalcone synthase) by 1.32 folds, PAL (phenylalanine ammonia lyase) by 1.16 folds, CS (citrate synthase)1.6 folds, SUCLG1 (succinyl Co-A ligase) by 1.19 folds, SDH (succinate dehydrogenase) by 1.92 folds, FH (fumarate hydratase) by 2.4 foldsand malate synthase (MS) by 1.26 folds and further upregulated after PGPR inoculation. This study demonstrates the importance of PGPR in managing nematode infection in plants through alteration in the synthesis of different secondary metabolites in plants.

Additive interaction between a root-knot nematode Meloidogyne javanica and a root-feeding flea beetle Longitarsus bethae on their host Lantana camara.

Changes in plants induced by one species have indirect effects on interactions with other species, thus shaping their abundances. The root-feeding beetle Longitarsus bethae released as a biological control agent for Lantana camara has established at a few sites in South Africa. Lantana camara plants infected with the root-knot nematode Meloidogyne javanica often exhibit an increase in L. bethae abundance, suggesting that nematode-infected plants could be enhancing the development of the beetle. This study investigated the interaction between L. bethae and M. javanica. The study showed that galling by M. javanica occurred at the highest inoculation of 300 eggs of L. bethae per plant. Longitarsus bethae performed over twofold better on M. javanica-infected L. camara roots compared with healthy roots, and 275 adult L. bethae progeny, with slightly larger body size, emerged from M. javanica-infected compared with 167 adults that emerged from healthy plants. Fresh gall weight from treatments where both L. bethae and M. javanica were combined was 36% higher than that from M. javanica only, suggesting that the combination of both species induces more galling than the nematode does alone. The total biomass of plants with M. javanica only, L. bethae only, and the two species combined was reduced by 48%, 24% and 50%, respectively. Meloidogyne javanica improves the performance of L. bethae, and combination of the two species has an additive negative effect on L. camara. The interaction between M. javanica and L. bethae could enhance the biological control of L. camara. © 2019 Society of Chemical Industry.

Consortia of anti-nematode fungi and bacteria in the rhizosphere of soybean plants attacked by root-knot nematodes.

Cyst and root-knot nematodes are major risk factors of agroecosystem management, often causing devastating impacts on crop production. The use of microbes that parasitize or prey on nematodes has been considered as a promising approach for suppressing phytopathogenic nematode populations. However, effects and persistence of those biological control agents often vary substantially depending on regions, soil characteristics and agricultural practices: more insights into microbial community processes are required to develop reproducible control of nematode populations. By performing high-throughput sequencing profiling of bacteria and fungi, we examined how root and soil microbiomes differ between benign and nematode-infected plant individuals in a soybean field in Japan. Results indicated that various taxonomic groups of bacteria and fungi occurred preferentially on the soybean individuals infected by root-knot nematodes or those uninfected by nematodes. Based on a network analysis of potential microbe–microbe associations, we further found that several fungal taxa potentially preying on nematodes (Dactylellina (Orbiliales), Rhizophydium (Rhizophydiales), Clonostachys (Hypocreales), Pochonia (Hypocreales) and Purpureocillium (Hypocreales)) co-occurred in the soybean rhizosphere at a small spatial scale. This study suggests how ‘consortia’ of anti-nematode microbes can derive from indigenous (resident) microbiomes, providing basic information for managing anti-nematode microbial communities in agroecosystems.

Water availability and root-knot nematode management alter seedcotton yield through similar effects on fruit distribution patterns

Both root-knot nematode (RKN) infection and water deficit negatively affect yields in many cotton growing regions of the southern United States. The objective of the current study was to determine whether seedcotton yield limitations due to drought and RKN infection were brought about through similar effects on yield components and boll distribution patterns. To this end, yield component and boll distribution assessments were conducted for a seven-year study in Tifton, Georgia that included three irrigation treatments and two fumigant treatments to manage nematodes. Seedcotton yield was strongly affected by year, irrigation treatment and fumigant treatment, but no interactions were observed between the two factors, illustrating that the yield limiting effects of nematode infection could not be mitigated by providing a water-replete condition. Yield declines due to nematode infection and water deficit were primarily driven by a decline in total boll density. Yield distribution patterns revealed that water deficit negatively affected boll numbers for all branch types and at all positions along a fruiting; furthermore, the mainstem node of peak boll distribution was lower under drought. The trend was similar for nematode infected plants (except that boll density at position two was not affected by fumigation and retention at position three increased slightly). One notable difference between drought and nematode effects was that the relative decline in boll density for drought-stressed plants was greater at sympodial positions further from the mainstem, but this was not the case due to nematode infection.