Vanillin in Resistant Tomato Plant Root Exudate Suppresses Meloidogyne incognita Parasitism.

Tomato (Solanum lycopersicum) plants are susceptible to infection by root-knot nematodes, which cause severe economic losses. Planting resistant tomato plants can reduce nematode damage; however, the effects of resistant tomato root exudates in suppressing Meloidogyne incognita remain insufficiently understood. Here, we determined that the resistant tomato plant Lycopersicon esculentum cv. Xianke-8 (XK8) alleviates nematode damage by downregulating the expression of the essential parasitic nematode gene Mi-flp-18 to reduce the infection and reproduction of M. incognita. Using gas chromatography-mass spectrometry, we identified vanillin as a unique compound (compared to susceptible tomato cultivars) in XK8 root exudates that acts as a lethal trap and inhibitor of egg hatching. Moreover, the soil application of 0.4-4.0 mmol/kg vanillin significantly reduced galls and egg masses. The parasite gene Mi-flp-18 was downregulated upon treatment with vanillin, both in vitro and in pot experiments. Collectively, our results reveal an effective nematicidal compound that can use in feasible and economical strategies to control RKNs.

Watermelon Root Exudates Enhance Root Colonization of Bacillus amyloliquefaciens TR2.

Bacillus amyloliquefaciens TR2, one of plant growth-promoting rhizobacteria (PGPR), is capable of colonizing plant roots in a large population size. However, the interaction of watermelon root exudates and colonization of the strain TR2 has not yet been clearly elucidated. In this investigation, we demonstrated that B. amyloliquefaciens TR2 promoted watermelon plants growth and exhibited biocontrol efficacy against watermelon Fusarium wilt under greenhouse conditions. Collected watermelon root exudates significantly induced chemotaxis, swarming motility, and biofilm formation of the strain TR2. We also tested the components of root exudates (organic acids: malic acid, citric acid, succinic acid, and fumaric acid; amino acids: methionine, glutamic acid, alanine, and aspartic acid; phenolic acid: benzoic acid) and the results showed that a majority of these compounds could promote chemotactic response, swarming motility, and biofilm formation in a different degree. Benzoic acid induced the strongest chemotactic response; however, the swarming motility and biofilm formation of the strain TR2 were maximumly enhanced by supplement of fumaric acid and glutamic acid, respectively. In addition, the root colonization examination indicated that the population of B. amyloliquefaciens TR2 colonized on watermelon root surfaces was dramatically increased by adding concentrated watermelon root exudates. In summary, our studies provide evidence suggesting that root exudates are important for colonization of B. amyloliquefaciens TR2 on plant roots and help us to understand the interaction between plants and beneficial bacteria.

Maize Root Exudates Recruit Bacillus amyloliquefaciens OR2-30 to Inhibit Fusarium graminearum Infection.

Bacillus spp. can exert plant growth-promoting effects and biocontrol effects after effective colonization, and bacterial chemotaxis toward plant root exudates is the initial step to colonize. Under biotic stress, plants are able to alter their root exudates to attract or avoid different types of microbes. Hence, Bacillus chemotaxis toward root exudates after pathogen infection is crucial for exerting their beneficial effects. In this study, the Bacillus amyloliquefaciens OR2-30 strain, which exhibited greater chemotaxis ability toward maize root exudates after Fusarium graminearum infection, was screened from 156 rhizosphere microorganisms. The infected maize root exudates were further confirmed to improve the swarming and biofilm formation ability of the OR2-30 strain. Chemotaxis, swarming, and biofilm formation ability were able to influence bacterial colonization. Indeed, the the OR2-30 strain displayed more effective colonization ability in the maize rhizosphere after F. graminearum inoculation. Moreover, lipopeptides produced by OR2-30 were identified as iturins and responsible for suppressing F. graminearum growth. Further study showed that lipopeptides suppressed the growth of F. graminearum by inhibiting conidia formation and germination, inducing reactive oxygen species production and causing cell death in mycelium. Eventually, the OR2-30 strain increased maize resistance against F. graminearum. These results suggested that maize root exudates could recruit B. amyloliquefacines OR2-30 after F. graminearum infection, and that OR2-30 then suppresses the F. graminearum by producing lipopeptides, such as iturins, to protect maize.

Faba bean root exudates alter pea root colonization by the oomycete Aphanomyces euteiches at early stages of infection.

Aphanomyces euteiches is an oomycete pathogen that causes the pea root rot. We investigated the potential role of early belowground defense in pea (susceptible plant) and faba bean (tolerant plant) at three days after inoculation. Pea and faba bean were inoculated with A. euteiches zoospores. Root colonization was examined. Root exudates from pea and faba bean were harvested and their impact on A. euteiches development were assessed by using in vitro assays. A. euteiches root colonization and the influence of the oomycete inoculation on specialized metabolites patterns and arabinogalactan protein (AGP) concentration of root exudates were also determined. In faba bean root, A. euteiches colonization was very low as compared with that of pea. Whereas infected pea root exudates have a positive chemotaxis index (CI) on zoospores, faba bean exudate CI was negative suggesting a repellent effect. While furanoacetylenic compounds were only detected in faba bean exudates, AGP concentration was specifically increased in pea.This work showed that early in the course of infection, host susceptibility to A. euteiches is involved via a plant-species specific root exudation opening new perspectives in pea root rot disease management.

Activity of Adesmia boronioides resinous exudate against phytopathogenic bacteria.

Resinous exudate obtained from the aerial parts of Adesmia boronioides Hook.f. were evaluated to determine anti-phytopathogenic effects. Briefly, resinous exudate was obtained by dipping fresh plant material in dichloromethane; chemical composition was determined by GC-MS; and minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were evaluated against four phytopathogenic bacteria. Resinous exudate yield was 8.5% (resin/fresh plant), of which esquel-6-en-9-one (14.25%), esquel-7-en-9-one (5.86%), and veratric acid (2.59%) were the effective antibacterial compounds. Tested against Pectobacterium carotovorum subsp. carotovora, Erwinia amylovora, Bacillus subtilis, and Pseudomonas syringae, MICs and MBCs ranged from 16 to 128 µg/mL and 32-256 µg/mL, respectively. These results provide initial evidence that resinous bush A. boronioides is a new and alternative source of substances with agricultural interest.

Constituents Leached by Tomato Seeds Regulate the Behavior of Root-Knot Nematodes and Their Antifungal Effects against Seed-Borne Fungi.

Germinating seeds can release diverse phytochemicals that repel, inhibit, or kill pathogens such as root-knot nematodes and seed-borne fungi. However, little is known about the composition of these phytochemicals and their effects on pathogens. In this study, we demonstrated that tomato seed exudates can attract the nematode Meloidogyne incognita using a dual-choice assay. Eighteen compounds were then isolated and identified from the exudates. Of these, esters (1-3), fatty acids (4-6), and phenolic acids (10-12) were proven to be the signaling molecules that facilitated the host-seeking process of second-stage juveniles (J2s) of nematodes, while alkaloids (17 and 18) disrupted J2s in locating their host. Furthermore, some phenolic acids and alkaloids showed antifungal effects against seed-borne fungi. In particular, ferulic acid (12) showed obvious activity against Aspergillus flavus (minimum inhibitory concentration (MIC), 32 µg/mL), while dihydrocapsaicin (17) showed noticeable activity against Fusarium oxysporum (MIC, 16 µg/mL). Overall, this study presents the first evidence that M. incognita can be attracted to or deterred by various compounds in seed exudates through identification of the structures of the compounds in the exudates and analysis of their effects on nematodes. Furthermore, some antifungal compounds were also found. The findings of this work suggest that seed exudates are new source for finding insights into the development of plant protective substances with nematocidal and antifungal effects.

Co-cultivation of Beta vulgaris limits the pre-harvest colonization of foodborne pathogen (Salmonella spp.) on tomato.

Soil-borne Salmonella is associated with a large number of food-related disease outbreaks linked to pre-harvest contamination of plants (like tomato) in agricultural fields. Controlling the spread of Salmonella at field is very important in order to prevent various food-borne illnesses. One such approach involves the utilization of antimicrobial secondary metabolite of plant origin. We screened common salad vegetables for anti-Salmonella activity. Beta vulgaris root (beetroot) had very low colonization of Salmonella under in vitro conditions. We hypothesized that beetroot can be used to reclaim the soil contaminated with Salmonella. Cultivation of B. vulgaris in Salmonella treated soil brings down its CFU significantly. Since these antimicrobial effects are non-specific, a co-cultivation system of beet and tomato (a Salmonella susceptible plant) was used to analyze the effect on soil and its microbiota. The soil physicochemical properties and bacterial diversity were unaffected when tomato and beet co-cultivation was used. However, Salmonella burden on the tomato was reduced and its yield was restored. Thus, the inclusion of these crops in the crop-rotation or as a mixed/intercrop or as a bio-control crop can be a fruitful tool to reclaim the Salmonella contaminated soil.

Phytochemical Study of Safflower Roots (Carthamus tinctorius) on the Induction of Parasitic Plant Germination and Weed Control.

Weeds have been a major threat in agriculture for several generations as they lead to decreases in productivity and cause significant economic losses. Parasitic plants are a specific type of weed causing losses in crops of great relevance. A new strategy has emerged in the fight against parasitic plants, which is called 'suicidal germination' or the 'honey-pot strategy'. Regarding the problem of weed control from an ecological point of view, it is interesting to investigate new natural compounds with allelopathic activity with the aim of developing new natural herbicides that can inhibit the growth of weeds without damaging the environment. Safflower crops have been affected by parasitic plants and weeds and, as a consequence, the secondary metabolites exuded by safflower roots have been studied. The sesquiterpene lactone dehydrocostuslactone was isolated and characterised, and the structurally related costunolide was identified by UHPLC-MS/MS in safflower root exudates. These sesquiterpene lactones have been shown to stimulate germination of Phelipanche ramosa and Orobanche cumana seeds. In addition, these compounds were phytotoxic on three important weeds in agriculture, namely Lolium perenne, Lolium rigidum and Echinochloa crus-galli. The exudation of the strigolactones solanacol and fabacyl acetate have also been confirmed by UHPLC-MS/MS. The study reported here contributes to our knowledge of the ecological role played by some secondary metabolites. Moreover, this knowledge could help identify new models for the development of future agrochemicals based on natural products.

Therapeutic Effect of Bilsaan, Sambucus nigra Stem Exudate, on the OVA-Induced Allergic Asthma in Mice.

Asthma is characterized by the elevated level of Th2 immune responses, oxidative stress, and airway inflammation. Bilsaan, an exudate from the stem of Sambucus nigra, has been traditionally used in the treatment of various ailments in Saudi Arabia. Here, we investigated the therapeutic potential of Bilsaan against ovalbumin- (OVA-) induced allergic asthma in a mouse model. In order to induce allergic asthma, mice were intraperitoneally injected with alum-emulsified-OVA (20 µg/mouse) on days 0, 14, and 21 that is followed by an intranasal OVA exposure from days 22 to 30. During this time, mice were orally administered with Bilsaan at the doses of 5, 10, and 25 mg/kg. The numbers of total and differential inflammatory cells and the levels of Th2 cytokines (IL-4, IL-5, and IL-13) and IgE were determined in bronchoalveolar lavage fluid (BALF). Moreover, the therapeutic effect of Bilsaan was also assessed to analyze the oxidative stress and inflammatory changes in the lung tissues. The results demonstrated that Bilsaan treatment significantly reduced the total and differential inflammatory cell count in the BALF. The BALF from the mice treated with Bilsaan showed significantly lower levels of IL-4, IL-5, IL-13, and IgE. Interestingly, a similar pattern was observed in IL-4, IL-5, and IL-13 secreted by OVA-sensitized splenocytes from the mice of various groups. Bilsaan treatment alleviated the status of oxidative stress by modulating malondialdehyde (MDA), superoxide dismutase (SOD), and catalase levels in the lung. Moreover, Bilsaan treatment reduced the infiltration of inflammatory cells, thickening of alveolar wall, and congestion in the lung tissues. The findings of the present study demonstrated an antiasthmatic effect of Bilsaan through the modulation of Th2 immune responses, inflammation, and the oxidative stress.

Influence of Herbal Medicines on HMGB1 Release, SARS-CoV-2 Viral Attachment, Acute Respiratory Failure, and Sepsis. A Literature Review.

By attaching to the angiotensin converting enzyme 2 (ACE2) protein on lung and intestinal cells, Sudden Acute Respiratory Syndrome (SARS-CoV-2) can cause respiratory and homeostatic difficulties leading to sepsis. The progression from acute respiratory failure to sepsis has been correlated with the release of high-mobility group box 1 protein (HMGB1). Lack of effective conventional treatment of this septic state has spiked an interest in alternative medicine. This review of herbal extracts has identified multiple candidates which can target the release of HMGB1 and potentially reduce mortality by preventing progression from respiratory distress to sepsis. Some of the identified mixtures have also been shown to interfere with viral attachment. Due to the wide variability in chemical superstructure of the components of assorted herbal extracts, common motifs have been identified. Looking at the most active compounds in each extract it becomes evident that as a group, phenolic compounds have a broad enzyme inhibiting function. They have been shown to act against the priming of SARS-CoV-2 attachment proteins by host and viral enzymes, and the release of HMGB1 by host immune cells. An argument for the value in a nonspecific inhibitory action has been drawn. Hopefully these findings can drive future drug development and clinical procedures.

Organic acids and root exudates of Brachypodium distachyon: effects on chemotaxis and biofilm formation of endophytic bacteria.

Root colonization by plant-growth-promoting bacteria could not be useful without the beneficial properties of the bacterium itself. Thus, it is necessary to evaluate the bacterial capacity to form biofilms and establish a successful interaction with the plant roots. We assessed the ability of growth-promoting bacterial strains to form biofilm and display chemotactic behaviour in response to organic acids and (or) root exudates of the model plant Brachypodium distachyon. This assessment was based on the evaluation of single strains of bacteria and a multispecies consortium. The strains coexisted together and formed biofilm under biotic (living root) and abiotic (glass) surfaces. Citric acid stimulated biofilm formation in all individual strains, indicating a strong chemotactic behaviour towards organic acids. Recognizing that the transition from single strains of bacteria to a "multicellular" system would not happen without the presence of adhesion, the alginate and exopolysaccharide (EPS) contents were evaluated. The EPS amounts were comparable in single strains and consortium forms. Alginate production increased 160% in the consortium subjected to drought stress (10% PEG). These findings demonstrated that (i) bacteria-bacteria interaction is the hub of various factors that would not only affect their relation but also could indirectly affect the balanced plant-microbe relation and (ii) root exudates could be very selective in recruiting a highly qualified multispecies consortium.

Oral treatment with Aloe polysaccharide ameliorates ovalbumin-induced atopic dermatitis by restoring tight junctions in skin.

Atopic dermatitis (AD) is a chronic inflammatory skin disease. A hallmark of AD is dry itchy skin that results from defects in the epidermal barrier function. Aloe vera is used widely to promote general health and is administered topically to treat skin conditions such as eczema, burns and wounds. However, effects of A vera on AD were not fully elucidated. In this study, we investigated the oral administration of processed A vera gel (PAG) containing low molecular weight Aloe polysaccharides to treat ovalbumin (OVA)-induced AD in mice. Oral administration of PAG suppressed total and OVA-specific IgE production in sera and decreased the epidermal thickness of skin. Numbers of Ki-67-positive cells were reduced by PAG treatment. Expression levels of tight junction genes, including those that encode ZO-1, Claudin-1 and Claudin-8, were decreased in AD skin lesions, whereas oral administration of PAG partially restored the expression levels of tight junction genes. In addition, IL-4 and IL-17A mRNA transcript levels were reduced in skin lesions after PAG treatment. Taken together, our findings suggest that oral administration of PAG ameliorated AD, normalized tight junction gene expression and suppressed inflammatory cytokines in AD skin.

Effect of common bean seed exudates on growth, lipopolysaccharide production, and lipopolysaccharide transport gene expression of Rhizobium anhuiense.

Lipopolysaccharide (LPS) is essential for successful nodulation during the symbiosis of rhizobia and legumes. However, the detailed mechanism of the LPS in this process has not yet been clearly elucidated. In this study, the effects of common bean seed exudates on the growth, lipopolysaccharide production, and lipopolysaccharide transport genes expression (lpt) of Rhizobium anhuiense were investigated. Rhizobium anhuiense exposed to exudates showed changes in LPS electrophoretic profiles and content, whereby the LPS band was wider and the LPS content was higher in R. anhuiense treated with seed exudates. Exudates enhanced cell growth of R. anhuiense in a concentration-dependent manner; R. anhuiense exposed to higher doses of the exudate showed faster growth. Seven lpt genes of R. anhuiense were amplified and sequenced. Sequences of six lpt genes, except for lptE, were the same as those found in previously analyzed R. anhuiense strains, while lptE shared low sequence similarity with other strains. Exposure to the exudates strongly stimulated the expression of all lpt genes. Approximately 6.7- (lptG) to 301-fold (lptE) increases in the transcriptional levels were observed after only 15 min of exposure to exudates. These results indicate that seed exudates affect the LPS by making the cell wall structure more conducive to symbiotic nodulation.

Role of Maize Root Exudates in Promotion of Colonization of Bacillus velezensis Strain S3-1 in Rhizosphere Soil and Root Tissue.

Bacillus velezensis strain S3-1 has a broad range of hosts and is used as a biocontrol agent and biofertilizer. However, the interaction of maize root exudates and colonization of the strain S3-1 has not yet been investigated. In our study, strain S3-1 effectively colonized both rhizosphere soil and root tissue. Collected maize root exudates significantly induced the chemotaxis, cluster movement, and biofilm formation of strain S3-1, showing increases of 1.43, 1.6, and 2.08 times, respectively, compared with the control. In addition, the components of root exudates (organic acids: citric acid, malic acid, and oxalic acid; amino acids: glycine, proline and phenylalanine; sugars: glucose, fructose, and sucrose) were tested. Each of these compounds could induce chemotactic response, swarming motility, and biofilm formation significantly. The strongest chemotactic response and swarming motility were found when malic acid was applied, but maximal ability of biofilm formation was stimulated by proline. Furthermore, we found that these compounds of root exudates stimulated the population of S3-1 adhering to the maize root surface, especially in the presence of malic acid. These results indicate that maize root exudates play an important role in the colonization of S3-1, and provide a deeper understanding of the interaction between plants and microorganisms.

In silico and in vitro comparative activity of green tea components against Leishmania infantum.

OBJECTIVES: Green tea contains a predominant set of polyphenolic compounds with biological activities. The aim of this study was to investigate the antileishmanial activities of the main components of green tea, including catechin, (-)-epicatechin, epicatechin gallate (ECG) and (-)-epigallocatechin 3-O-gallate (EGCG), against Leishmania infantum promastigotes. METHODS: Green tea ligands and the control drug pentamidine were docked using AutoDock 4.3 software into the active sites of trypanothione synthetase and arginase, which were modelled using homology modelling programs. The colorimetric MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay was used to measure L. infantum promastigotes at different concentrations of green tea compounds in a concentration- and time-dependent manner. Results were expressed as 50% and 90% inhibitory concentrations (IC50 and IC90, respectively). RESULTS: In silico and in vitro assays showed that all of the green tea compounds have antileishmanial activity. EGCG and ECG were the most active compounds against L. infantum promastigotes, with IC50 values of 27.7µM and 75µM and IC90 values of 88.4µM and 188.7µM, respectively. Pentamidine displayed greater growth inhibition than all of the other tested compounds in a concentration- and time-dependent manner. CONCLUSION: In this study, in silico and docking results were in accordance with the in vitro activity of the compounds. Moreover, EGCG and ECG showed reasonable levels of selectivity for Leishmania.

[Chemotactic response of ginseng endophyte to ginseng root exudates].

The ginseng endophytic bacteria F1 is a potential biocontrol agent for ginseng bacterial soft rot. In this paper,the chemotactic response of ginseng endophytic bacteria F1 on 8 kinds of sugar and amino acids was detected by capillary method to explore its biocontrol mechanism. The chemotactic response of F1 strain to 4 kinds of better chemotaxis substances such as glucose,glycine,L-rhamnoseand L-glutamic acid under parameters( concentration,time,temperature and pH) was studied. The results showed that under the same experimental conditions( incubation temperature 25 ℃,incubation time 60 min,chemotaxis concentration 1 mg·L~(-1)),ginseng endophytic bacteria F1 showed different degrees of response to the eight substances tested. The phenomenon of positive chemotaxis of the measured sugars and amino acids was obvious,and the chemotactic response to total ginsenosides was low. The degree of chemotaxis response is positively correlated with the chemotaxis index within a certain range of parameters,but as the temperature,p H,time,concentration and other factors continue to increase,the chemotaxis effect decreases,and F1 optimizes the chemotaxis of the four substances. The parameters are as follows: glucose: 25 ℃,10 mg·L~(-1),45 min,pH 7; glycine: 30 ℃,10 mg·L~(-1),75 min,pH7; L-rhamnose: 30 ℃,1 mg·L~(-1),30 min,pH 6; L-glutamic acid: 25 ℃,0. 1 mg·L~(-1),45 min,pH 8. The chemotactic response is more sensitive to low concentrations of chemotactic substances.

Elicitation of Differential Responses in the Root-Knot Nematode Meloidogyne incognita to Tomato Root Exudate Cytokinin, Flavonoids, and Alkaloids.

Root exudates of plants mediate interactions with a variety of organisms in the rhizosphere, including root-knot nematodes (RKNs, Meloidogyne spp.) We investigated the responses of the motile stage second-stage juveniles (J2s) of Meloidogyne incognita to non-volatile components identified in the root exudate of tomato. Using stylet thrusting, chemotaxis assays, and chemical analysis, we identified specific metabolites in the root exudate that attract and repel J2s. Liquid chromatography quadrupole time-of-flight mass spectrometry analysis of bioactive fractions obtained from the root exudate revealed a high diversity of compounds, of which five were identified as the phytohormone zeatin (cytokinin), the flavonoids quercetin and luteolin, and alkaloids solasodine and tomatidine. In stylet thrusting and chemotaxis assays, the five compounds elicited concentration-dependent responses in J2s relative to 2% dimethyl sulfoxide (negative control) and methyl salicylate (positive control). These results indicate that J2 herbivory is influenced by root exudate chemistry and concentrations of specific compounds, which may have potential applications in RKN management.

Potential of Grape Wastes as a Natural Source of Bioactive Compounds.

Grapes are widely used in the wine and juice industries, which can lead to massive amounts of waste, mostly grape peels and seeds. The antioxidant capacities, total phenolic and flavonoid contents and phenolic profiles of peels and seeds from 30 grape varieties were systemically assessed. The antioxidant activities of fat-soluble, water-soluble and insoluble-bound fractions of grape peels and seeds were evaluated using ferric-reducing antioxidant power and Trolox equivalent antioxidant capacity assays, and their total phenolic contents and total flavonoid contents were determined by the Folin-Ciocalteu method and AlCl3 colorimetry, respectively. It was found that the antioxidant capacities were diverse among different grape peels and seeds. Moreover, several phenolic compounds were identified and quantified, including gallic acid, cyanidin-3-glucoside, epicatechin, catechin gallate, ferulaic acid, rutin and resveratrol, which could contribute to the antioxidant capacities of these grape peels and seeds. Several grape wastes with strong antioxidant activity could be abundant sources of natural bioactive compounds, and have the potential for development into functional foods, food additives and pharmaceuticals.

Responses of Heterodera glycines and Meloidogyne incognita Infective Juveniles to Root Tissues, Root Exudates, and Root Extracts from Three Plant Species.

The infective juvenile (J2) stage of endoparasitic plant nematodes uses plant chemical signals, released from roots, to localize and infect hosts. We examined the behaviors of soybean cyst nematode (Heterodera glycines) and root-knot nematode (Meloidogyne incognita) J2 in the presence of root signals from marigold (Tagetes patula), soybean (Glycine max), and pepper (Capsicum annuum). Signals were obtained from sources commonly used in phytoparasitic nematode chemotaxis studies: root tips, root exudates, and root extracts. Root tips from each plant species attracted M. incognita but H. glycines was attracted only to soybean. In contrast, root exudates prepared from marigold, pepper, or soybean seedlings were attractive to H. glycines but were repellent to M. incognita. Root extracts had the same effect as exudates. Fractionation of exudates by reversed-phase high-performance liquid chromatography (HPLC) (acetonitrile [CH3CN] and 0.1% trifluoroacetic acid) revealed highly polar and less polar components affecting behaviors. Fractions eluting at 12% CH3CN from all three plants attracted H. glycines and repelled M. incognita. None of the less polar HPLC fractions (>15% CH3CN) affected H. glycines but those from G. max and T. patula repelled M. incognita. Differences among exudates and effects of fractionation on behavior are discussed.

Potent Attractant for Root-Knot Nematodes in Exudates from Seedling Root Tips of Two Host Species.

Root-knot nematodes (RKN; Meloidogyne spp.) can parasitize over 2,000 plant species and are generally considered to be the most agriculturally damaging group of plant-parasitic nematodes worldwide. Infective juveniles (J2) are non-feeding and must locate and invade a host before their reserves are depleted. However, what attracts J2 to appropriate root entry sites is not known. An aim of this research is to identify semiochemicals that attract RKN to roots. J2 of the three RKN species tested are highly attracted to root tips of both tomato and Medicago truncatula. For both hosts, mutants defective in ethylene signaling were found to be more attractive than those of wild type. We determined that cell-free exudates collected from tomato and M. truncatula seedling root tips were highly attractive to M. javanica J2. Using a pluronic gel-based microassay to monitor chemical fractionation, we determined that for both plant species the active component fractionated similarly and had a mass of ~400 based on size-exclusion chromatography. This characterization is a first step toward identification of a potent and specific attractant from host roots that attracts RKN. Such a compound is potentially a valuable tool for developing novel and safe control strategies.