Plant-parasitic Nematode Meloidogyne Incognita Research Articles

Suitability of crops, fruit trees/plants to plant parasitic nematodes

Fifteen economically important plant species were tested for their suitability to commonly occurring plant parasitic nematodes viz, Hoplolaimus indicus, Helicotylenchus indicus, Tylenchus filiformis, Rotylenchulus reniformis, Tylenchorhynchus brassicae, Pratylenchus zeae and Meloidogyne incognita. The plants reacted differently to different nematodes. Moreover, eight fruit trees/plants were also tested for their suitability to nematodes.

Comparative analysis of two 14-3-3 homologues and their expression pattern in the root-knot nematode Meloidogyne incognita

14-3-3 proteins are highly conserved ubiquitous proteins found in all eukaryotic organisms. They are involved in various cellular processes including signal transduction, cell-cycle control, apoptosis, stress response and cytoskeleton organisation. We report here the cloning of two genes encoding 14-3-3 isoforms from the plant parasitic root-knot nematode Meloidogyne incognita, together with an analysis of their expression. Both genes were shown to be transcribed in unhatched second stage larvae, infective second stage larvae, adult males and females. The Mi-14-3-3- a gene was shown to be specifically transcribed in the germinal primordium of infective larvae, whereas Mi-14-3-3- b was transcribed in the dorsal oesophageal gland in larvae of this stage. The MI-14-3-3-B protein was identified by mass spectrometry in in vitro-induced stylet secretions from infective larvae. The stability and distribution of MI-14-3-3 proteins in host plant cells was assessed after stable expression of the corresponding genes in tobacco BY2 cells.

Biological activities of an extract from Cleome viscosa L. (Capparaceae)

Electron micrograph examination of the leaf and stem surfaces of Cleome viscosa L (Family Capparaceae) revealed the presence of secretory glandular trichomes with club-cylinder and cylinder morphologies. In the present study, the leaves and stems of C. viscosa were extracted with hexane and the extract was evaluated for the following biological activities: anti-bacterial, anti-fungal, contact insecticidal and nematicidal. The extract was found to be a potent anti-bacterial agent according to the thin layer chromatography autobiographic assay. Activity-directed isolation studies of the anti-bacterially active compounds led to a 14-member ring cembranoid diterpene being identified as one of the effective agents. Minimum inhibitory concentration (MIC) values (microg/spot) of 5.0 microg/spot and 1.0 microg/spot were found for the diterpene on Bacillus subtilis (Gram-positive) and Pseudomonas fluorescens (Gram-negative), respectively. The diterpene did not inhibit the growth of the fungus Cladosporium cucumerinum. The extract demonstrated a pyrethroid type of contact insecticidal activity on adult Cylas formicarius elegantulus Summer (Coleoptera: Curculionidae). The extract also had high nematicidal activity with a percentage Abbott's value of 72.69 on the plant parasitic nematode Meloidogyne incognita Chitwood; however, the extract lost its potency upon subfractionation.

Molecular cloning and characterization of an intestinal cathepsin L protease from the plant-parasitic nematode Meloidogyne incognita

A cathepsin L protease full-length cDNA (named Mi-cpl-1) was characterised from infective second-stage juveniles of the root-knot nematode Meloidogyne incognita by SL1-primed PCR and 3′ rapid amplification of cDNA ends (3′-RACE). A single open reading frame was identified, encoding a putative 383-amino acid protein predicted to contain a putative N-terminal short secretion signal peptide, which suggests that Mi-CPL-1 should function as an extracellular protein. The putative mature enzyme included several conserved amino acid residues/motives, among which the typical catalytic triad of the active site. In situ mRNA hybridization analyses showed that transcripts of Mi-cpl-1 accumulated specifically in the intestinal cells of specimens, which suggests that the protein could be involved in the digestive processes of the nematode. However, expression of Mi-cpl-1 was shown to occur exclusively in the developmental stages which are in close interaction with the root tissues (i.e. second-stage juveniles and females). This may indicate that some function of the cathepsin L cysteine protease in M. incognita is more directly related to the parasitic aspects of the plant-nematode relationship, e.g. pathogenicity and/or evasion of primary host plant defence systems.

Molecular cloning and life stage expression pattern of a new acetylcholinesterase gene from the plant-parasitic nematode Meloidogyne incognita

AbstractA new cDNA, named Mi-ace-2, encoding an acetylcholinesterase, was isolated from Meloidogyne incognita. The full-length cDNA, carrying the trans-spliced SL1 leader sequence, was 2122 bp long with an open reading frame of 2058 bp. The predicted protein shared 32.3% identity with the previously identified MI ACHE and 49.1% identity with the C. elegans ACE-2. The conserved motifs involved in the catalytic triad, the choline binding site and 11 aromatic residues lining the catalytic gorge were present in the MI-ACE-2 deduced protein. RT-PCR analysis showed that Mi-ace-2 is transcribed in second stage juveniles before and after hatching, in females and in males. Phylogenetic analysis showed that MI-ACE-2 and ACE-2 were clustered in a distinct group closely related to the acetylcholinesterases secreted by animal-parasitic nematodes.

Potato-associated bacteria and their antagonistic potential towards plant-pathogenic fungi and the plant-parasitic nematode Meloidogyne incognita (Kofoid & White) Chitwood.

To study the effect of microenvironments on potato-associated bacteria, the abundance and diversity of bacteria isolated from the rhizosphere, phyllosphere, endorhiza, and endosphere of field grown potato was analyzed. Culturable bacteria were obtained after plating on R2A medium. The endophytic populations averaged 10(3) and 10(5) CFU/g (fresh wt.) for the endosphere and endorhiza. respectively, which were lower than those for the ectophytic microenvironments, with 10(5) and 10(7) CFU/g (fresh wt.) for the phyllosphere and rhizosphere, respectively. The composition and richness of bacterial species was microenvironment-dependent. The occurrence and diversity of potato-associated bacteria was additionally monitored by a cultivation-independent approach using terminal restriction fragment length polymorphism analysis of 16S rDNA. The patterns obtained revealed a high heterogeneity of community composition and suggested the existence of microenvironment-specific communities. In an approach to measure the antagonistic potential of potato-associated bacteria, a total of 440 bacteria was screened by dual testing for in vitro antagonism towards the soilborne pathogens Verticillium dahliae and Rhizoctonia solani. The proportion of isolates with antagonistic activity was highest for the rhizosphere (10%), followed by the endorhiza (9%), phyllosphere (6%), and endosphere (5%). All 33 fungal antagonists were characterized by testing their in vitro antagonistic mechanisms, including their glucanolytic, chitinolytic, pectinolytic, cellulolytic, and proteolytic activity, and by their BOX-PCR fingerprints. In addition, they were screened for their biocontrol activity against Meloidogyne incognita. Overall, nine isolates belonging to Pseudomonas and Streptomyces species were found to control both fungal pathogens and M. incognita and were therefore considered as promising biological control agents.

Effects of phytohormones on the surfaces of plant-parasitic nematodes.

The direct effects of phytohormones (auxin and kinetin) and root diffusates on the surface lipophilicity of the plant parasitic nematodes Globodera rostochiensis and Meloidogyne incognita were investigated. The fluorescent lipid probe AF18 (5-N(octodecanoyl) aminofluorescein) was used to detect surface changes. Root diffusates increased AF18 uptake by G. rostochiensis while it had no effect on M. incognita. Kinetin and auxin decreased AF18 uptake in G. rostochiensis, while they had the opposite effect on M. incognita. Auxin/kinetin ratio was also found to be important in triggering the surface changes, especially at high concentrations. Whether plant nematodes have auxin and/or kinetin binding proteins is discussed as well as the mechanism behind the surface lipophilicity changes due to root diffusates and phytohormones.

A polygalacturonase of animal origin isolated from the root-knot nematode Meloidogyne incognita

The first animal polygalacturonase (PG, EC 2.1.15) encoding cDNA, Mi-pg-1, was cloned from the plant parasitic nematode Meloidogyne incognita. The enzymatic activity of MI-PG-1 was confirmed after heterologous expression in Escherichia coli. The presence of a predicted signal peptide on the MI-PG-1 sequence together with the specific localization of the transcripts of the Mi-pg-1 gene in the oesophageal glands of infective juveniles imply that MI-PG-1 could be secreted into plant tissues. The potential role of MI-PG-1 in parasitism is discussed.

Characterization of a cDNA related to K-Cl Cotransporters in the root-knot nematode Meloidogyne incognita.

We report the cloning of a full-length cDNA from the plant-parasitic nematode Meloidogyne incognita, which encodes a putative protein of 1082 amino acids showing high similarity with K-Cl cotransporters (KCCs) from the free-living nematode Caenorhabditis elegans (54% identity) and from a number of mammals, including human. Hydropathy analysis indicates typical KCC topology patterns, with a hydrophylic NH2-terminal region, 12 membrane-spanning domains, and a long COOH-terminal hydrophylic region. Alignment of the nematode sequences with eleven KCC sequences from mammals suggests that the nematode proteins may constitute a separated family of KCCs. The M. incognita gene was shown to be expressed in both motile and sedentary stages, which suggests an important function in general physiology of the nematode. By analogy with known proteins, it is hypothesized that this gene is involved in the regulation of cell osmotic pressure to maintain nematode body fluids hyperosmotic to the environment.

CDNA cloning and expression analysis of a calponin gene from the plant-parasitic nematode Meloidogyne incognita

cDNA cloning and expression analysis of a calponin gene from the plant-parasitic nematode Meloidogyne incognita

Effectiveness of Glomus species in protecting white clover against nematode damage

Three species of arbuscular mycorrhizal (AM) fungi, Glomus aggregatum Schenck and Smith emend. Koske, Glomus intraradices Schenck and Smith, and Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappe, were evaluated for their effectiveness to suppress the plant parasitic nematode Meloidogyne incognita (Kofoid and White) Chitwood in white clover (Trifolium repens L.) in a greenhouse study. Forty 1-day-old seedlings not colonized or colonized to the same extent by the fungi were transplanted into a growth medium uninoculated or inoculated with 10 000 M. incognita eggs. After 40 days of further growth, root mass, shoot mass, extent of galling, number of nematodes and nematode eggs in roots, and extent of mycorrhizal colonization of roots were determined. Growth of white clover was significantly stimulated by mycorrhizal colonization, and nematodes caused the greatest damage when plants were not colonized by the fungi. The degree to which mycorrhizal fungi reduced nematode damage varied with the species of mycorrhizal fungus; the extent of damage reduction ranged from 19 to 49.8%, based on loss of shoot mass. The effectiveness of the mycorrhizal fungal species in suppressing nematodes was not related to the degree to which they colonized roots or their effectiveness in enhancing host growth.Key words: AM colonization, galls, Glomus aggregatum, Glomus intraradices, Glomus mosseae, inoculum potential, Meloidogyne incognita, nematode eggs, phosphorus.

Evaluation of methyl iodide as a soil fumigant in container and small field plot studies

Methyl iodide was evaluated as a soil fumigant as a potential replacement for the widely used soil fumigant methyl bromide. In container trials, methyl iodide was significantly more effective than methyl bromide against the plant parasitic nematodes Meloidogyne incognita, Heterodera schachtii and Tylenchulus semipenetrans and the plant pathogenic fungus Rhizoctonia solani. In small field plots, soil populations of root-knot nematodes were no longer detected after methyl iodide fumigation at an application rate of 112 kg ha-1. However, after growing a susceptible lima bean host for two months, substantial root-knot galling occurred, while Rhizobium nodulation was absent. At 168 kg ha-1 of methyl iodide, root-knot galling was reduced to less than 1%, and no Pythium propagules were recovered on selective detection media. These efficacy data support the conclusion that methyl iodide is a likely candidate for replacing methyl bromide as a soil fumigant. © 1998 SCI.

Information Is Where You Find It.

A basic problem of foraging is how to obtain information about the location and quality of food. Relevant information is obtained from immediate stimulation, from previous sensory experience stored in memory, and through the genes. Apparently, even the simplest organisms can use information from all these sources. A good example comes from infective juveniles of the plant-parasitic nematode Meloidogyne incognita, which only feed after they locate the root of a suitable host plant. Available evidence indicates that carbon dioxide from host roots attracts the juveniles but that it would also be useful for the juveniles to move to an optimal soil depth in which to search for chemical gradients. Although there are few cues to soil depth, M. incognita is able to solve this problem in a surprising way. Juveniles can orient to extremely shallow temperature gradients that are nearly always present in the environment. The juveniles also have the peculiar property of moving toward a preferred temperature that is set several degrees above the temperature to which they are acclimated. Computer modeling of this behavior demonstrates that it provides a mechanism for moving to a particular soil depth. Although average temperature is the same at all depths, the amplitude of daily temperature variation declines with depth and provides the required information, which is extracted by interactions among environmental temperature, preferred temperature, rate of acclimation, rate of locomotion, and temperature range of locomotion. Pseudoplasmodia of the slime mold Dictyostelium have similar capabilities. This behavior resembles true navigation in that the stimulus used for guidance has no connection to the goal and suggests that even simple organisms can extract useful information from surprisingly complex stimulus patterns.

Identification and analysis of a cuticular collagen-encoding gene from the plant-parasitic nematode Meloidogyne incognita

The vast majority of proteins in the nematode cuticle are collagens. Cuticular collagen-encoding genes (col) have been described for the animal parasites Ascaris suum and Haemonchus conforms and for the free-living Caenorhabditis elegans. The proteins encoded by all these genes seem to have the same basic structure, indicating that there is a conserved subfamily of cuticular col in these nematodes. In this paper, we describe the identification and characterization of a cDNA (Lemmi 5) which corresponds to a cuticular col of the plant-parasitic nematode Meloidogyne incognita. The derived protein structure is very similar to the basic structure of the C. elegans cuticular collagens. Using PCR technology, we have shown the presence of Lemmi 5-related sequences in the genome of Ditylenchus destructor. Our data strongly support the existence of a cuticular col subfamily which is highly conserved in the phylum Nemata.

Characterization of stage-specific cuticular proteins of Meloidogyne incognita by radio-iodination

The cuticular proteins of second-stage juveniles and adult females of the plant parasitic nematode Meloidogyne incognita have been investigated by surface radio-iodination and detergent solubilization techniques. This approach revealed a restricted number of surface proteins which were stage-specific after extraction with either sodium deoxycholate or sodium dodecyl sulphate (SDS)/β-mercaptoethanol. SDS-polyacrylamide gel electrophoresis of radiolabelled proteins detected some proteins from both stages that were superficially located on the nematode cuticle. These molecules may offer targets for immunological detection of this pest and may also play a role in the host-parasite relationship.

A simple animal can use a complex stimulus pattern to find a location: Nematode thermotaxis in soil

Newly hatched infective juveniles of the plant-parasitic nematode Meloidogyne incognita have recently been found to migrate in very shallow thermal gradients to a preferred temperature that is several °C above the temperature to which they were acclimated. Possible functions of this unusual behavior were explored by computer modeling of the movement of such nematodes in the dynamic thermal environment typical of soil. Reliable estimates were available for all the required parameters. The model predicts that, as the diurnal temperature fluctuations at the surface penetrate into the soil, a nematode located below the surface will move upward during part of the day and downward during the rest of the day. However, the distances moved upward and downward do not balance and there is a net change in depth over a period of days. The net change is upward or downward depending on the physiological parameters of the nematode and its depth. Using the best estimates available for the parameters, it is predicted that nematodes starting at any depth between 0 and 15 cm would move toward an intermediate depth of about 5 cm. It is hypothesized that, in the absence of chemical cues, this response leads the nematodes toward a level that is optimal for locating the roots of host plants. This suggests that simple organisms may make use of much more complex stimulus patterns than was previously realized.

Isolation and structure determination of new nematicidal triglyceride fromArgemone mexicana

The petroleum ether extract ofArgemone mexicana seeds was found to possess nematicidal activity against the plant parasitic nematodeMeloidogyne incognita. The active nematicidal compound has been isolated from the crude extract by column Chromatographic techniques and purified by TLC. Chemical structure has been determined by chemical and spectro-scopic methods to be that of a triglyceride, sn-glycerol-1-eicosa-9, 12-dien-oate-2-palmitoleate-3-linoleate.

Nematode Chemotaxis and Possible Mechanisms of Host/Prey Recognition

It has long been recognized that free-living nematodes utilize specific recogni­ tion mechanisms for finding their hosts or prey in the soil. One of the earliest observations described the attraction of the plant parasitic nematode Meloidogyne incognita to tomato roots grown in sterile petri plates (62). If nematodes were unable to detect signals emanating from a food source, food finding would be a random, inefficient process. Such is not the case. The general consensus, based on experimental evidence and the morphologic con­ figuration of purported sensory structures located in the cephalic region, is that in nematodes the primary food-finding mechanisms are governed by chemotac­ tic factors emanating from the host or prey (22). Other stimuli, such as thermal, vibratory, or tactile stimuli (29), are believed to play a minor role, if any, in food-finding behavior. Once the nematode reaches the potential food source, it faces further barriers before it can commence feeding. For plant nematodes this includes recognition of an area of the root susceptible to attack. For bacteriophagous nematodes, recognizing certain species of bacteria as food sources is vital, for these nematodes will not grow and reproduce on all bacteria. Molecular recognition of good and bad bacteria undoubtedly comes into play, but here again definitive data are lacking.

Bacterial parasite of a plant nematode: morphology and ultrastructure.

The life cycle of a bacterial endoparasite of the plant-parasitic nematode Meloidogyne incognita was examined by scanning and transmission electron microscopy. The infective stage begins with the attachment of an endospore to the surface of the nematode. A germ tube then penetrates the cuticle, and mycelil colonies form in the pseudocoelom. Sporulation is initiated when terminal cells of the mycelium enlarge to form sporangia. A septum within each sporangium divides the forespore from the basal or parasporal portion of the cell. The forespore becomes enclosed by several laminar coats. The parasporal cell remains attached to the forespore and forms the parasporal microfibers. After the newly formed spores are released into the soil, these microfibers apparently enable a mature spore to attach to the nematode. These results indicate that the endoparasite is a procaryotic organism having structural features that are more common to members of Actinomycetales and to the bacterium Pasteuria ramosa than to the sporozoans or to the family Bacillaceae, as previous investigatios have concluded.

Lethal effect of electrolysis on nematodes (Meloidogyne incognita)

Electrolysis of salt solutions produces mortality of a plant-parasitic nematodeMeloidogyne incognita. The mortality depends on the nature and amount of the, products of electrochemical reactions and is enhanced in presence of Cu-electrodes. Application of magnetic fields on electric fields alters nematode mortality in ferro-magnetic electrolytes.