Plant-parasitic Nematode Species Research Articles

The Response of Plant-Parasitic Community to Grazing Disturbance Gradien of Meadow Grassland

The correlation between the number, variety dominance of plant nematode community and cover standing vegetation of plant community in Meadow grassland soil was studied under Grazing Disturbance Gradien, namely,Light grazing Moderate grazing Excessive grazing rest-grazing respectively.The result is as follows: in regions of different grazing systems the species of Plant-parasitic nematode were similar, while the total number of nematodes was significant. The plant-parasit nematode dominance was in following sequence under different grazing systems: excessive grazing site> Moderate grazing site > Light grazing > rest-grazing;The dominant genus of excessive grazing site is Xiphinema、Tylenchus、Helicotylenchus.The dominant genuses of the are rest-grazing Xiphinema、Tylenchus、Ditylenchu、Helicotylenchus、Longidorus ,plant parasite nematode sweremore sensitive to the excessive grazing site，correlation of plant-parasit nematode number with plant community standing vegetation was significantly positive, while that of plant-parasite dominance(%) was significantly negative.

Taxonomy and morphology of plant-pa<a href="http://web.ebscohost.com/ehost/viewarticle?data=dGJyMPPp44rp2%2fdV0%2bnjisfk5Ie46bNQsKi3SbOk63nn5Kx95uXxjL6nr0ewqa1KrqevOK%2bmuEi2sK9PnrfLPvLo34bx1%2bGM5%2bXsgeKztU%2bwq7BOtq21PurX7H%2b72%2bw%2b4ti7hN%2fepIzf3btZzJzfhruorkmuqa5JtauwTqTc7Yrr1%2fJV5OvqhPLb9owA&hid=25">rasitic </a>nematodes associated with turfgrasses in North and South Carolina, USA

Twenty-nine species of plant-parasitic nematodes were recovered from 282 soil samples collected from turfgrasses in 19 counties in North Carolina (NC) and 20 counties in South Carolina (SC) during 2011 and from previous collections. These nematodes belong to 22 genera in 15 families, including Belonolaimus longicaudatus, Dolichodorus heterocephalus, Filenchus cylindricus, Helicotylenchus dihystera, Scutellonema brachyurum, Hoplolaimus galeatus, Mesocriconema xenoplax, M. curvatum, M. sphaerocephala, Ogma floridense, Paratrichodorus minor, P. allius, Tylenchorhynchus claytoni, Pratylenchus penetrans, Meloidogyne graminis, M. naasi, Heterodera sp., Cactodera sp., Hemicycliophora conida, Loofia thienemanni, Hemicaloosia graminis, Hemicriconemoides wessoni, H. chitwoodi, Paratylenchus goldeni, Xiphinema americanum sensu lato, X. bakeri, X. chambersi, Longidorus paralongicaudatus, and Aphelenchoides myceliophagus. Eleven species (Meloidogyne graminis, M. naasi, Cactodera sp., Pratylenchus penetrans, Hemicycliophora conida, Hemicaloosia graminis, Mesocriconema xenoplax, M. sphaerocephala, Ogma floridense, Paratrichodorus allius, Dolichodorus heterocephalus) were new records from turfgrass in both states; five (Heterodera sp., Loofia thienemanni, M. curvatum, Longidorus paralongicaudatus, Filenchus cylindricus) were new in SC; and three (Hemicriconemoides wessoni, Xiphinema bakeri, Aphelenchoides myceliophagus) were new in NC. The morphological and morphometric characteristics of these species are presented.

Comparison of two methods for in vitro multiplication of Radopholus similis and Pratylenchus brachyurus in carrot cylinders

The use of in vitro mass multiplication of nematodes under axenic conditions allows intensification of studies on taxonomy, biology, epidemiology and control of these pathogens. In the present study, two methods were compared for in vitro multiplication of two species of plant-parasitic nematodes, Radopholus similis and Pratylenchus brachyurus in 20, 40 and 60 day-periods. Both techniques involved the use of carrot cylinders placed in jars with lids, with water-agar in the bottom of the flasks (WA+) or without (WA-). In WA- the nematodes were treated with a 1% solution of ampicillin whilst for WA+ the axenization was carried out with a solution of mercuric chloride (0.01%), and streptomycin sulfate 0.02%. The WA+ condition was the most favorable for multiplication of both species of nematodes, resulting in a population increase of about 280 times for R. similis and 226 times for P. brachyurus in relation to the founding population of 25 individuals. For WA- a population increase of only five times after 60 days for R. similis and a duplication of the population after 60 days for P. brachyurus was obtained. Overall, the largest amount of nematodes occurred at 60 days after inoculation.

A molecular analysis of desiccation tolerance mechanisms in the anhydrobiotic nematode Panagrolaimus superbus using expressed sequenced tags

BackgroundSome organisms can survive extreme desiccation by entering into a state of suspended animation known as anhydrobiosis. Panagrolaimus superbus is a free-living anhydrobiotic nematode that can survive rapid environmental desiccation. The mechanisms that P. superbus uses to combat the potentially lethal effects of cellular dehydration may include the constitutive and inducible expression of protective molecules, along with behavioural and/or morphological adaptations that slow the rate of cellular water loss. In addition, inducible repair and revival programmes may also be required for successful rehydration and recovery from anhydrobiosis.ResultsTo identify constitutively expressed candidate anhydrobiotic genes we obtained 9,216 ESTs from an unstressed mixed stage population of P. superbus. We derived 4,009 unigenes from these ESTs. These unigene annotations and sequences can be accessed at http://www.nematodes.org/nembase4/species_info.php?species=PSC. We manually annotated a set of 187 constitutively expressed candidate anhydrobiotic genes from P. superbus. Notable among those is a putative lineage expansion of the lea (late embryogenesis abundant) gene family. The most abundantly expressed sequence was a member of the nematode specific sxp/ral-2 family that is highly expressed in parasitic nematodes and secreted onto the surface of the nematodes' cuticles. There were 2,059 novel unigenes (51.7% of the total), 149 of which are predicted to encode intrinsically disordered proteins lacking a fixed tertiary structure. One unigene may encode an exo-β-1,3-glucanase (GHF5 family), most similar to a sequence from Phytophthora infestans. GHF5 enzymes have been reported from several species of plant parasitic nematodes, with horizontal gene transfer (HGT) from bacteria proposed to explain their evolutionary origin. This P. superbus sequence represents another possible HGT event within the Nematoda. The expression of five of the 19 putative stress response genes tested was upregulated in response to desiccation. These were the antioxidants glutathione peroxidase, dj-1 and 1-Cys peroxiredoxin, an shsp sequence and an lea gene.ConclusionsP. superbus appears to utilise a strategy of combined constitutive and inducible gene expression in preparation for entry into anhydrobiosis. The apparent lineage expansion of lea genes, together with their constitutive and inducible expression, suggests that LEA3 proteins are important components of the anhydrobiotic protection repertoire of P. superbus.

Plant-parasitic nematodes associated with weeds in subsistence agriculture in South Africa

Twenty-nine plant-parasitic nematode species belonging to 15 genera, as well as two fungus-feeding nematode genera and one species, were identified from soil and root samples of weeds collected from 67 localities situated in subsistence production regions of South Africa during a survey from 2005-2006. Of these, 16 nematode species from four genera were reported for the first time to infect or to be associated with weeds. The predominant endo- and semi-endoparasites identified both from soil and root samples were Meloidogyne species, Pratylenchus zeae, Helicotylenchus dihystera and Rotylenchus unisexus. Based on PCR technology, three Meloidogyne species, M. hapla, M. incognita and M. javanica, have been identified in roots of weeds sampled. Thirty weed species representing 26 genera were identified as hosts of Meloidogyne species, while 38 belonging to 35 genera were associated with various other plant-parasitic nematodes. Meloidogyne species were predominant in the roots of Chloris virgata, Cynodon dactylon and Amaranthus hybridus. The frequency of occurrence of Meloidogyne species, H. dihystera and R. unisexus was significantly and positively correlated with localities in terms of % clay and % silt. The same trend was evident for these three taxa in terms of rainfall, while the opposite was observed in terms of their frequency of occurrence and pH. Principal component analysis results substantiated the latter. It also suggested that all four predominant plant-parasitic nematode species tend to occur more frequently at localities where maize was mono-cropped as well as where maize and vegetables were planted in rotation. Cynodon dactylon, Cyperus rotundus, Datura stramonium, Tagetes minuta and Eleusine corocana had the highest frequency of occurrence of weeds sampled. Identification of weeds that maintain plant-parasitic nematodes, particularly Meloidogyne species, suggested that these pathogens can have a negative impact on crop production when not controlled timely and effectively.

Resistance screening of Coffea spp. accessions for Pratylenchus coffeae and Radopholus arabocoffeae in Vietnam

Coffee varieties with resistance for the plant-parasitic nematodes Pratylenchus coffeae and Radopholus arabocoffeae are limited in Vietnam. A selection of imported varieties and high yield varieties of Arabica coffee in Vietnam were evaluated for resistance to both plant-parasitic nematode species in Northern Vietnam. The same experiments were carried out with hybrid arabica coffee, three selected clones of Coffea canephora and one clone of Coffea excelsa in the Western Highland of Vietnam. The screened coffee accessions from Ethiopia (KH1, KH13, KH20, KH21, KH29, and KH31) were susceptible and good host for P. coffeae. Also accessions 90P4 (Portugal) and Oro azteca (Mexico) had a reproduction factor Rf > 1. Pluma Hidalgo (Mexico), 90/6 (Vietnam), 90P3 (Portugal), 90P2 (Vietnam), Variedad (Mexico), 90T (Portugal), and Garnica (Mexico) were poor hosts (Rf 1. Pluma Hidalgo, 90/6, 90P3, 90P2, 90T, Oro azteca, and Garnica were poor hosts (Rf < 1). In the Western Highland experiment, all arabica coffee accessions were susceptible for P. coffeae with Rf ranging from 1.41 to 1.59. Tolerance to P. coffeae was found in C. liberica var. Dewevrei, Hong34 and Nhuantren. Coffea excelsa, Hong34, Nhuantren, and H1C19 were tolerant to R. arabocoffeae at the highest inoculation density (4,000 nematodes/pot). The most susceptible accessions were Nhuantren and K55. Resistance (Rf < 1) to R. arabocoffeae was found in C. liberica var. Dewevrei and Hong34. This article reports on the first screening for resistance and tolerance to P. coffeae and R. arabocoffeae in coffee accessions in Vietnam and shows promising results for enhanced coffee-breeding.

Higher‐tier assessment of the potential for groundwater issues due to the use of 1,3‐D soil fumigant; evaluation of the active ingredient, metabolites and potentially related chlorinated compounds

1,3-Dichloropropene (1,3-D, CAS No. 542-75-6) is a broad-spectrum soil fumigant used to control numerous species of soilborne plant-parasitic nematodes. 1,3-D consists of two isomers, (Z)- and (E)-1,3-D. There are a number of low-level chlorinated compounds that could potentially be produced as a part of the 1,3-D manufacturing process. 1,3-D and its metabolites, as well as potentially related chlorinated compounds, represent potential groundwater contaminants. This study has investigated the hydrolytic stability, under biotic and abiotic conditions in the laboratory, of an extensive representative list of 1,3-D and potentially related chlorinated compounds in order to predict their environmental fate. All of these compounds showed intrinsic hydrolytic instability under both abiotic and biotic test conditions. Furthermore, a monitoring programme was carried out. Twenty-five wells were monitored in five Italian regions characterised by historical and existing use of 1,3-D. The parent compound, its two major metabolites and potentially related chlorinated compounds were not detected in the well water at > 0.1 µg L(-1) at any sampling location. The soil fumigant (E,Z)-1,3-D, its metabolites and potentially related chlorinated compounds constitute a low risk to groundwater.

Rapid detection of Meloidogyne spp. by LAMP assay in soil and roots

Loop-mediated isothermal amplification (LAMP), a novel DNA amplification technique, has been used to detect a variety of pathogens including viruses, fungi, bacteria and parasites. However, diagnosis of sedentary plant-parasitic nematode (PPN) species has not yet been attempted. In this study, we developed a universal LAMP set (RKN-LAMP) for the diagnosis of four common Meloidogyne species ( Meloidogyne incognita, M. arenaria, M. javanica and M. hapla), and M. incognita-specific LAMP set (Mi-LAMP). In both assays, a typical ladder-like pattern on gel electrophoresis was observed in all positive samples but not in the negative controls. Amplification products were further confirmed using restriction analysis of the Hpa II enzyme, detection by visual inspection using SYBR Green I and the lateral flow dipstick (LFD) assay. The two LAMP sets were specifically able to detect four common Meloidogyne species and M. incognita populations having several different geographical origins and pathotypes. No cross reaction with DNA of other PPNs was observed. Sensitivity of the RKN- and Mi-LAMP was 10 and 100 fg of pure genome DNA respectively. Both LAMP sets could also amplified crude DNA isolated from the galled root tissue and from soil containing juveniles of M. incognita. The RKN- and Mi-LAMP sets offer the advantages of simplicity, rapidity and cost effectiveness. Both LAMP sets will be instrumental for the diagnosis of Meloidogyne spp. by local extension and regulatory personnel.

Discovery and initial analysis of novel viral genomes in the soybean cyst nematode

Nematodes are the most abundant multicellular animals on earth, yet little is known about their natural viral pathogens. To date, only two nematode virus genomes have been reported. Consequently, nematode viruses have been overlooked as important biotic factors in the study of nematode ecology. Here, we show that one plant parasitic nematode species, Heterodera glycines, the soybean cyst nematode (SCN), harbours four different RNA viruses. The nematode virus genomes were discovered in the SCN transcriptome after high-throughput sequencing and assembly. All four viruses have negative-sense RNA genomes, and are distantly related to nyaviruses and bornaviruses, rhabdoviruses, bunyaviruses and tenuiviruses. Some members of these families replicate in and are vectored by insects, and can cause significant diseases in animals and plants. The novel viral sequences were detected in both eggs and the second juvenile stage of SCN, suggesting that these viruses are transmitted vertically. While there was no evidence of integration of viral sequences into the nematode genome, we indeed detected transcripts from these viruses by using quantitative PCR. These data are the first finding of virus genomes in parasitic nematodes. This discovery highlights the need for further exploration for nematode viruses in all tropic groups of these diverse and abundant animals, to determine how the presence of these viruses affects the fitness of the nematode, strategies of viral transmission and mechanisms of viral pathogenesis.

Constitutive and induced subterranean plant volatiles attract both entomopathogenic and plant parasitic nematodes

Summary 1. Indirect plant defences are well documented for the above‐ground constituents of plants. Although less investigated to date, below‐ground defences that mediate multitrophic interactions are equally important. Entomopathogenic nematodes (Steinernema diaprepesi) are attracted to herbivore‐induced volatiles from Swingle var. (Citrus paradisi×Poncirus trifoliata) when fed upon by root weevil, Diaprepes abbreviatus. 2. We examined the extent to which below‐ground volatiles modify behaviour of nematode species representing various foraging strategies (cruisers versus ambushers) and trophic levels (plant parasites versus entomopathogens). We compared attraction to volatiles of weevil‐infested and non‐infested roots from Swingle citrus rootstock and a parent line of the Swingle hybrid, Poncirus trifoliata (Pt). 3. Swingle weevil‐infested roots attracted more nematodes than non‐infested roots irrespective of nematode foraging strategy and trophic status. The parental line, Pt, attracted all nematode species irrespective of insect herbivory. 4. Dynamic in situ collection and GC–MS analysis of volatiles from soil revealed that Pt roots release attracting cues constitutively. A different non‐hybrid citrus species (sour orange, Citrus aurantium) released nematode attracting cues only in response to larval feeding, similar to responses found in Swingle. Volatile collections from above‐ and below‐ground portions of citrus plants revealed that above‐ground feeding by weevils does not induce production of nematode attracting cues analogous to that induced by root damage, nor does damage by larvae below‐ground induce a similar volatile above ground. 5. Synthesis. Our results suggest that release of nematode attractants by citrus roots occurs broadly and can be constant or herbivore‐induced. The major constituent of this indirect defence is produced by roots and not shoots and in response to below‐ground, but not above‐ground herbivory. Our findings suggest that this cue acts on nematode species broadly, attracting entomopathogenic nematodes that exhibit various foraging strategies. Unexpectedly, we also found that this cue attracts a plant parasitic nematode species. It appears, thus, that release of nematode attracting cues by citrus plants can cause ecological costs. The plants, however, appear to counteract against these costs, because constitutive release was found only in a cultivar that is resistant to phytopathogenic nematodes, while herbivore‐induced release occurred in lines susceptible to pathogenic nematode species.

Nematode Diversity in Banana Rhizosphere From West Bengal, India

Nematode Diversity in Banana Rhizosphere From West Bengal, IndiaSurvey on plant and soil nematodes associated with banana plantations in different banana growing districts of West Bengal (India), revealed that the occurrence of the most economically important genera of plant parasitic nematodes werePratylenchus, Meloidogyne, Helicotylenchus, Tylenchorhynchus, Hoplolaimus, Rotylenchulus, Hirschmanniella, Criconemoides.Altogether there were seventeen species of plant parasitic nematodes viz.Pratylenchus coffeae, P. brachyurus, P. similis, Meloidogyne incognita, M. javanica, Hoplolaimus indicus, Rotylenchulus reniformis, Helicotylenchus multicinctus, H. abunaamai, H. incisus, H. gratus, H. dihystera, Tylenchorhynchus nudus, T. mashhoodi, T. coffeae, Hirschmanniella mucronataandCriconemoidessp. Among the plant parasitic nematodes,P. coffeae, P. brachyurus, M. incognita, H. multicinctusandR. reniformiswere found as serious pests of banana in West Bengal. The occurrence of the most damaging species,Radopholus similisandHeterodera oryzicolawas not detected in West Bengal, althoughR. similisis reported to occur in Midnapore and Jalpaiguri. Distribution of plant parasitic nematodes associated with the rhizosphere of banana in important banana growing districts of West Bengal, was presented on the basis of information available in the state. Observation of the effects of some banana cultivars/types on the nematode fauna, showed that the cooking banana typeMusa(ABB) cv. Kanchakala andMusa(BBB) cv. Seed Banana supported a huge population ofM. incognitawhich induced severe root galling symptoms. The lesion nematode,P. coffeaewas found infesting all the cultivars/types. It maintained high population densities in the rhizosphere ofMusa(AA) cv. Matti andMusa(ABB) cvs. Kanchkala, Krishna Kanthali whereas the Seed Banana cultivar had a suppressive effect onP. coffeae.The rhizosphere of banana cultivar, Matti exhibited a high population ofH. multicinctus, R. reniformispopulation was recorded in extremely high levels in the rhizosphere of all cultivars/types. Free-living nematodes including rhabditids, dorylaimids, mononchids, were found in abundance in the banana rhizosphere.

Phytonematodes: A severe menace for successfulcultivation of menthol mint in Indo-Gangetic plains

The overall development of nation relies on optimisation of crop production, enhancement in the export andlimitation on avoidable imports. The availability of nutritious and healthy food, disease controlling food supplementsand therapeutics are, among several factors, the determinants of quality of life of people all around the world.Phytonematodes constitute one of the most important groups of pathogenic organisms prevalent in and around therhizosphere, play a potential role in reducing crop production and yield. Undoubtedly, these phytonematodes areassociated with most of the medicinal and aromatic plants (MAPs) and cause severe damage, but the magnitudeof crop damage has been established in only a few MAPs. Among different MAPs, menthol mint is on frontlinebecause of higher net returns and greater demand in world market. Importantly two species of plant parasiticnematodes viz. Root-knot nematode (Meloidogyne incognita and M. javanica) and root lesion nematode (Pratylenchusthornei) affect cultivation of menthol mint. Some of the models and techniques have been suggested to avoid theeconomic loss caused by nematode pest to menthol mint.

Plant parasitic nematodes associated with Indian Pennywort Centella asiatica (L.) Urban in Manipur

A survey of the plant parasitic nematodes associated with Centella asiatica (L.) Urban was conducted in different localities of Manipur. Twenty one species of plant parasitic nematodes belonging to 12 genera were found to occur. Tylenchorhynelms mashhoodi, Aphelenchus avenae and Helicotylenchus dihystera were predominant with absolute densities ranging from 338 - 498 per 500g soil. Basiria varians and T.mashhoodi were recorded with highest absolute frequency and absolute density respectively.

Studies on soil and plant parasitic nematodes associated with banana in West Midnapur, West Bengal, India

During a taxonomic survey from March 2004 to February 2006, a total of 46 species of soil and plant parasitic nematodes, associated with banana plantations (Musa paradisiaca L. cv. Kanthali) have been encountered from different localities of Paschim Medinipur district of West Bengal, India. Of these, 29 species belonging to 21 genera were recorded under the order Dorylaimida and 17 species belonging to 11 genera were under the order Tylenchida. Most of the species are represented through female sex. The typical plant parasitic nematode genus Helicotylenchus Steiner, 1945 holds maximum number of species.

Nematicidal plants with potential to control plant-parasitic nematodes of some economic food crops

An inventory was made of plant parasitic nematode species, the crops they infest and plants that could be used to control the various nematodes. Effective nematicidal plants and their chemical constituents were also highlighted. It was observed that many plant materials had been used in the control of plant parasitic nematodes worldwide. Concentrations of plant materials, forms of application, the effective nematicidal plant parts and the chemical constituents in plants varied tremendously. From the information available it appears that the wide use of nematicidal plants in the control of plant parasitic nematodes could be easily adopted by growers worldwide.

Functional characterisation of a cyst nematode acetylcholinesterase gene using Caenorhabditis elegans as a heterologous system

Migration of plant–parasitic nematode infective larval stages through soil and invasion of roots requires perception and integration of sensory cues culminating in particular responses that lead to root penetration and parasite establishment. Components of the chemoreceptive neuronal circuitry involved in these responses are targets for control measures aimed at preventing infection. Here we report, to our knowledge, the first isolation of cyst nematode ace-2 genes encoding acetylcholinesterase (AChE). The ace-2 genes from Globodera pallida ( Gp-ace-2) and Heterodera glycines ( Hg-ace-2) show homology to ace-2 of Caenorhabditis elegans ( Ce-ace-2). Gp-ace-2 is expressed most highly in the infective J2 stage with lowest expression in the early parasitic stages. Expression and functional analysis of the Globodera gene were carried out using the free-living nematode C. elegans in order to overcome the refractory nature of the obligate parasite G. pallida to many biological studies. Caenorhabditis elegans transformed with a GFP reporter construct under the control of the Gp-ace-2 promoter exhibited specific and restricted GFP expression in neuronal cells in the head ganglia. Gp-ACE-2 protein can functionally complement its C. elegans homologue. A chimeric construct containing the Ce-ace-2 promoter region and the Gp-ace-2 coding region and 3′ untranslated region was able to restore a normal phenotype to the uncoordinated C. elegans double mutant ace-1;ace-2. This study demonstrates conservation of AChE function and expression between free-living and plant-parasitic nematode species, and highlights the utility of C. elegans as a heterologous system to study neuronal aspects of plant–parasitic nematode biology.

First record ofHoplolaimus galeatus in Australia

Hoplolaimus galeatus was identified in turf samples from New South Wales and Western Australia. This is the first record of this species of plant-parasitic nematode in Australia.

Molecular phylogeny of the genus Rotylenchus (Nematoda, Tylenchida) and description of a new species

A description of a new species of plant parasitic nematodes of the genus Rotylenchus from the family Hoplolaimidae is given and a recognition of Rotylenchus jaeni comb. n., previously known as subspecies R. magnus jaeni, as separate species is proposed. Rotylenchus montanus sp. n. is characterized by a hemispherical lip region with six rarely seven annuli, stylet 33–37 µm, female tail rounded, regularly annulated tip with 12–18 annuli and phasmid located 2–9 annuli anterior to anus. Rotylenchus montanus sp. n. is close to species of the monosexual group R. arsenjevi, R. corsicus, R. fragaricus, R. helicus, R. indorobustus and R. neorobustus, by a number of specific characteristics resulting from its specific matrix code: A5, B1, C1, D4, E2, F2, G3, H2, I2, J2, K2. Molecular characterization of R. montanus sp. n. and other Rotylenchus species are provided using D2–D3 expansion segments of 28S and the ITS1 of rRNA genes. The D2–D3 of 28S rRNA and the ITS1–rRNA sequences of R. montanus sp. n. differed in one nucleotide and in 16–20 nucleotides from those of an unidentified Rotylenchus species from Russia, respectively. Molecular analysis of populations of R. magnus and R. jaeni comb. n. demonstrated differences in the D2–D3 and the ITS1–rRNA sequences. These genetic differences together with some minor morphological characters support that both subspecies should be considered as two cryptic sibling species and warranted their elevation to species rank. The result of phylogenetic analysis of Hoplolaimidae for 45 sequences of the D2 and D3 expansion regions of 28S rRNA gene using Bayesian inference analysis under the complex model is presented. Phylogenetic tree of Rotylenchus species represents seven moderate to highly supported lineages. Grouping of Rotylenchus species within other hoplolaimids and analysis of phylogenetic relationships within the genus Rotylenchus using the ITS1 of rRNA gene sequences are also discussed.

Plant-Parasitic Nematodes Attacking Chickpea and Their In Planta Interactions with Rhizobia and Phytopathogenic Fungi.

Chickpea (Cicer arietinum) is a coolseason food legume second in importance as a pulse crop in the world after beans (Phaseolus vulgaris). It is an important protein source in many regions of the semi-arid tropics (30). Chickpea is grown in 47 countries and is a significant component of subsistence cropping systems for farmers in the Indian Subcontinent, West Asia, the Mediterranean Basin, and certain areas of East and North Africa. More than 90% of the chickpea crops are grown in eight countries, including India, Pakistan, Iran, Turkey, Ethiopia, Mexico, Australia, and Canada, in decreasing order. Many species of plant-parasitic nematodes have been reported in the roots and rhizosphere of chickpea in the major growing regions in the world (Table 1). However, only certain nematode species are considered constraints to chickpea production, causing an estimated 14% in annual yield losses (61,68). The symptoms and signs of nematode parasitism on chickpea differ depending upon the nematode’s feeding habit. Moreover, nematode attacks can make plants more sensitive to other biotic and abiotic stresses, and overall result in stunting and poor yield (70). Symptoms caused by nematode attack are nonspecific and nondescript, and they are largely a consequence of disruption of normal processes of plant growth, and absorption and translocation of water and nutrients. Consequently, damage by nematodes to chickpea often goes unnoticed and is attributed to other causes, such as lack of fertility or deficient soil moisture. For example, even 50% reductions in chickpea yield caused by the chickpea cyst nematode, Heterodera ciceri, cannot be predicted by inspection of the upper part of the plant (35). For these reasons, plantparasitic nematodes are often referred to as the “unseen enemies” of crops. The most important nematode pathogens of chickpea include root-knot nematodes (Meloidogyne spp.), root-lesion nematodes (Pratylenchus spp.), cyst-forming nematodes (Heterodera spp.), and the reniform nematode (Rotylenchulus reniformis). In this paper, we will focus on the geographical distribution and pathogenicity of these nematodes, along with the symptoms, epidemiology, and management of the diseases they cause on chickpea. In addition, we will describe some of the most common and efficient diagnostic methods that are available for nematodes. Finally, we will address the complex interactions that occur between some nematodes and other microorganisms that coinfect chickpea, including rhizobia and the fungal pathogen Fusarium oxysporum f. sp. ciceris, which causes Fusarium wilt.

Detection and quantification of root-knot nematode (Meloidogyne javanica), lesion nematode (Pratylenchus zeae) and dagger nematode (Xiphinema elongatum) parasites of sugarcane using real-time PCR

A number of different plant parasitic nematode species are found associated with sugarcane in South Africa. Of these, the root-knot nematode (Meloidogyne javanica), the lesion nematode (Pratylenchus zeae) and the dagger nematode (Xiphinema elongatum) are potentially the most damaging pests. Identification and enumeration of the number of these nematodes are necessary for providing advice to farmers as well as studying the effects of various treatments in field and glasshouse trials. We report on the development, use, and extent of specificity of three sets of primers, for M. javanica, P. zeae and X. elongatum, and on tests to detect and quantify the number of these nematodes in soil samples using SYBR Green I dye and real-time PCR technology. Amplicons from the three target species (obtained with their respective primer sets) are discernible in size by gel electrophoresis (380bp for M. javanica, 250bp for P. zeae and 500bp for X. elongatum). Also, these amplicons have characteristic melting temperatures of 83.8 degrees C (M. javanica), 86.6 degrees C (P. zeae) and 86.1 degrees C (X. elongatum). Investigations into multiplex reactions found competition between species with M. javanica competing with P. zeae and X. elongatum. Subsequent single tube (simplex) assays, enabled the construction of calibration curves for each of the three species. These were then used for quantification of the numbers of each of these species in nematode samples extracted from the field, with a high (R2=0.83) and significant positive correlation between real-time PCR and counts performed with microscopy.