Effect of tillage,subsidiary crops and fertilisation on plant‐parasitic nematodes in a range of agro‐environmental conditions within Europe

The overall goal in nematode management is to develop sustainable systems where nematode populations are kept under the economic damage threshold. Conservation tillage and subsidiary crops, applied as cover crops and living mulches, generally improve soil health by increasing soil organic matter content and stimulating soil microbial activity. However, more permanent crop and weed cover associated with subsidiary crops and noninversion tillage, respectively, may benefit plant‐parasitic nematodes with broad host spectra such as Meloidogyne and Pratylenchus. These genera are major constraints to many field crops throughout Europe and there is a need to identify effective and reliable management options that can be applied to avoid excessive infestations. The dynamics of the indigenous fauna of plant‐parasitic nematodes were studied in eight coordinated multi‐environment field experiments (MEEs) under four agro‐environmental conditions in Europe (Continental, Nemoral, Atlantic North and Mediterranean North). The MEEs consisted of a 2‐year sequence of wheat combined with a living mulch or subsequent cover crops and second main crops maize, potatoes or tomatoes depending on site. Additionally, the effects of inversion tillage using the plough were compared with various forms of conservation tillage (no‐tillage, shallow and deep noninversion tillage). Overall, Helicotylenchus, Paratylenchus, Pratylenchus and Tylenchorhynchus were the most frequent genera across sites while Meloidogyne occurred only in Germany at very low densities. During the wheat–maize sequences in Switzerland, the populations of Pratylenchus increased from 63 to 146 nematodes per 100 mL soil and Helicotylenchus from 233 to 632 nematodes per 100 mL soil. The effects of tillage on plant‐parasitic nematodes were generally minor, although no tillage in Italy supported higher densities of Pratylenchus (184 nematodes per 100 mL soil) than inversion tillage (59 nematodes per 100 mL soil). Furthermore, Pratylenchus densities were 160 nematodes per 100 mL soil when leguminous subsidiary crops were grown, 122 nematodes per 100 mL soil in the green fallow and 84 nematodes per 100 mL soil after growing black oat (Avena strigosa) or oilseed radish (Raphanus sativus). The differences were greatest in Italy, in a sandy soil with low organic matter. Application of compost or nitrogen fertiliser had no consistent effects on plant‐parasitic nematodes. We conclude that crop rotations including specific subsidiary crops are prominent factors affecting the indigenous nematode community, while tillage and fertiliser are of lower importance.     

Nematode and Grape Rootstock Interactions Including an Improved Understanding of Tolerance

Sixteen cultivars of grape were screened over a two-year period in the presence or absence of 10 different nematode populations. Populations of Meloidogyne spp., Xiphinema index, and Mesocriconema xenoplax developed more rapidly and caused greater damage than populations of X. americanum and Tylenchulus semipenetrans. Populations of mixed Meloidogyne spp. having a history of feeding on grape were among the fastest developing populations. Tolerance to nematode parasitism appeared to be based on different mechanisms. Slow developing, less pathogenic nematode populations often stimulated vine growth, thus vines appeared to possess tolerance. Likewise, cultivars selected for nematode resistance often stimulated vine growth when fed upon by the nematode. However, tolerance sources that resulted from nematode resistance are vulnerable due to the occurrence of populations that break resistance mechanisms. Growth of cultivars with phylloxera (Daktalospharia vitifoliae) resistance was unchanged by the presence of nematodes, indicating that phylloxera resistance may provide a useful source of nematode relief. These and several additional sources of specific tolerance are discussed.     

Host Suitability of the Olive Cultivars Arbequina and Picual for Plant-Parasitic Nematodes

Host suitability of olive cultivars Arbequina and Picual to several plant-parasitic nematodes was studied under controlled conditions. Arbequina and Picual were not suitable hosts for the root-lesion nematodes Pratylenchus fallax, P. thornei, and Zygotylenchus guevarai. However, the ring nematode Mesocriconema xenoplax and the spiral nematodes Helicotylenchus digonicus and H. pseudorobustus reproduced on both olive cultivars. The potential of Meloidogyne arenaria race 2, M. incognita race 1, and M. javanica, as well as P. vulnus and P. penetrans to damage olive cultivars, was also assessed. Picual planting stocks infected by root-knot nematodes showed a distinct yellowing affecting the uppermost leaves, followed by a partial defoliation. Symptoms were more severe on M. arenaria and M. javanica-infected plants than on M. incognita-infected plants. Inoculation of plants with 15,000 eggs + second-stage juveniles/pot of these Meloidogyne spp. suppressed the main height of shoot and number of nodes of Arbequina, but not Picual. Infection by each of the two lesion nematodes (5,000 nematodes/pot) or by each of the three Meloidogyne spp. suppressed (P < 0.05) the main stem diameter of both cultivars. On Arbequina, the reproduction rate of Meloidogyne spp. was higher (P < 0.05) than that of Pratylenchus spp.; on Picual, Pratylenchus spp. reproduction was higher (P < 0.05) than that of Meloidogyne spp.     

Population dynamics of the parasitic stages of Ostertagia spp. in sheep

Callinan A. P. L. and Arundel J. H. 1982. Population dynamics of the parasitic stages of Ostertagia spp. in sheep. International Journal for Parasitology12: 531–535. The development and survival of continuing infections of Ostertagia spp. in weaner sheep were studied in order to develop a general model of the parasitic stages of the life cycle of these sheep nematodes. After 10 days, 13.8% of infective larvae (L₃) given at the rate of 1 dose of 1000 L₃ twice per week (group 1) and 20.8% of L₃ given at the rate of 10,000 L₃ twice per week (group 2) were recovered in the first of the serial nematode counts. In the final counts at 137 days, 7.7 and 0.7% were recovered in these groups. The build up and maintenance of nematode populations was regulated and related to the level of infection. A model in which the death rate of the parasitic stages was a function of the time of exposure to infection and rate of infection was used to describe the serial total nematode counts. During the experiment there was no noticeable trend in numbers of fourth stage larvae (L₄) in nematode counts, the size of adult nematodes, nematode egg counts (EPG) and egg output per female nematode (EPF). After 112 days, liveweight gains were significantly reduced in group 2 only, but increases in wool lengths were significantly reduced in both groups.     

Gall-forming root-knot nematodes hijack key plant cellular functions to induce multinucleate and hypertrophied feeding cells

Among plant-parasitic nematodes, the root-knot nematodes (RKNs) of the Meloidogyne spp. are the most economically important genus. RKN are root parasitic worms able to infect nearly all crop species and have a wide geographic distribution. During infection, RKNs establish and maintain an intimate relationship with the host plant. This includes the creation of a specialized nutritional structure composed of multinucleate and hypertrophied giant cells, which result from the redifferentiation of vascular root cells. Giant cells constitute the sole source of nutrients for the nematode and are essential for growth and reproduction. Hyperplasia of surrounding root cells leads to the formation of the gall or root-knot, an easily recognized symptom of plant infection by RKNs. Secreted effectors produced in nematode salivary glands and injected into plant cells through a specialized feeding structure called the stylet play a critical role in the formation of giant cells. Here, we describe the complex interactions between RKNs and their host plants. We highlight progress in understanding host plant responses, focusing on how RKNs manipulate key plant processes and functions, including cell cycle, defence, hormones, cellular scaffold, metabolism and transport.     

The Surface Coat of Plant-Parasitic Nematodes: Chemical Composition,Origin, and Biological Role—A Review

Chemical composition, origin, and biological role of the surface coat (SC) of plant-parasitic nematodes are described and compared with those of animal-parasitic and free-living nematodes. The SC of the plant-parasitic nematodes is 5-30 nm thick and is characterized by a net negative charge. It consists, at least in part, of glycoproteins and proteins with various molecular weights, depending upon the nematode species. The lability of its components and the binding of human red blood cells to the surface of many tylenchid plant-parasitic nematodes, as well as the binding of several neoglycoproteins to the root-knot nematode Meloidogyne, suggest the presence of carbohydrate-recognition-domains for host plants and parasitic or predatory soil microorganisms (Pasteuria penetrans and Dactylaria spp., for example). These features may also assist in nematode adaptations to soil environments and to plant hosts with defense mechanisms that depend on reactions to nematode surfaces. Surface coat proteins can be species and race specific, a characteristic with promising diagnostic potential.     

Nematicidal activity of essential oils: a review

Plant parasitic nematodes are the most destructive group of plant pathogens worldwide and their control is extremely challenging. Plant Essential oils (EOs) and their constituents have a great potential in nematode control since they can be developed for use as nematicides themselves or can serve as model compounds for the development of derivatives with enhanced activity. This study reviews the plant EOs evaluated as potential nematicides and their toxic effects against pinewood nematode (Bursaphelenchus xylophilus) and root-knot nematodes (Meloidogyne spp.). Additionally, the nematicidal activity to M. javanica of several EOs from Spanish aromatic plants and their components is described.     

Calcium sulfate and calcium carbonate as root-knot-nematode attractants and possible trap materials to protect crop plants

Root-knot nematodes (RKNs, genus Meloidogyne) are a class of plant parasites that seek out and infect the roots of many plant species. The identification of RKN attractants can be used in agriculture in conjunction with nematode-trapping technology to redirect RKN movements and eventually reduce their prevalence in the field. Here, we discovered that some commercial silica gels can attract nematodes. Silica gels that attract nematodes contain calcium sulfate. Calcium sulfate and calcium carbonate showed strong nematode attraction properties. When plant seeds were surrounded by calcium sulfate or calcium carbonate, nematodes were not attracted to the plant seeds. We propose that calcium sulfate and calcium carbonate can be used in agriculture as a novel material to trap RKN.     

Utilization of noxious weeds for the management of plant-parasitic nematodes infesting some vegetable crops: Einsatz von schädlichen unkräutern zur bekämpfung von pflanzenparasitären nematoden auf verschiedenen gëmusekulturen

Significant reduction was observed in the population of plant-parasitic nematodes, Meloidogyne incognita, Rotylenchulus reniformis and Tylenchorhynchus brassicae infesting eggplant and cauliflower when given root-dip treatment in the leaf extracts of Argemone maxicana and Solanum xanthocarpum at different concentrations and dip durations. The root-knot development and larval penetration of second stage juveniles of M. incognita were also inhibited, may be due to bare-root dip treatment in leaf extracts of both the weed plants. Leaf extracts of S. xanthocarpum caused more inhibition in root-knot development, nematode multiplication of reniform and stunt nematodes than that of A. maxicana. Plant growth improvement was noted which seems to be due to dip treatment and reduction in the population of parasitic nematodes. The efficacy of root-dip treatment with respect to improvement in plant growth of eggplant and cauliflower and reduction in root-knot development and nematode population, increased with increasing the concentration of leaf extracts and dip durations.     

Understanding the movement of root-knot nematodes encumbered with or without Pasteuria penetrans

Pasteuria penetrans is a naturally occurring bacterial parasite of plant parasitic nematodes showing satisfactory results in a biocontrol strategy of root-knot nematodes (Meloidogyne spp.). The endospores attach to the outside nematode body wall (cuticle) of the infective stage second-stage juveniles (J2) of Meloidogyne populations. Optimal attachment level should be around 5–10 endospores per juvenile, as enough endospores will initiate infection without reducing the ability of the nematode to invade roots. Greater than 15 endospores may disable the nematode in its movements, and invasion may not take place. In this research, evidence is provided that P. penetrans spores disturbed the nematode forward movement by disorganising the nematode's head turns. The results based on Markov chain and Cochran probability model show that even a low number of 5–8 spores of P. penetrans attached to the nematode cuticle have a significant impact on that movement, which plays a role in nematode locomotion.     

Evaluation of 31 Potential Biofumigant Brassicaceous Plants as Hosts for Three Meloiodogyne Species

Brassicaceous cover crops can be used for biofumigation after soil incorporation of the mowed crop. This strategy can be used to manage root-knot nematodes (Meloidogyne spp.), but the fact that many of these crops are host to root-knot nematodes can result in an undesired nematode population increase during the cultivation of the cover crop. To avoid this, cover crop cultivars that are poor or nonhosts should be selected. In this study, the host status of 31 plants in the family Brassicaceae for the three root-knot nematode species M. incognita, M. javanica, and M. hapla were evaluated, and compared with a susceptible tomato host in repeated greenhouse pot trials. The results showed that M. incognita and M. javanica responded in a similar fashion to the different cover cultivars. Indian mustard (Brassica juncea) and turnip (B. rapa) were generally good hosts, whereas most oil radish cultivars (Raphanus. sativus ssp. oleiferus) were poor hosts. However, some oil radish cultivars were among the best hosts for M. hapla. The arugula (Eruca sativa) cultivar Nemat was a poor host for all three nematode species tested. This study provides important information for chosing a cover crop with the purpose of managing root-knot nematodes.     

The Root-Knot Nematode Producing Galls on Spartina alterniflora Belongs to the Genus Meloidogyne: Rejection of Hypsoperine and Spartonema spp.

Root-knot nematodes are a major group of plant-parasitic nematodes, but their sister group within the Tylenchida remains to be identified. To find the sister group and for any investigation of the evolutionary biology of the genus Meloidogyne, it would be useful to identify the most basal species within Meloidogyninae. Meloidogyne spartinae, a root-knot nematode parasitic on cordgrass (Spartina spp.), constitutes a potentially interesting early diverging (or at least highly divergent) root-knot nematode because it was originally described in a different genus, Hypsoperine (and later Spartonema), due to its unique anatomy and biology (although it was later put in synonymy by some, but not all, taxonomists). We have sequenced the whole 18S rDNA of this species and compared it to other sequences of this region that are available in GenBank for numerous Meloidogyne species. Phylogenetic analysis unambiguously locates the branch corresponding to M. spartinae as a lately diverging species, more closely related to M. maritima, M. duytsi or the M. ardenensis-hapla group. Thus, the distinction of a separate genus (Hypsoperine or Spartonema) for this species is not justified.     

Behavioral Effects of Carbofuran and Phenamiphos on Pratylenchus vulnus. III. Penetration and Development

Penetration of bean roots by Pratylenchus vulnus was inhibited by continuous exposure of the nematode to carbofuran and phenamiphos and by drenches of higher concentrations of these chemicals. The inhibition was explicable by inhibition of motility, dispersion, and attraction. If incubated in aerated distilled water, nematodes treated with carbofuran and phenamiphos recovered and reproduced as well as untreated nematodes. Foliar treatments were ineffective. Apparently, no basipetal transport of carbofuran and phenamiphos occurs in beans. Both nematicides arrested nematode development by interfering with egg production and transitions between life stages.     

Effects of Pseudomonas fluorescens strain UTPF5 on the mobility,mortality and hatching of root-knot nematode Meloidogyne javanica

The root-knot nematode Meloidogyne spp. includes important plant pathogens worldwide. This study has considered nematode Meloidogyne javanica second stage larvae activity in the extracts of Pseudomonas fluorescens strains UTPF5 and cytotoxic effect of the strain on the nematode. The movement of second stage larvae of nematodes in water agar medium at four concentrations of bacterial extracts and second stage larvae mortality rate of hatching nematode and bacterial strains in vitro were affected. Different concentrates of the strain UTPF5 effect nematode larvae movement and disposal of the same. Bacterial extraction kills almost 100% of the larvae hatching after 24?h and a complete ban on egg hatch of biocontrol nematodes and nematode indicated that root-knot nematode larvae movement on the right attract the bacteria P. fluorescens to extract in the first place.     

Effects of Tagetes patula on Active and Inactive Stages of Root-Knot Nematodes

Although marigold (Tagetes patula) is known to produce allelopathic compounds toxic to plant-parasitic nematodes, suppression of Meloidogyne incognita can be inconsistent. Two greenhouse experiments were conducted to test whether marigold is more effective in suppressing Meloidogyne spp. when it is active rather than dormant. Soils infested with Meloidogyne spp. were collected and conditioned in the greenhouse either by 1) keeping the soil dry (DRY), 2) irrigating with water (IRR), or 3) drenching with cucumber (Cucumis sativus) leachate (CL) for 5 wk. These soils were then either planted with cucumber, marigold or remained bare for 10 wk. Suppression of nematode by marigold was then assayed using cucumber. DRY conditioning resulted in the highest number of inactive nematodes, whereas CL and IRR had higher numbers of active nematodes than DRY. At the end of the cucumber bioassay, marigold suppressed the numbers of Meloidogyne females in cucumber roots if the soil was conditioned in IRR or CL, but not in DRY. However, in separate laboratory assays, marigold root leachate slightly reduced M. incognita J2 activity but did not reduce egg hatch (P > 0.05). These finding suggest that marigold can only suppress Meloidogyne spp. when marigold is actively growing. This further suggests that marigold will more efficiently suppress Meloidogyne spp. if planted when these nematodes are in active stage.     

First report with morphometrics and molecular characterization of phtyonematodes associating mango trees in the tropics of Saudi Arabia

A sum of 218 composite rhizosphere soil samples were collected from around the feeder roots of mango, Mangifera indica growing in Jazan region, the tropical south west corner of Saudi Arabia. Samples were rendered for nematodes extraction using the centrifugal floatation method, and the stylet-bearing nematodes were morphologically identified according to the standardized taxonomical keys. A list of 14 stylet-bearing nematode genera and/or species were found to be associating the roots of mango in this study. Species identification of the most important parasitic nematodes, in this list, was carried-out, based on morphometrics and morphological features. Identification of these species was then molecularly confirmed using the D3 expansion region of 28S ribosomal RNA (rRNA) gene. These nematodes included; Tylenchorhynchus mediterraneus, Hoplolaimus seinhorsti, Hemicriconemoides strictathecatus, Longidorus latocephalus and Xiphinema elongatum. Some new local nematode-host records in Saudi Arabia were recorded including; Aphelenchus sp., H. strictathecatus, L. latocephalus, and T. mediterraneus. Some new world nematode-host records were also reported including; L. latocephalus and T. mediterraneus.     

Plant-parasitic nematodes associated with organic and conventional vegetable farms in Laguna Province,Philippines

A survey was conducted to determine the prevalence of plant-parasitic nematodes associated with vegetable crops grown in organic and conventional farms in Laguna province, Philippines. Seven nematode genera (Aphelenchoides, Aphelenchus, Helicotylenchus, Meloidogyne, Pratylenchus, Rotylenchulus and Tylenchus) from organic farms and five (all those found in organic except Aphelenchoides and Pratylenchus) from conventional farms were isolated using modified Baermann tray method. Among these taxa, Meloidogyne and Rotylenchulus were the most prevalent and abundant in both organic and conventional farms. Pratylenchus was also prevalent in organic farms and Helicotylenchus in conventional farms. Rotylenchulus was found associated with every vegetable in both organic and conventional farms and Meloidogyne was also observed with all vegetables in conventional farms. Organic vegetable farms were more diverse in terms of genera of plant-parasitic nematodes than conventional farms.     

Biocontrol of root-knot nematode infected banana plants by some marine algae

Root-knot nematodes are serious pests that cause losses of a wide range of different crops. Nematodes are controlled mainly by nematicides which cause pollution and have serious effects on all living organisms including human beings. Therefore, discovering alternative methods to control plant parasitic nematodes was attempted during the last few years to avoid pesticides hazards. Four species of marine algae (Ulva lactuca, Jania rubens, Laurencia obtusa and Sargassum vulgare) were tested to control root-knot nematode, (Meloidogyne spp.) infecting banana plants (Musa spp.). All the treatments significantly (p ≤ 0.05) reduced the rate of build-up compared with the check. U. lactuca alga gave the best results in reducing the number of galls (73.68%) and the final population of nematode (56.78%). The chemical analysis of all tested materials revealed that U. lactuca had the highest amount of phenolics (10.39 mg GAE/g dry wt). This may explain the remarkable high capability of U. lactuca to control root-knot nematode infections. Also, the same alga was the best treatment and showed maximum growth when compared with other algae and the check. For instance, shoot weight of U. lactuca surpassed the other treatments, even that of non-nematizied check one, giving high increase percentage.     

Cytogenetic Status of Meloidogyne (Hypsoperine) spartinae in Relation to Other Meloidogyne Species

Four populations of Meloidogyne spartinae from the coast of North and South Carolina were identical cytogenetically. Fourteen rod-shaped chromosomes were present in oogonia and spermatogonia, whereas seven bivalents were observed in oocytes and spermatocytes. There were no distinguishable sex chromosomes. Chromosome behavior was similar to that of other Meloidogyne species. A slight deviation in morphology of prometaphase bivalents was attributed to an increase in frequency of chiasmata that may be associated with the obligatorily amphimictic reproduction of this nematode. The anatomy of the oviduct-spermatotheca region and most cytogenetic features studied suggested that M. spartinae can be regarded as a root-knot nematode. Its position in the genus Meloidogyne or Hypsoperine can be decided by taxonomists. Its small chromosome number (n = 7) compared to the larger number (n = 13-19) of other Meloidogyne species suggests that, cytologically, M. spartinae stands closer to the ancestral form from which the prescent day root-knot nematodes have evolved.