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.     

Horizontally transferred genes in plant-parasitic nematodes: a high-throughput genomic approach

Background  

Published accounts of horizontally acquired genes in plant-parasitic nematodes have not been the result of a specific search for gene transfer per se, but rather have emerged from characterization of individual genes. We present a method for a high-throughput genome screen for horizontally acquired genes, illustrated using expressed sequence tag (EST) data from three species of root-knot nematode, Meloidogyne species.     

A new species of catenaria parasitic on nematodes of sugarcane

Summary A new species,Catenaria vermicola, is named and described. It attacks several plant-parasitic nematodes of economic importance in sugarcane soils of Louisiana. The fungus forms numerous zoospores which encyst on the cuticle, generally near natural openings of the nematode, thereby causing infection. Within the parasitized nematodes hyphae and sporangia quickly form and destroy the victim completely. The following plant-parasitic nematodes were attacked and destroyed:Belonolaimus longicaudatus, Criconemoides rusticum, Hemicycliophora gigas, Hoplolaimus tylenchiformis, Meloidogyne larvae,Pratylenchus brachyurus, P. zeae, Radopholus similis, Tylenchulus semipenetrans larvae,Tylenchorhynchus martini, andXiphinema chambersi.     

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.     

Techniques for image analysis of movement of juveniles of root-knot nematodes encumbered with Pasteuria penetrans spores

Root-knot nematodes (Meloidogyne spp.) are the most significant plant-parasitic nematodes that damage many crops all over the world. The free-living second stage juvenile (J2) is the infective stage that enters plants. The J2s move in the soil water films to reach the root zone. The bacterium Pasteuria penetrans is an obligate parasite of root-knot nematodes, is cosmopolitan, frequently encountered in many climates and environmental conditions and is considered promising for the control of Meloidogyne spp. The infection potential of P. penetrans to nematodes is well studied but not the attachment effects on the movement of root-knot nematode juveniles, image analysis techniques were used to characterize movement of individual juveniles with or without P. penetrans spores attached to their cuticles. Methods include the study of nematode locomotion based on (a) the centroid body point, (b) shape analysis and (c) image stack analysis. All methods proved that individual J2s without P. penetrans spores attached have a sinusoidal forward movement compared with those encumbered with spores. From these separate analytical studies of encumbered and unencumbered nematodes, it was possible to demonstrate how the presence of P. penetrans spores on a nematode body disrupted the normal movement of the nematode.     

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.     

Ruscus hypophyllum: A New Host for Aphelenchoides fragariae

Aphelenchoides fragariae was isolated from the phylloclades of the ornamental plant Ruscus hypophyllum (Liliaceae). Rotylenchus buxophilus, Scutellonema brachyurum, and Meloidogyne were identified as the most common plant-parasitic nematodes in the soil near the roots. The pathology and life history of A. fragariae were closely related to the climate. To our knowledge, this is the first report of R. hypophyllum as a host of plant-parasitic nematodes.     

Nematode Community Structure in a Vineyard Soil

Distribution of the nematode community in a California vineyard was studied over a 13-month period. Omnivorous and microbivorous nematodes were similarly distributed in the root zone, with greatest densities occurring between vine rows and near the soil surface. Greatest densities of plant-parasitic nematodes were found in the vine row, with the individual species differing in their vertical distribution. Total nematode biomass was greatest between rows near the surface. Biomass of plant parasites was greatest in the upper 30 cm of soil in the row, whereas biomass of microbivores was greatest in this region between rows. Of the plant-parasitic nematodes, the variability in distribution among vines was greatest for Paratylenchus hamatus and least for Meloidogyne spp.     

Preponderance and distribution of plant-parasitic nematodes in Nassarawa State,North Central Nigeria: Consequences for healthy tuber production and export

One of the most cosmopolitan pests responsible for considerable negative economic impacts on yam is the plant-parasitic nematodes. They are also capable of facilitating fungal, bacterial and viral infections of yams. In order to produce healthy yam seeds to meet local demand and tubers for export, there is a need to identify nematode-free areas in Nassarawa, one of the hubs of yam production in Nigeria. To this end, 30 major yam growing communities of the state were surveyed to identify nematode-free areas. Structured questionnaires were administered to three farmers in each of the 10 local government areas selected. Results showed that 97% of the study areas investigated was seriously infested with the three key genera of plant-parasitic nematodes namely Scutellonema, Pratylenchus and Meloidogyne. Incidence and severity of tuber deterioration in transit threatened acceptability of the tubers when it eventually reached England. Healthy yams would attract more income than damaged ones.     

Molecular Diagnosis of Meloidogyne Species

Genetic variation within nuclear and mitochondrial DNA of Meloidogyne species and host races has been evaluated for the development of root-knot nematode molecular diagnostics. This review summarizes the distinctive features of several useful DNA-based assays for plant-parasitic nematodes, focusing upon the direct application of these procedures for Meloidogyne detection, identification, and systematics.     

Plant-parasitic Nematode Communities and Their Associations with Soil Factors in Organically Farmed Fields in Minnesota

A survey was conducted to determine the assemblage and abundance of plant-parasitic nematodes and their associations with soil factors in organically farmed fields in Minnesota. A total of 31 soil samples were collected from southeast (SE), 26 samples from southwest (SW), 28 from west-central (WC), and 23 from northwest (NW) Minnesota. The assemblage and abundance of plant-parasitic nematodes varied among the four regions. The soybean cyst nematode, Heterodera glycines, the most destructive pathogen of soybean, was detected in 45.2, 88.5, 10.7, and 0% of organically farmed fields with relative prominence (RP) values of 10.3, 26.5, 0.6, and 0 in the SE, SW, WC, and NW regions, respectively. Across the four regions, other common genera of plant-parasitic nematodes were Helicotylenchus (42.6, RP value, same below), Pratylenchus (26.9), Tylenchorhynchus and related genera (9.4), Xiphinema (5.6), and Paratylenchus (5.3). Aphelenchoides, Meloidogyne, Hoplolaimus, Mesocriconema, and Trichodorus were also detected at low frequencies and/or low population densities. The similarity index of plant-parasitic nematodes between two regions ranged from 0.44 to 0.71 and the similarity increased with decreasing distance between regions. The densities of most plant-parasitic nematodes did not correlate with measured soil factors (organic matter, pH, texture). However, the densities of Pratylenchus correlated negatively with % sand, and Xiphinema was correlated negatively with soil pH.     

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.     

Review of Nematode Interactions with Hemp (Cannabis Sativa)

The many decades during which the cultivation of Cannabis sativa (hemp) was strongly restricted by law resulted in little research on potential pathogenic nematodes of this increasingly important crop. The primary literature was searched for hemp-nematode papers, resulting in citations from 1890 through 2021. Reports were grouped into two categories: (i) nematodes as phytoparasites of hemp, and (ii) hemp and hemp products and extracts for managing nematode pests. Those genera with the most citations as phytoparasites were Meloidogyne (root-knot nematodes, 20 papers), Pratylenchus (lesion nematodes, 7) and Ditylenchus (stem nematodes, 7). Several Meloidogyne spp. were shown to reproduce on hemp and some field damage has been reported. Experiments with Heterodera humuli (hop cyst nematode) were contradictory. Twenty-three papers have been published on the effects of hemp and hemp products on plant-parasitic, animal-parasitic and microbivorous species. The effects of hemp tissue soil incorporation were studied in five papers; laboratory or glasshouse experiments with aqueous or ethanol extracts of hemp leaves accounted for most of the remainder. Many of these treatments had promising results but no evidence was found of large-scale implementation. The primary literature was also searched for chemistry of C. sativa roots. The most abundant chemicals were classified as phytosterols and triterpenoids. Cannabinoid concentration was frequently reported due to the interest in medicinal C. sativa. Literature on the impact of root-associated chemicals on plant parasitic nematodes was also searched; in cases where there were no reports, impacts on free-living or animal parasitic nematodes were discussed.     

Infection of plant-parasitic nematodes by Paecilomyces lilacinus and Monacrosporium lysipagum

Studying the mode of infection of a biocontrol agent is important in order to assess its efficiency. The mode and severity of infection of nematodes by a soil saprophyte Paecilomyces lilacinus (Thom) Samson and a knob-producing nematode trapping fungus Monacrosporium lysipagum (Drechsler) Subram were studied under laboratory conditions using microscopy. Infection of stationary stages of nematodes by P. lilacinus was studied with three plant-parasitic nematodes Meloidogyne javanica (Treub) Chitwood, Heterodera avenae Wollenweber and Radopholus similis (Cobb) Thorne. Paecilomyces lilacinus infected eggs, juveniles and females of M. javanica by direct hyphal penetration. The early developed eggs were more susceptible than the eggs containing fully developed juveniles. As observed by transmission electron microscopy, fungal hypha penetrated the M. javanica female cuticle directly. Paecilomyces lilacinus also infected immature cysts of H. avenae including eggs in the cysts and the eggs of R. similis. Trapping and subsequent killing of mobile stages of nematodes by M. lysipagum were studied with the above three nematodes. In addition, plant-parasitic nematodes Pratylenchus neglectus (Rensch) Chitwood and Oteifa and Ditylenchus dipsaci (Kuhn) Filipjev were tested with M. lysipagum. This fungus was shown to infect mobile stages of all the plant-parasitic nematodes. In general, juveniles except those of P. neglectus, were more susceptible to the attack than adults.     

Sterol Composition and Ecdysteroid Content of Eggs of the Root-knot Nematodes Meloidogyne incognita and M. arenaria

Free and esterified sterols of eggs of the root-knot nematodes Meloidogyne incognita races 2 and 3 and M. arenaria race 1 were isolated and identified by gas-liquid chromatography-mass spectrometry. The major sterols of eggs of each race were 24-ethylcholesterol (33.4-38.8% of total sterol), 24-ethylcholestanol (18.3-25.3%), 24-methylcholesterol (8.6-11.7%), 24-methylcholestanol (7.7-12.5%), and cholesterol (4.6-11.6%). Consequently, the major metabolic transformation performed by Meloidogyne females or eggs upon host sterols appeared to be saturation of the sterol nucleus. The free and esterified sterols of the same race did not differ appreciably, except for a slight enrichment of the steryl esters in cholesterol. Although the sterol composition of Meloidogyne eggs differed from that of other life stages of other genera of plant-parasitic nematodes, the three Meloidogyne races could not be distinguished from each other by their egg sterols. Ecdysteroids, compounds with hormonal function in insects, were not detected by radioimmunoassay in the Meloidogyne eggs either as free ecdysteroids or as polar conjugates.     

Isolation and screening of fungi associated with eggs and females of root-knot nematodes and their biocontrol potential against Meloidogyne incognita in Bangladesh

A total of 297 fungal isolates belonging to 20 genera and 33 species were isolated and identified from eggs and females of Meloidogyne spp. in Bangladesh. The predominant genera were Fusarium, Aspergillus and Penicillium; and the significant ones were Purpureocillium, Trichoderma and Pochonia. The 24 well tissue culture plate screening technique was applied for pathogenicity tests against Meloidogyne incognita in vitro. The average percentages of egg parasitism, egg hatch inhibition and juvenile mortality varied significantly and were ranged from 8.2 to 64.9% (p = 0.05), 24.8 to 72.4% (p = 0.05), and 2.3 to 33.1% (p = 0.05), respectively. Two isolates of Purpureocillium lilacinum (PLSAU 1 and PLSAU 2) and one isolate of Pochonia chlamydosporia (PCSAU 1) reduced more than 60% average root galls of tomato, eggplant and cucumber in greenhouse experiments. This is the first investigation of fungi associated with nematodes in the country and their biological control potential against M. incognita.     

Genetic Diversity and Population Structure of Celosia argentea and Related Species Revealed by SRAP

Genetic diversity of 16 populations of Celosia argentea L. and 6 populations of Celosia cristata L. in China was investigated using sequence-related amplified polymorphism (SRAP). Ten SRAP primer combinations generated 507 scorable amplification bands ranging from 50 to 2000 bp, among which 274 were polymorphic, with an average of 54 polymorphic bands per primer combination. The unweighted pair group method of arithmetic averages (UPGMA) cluster analysis enabled construction of a phylogenetic tree for estimating genetic distance among populations, which agreed well with the geographic origin information. Twenty-two populations were distinctly separated into two major genetic groups. One typical representative fragment, M1E6 in C. argentea, provided an alternative approach to distinguish C. argentea from C. cristata. Also, great genetic diversity found in C. argentea populations by significant geographic difference was confirmed by a high level of population genetics parameters. The information may be beneficial to future breeding selection and conservation management for populations of C. argentea.     

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.     

Plant and soil nematode population changes in wheat grown continuously in ploughed and in unploughed soil

In general, more migratory plant-parasitic nematodes are found in soil under cereals drilled after ploughing than in unploughed land drilled after being sprayed with weed-killer; but some non-parasitic nematodes are more numerous in the unploughed, herbicide-sprayed soil. Spraying a mixture of DDT, diazinon, chlordane and thionazin on the soil before drilling did not affect populations of soil nematodes.     

Reproductive mode evolution in nematodes: insights from molecular phylogenies and recently discovered species

The Phylum Nematoda has long been known to contain a great diversity of species that vary in reproductive mode, though our understanding of the evolutionary origins, causes and consequences of nematode reproductive mode change have only recently started to mature. Here we bring together and analyze recent progress on reproductive mode evolution throughout the phylum, resulting from the application of molecular phylogenetic approaches and newly discovered nematode species. Reproductive mode variation is reviewed in multiple free-living, animal-parasitic and plant-parasitic nematode groups. Discussion ranges from the model nematode Caenorhabditis elegans and its close relatives, to the plant-parasitic nematodes of the Meloidogyne genus where there is extreme variation in reproductive mode between and even within species, to the vertebrate-parasitic genus Strongyloides and related genera where reproductive mode varies across generations (heterogony). Multiple evolutionary transitions from dioecous (obligately outcrossing) to hermaphroditism and parthenogenesis in the phylum are discussed, along with one case of an evolutionary transition from hermaphroditism to doioecy in the Oscheius genus. We consider the roles of underlying genetic mechanisms in promoting reproductive plasticity in this phylum, as well as the potential evolutionary forces promoting transitions in reproductive mode.