Nematode Populations Research Articles

A simple protocol for cultivating the bacterivorous soil nematode Caenorhabditis elegans in its natural ecology in the laboratory.

The complex interplay between an animal and its surrounding environment requires constant attentive observation in natural settings. Moreover, how ecological interactions are affected by an animal's genes is difficult to ascertain outside the laboratory. Genetic studies with the bacterivorous nematode Caenorhabditis elegans have elucidated numerous relationships between genes and functions, such as physiology, behaviors, and lifespan. However, these studies use standard laboratory culture that does not reflect C. elegans true ecology. C. elegans is found growing in nature and reproduced in large numbers in soils enriched with rotting fruit or vegetation, a source of abundant and diverse microbes that nourish the thriving populations of nematodes. We developed a simple mesocosm we call soil-fruit-natural-habitat that simulates the natural ecology of C. elegans in the laboratory. Apples were placed on autoclaved potted soils, and after a soil microbial solution was added, the mesocosm was subjected to day-night, temperature, and humidity cycling inside a growth chamber. After a period of apple-rotting, C elegans were added, and the growing worm population was observed. We determined optimal conditions for the growth of C. elegans and then performed an ecological succession experiment observing worm populations every few days. Our data showed that the mesocosm allows abundant growth and reproduction of C. elegans that resembles populations of the nematode found in rotting fruit in nature. Overall, our study presents a simple protocol that allows the cultivation of C. elegans in a natural habitat in the laboratory for a broad group of scientists to study various aspects of animal and microbial ecology.

Influence of Seasonal Variations on Population Dynamics of Phyto-Parasitic Nematodes in Soil and Roots of Bell Pepper (Capsicum annuum L.) in Otari, Rivers State, Nigeria

Weather instability affects nematode proliferation in soil, affecting plant growth. Identifying endemic species and favourable seasons can guide farmers in cultivating crops during specific seasons, minimizing infections and improving yield. A survey to evaluate the influence of seasonal disparity on plant parasitic nematodes population in soil and roots of bell pepper (Capsicum annuum L.) was carried out during dry and rainy seasons in Otari, Abua/Odual Local Government Area of Rivers State, Nigeria. Five bell pepper cultivated fields were randomly selected and a total of 300 soil samples were collected and assayed for soil nematodes. The soil samples were collected using a soil auger at 0-15 cm depth, and roots were collected by the use of sterilized kitchen knife simultaneously for the isolation of nematode. The modified sieve plate method was employed for the extraction of nematodes. Nematode identification was carried out using a pictorial key. A total of 2,220 nematodes from 11 genera were reported in this study, among which 1,290 (58.1%) were recovered during the rainy season while the dry season showed 930 (41.9%) nematodes. Nematode population vary significantly between seasons in soil (P = .13) and roots of bell pepper (P = 3.90), with Heterodera species having higher density (1.44 and 1.03) during the rainy and dry seasons respectively in the soil. High density of Meloidogyne (0.97) was recorded during the rainy season and Radopholus spp (1.40) during the dry season in the root of bell pepper plant. The study showed that seasonal variations impacted on nematode population abundance in fields, establishing that nematodes are responsive to every unsteady condition of the soil environment resulting from seasonal disparity, and only species who adapt rapidly survive. Farmers should increase crop cultivation during the rainy season to boost yield, as nematodes population decline as rainfall increases.

Plant-parasitic nematodes associated with Panicum maximum and Mimosa hirsutissima in a pasture field

Pastures and weed plants can host plant-parasitic nematodes of economic importance, with the limited yield of pastures representing a continuous challenge for agriculture, especially in the lower Jequitinhonha Valley in southeastern Brazil, where dairy and beef cattle play a crucial role in the local economy. From this perspective, this study aimed to provide information on the population density of plant-parasitic nematodes associated with Panicum maximum cv. Mombaça and Mimosa hirsutissima, weed species commonly found in pasture areas cropped with this grass in the municipality of Almenara, MG, in the Jequitinhonha Valley region of southeastern Brazil. Soil and root samples were collected from the field and placed in plastic bags, which were labeled and taken to the laboratory for nematode extraction. Nematode population densities were estimated in a Peters counting slide under a light microscope, and genera identification was based on morphological traits. In rhizosphere soil (100 g) of P. maximum cv. Mombaça, the highest population densities were observed for Helicotylenchus sp. (3,999), followed by Tylenchus sp. (1,191), Meloidogyne spp. (939), and Pratylenchus sp. (544). In roots (1 g), on the other hand, the highest values corresponded to Pratylenchus sp. (19.6) and Meloidogyne spp. (15.5). However, in rhizosphere soil of M. hirsutissima, the highest population densities were recorded for Tylenchus sp. (2,072), Helicotylenchus sp. (1,883), Pratylenchus sp. (751), and Meloidogyne spp. (307). In contrast, in the roots, the highest values were observed for Meloidogyne spp. (6.9), Tylenchus sp. (4.4), and Pratylenchus sp. (2.7). These findings are essential to take decisions on the management of plant-parasitic nematodes.

Influence of Eisenia fetida on the Nematode Populations during Vermicomposting Process

Vermicomposting stands as a sustainable and environmentally friendly waste management practice, leveraging the metabolic prowess of earthworms to facilitate the decomposition of organic matter into nutrient-rich compost. The aim of this experiment was to study the influence of Eisenia fetida on the density and the tropic structure of a nematode community during the vermicomposting process over a period of 3 months. Sewage sludge and green waste served as composting substrates. Overall, six compost variants were prepared consisting of three variants incorporating E. fetida and three control variants lacking E. fetida. Throughout the investigation, samples were gathered on a monthly basis, with each variant undergoing three repetitions. The aim was to isolate nematodes, determine the population density of the five trophic groups, and identify the dominant community. The anaysis was conducted employing both microscopic examination and molecular metabarcoding (NGS). It was shown that the bacterial-feeding community maintained dominance. The introduction of E. fetida into the compost led to a significant rise in the abundance of Diplogasteridae. In the variant without E. fetida, the amount of Diplodasteridae exceeded 0.1% only after the 30th (C3) or the 60th (C1, C2) day of composting, while in the compost with E. fetida, they were present in large amounts (ranging from 11.0% to 28.0%) already on the 30th day of composting. The introduction of Eisenia fetida also led to a notable reduction in H. gingivalis with significant implications for mitigating the risk of halicephalobiosis. The introduction of E. fetida resulted in reducing H. gingivalis to levels below 0.1% in all compost variants.

Insights into the Belowground Biodiversity and Soil Nutrient Status of an Organic Apple Orchard as Affected by Living Mulches

The impact of living mulches established with three officinal plants (Alchemilla vulgaris, Fragaria vesca and Mentha x piperita) on the soil bacterial microbiome and activity, the nematodes population, and the nutrient status of an organic apple orchard was assessed. The composition and diversity of the bacterial communities were differentially modified by living mulches. The activity of the bacterial microbiome associated with F. vesca was higher and utilized more C sources in comparison to other treatments. The combined analysis of the core bacterial microbiome and metabolic activity pointed to a potential effect of F. vesca on different levels of the soil’s trophic network. The living mulches did not affect the overall number of nematodes, but in some cases, they modified the structure of the population: F. vesca induced the highest share of bacteria feeders and the lowest number of herbivores and fungal feeders. The living mulches modified the availability of some nutrients and the pH. Multivariate analysis of the whole dataset showed several potential inter-dependencies between the assessed parameters that are worthy of further study. In conclusion, the introduction of multifunctional living mulches based on officinal plants induced changes to the soil’s genetic and functional biodiversity and chemical properties. These modifications could deliver ecosystem services particularly relevant to organic apple orchards.

Light and Electron Microscopy Study of Opportunistic Free-Living Nematodes Scavenging and Thriving within Buried Dinosaur Bones

Abstract Nematode worms are the most abundant multicellular organism on Earth. They thrive in every habitat known, and they are voracious feeders within the top 70 cm of soils. Their sturdy cuticle protects them from environmental factors and predators. Nematodes play a significant role in the decomposition of vertebrate remains in soil and serve as indicators of nutrients that enter soils during decomposition. Certain parasitic nematodes have been identified in fossil remains, but reports of fossil worms are rare. We demonstrate the abundant presence of opportunistic nematodes feeding within dinosaur bones from the Hell Creek formation, MT. The presence of visible worm ultrastructure indicates that they were alive when preserved within the dinosaur bones. Our findings are identical to worms characterized as “blood parasites” in a dinosaur bone from Brazil, demonstrating that there is sufficient soft tissue within dinosaur bone canals to sustain large populations of nematodes post-mortem.

DNA barcoding of Australian cereal cyst nematode populations with comments on likely origin and taxonomy (Tylenchoidea: Heterodera)

A species of Heterodera has been known to parasitise cereals in Australia since the 1930s. It caused significant yield losses across Australia’s cereal growing regions until resistance breeding largely brought it under control, although it still occurs occasionally, especially in South and Western Australia. Australian cereal cyst nematode has long been considered to represent Heterodera avenae. However, in 2002 the name Heterodera australis was proposed for Australian cereal cyst nematode, as it could be distinguished from all non-Australian populations of H. avenae via biochemical and molecular methods. This new species proposal came with speculation that both H. avenae and H. australis might occur in Australia, and that H. australis might represent a native species. The name H. australis has generally not been accepted by Australian scientists, nor the notion that it is native. There remains some uncertainty as to the validity of H. australis and whether more than one species of cereal cyst nematode occur in Australia. Using a molecular barcoding approach (COI, 18S, ITS, 28S) we examined the species composition of cyst nematodes present in soil samples collected between 1989–2023 from Australian cereal growing regions. We find only one species of Heterodera parasitising cereals and, based on phylogenetic analyses, accept the validity of H. australis as the name best representative of this species. We also argue that, based on presently available evidence, H. australis is not native and was most likely introduced into Australia from Asia in the 1850s, rather than from Europe as has been generally assumed.

A taxonomic update on Tylenchorhynchus annulatus (Nematoda: Dolichodoridae), a widely distributed stunt nematode species

Summary The stunt nematode species, Tylenchorhynchus annulatus (Cassidy, 1930) Golden, 1971, is a widely distributed plant parasite found associated with various major agricultural crops. In the current work, a population of T. annulatus detected from a sugarcane field in Everglades, Florida, USA, was morphologically and molecularly characterised. A comparative study was also done including the stunt nematode populations identified morphologically and molecularly by different research groups as T. agri, T. annulatus or T. crassicaudatus from China, Indonesia, Iran, Korea, Niger, Nigeria, Tanzania and the USA, revealing highly similar morphology and overlapping morphometric data among the populations. However, these populations were found separated into two maximally supported clades in phylogenetic trees based on rRNA gene sequences (28S and ITS). One clade comprised populations from China, Indonesia, Iran, Nigeria, South Korea, Tanzania and the USA, and the other clade only populations from the USA. This study also strongly supported the view that T. crassicaudatus is a junior synonym of T. annulatus.

Effect of Fluopyram on Pratylenchus penetrans on Corn in the Field and In Vitro.

The effects of a fluopyram seed treatment on lesion nematodes (Pratylenchus spp.) and other plant-parasitic nematodes (PPNs) were evaluated on corn in multiple field locations in 2020 and 2021. The highest rate of fluopyram seed treatment (0.15 mg seed-1) reduced early season population density of lesion nematodes compared with the base treatment control in 2020 only. However, fluopyram did not affect late season lesion nematode population density and corn yields. Fluopyram seed treatment also had minimal or nonsignificant effects on other PPN species. Based on these results, the effects of fluopyram were tested in vitro on Pratylenchus penetrans. Results demonstrated that fluopyram severely affected motility in P. penetrans. The sensitivity of P. penetrans second-stage juveniles (J2s) to fluopyram was significantly higher than at J4 and adult, suggesting that sensitivity to fluopyram is dependent on developmental stage. In addition, the effects of fluopyram were reversible at an EC50 but were irreversible at the maximum concentration (25 μg/ml). Overall, our results indicate that fluopyram has potential for controlling P. penetrans, but its efficacy is variable depending on nematode developmental stage and chemical concentration. Further research is needed to determine if these impacts can translate to field scenarios.

Colony level fitness analysis identifies a trade-off between population growth rate and dauer yield in Caenorhabditis elegans

BackgroundIn the evolution from unicellular to multicellular life forms, natural selection favored reduced cell proliferation and even programmed cell death if this increased organismal fitness. Could reduced individual fertility or even programmed organismal death similarly increase the fitness of colonies of closely-related metazoan organisms? This possibility is at least consistent with evolutionary theory, and has been supported by computer modelling. Caenorhabditis elegans has a boom and bust life history, where populations of nematodes that are sometimes near clonal subsist on and consume food patches, and then generate dauer larva dispersal propagules. A recent study of an in silico model of C. elegans predicted that one determinant of colony fitness (measured as dauer yield) is minimization of futile food consumption (i.e. that which does not contribute to dauer yield). One way to achieve this is to optimize colony population structure by adjustment of individual fertility.ResultsHere we describe development of a C. elegans colony fitness assay, and its use to investigate the effect of altering population structure on colony fitness after population bust. Fitness metrics measured were speed of dauer production, and dauer yield, an indirect measure of efficiency of resource utilization (i.e. conversion of food into dauers). We find that with increasing founder number, speed of dauer production increases (due to earlier bust) but dauer yield rises and falls. In addition, some dauer recovery was detected soon after the post-colony bust peak of dauer yield, suggesting possible bet hedging among dauers.ConclusionsThese results suggest the presence of a fitness trade-off at colony level between speed and efficiency of resource utilization in C. elegans. They also provide indirect evidence that population structure is a determinant of colony level fitness, potentially by affecting level of futile food consumption.

Nematode egg parasitic fungus, Purpureocillium lilacinum: efficacy of indigenous strains for the management of Meloidogyne incognita in chickpea

BackgroundNematode egg parasitic fungus, Purpureocillium lilacinum is the most effective biocontrol agent and has been widely used commercially in many countries for the management of root-knot nematode, Meloidogyne incognita. Availability of indigenous potential strains specific to an agro ecosystem is very crucial for their successful commercial exploitation for suppression of nematode population. Hence, an attempt was made to isolate, characterize, evaluate and identify potential indigenous strains of P. lilacinum from pulse ecosystem for root-knot nematode management in chickpea.ResultsThe fungal colony was initially white and when spore was formed it turned into pink colour in 72 to 96 h. Hyphae was hyaline and septate, conidiophore was blunt, and phialides were with wide base and long neck bearing round to oval conidia in chains. Molecular identification of the species, P. lilacinum was carried out based on ITS1-5.8S-ITS2 region of the genomic DNA. In vitro bioassay of cultural filtrates on juvenile mortality revealed that maximum percentage of mortality was observed in IIPR-Pl-11 (88.36%). Spectrophotometric assay on chitinolytic activity showed that the strain IIPR-Pl-11 produced significantly high chitinolytic activity, chitinase enzyme and total protein content (0.139, 51.1 and173.75 µg/ml at 5days); (0.245, 90.1 and 272.67 µg/ml at 10 days) and (0.273, 100.4 and 306.25 µg/ml), respectively, at 15 days of culturing in colloidal chitin-enriched medium C. 2D gel electrophoresis of the crude chitinase suspension showed the presence of chitinase (32, 46 kDa size) in the sample from chitinase-induced medium C. In vitro bioassay of the cultural filtrates of the fungus grown in chitin-enriched medium C on inhibition on egg hatching revealed that the highest percent inhibition on egg hatching showed by IIPR-Pl-8 strain at 5 days of inoculation (42.6%) and IIPR-Pl-11 at 10 and 20 days of inoculation (62.80 and 93.50%), respectively. In vivo pot experiment revealed that among all strains, IIPR-Pl-11 was efficient in promoting plant growth very effectively by reducing gall number (41.3 per plant), egg mass (28.3 per plant) and soil population (284.3 per 200cc of soil) compared to control.ConclusionP. lilacinum strain IIPR-Pl-11 was the highest potential strain from pulse rhizosphere for the management of root-knot nematode, M. incognita in chickpea.

Does sargassum contribute to meiofauna dispersal? The case of tardigrades and nematodes in the Mexican Caribbean

The knowledge of the long-distance dispersal mechanisms of meiofauna is still limited. Rafting is considered as the main mechanism of dispersal of the meiofauna. The recent events of the Sargassum spp. arrival in the Caribbean provides the opportunity to explore long distance mechanisms. Four samples of floating Sargassum spp. were collected from the water column in Xcalak, Quintana Roo, which arrived at the Reef lagoon and Mangrove fringe. A total of 425 organisms were present, 388 nematodes, 36 tardigrades, and a single acarus. Tardigrades were represented by three species, whereas nematodes were represented by 16 morphotypes. The population of both tardigrades and nematodes was composed of mature and juvenile specimens. One tardigrade was collected during their ecdysis process. Our results suggest that not only the nematodes, but also tardigrades and acari can reach the floating Sargassum spp., maintaining in the algae, growing, and reproducing, while they are transported in the sea. We can conclude that in the Caribbean Sea, the floating Sargassum spp. floating is a dispersal mechanism of nematodes and tardigrades.

Use of manganese oxide nanoparticle (MnO2 NPs) and Pseudomonas putida for the management of wilt disease complex of carrot

Wilt disease complex of carrot is caused by Ralstonia solancearum and Meloidogyne incognita and is responsible for considerable yield loss. Manganese oxide nanoparticle (MnO2 NPs) and Pseudomonas putida were used alone and in combination for the management of wilt disease complex. In vitro, MnO2 NPs 0.10 g.L-l caused 49.36% reduction in hatching and 14.23% mortality of second stage juveniles (J2) of M. incognita while paper disc dipped in MnO2 NPs suspension caused 0.51 mm inhibition zone around R. solanacearum in nutrient agar medium. Inoculation of P. putida to plants with pathogens caused a similar increase in plant growth, chlorophyll and carotenoid contents as caused by foliar spray with 0.10 g.L−1 MnO2 NPs. Use of P. putida with NPs foliar spray to plants with pathogens caused a greater increase in plant growth, chlorophyll and carotenoid contents than with P. putida or NPs foliar spray. Inoculation of M. incognita/R. solanacearum/M. incognita plus R. solanacearum/P. putida/MnO2 NPs and MnO2 NPs plus P. putida caused increase in proline contents. Root colonization by P. putida was reduced in plants with test pathogens. Foliar application of MnO2 NPs and P. putida reduce wilt disease indices. Galling and populations of M. incognita was also reduced in plants co-inoculated with R. solanacearum. The greatest reduction in nematode populations and galling was observed in plants with NPs spray together with P. putida. Principal component analysis demonstrated a clear influence of NPS and P. putida and their combination on various studied parameters in diseased plants.

Host Status of Ornamental Shade Trees and Shrubs to Plant Parasitic Nematodes.

Oregon leads the United States in nursery production of shade trees and is third in deciduous and broadleaf evergreen shrub production. Plant-parasitic nematodes have been implicated in problems with the growth of plants in nurseries and are also of phytosanitary risk. A greenhouse experiment was conducted to evaluate the host status of four trees (Quercus alba, Quercus garryana, Acer campestre, Thuja occidentalis) and two shrubs (Buxus sempervirens, Rhododendron catawbiense) to Meloidogyne incognita, Meloidogyne hapla, and Pratylenchus neglectus. Each plant/nematode treatment was replicated five times, and the experiment was conducted twice. Plants were inoculated with 3,000 eggs of M. incognita or M. hapla and 2,500 individuals of P. neglectus two weeks after planting. After three months, the plants were harvested, and the total density of nematodes in soil and roots for P. neglectus and the total density of second-stage juveniles (J2) in soil and eggs on roots for M. hapla and M. incognita were determined. The final nematode population (Pf) and reproductive factor (RF = Pf/initial population density) were calculated. For M. incognita and M. hapla, all of the ornamental trees and shrubs would be considered as fair to good hosts with RF values > 1. Meloidogyne incognita had the highest Pf (5,234 total J2 and eggs/pot) and RF value (28.4) on A. campestre. For P. neglectus, all of the ornamental trees and shrubs were fair to good hosts, except for B. sempervirens. Buxus sermpervirens was not a host for P. neglectus, with an RF value of almost 0. This is the first report of Q. alba, Q. garryana, and A. campestre as hosts for M. incognita, M. hapla, and P. penetrans. This is also the first report of T. occidentalis and R. catawbiense as hosts for P. penetrans and the non-host status of B. sermpervirens for P. penetrans.

Altered larval activation response associated with multidrug resistance in the canine hookworm Ancylostoma caninum.

Parasitic gastrointestinal nematodes pose significant health risks to humans, livestock, and companion animals, and their control relies heavily on the use of anthelmintic drugs. Overuse of these drugs has led to the emergence of resistant nematode populations. Herein, a naturally occurring isolate (referred to as BCR) of the dog hookworm, Ancylostoma caninum, that is resistant to 3 major classes of anthelmintics is characterized. Various drug assays were used to determine the resistance of BCR to thiabendazole, ivermectin, moxidectin and pyrantel pamoate. When compared to a drug-susceptible isolate of A. caninum, BCR was shown to be significantly resistant to all 4 of the drugs tested. Multiple single nucleotide polymorphisms have been shown to impart benzimidazole resistance, including the F167Y mutation in the β-tubulin isotype 1 gene, which was confirmed to be present in BCR through molecular analysis. The frequency of the resistant allele in BCR was 76.3% following its first passage in the lab, which represented an increase from approximately 50% in the founding hookworm population. A second, recently described mutation in codon 134 (Q134H) was also detected at lower frequency in the BCR population. Additionally, BCR exhibits an altered larval activation phenotype compared to the susceptible isolate, suggesting differences in the signalling pathways involved in the activation process which may be associated with resistance. Further characterization of this isolate will provide insights into the mechanisms of resistance to macrocyclic lactones and tetrahydropyrimidine anthelmintics.

EFFICACY OF AQUEOUS AND POWDERED LEAF EXTRACTS OF Chromolaena odorata (ASTERALES: ASTERACEAE) AND Ficus mucuso (ROSALES: MORACEAE) BOTANICALS ON ROOT-KNOT NEMATODE INFECTING WATERMELON IN KWARA STATE, NIGERIA

Watermelon production in Kwara State, Nigeria, is affected by root-knot nematode (RKN), as all varieties of the crop are susceptible. The aim of this study was to identify readily available and environmentally safe nematicides for the management of RKN. The field was located at the Teaching and Research Farm of the University of Ilorin and set out in a randomised complete block design, with four replications. Aqueous and powdered extracts of Chromolaena odorata (L) King and Robinson and Ficus mucuso Welw. ex Ficalho were applied alone and in combination. There were seven total treatments: C. odorata aqueous, F. mucuso aqueous, C. odorata powder, F. mucuso powder, C. odorata and F. mucuso aqueous, C. odorata and F. mucuso powder, and the control. Data were collected on growth, yield and nematode populations. All data collected were subjected to analysis of variance, and treatments were compared using Duncan’s multiple range test at a 5% level of significance. The essential oil of each botanical was determined using gas chromatography-mass spectrometry. The vine length (185.61) and yield (2401.05) of plants treated with botanicals were significantly higher than those of the control at P<0.005. The nematode population was also significantly lower in plants treated with botanicals than in the control (318.30 and 230.00, first and second year, respectively) at P<0.005. Among the treatments, the combination of C. odorata and F. mucuso powders was the most effective, with higher growth and yield performance. The experiment showed that aqueous and powdered extracts of C. odorata and F. mucuso were effective in managing RKN in the field.

Prevalence, Spatial Distribution, and Population Density of Plant-Parasitic Nematodes in Vegetable Fields of North Carolina, South Carolina, and Tennessee Counties

Plant-parasitic nematodes are a diverse group of soilborne plant pathogens that limit the yield of numerous vegetable crops globally. Few studies have investigated nematode populations affecting vegetable crops in Tennessee and North and South Carolina. Between December 2020 and October 2022, vegetable fields in selected counties of these states were sampled for plant-parasitic nematodes. Data on the prevalence, spatial distribution, and population density of seven genera of plant-parasitic nematodes, identified via morphology, were collected. Root-knot nematodes were identified in 60% of the fields sampled, with population densities ranging from 10 to 10,400 nematodes per 500 cm3 of soil. Detection rates of other genera as percentages of total fields sampled were: spiral (42%), stubby root (32%), stunt (21%), ring (13%), and lesion (8%) nematodes. Out of eight crops sampled, fields either currently or formerly planted to tomato or pepper were the most frequently sampled in the survey (77% of total fields). This is the first survey to collect data on populations of plant-parasitic nematodes in this region, and the results highlight the need for continued surveillance and study of their impact in vegetable production.

Abundance of Tylenchid Nematodes in Banana (Musa sp.) fields with soil abiotic factors in Vasai, Palghar (M.S), India

Bananas are a major commercial crop that the Vasai region majority of farmers cultivate. One of the biggest challenges to the cultivation of bananas is nematodes. Tylenchids have long been recognized as a major challenge to banana production, leading to significant yield losses. As a result, this study aims to examine how the abundance of tylenchid nematodes changes in response to various abiotic soil factors. According to the results of the current study, the tylenchid nematodes population were high throughout the rainy, winter and remained comparatively lower in the summer season.

Rearing and Conservation of Nematode Populations Under Greenhouse or Axenic Conditions.

Once a nematode has been identified, to conduct studies for screening programs or pathogenicity tests, it is necessary a supply of large numbers of nematodes from field crops or reproduced and stored to be used in periods of the year when they are not available from fields. Therefore, nematodes must be reared in greenhouse or under in vitro conditions and stored for future needs. In this chapter, suggestions are given on how to obtain nematodes from fields and reproduce most of them on host plants in greenhouse (mainly Meloidogyne spp. and Globodera spp.) or in vitro. Reproductions in vitro include: On suitable callus of host plants (Pratylenchus spp., Ditylenchus spp.) On fungal cultures mainly of Botrytis cinerea or Alternaria spp. for Aphelenchoides spp. and other aphelenchids, including Bursaphelenchus xylophilus. On carrot disks for Pratylenchus spp. and Ditylenchus spp. Other specific media, such as garlic, potato, and sweet potato for D. destructor, and cocoyam disks for Radopholus similis. Guidelines are also given to store different nematodes for rather long times, including in vitro methods and in infected seeds, hay, and other plant parts. No information is given on how to prepare and store fixed materials.

Sampling and Extraction of Plant Parasitic Nematodes.

The study of nematodes requires availability of nematode specimens and their population densities in plants and soil. This can be achieved using adequate sampling schemes and extraction methods. In this chapter, the most common and suitable sampling and extraction procedures and equipment are described. These include the use of Baermann's funnels, Cobb's decanting and sieving, floating methods such as the Oostenbrink method and Fenwick can, elutriators such as Seinhorst methods, centrifugation methods including that of Coolen, and mechanical and enzymatic maceration. The combination of different methods for cleaning the nematode suspensions is described, such as Cobb's sieving with Baermann's funnels or centrifugation, and for cysts combining Seinhorst's elutriator or Fenwick can with the alcohol methods. Methods for extraction of eggs and/or juveniles of cyst and egg mass forming nematodes, to be used as inoculum or to ascertain egg viability, are also described. Only little information is also noted on the use of molecular tools to identify and quantify nematode populations in soil and roots.