Genera Of Plant Parasitic Nematodes Research Articles

Prevalence and abundance of plant-parasitic nematodes in New Zealand maize fields: effects of territory, soil orders, crop stage, and sampling time

ABSTRACT Plant-parasitic nematodes (PPNs) are significant agricultural pests that can reduce maize yields. This study examines the prevalence, abundance, and diversity of PPNs in New Zealand maize fields, focusing on the effects of territory, soil orders, crop stages, and sampling times. Seven PPN genera were identified: Pratylenchus spp. (root-lesion), Helicotylenchus spp. (spiral), Meloidogyne spp. (root-knot), Heterodera spp. (cyst), Paratylenchus spp. (pin), Criconemella spp. (ring), and Tylenchus spp. PPNs were present in 98% of the samples, with Pratylenchus spp. being the most prevalent (91%), followed by Helicotylenchus spp. (38%). Compared to Waikato and Manawatu-Whanganui, Canterbury had the highest nematode populations, particularly of Pratylenchus spp. and Helicotylenchus spp. Brown and pallic soils supported higher PPN abundances. Sampling during the maize harvesting stage and late autumn resulted in the highest nematode populations and diversity indices. Pratylenchus spp. populations often exceeded the economic threshold of 500 Pratylenchus kg−1 of soil, suggesting a significant threat to maize yield in New Zealand. The findings highlight the need for further research to assess the impact of Pratylenchus spp. on maize yield and to develop effective management practices for maize cultivation in the country.

Prevalence and Characterization of Plant-Parasitic Nematodes Existing in RD41 Rice Fields in Pathum Thani Province, Thailand, with Emphasis on Hirschmanniella mucronata and Meloidogyne graminicola

Plant parasitic nematodes (PPNs) are one of the most destructive pests affecting rice growth worldwide. In this study, populations of PPNs associated with RD41 rice fields in Pathum Thani Province, Thailand, were surveyed and the dominant PPNs found in the fields were identified using a combination of morphological and molecular traits. A total of 105 soil or root samples were taken from 21 paddy fields in 7 districts of Pathum Thani, and nematode extraction was processed in a laboratory. In all sampled rice fields, 6 nematode genera, namely Hirschmanniella sp., Meloidogyne sp., Pratylenchus sp., Tylenchorhynchus sp., Helicotylenchus sp., and Tylenchus sp., were extracted. Of these 6 nematode genera, Hirschmanniella sp. was the most prevalent in both soil and root samples (66.7 - 100 % occurrence observed), followed by Meloidogyne sp., which was found in only 4 districts of the province (0.2 to 8.7 % occurrence observed). The species of these predominant PPNs were morphologically and molecularly characterized. The identification results remained consistent across morphological features and molecular techniques, confirming the presence of Hirschmanniella mucronata and Meloidogyne graminicola in the studied rice fields. The results of this study provide useful baseline data of the occurrence of PPNs in Thailand's rice fields. The incidence of some PPNs found in this study is likely to become a significant factor limiting rice production yields if they are not better managed. HIGHLIGHTS Plant-parasitic nematode (PPN) populations in RD41 rice fields located in Pathum Thani province, Thailand were examined Six PPN genera were extracted from soil and root samples The predominant PPNs were characterized using morphological and molecular traits The main PPNs were identified as mucronata and M. graminicola This study provides useful baseline data of PPNs found in Thailand's rice fields GRAPHICAL ABSTRACT

Draft Genome Resource of a Wolbachia Endosymbiont in Heterodera humuli

The bacterial endosymbiont Wolbachia is known to be associated with different arthropods and only two genera of plant-parasitic nematodes, Pratylenchus and Radopholus. This effort employed a genome skimming approach to discover the presence of endosymbionts in a population of Heterodera humuli sequenced with PacBio long-read sequencing. Wolbachia was found associated with the nematode. The genome of this Wolbachia is 1,051,007 bp and has a GC percentage (32.6%) within the expected range for the genus. A phylogenetic analysis placed the Wolbachia strain from H. humuli in a clade with another nematode-associated Wolbachia strain reported in Texas, with a bootstrap value of 1. To our knowledge, this is the first published report of Wolbachia associated with H. humuli, expanding the known association of this endosymbiont to three genera of plant-parasitic nematodes. This finding will enhance sequence resources for further comparisons of Wolbachia diversity. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2024.

Meloidogyne hapla dominates plant‐parasitic nematode communities associated with kiwifruit orchards in Portugal

AbstractKiwifruit, Actinidia spp., is an important crop worldwide and its cultivation has been increasing in Portugal. Kiwifruit plants are susceptible to plant‐parasitic nematodes (PPNs), including Meloidogyne spp. M. hapla and M. incognita have been reported to affect kiwifruit in major production regions worldwide, although information is lacking on the distribution and identity of PPNs associated with kiwifruit orchards in Portugal. Moreover, research is scarce on the drivers of PPN communities in this crop. Our primary objective was to investigate the diversity, density and distribution of PPNs within kiwifruit orchards of Portugal and to elucidate the influence of environmental factors on their community composition. Additionally, we aimed to evaluate population densities and identity of Meloidogyne spp. Nematodes were extracted from composite soil and root samples collected from orchards. Analysis of soil nematode communities suggested bacterial‐driven decomposition and high nutrient enrichment in these soils. Sixteen different genera of PPNs were detected, with Meloidogyne spp. as the dominant genus, mostly represented by a single species, M. hapla. PPN communities exhibited low richness, and β‐diversity analysis indicated a high degree of similarity among them. Additionally, their composition was significantly influenced by soil and climatic parameters. We found that 37 out of 40 kiwifruit orchards in Portugal were infested by root‐knot nematodes. The unexpectedly low species diversity, dominated by M. hapla, merits further research to establish underlying factors for its high incidence in this crop and to assess the impact of these nematodes on kiwifruit performance and productivity.

Antagonistic Efficacy of Symbiotic Bacterium Xenorhabdus sp. SCG against Meloidogyne spp.

The inhabitation and parasitism of root-knot nematodes (RKNs) can be difficult to control, as its symptoms can be easily confused with other plant diseases; hence, identifying and controlling the occurrence of RKNs in plants remains an ongoing challenge. Moreover, there are only a few biological agents for controlling these harmful nematodes. In this study, Xenorhabdus sp. SCG isolated from entomopathogenic nematodes of genus Steinernema was evaluated for nematicidal effects under in vitro and greenhouse conditions. The cell-free filtrates of strain SCG showed nematicidal activity against Meloidogyne species J2s, with mortalities of > 88% at a final concentration of 10%, as well as significant nematicidal activity against the three other genera of plant-parasitic nematodes in a dose-dependent manner. Thymine was isolated as active compounds by assay-guided fractionation and showed high nematicidal activity against M. incognita. Greenhouse experiments suggested that cell-free filtrates of strain SCG efficiently controlled the nematode population in M. incognita-infested tomatoes (Solanum lycopersicum L., cv. Rutgers). In addition, a significant increase in host plant growth was observed after 45 days of treatment. To our knowledge, this is the first to demonstrate the nematicidal activity spectrum of isolated Xenorhabdus species and their application to S. lycopersicum L., cv. Rutgers under greenhouse conditions. Xenorhabdus sp. SCG could be a promising biological nematicidal agent with plant growth-enhancing properties.

Occurrence and Distribution of Plant Parasitic Nematodes in Mungbean in Jaipur District, Rajasthan, India

Aim: Mungbean (Vigna radiata (L.) R. Wilczek) is one of the important pulse crops grown in India. Considering the economic importance of nematodes as disease causing organism of mungbean the present investigation was carried out to know the distribution of plant parasitic nematodes in mungbean crops in Jaipur district of Rajasthan. Methodology: A total 139 soil samples were collected from mungbean fields of 12 different localities in Jaipur district. The samples were processed using Cobb's sieving and decanting technique followed by Baermann's funnel technique and nematode population was counted in suspension and identified on the basis of their morphological characters. Results: The samples were infected with mainly four genera of plant parasitic nematodes i.e., Meloidogyne spp., Helicotylenchus spp., Pratylenchus spp. and Tylenchorhynchus spp. etc. Out of 139 soil samples, 120 samples showed the presence of Meloidogyne javanica with 86.33 % occurrence, 18.82 % absolute density, 83.81 % relative density and 15.85 % prominence value and found most predominant in different surveyed localities in Jaipur district.

Counting nematodes made easy: leveraging AI-powered automation for enhanced efficiency and precision.

Counting nematodes is a labor-intensive and time-consuming task, yet it is a pivotal step in various quantitative nematological studies; preparation of initial population densities and final population densities in pot, micro-plot and field trials for different objectives related to management including sampling and location of nematode infestation foci. Nematologists have long battled with the complexities of nematode counting, leading to several research initiatives aimed at automating this process. However, these research endeavors have primarily focused on identifying single-class objects within individual images. To enhance the practicality of this technology, there's a pressing need for an algorithm that cannot only detect but also classify multiple classes of objects concurrently. This study endeavors to tackle this challenge by developing a user-friendly Graphical User Interface (GUI) that comprises multiple deep learning algorithms, allowing simultaneous recognition and categorization of nematode eggs and second stage juveniles of Meloidogyne spp. In total of 650 images for eggs and 1339 images for juveniles were generated using two distinct imaging systems, resulting in 8655 eggs and 4742 Meloidogyne juveniles annotated using bounding box and segmentation, respectively. The deep-learning models were developed by leveraging the Convolutional Neural Networks (CNNs) machine learning architecture known as YOLOv8x. Our results showed that the models correctly identified eggs as eggs and Meloidogyne juveniles as Meloidogyne juveniles in 94% and 93% of instances, respectively. The model demonstrated higher than 0.70 coefficient correlation between model predictions and observations on unseen images. Our study has showcased the potential utility of these models in practical applications for the future. The GUI is made freely available to the public through the author's GitHub repository (https://github.com/bresilla/nematode_counting). While this study currently focuses on one genus, there are plans to expand the GUI's capabilities to include other economically significant genera of plant parasitic nematodes. Achieving these objectives, including enhancing the models' accuracy on different imaging systems, may necessitate collaboration among multiple nematology teams and laboratories, rather than being the work of a single entity. With the increasing interest among nematologists in harnessing machine learning, the authors are confident in the potential development of a universal automated nematode counting system accessible to all. This paper aims to serve as a framework and catalyst for initiating global collaboration toward this important goal.

Nematode community structure in sugarcane fields under continuous vinasse fertigation

Sugarcane vinasse is a residue from ethanol production, which has high content of nutrients and organic matter, improving chemical, physical and biological changes in the soil. This study evaluated nematode community structure, food web, metabolic footprint, and soil quality in sugarcane fields under continuous vinasse fertigation. Soil samples were collected from four sugarcane fields in Pernambuco State, Brazil, under continuous vinasse fertigation for nematode identification at the genus (plant parasites) and family (free-living) level, physical and chemical analyses of the soil. Nine genera of plant-parasitic nematodes and five families of free-living nematodes were identified in sugarcane fields. Plant-parasitic nematodes were dominant, except in the field with five years of continuous vinasse application. The genera Mesocriconema, Meloidogyne, Helicotylenchus and Pratylenchus were frequent in all fields. Predators and fungivores nematodes were few abundant, although, according to the soil food web, all sugarcane fields were low to moderately disturbed environments. A positive correlation was observed between the microbial respiration and Rhabdtidae in fields with five years of vinasse application, and between the electrical conductivity of the soil and Meloidogyne in fields without vinasse application. We highlight those alterations in the structure and composition of the nematode community, and soil characteristics that can occur due to vinasse fertigation in sugarcane fields.

Identification of Plant Parasitic Nematodes Associated with Citrus in Dibrugarh District

The present investigation was carried out to determine the occurrence and distribution of plant parasitic nematodes associated with citrus plants of different citrus orchards in Dibrugarh district. A total of 149 soil and root samples were collected randomly from the rhizosphere of citrus plants from the twenty four different citrus orchards of seven blocks from Dibrugarh district. Eight genera of plant parasitic nematodes were found to be associated with citrus plants of Dibrugarh district. Genera of plant parasitic nematodes recorded were namely Tylenchulus, Hoplolaimus, Helicotylenchus, Tylenchorhynchus, Meloidogyne, Xiphinema, Paratylenchus and also nematodes genera found under criconematids. Among them Hoplolaimus sp., Helicotylenchus sp., Tylenchorhynchus sp. and T. semipenetrans were found to be present in most of the samples. Community analysis of plant parasitic nematodes revealed that the genus Hoplolaimus ranked first in relative frequency, absolute frequency, absolute density, relative density and prominence value. Genus Helicotylenchus ranked second in absolute density, relative density and prominence value and genus Tylenchorhynchus ranked third in case of absolute density absolute frequency and prominence value. Results shown that Tylenchulus semipenetrans ranked second in absolute frequency and relative frequency and fourth in prominence value.

Drivers of plant parasitic nematode community structures associated with tobacco‐growing areas in southern Brazil

AbstractTobacco (Nicotiana tabacum L.) is one of the most important crops in southern Brazil, but little is known about the distribution and diversity of plant parasitic nematodes (PPNs). We surveyed the occurrence and diversity of PPNs in 36 tobacco‐growing areas in southern Brazil as well as evaluated their relationship with 19 bioclimatic variables. For these purposes, extracted nematodes (from soil and roots) were identified based on morphological and biochemical traits and estimates of incidence and abundance were obtained, which were used to compute diversity indices. Furthermore, the relationship between taxa and diversity and the influence of bioclimatic variables were studied using principal component analysis (PCA) and generalized linear models (GLMs), respectively. We observed diversity across the sampled sites, with values varying from 0.03 to 1.22 and from 0.05 to 0.76 according to the Shannon‐Wiener and Pielou's evenness indices, respectively. Seven genera of PPNs (Meloidogyne, Helicotylenchus, Tylenchus, Xiphinema, Pratylenchus, Paratylenchus and Mesocriconema) were identified, highlighting taxa with high incidence and abundance, such as Meloidogyne (100%; 1800 to 41,850 specimens/250 cm3), Helicotylenchus (100%; 50 to 9850 specimens/250 cm3), and Pratylenchus (86.1%; 50 to 1950 specimens/250 cm3). The PCA disclosed the major roles of Meloidogyne, Tylenchus, and Helicotylenchus in the structure of the PPN communities and their interplays. Among root‐knot nematodes, Meloidogyne javanica, M. arenaria and M. incognita were the predominant species. Using GLMs, we found that average annual temperature and annual precipitation strongly influenced the abundance of PPNs as well as the diversity indices (p < .01), with negative and/or positive interactions. Collectively, our findings fill gaps in knowledge about the current impact of PPNs and provide insights into future scenarios, including for other host crops.

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.

Ecological Interaction in the Proliferation of Phytoparasitic Nematodes in Coffee var. Typica

Phytoparasitic nematodes are a common problem in coffee production worldwide. In Peru, the proliferation of phytoparasitic nematodes in Coffea arabica L. var. Typica has negative impacts on coffee production and huge economic losses. The objective of this study was to determine the ecological interactions that influence the proliferation of phytoparasitic nematodes in C. arabica var. Typica in Quillabamba, Cusco, Peru. The density of phytoparasitic nematodes in the soil and root was evaluated using the modified Baermann channel method. Identification of genera and species of phytoparasitic nematodes was carried out in the different samples, based on descriptions and taxonomic keys. Physical and chemical parameters of the soil were evaluated. Principal component analysis (PCA) and a correlation network were employed to distribute the different species of nematodes. The variables soil texture, organic matter, pH, altitude, temperature and humidity were used. During the sampling, several genera of plant-parasitic nematodes were identified in addition to various categories of nematodes. Meloidogyne exigua, Pratylenchus coffeae, Allotrichodorus longispiculis and Helicotylenchus longicaudatus are among the specific species of nematodes identified. The genus with the highest incidence was Meloidogyne spp. with 77.3% in soil and 96% in roots, reaching an average density of 340 nematodes in 100 g of soil and 368 nematodes in 1 g of roots. The PCA results show that 63.7% of the variability of the data is retained in the first two components. PCA shows that the sampled areas were differentiated and grouped with the evaluated characteristics, while the nematodes overlap in the representation of the analysis, thus making it difficult to select them. Pearson’s correlation showed a negative correlation between altitude and soil nematode density (−0.22), suggesting that conditions at higher altitudes may be more unfavorable for nematode growth. In addition, a positive correlation was found between soil pH and organic matter (0.93, p < 0.001) and may influence nematode density. The factors that influence the density of nematodes in the soil and plant roots are multiple and complex, and their understanding is essential for the success of coffee production. The finding of the current study may be useful in the development of sustainable strategies for managing nematodes in coffee network production.

Aphelenchoides varicaudatus (Nematoda: Aphelenchoididae) and Helicotylenchus erythrinae (Nematoda: Hoplolaimidae) from Garlic Plantation in Magelang, Central Java, Indonesia.

There were two most found genera of plant parasitic nematodes from garlic plantation in Magelang, Central Java, Indonesia which suffered losses due to bulb rot, Aphelenchoides and Helicotylenchus. Polymerase Chain Reaction (PCR) was conducted using a pair of universal nematode primer (D2A/D3B) to determine the Aphelenchoides and Helicotylenchus species from those host. Both genera were amplified at ~780 bp. The Blast-N results for the Aphelenchoides showed high identity to Aphelenchoides varicaudatus from Yunnan China (HQ283353) with 99.47 % identity, while the Helicotylenchus showed 95.22 % identity to Helicotylenchus erythrinae from Colombia (MT321739). From morphological and molecular data, we confirm that the Aphelenchoides species is A. varicaudatus. Based on female morphological character, Helicotylenchus species refers to H. erythrinae. Which is also supported by its nucleotide alignment which has same region character as H. erythrinae (MT321739). This is the first report of molecular characterization of H. erythrinae in Indonesia.

Prevalence of major parasitic nematodes associated with tomatoes (Solanum lycopersicum L.) in two districts of Jimma, Ethiopia

This study assessed the diversity of plant parasitic nematodes associated with tomatoes in two major tomato producing districts. A total of 40 composite soil and root samples were collected, and extracted nematodes were identified morphologically to a genus level, however, Meloidogyne arenaria was identified based on molecular methods. Accordingly, eight plant parasitic nematode genera were identified, including Meloidogyne, Pratylenchus, Helicotylenchus, Scutellonema, Rotylenchulus, Criconema, Paratylenchus, and Globodera. The highest prominence value was recorded for Meloidogyne and the lowest being for Paratylenchus. In terms of Meloidogyne infestation, the highest mean root knot incidence was in the Dedo district, specifically at the Babo peasant association, where Meloidogyne could be considered a major threat to tomato production. The study further indicated that Meloidogyne density was higher in soil with a pH between 6.4 and 7.4, and an altitude above 1800 m. This result implies the need for immediate attention and implementation of feasible management strategies to reduce the damage caused by Meloidogyne sp.

Effect of Compost Along with Bio Agents on Root Knot Nematode (Meloidogyne spp.) in Okra (Abelmoschus esculentus L., Walp)

Okra [Abelmoschus esculentus L., Moench] a native of South-Africa and commonly known as ‘Bhindi’ is an annual malvaceous vegetable crop, especially grown in tropical and subtropical climates. It is also called “perfect villager’s vegetable”. Root-knot nematodes are considered among the top five major plant pathogens and the first among the ten most important genera of plant parasitic nematodes in the world. Amongst nematodes, root-knot nematode (Meloidogyne incognita and Meloidogyne javanica) causes severe damage to okra. Trichoderma viride, Pseudomonas fluorescene and Rhizobium were tested under field conditions during Rabi 2020-2021 for their efficacy against the Root knot nematode and growth & nematode population.

Molecular investigation of proteinase inhibitor (PI) gene in tomato plants induced by Meloidogyne species

BackgroundThe plant parasitic nematode genus Meloidogyne parasitize almost all flowering crops. Plants respond with a variety of morphological and molecular mechanisms to reduce the effects of pathogens. Proteinase inhibitors (PI), a special group of plant proteins which are small proteins, involve in protective role in the plants attacked by microorganisms. Still, the plant response using PI against nematodes has not been well understood. Therefore, this study was aimed to determine the expression of proteinase inhibitor I (PI-I) gene subsequent the infection of M. incognita, M. javanica, and M. chitwoodi in tomato plants post nematode infections. Molecular methods were used to determine the PI gene expressions at different days post nematode infections in host tissues. ResultsResults revealed that the population of M. incognita species reached the highest level of nematode population followed by M. javanica and M. chitwoodi, respectively. All Meloidogyne species induced expression of PI-I gene reached at the utmost level at 3 days post infection (dpi) in host tissues. Relative gene expression level was sharply dropped at 7 dpi, 14 dpi, and 21 dpi in M. incognita induced gene expression in host tissues. Similar results were observed in host tissues after infection of M. javanica and M. chitwoodi. ConclusionsThe commonalities of plant response across a diverse Meloidogyne species interaction and the expression of PI gene may be related to plant defense system. Increased level of PI gene expressions in early infection days in host tissues induced by parasitic nematodes may share resemblances to the mechanisms of resistance on biotrophic interactions.

'Candidatus Xiphinematincola pachtaicus' gen. nov., sp. nov., an endosymbiotic bacterium associated with nematode species of the genus Xiphinema (Nematoda, Longidoridae).

An intracellular bacterium, strain IAST, was observed to infect several species of the plant-parasitic nematode genus Xiphinema (Xiphinema astaregiense, Xiphinema incertum, Xiphinema madeirense, Xiphinema pachtaicum, Xiphinema parapachydermum and Xiphinema vallense). The bacterium could not be recovered on axenic medium. The 16S rRNA gene sequence of IAST was found to be new, being related to the family Burkholderiaceae, class Betaproteobacteria. Fungal endosymbionts Mycoavidus cysteinexigens B1-EBT (92.9 % sequence identity) and ‘Candidatus Glomeribacter gigasporarum’ BEG34 (89.8 % identity) are the closest taxa and form a separate phylogenetic clade inside Burkholderiaceae. Other genes (atpD, lepA and recA) also separated this species from its closest relatives using a multilocus sequence analysis approach. These genes were obtained using a partial genome of this bacterium. The localization of the bacterium (via light and fluorescence in situ hybridization microscopy) is in the X. pachtaicum females clustered around the developing oocytes, primarily found embedded inside the epithelial wall cells of the ovaries, from where they are dispersed in the intestine. Transmission electron microscopy (TEM) observations supported the presence of bacteria inside the nematode body, where they occupy ovaries and occur inside the intestinal epithelium. Ultrastructural analysis of the bacterium showed cells that appear as mostly irregular, slightly curved rods with rounded ends, 0.8–1.2 µm wide and 2.5–6.0 µm long, possessing a typical Gram-negative cell wall. The peptidoglycan layer is, however, evident only occasionally and not detectable by TEM in most cells. Another irregularly occurring shell surrounding the endosymbiont cells or the cell clusters was also revealed, probably originating from the host cell membrane. Flagella or spore-like cells do not occur and the nucleoid is diffusely distributed throughout the cell. This endosymbiont is transmitted vertically through nematode generations. These results support the proposal of IAST as a new species, although its obligate intracellular and obligate endosymbiont nature prevented isolation of a definitive type strain. Strain IAST is therefore proposed as representing ‘Candidatus Xiphinematincola pachtaicus’ gen. nov., sp. nov.

Spatial distribution and community analysis of plant-parasitic nematodes associated with rice (Oryza sativa L.) in Benue State, Nigeria

Plant-parasitic nematodes (PPNs), also known as phyto-parasitic or plant-destructive nematodes are microscopic, translucent, bilaterally symmetrical, pseudocoelomic, multicellular worm-like organisms which feed on plant root mostly, and seldom on other vegetative parts. Although these PPNs have been reported to constitute threat to rice production, documentation of their spatial distribution and densities in major rice-producing areas of Benue state, Nigeria is absent. Using multi-stage sampling procedure, surveillance for PPNs, their densities and community analyses were conducted in six major rice-producing local government areas (LGAs) of Benue. The LGAs included Agatu, Apa, Gwer West, Guma, Kwande and Makurdi LGAs and a total of 108 samples were collected comprising 54 soil and 54 root samples. Nine plant-parasitic nematode genera which included Criconemoides, Tylenchorhynchus, Trichodorus, Hirschmanniella, Xiphinema, Helicotylenchus, Scutellonema, Pratylenchus and Meloidogyne were recovered. In order of ranking, Meloidogyne sp., P. zeae and H. oryzeae had the highest population densities across all LGAs included in the study. The highest density of PPN was recorded in Kwande (ca. 133 PPNs/10mL of nematode suspension) while lowest population density was recorded in Makurdi (ca. 77 PPNs/10mL of suspension). Although Meloidogyne sp. recorded the highest average population density in all LGA except in Gwer West LGA where H. oryzae recorded the highest average population density of approximately 13 PPNs/10mL of suspension. Community analysis also revealed that Meloidogyne sp. was the most spatially distributed PPN closely followed by P. zeae and H. oryzae with prominence values of 37.78, 21.84 and 20.91, respectively. However, in the soil, the highest prominence value was recorded in H. oryzae making it the most spatially distributed PPN in the soil.

NEMATODE PARASITES OF WATERLEAF (Talinum triangulare) IN OBIO-AKPOR AND IKWERRE LOCAL GOVERNMENT AREAS OF RIVERS STATE, NIGERIA

Waterleaf, Talinum triangulare is cultivated in home gardens and fields to improve nutritional quality for the family and a source of livelihood for farmers. However, the role of T. triangulare is often counteracted by plant-parasitic nematodes (PPNs). Effective management of PPNs will depend on the identification and determination of their population and distribution. A survey was conducted in two Local Government Areas (LGAs), Ikwerre and Obio-Akpor of Rivers State to identify plant-parasitic nematodes associated with waterleaf. Multistage random sampling technique was employed in the collection of 60 bulked soil and root samples across six waterleaf monoculture farming communities. The nematodes were extracted, identified and their population determined using standard procedures. Occurrences, relative importance values (RIV) and diversity indices were determined. Other data were analysed using descriptive statistics and analysis of variance. Six plant-parasitic nematodes genera were encountered in this study, Helicotylenchus, Pratylenchus, Paratylenchus, Meloidogyne, Scutellonema and Tylenchulus. Pratylenchus and Helicotylenchus were the most frequently occurring nematode pest genera with equal relative frequency of occurrence of 38.89%. Pratylenchus species with RIV of 61.34% was the most important nematode pest associated with waterleaf across the six farm communities. The dominance index of 0.71 for the nematode genera showed that some nematode species dominated others. Alakahia farms had the highest population of plant-parasitic nematodes (2,780) across the six farm communities, whereas Omagwa farms had the lowest (250). The study showed that nematode pests are associated with waterleaf and could be contributing to yield losses in this crop

Distribution of plant-parasitic nematodes and comparative effects of fadama (hydromorphic) fields and upland fields on plant-parasitic nematodes and free-living nematodes on three indigenous vegetables commonly grown in Osun State Nigeria

Surveys were conducted in 2016 and 2017 to investigate the distribution of plant-parasitic nematodes and the effects of fadama fields and upland fields on plant-parasitic and free-living nematodes. A total of 84 soil samples were collected from seven Local Government Areas visited in Osun State. Soil samples were collected from two fadama fields and two upland fields in all the LGAs visited. Nematodes were extracted, counted and identified under a compound microscope according to the morphological characteristics of the nematodes. The results showed that sixteen genera of plant-parasitic nematodes were found associated with Solanum macrocarpon, Amaranthus cruentus and Telfairia occidentalis. Meloidogyne\\ Helicotylenchus and Rotylenchulus were the most abundant nematodes associated with the vegetables. Fadama fields significantly had lower populations of plant-parasitic nematodes and higher populations of free-living nematodes in comparison with upland fields in fields sown to the vegetables. Farmers are advised to take full advantage of fadama fields in vegetable production.