Diversity Of Plant-parasitic Nematodes Research Articles

Plant-Parasitic Nematode Genera Associated with Turfgrass in Maryland Golf Courses and Athletic Fields.

Field surveys were conducted to assess the occurrence and diversity of plant-parasitic nematodes (PPNs) in golf courses and athletic fields across Maryland, USA, during 2022 and 2023. A total of 28 golf courses and ten athletic fields were surveyed, revealing the prevalence and abundance of 13 PPNs taxa in the region. Criconemoides was identified as the most prevalent (94.9%) and Tylenchorhynchus as the most abundant (2.3) across all samples. Central golf courses (west side of the Chesapeake Bay) exhibited a high prevalence of Criconemoides and Tylenchorhynchus, while Eastern Shore golf courses and athletic fields displayed a higher prevalence of Helicotylenchus and Criconemoides. Further, Belonolaimus longicaudatus was reported for the first time from turfgrass in Maryland, raising concerns due to its potential to cause severe damage on both cool- and warm-season turfgrass. Biodiversity analysis indicated that richness (R2) was higher in athletic fields, while diversity (H') and evenness (J') were significantly greater in golf courses. This study provides baseline information for monitoring PPNs distribution in Maryland and also for the development of effective nematode management approaches in turfgrass ecosystems.

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.

Occurrence, abundance and distribution of soil nematodes associated with groundnut farming in Kenya

Groundnut is a major cash crop grown in tropical and subtropical regions. In Kenya, groundnut is mostly grown in the Western and Nyanza regions and has been ranked the fourth cash crop of the Lake Victoria Basin (LVB). However, groundnut production in Kenya has continued to decline with farmers attaining less than 50 % of the yield potential of 700 to 1400 kg/ha. Yearly statistical reports by Agriculture and Food Authority (AFA), Nuts and Oil Crops Directorate for the last seven years, show the decline has been consistent. In 2019/2020 AFA reported there was a decrease of 216 Mt in Homa Bay and 30 Mt in Kisumu. Yield loss is attributed to lack of quality improved seed and pests’ infestation during growth and storage. Plant parasitic nematodes (PPN) are the major pests of groundnut worldwide. This study sought to investigate the occurrence of nematode communities (PPN and non-parasitic nematodes (NPN) in soils cultivated with groundnuts in the LVB and to determine the effect of farmyard manure application on their presence. Six peanut varieties (4 improved and 2 local) were cultivated in Nyakach and Karachuonyo in March to August in 2021 and 2022. Soil samples, groundnut roots and pods were collected. A modified Baermann’s, maceration methods and filtration technique was used to isolate nematodes from the soil, groundnut pods and roots. Multi-stage Analysis of variance (ANOVA) was used to determine any significant differences in abundance and richness while the Shannon index compared diversity of PPN and NPN among the farms in two seasons and regions. Eleven genera of PPN: Aphelenchoides, Meloidogyne, Pratylenchus, Helicotylenchus, Tylenchus, Scutellonema, Trichodorus, Hemicycliophora, Tylenchorhynchus, Rotylenchulus and Criconema. spp., and three genera of NPN; Rhabdittes, Dorylaimus spp. and Predators were categorized. Aphelenchoides and Meloidogyne were the most abundant PPN and Rhabdites NPN in both regions and seasons. Application of farm yard manure led to decline of abundance of PPN and an increase in NPN. The results confirm the presence of PPN in the LVB groundnut growing regions and the potential use of farm yard manure in their management. This study recommends further investigation on actual damage potential of these PPN and their management strategies. Key words: Arachis hypogaea, Soil nematodes, Meloidogyne, Aphelenchoides, Rhabdites, Pratylenchus, Helicotylenchus

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.

Diversity of plant-parasitic nematodes in potato fields at different altitudes in Probolinggo District, East Java, Indonesia

Abstract. Prada AP, Pratiwi GNC, Wagiyana. 2022. Diversity of plant-parasitic nematodes in potato fields at different altitudes in Probolinggo District, East Java, Indonesia. Cell Biol Dev 6: 61-67. Plant parasitic nematodes (PPNs) are microorganisms sensitive to environmental conditions. Therefore, plant parasitic nematode diversity in a field may affect the decision of effective management tactics. This study aimed to assess the diversity of plant parasitic nematodes in potato fields at three different altitudes. The study was carried out in Probolinggo District, East Java, Indonesia. The sampling area was divided into three groups based on altitude variations, namely 1,008 m asl., 1,413 m asl., and 1,875 m asl. Soil samples were collected randomly in a zigzag pattern. Samples were collected from 20 points across each field at a depth of 20-30 cm below the soil surface. Each sub-sample included up to 500 g of soil. The white head tray method extracted nematodes from 500 g of soil from each subsample. After characterizing the extracted nematodes, the absolute density and dominance values were determined. The results revealed variations in the three areas with different altitudes. The total number of plant-parasitic nematodes (PPN) discovered on the field at an altitude of 1,008 m asl. was 57.00 ± 16.43. Furthermore, at an altitude of 1,413 m asl., the total number of PPNs discovered is 41.67 ± 10.98. The total number of nematodes on the field at an altitude of 1,875 m asl. was 50.50 ± 12.60. The findings of this study also indicated that Meloidogyne sp. was the genus with the highest population on the field, at an altitude of 1,008 m asl. On the other hand, Pratylenchus sp. is the most abundant nematode in the field between 1,413 and 1,875 m asl. An identical situation also occurred with the nematode dominance values in the three fields studied.

Vertical Distribution of Plant-Parasitic Nematodes in Sweet Potato.

Plant-parasitic nematodes (PPN) are harmful pests that have become a severe threat to crop production worldwide. Diversity of PPN at horizontal and spatial scales influence the effectiveness of control strategies. This study evaluated the vertical distribution of PPN genera at 0 cm to 30 cm and 30 cm to 60 cm in sweet potato fields in Central, Manyatta, and Nembure regions of Embu County, Kenya. A significant region × depth interaction was observed for Tylenchus. For all the other nematode genera, there were no significant variations in the abundance at 0 cm to 30 cm and 30 cm to 60 cm depths. However, Helicotylenchus, Meloidogyne, and Scutellonema occurred in greater numbers at both depths in all regions. Shannon and Simpson diversity indices were higher at 0 cm to 30 cm depth while Pielou’s evenness was similar at both depths in the three regions. Diversity partitioning of genus richness, Shannon, and Simpson diversities across all regions at 0 cm to 30 cm, indicated that β component contributed 61.9%, 35.6%, and 22.6% of γ diversity, respectively. Coinertia analysis indicated a significant covariation between nematode genera and soil properties. The results show that management of PPN in sweet potato fields should be targeted at soil depths that are not less than 60 cm.

Diversity and Identification of Plant-Parasitic Nematodes in Wheat-Growing Ecosystems.

Several nematode species can be found in different densities in almost any soil ecosystem, and their diversity in those ecosystems depends on numerous reasons, such as climatic conditions and host presence. Cereals are one of the main hosts of plant-parasitic nematodes (PPN), chiefly root-lesion nematodes (RLN, Pratylenchus spp.) and cereal cyst nematodes (CCN, Heterodera spp.). These nematodes are known as major parasites of the cereal crops; however, agricultural areas accommodate various nematodes showing biological variation. The diversity of parasitic nematodes on cereals in the Sakarya provinces of Türkiye, where cereals are intensively grown and located in the middle of two climatic zones, has not been well studied. Therefore, in this study, we aimed to determine the diversity, identification, and molecular phylogeny of PPNs in wheat-growing ecosystems in the Hendek, Pamukova, Geyve, Akyazı, and Central districts of Sakarya. The diversity of PPNs was calculated using the Shannon diversity index. Thirteen PPN genera were detected in 92% of soil samples. Heterodera filipjevi was identified in 24% of the soil samples using morphological, morphometrical, and molecular tools. In the morphological and molecular analyses, intraspecific polymorphism was observed in H. filipjevi populations. The result indicated that the high infestation rate of H. filipjevi was recorded from Geyve and Pamukova, followed by Hendek and Akyazı; however, a low infestation rate was detected in the Central district. The moderate value of the Shannon index of migratory nematode species was obtained in wheat fields as 2.31, whereas the value of evenness was 0.93, implying moderate diversity and high evenness of nematodes. This study is the first comprehensive report on H. filipjevi from wheat cropping areas in the Sakarya province. Intensified cereal cropping systems with/without non-cereal rotations increased the risk of plant-parasitic nematodes, especially RLNs and H. filipjevi infection of wheat production areas in the province.

Occurrence and Geographic Distribution of Plant-Parasitic Nematodes Associated with Citrus in Morocco and Their Interaction with Soil Patterns.

Plant-parasitic nematodes (PPNs) are found in citrus plantations throughout the world, but they are considered to be the most problematic pest in Morocco. Citrus fruit quality and yield have been adversely affected by PPNs. Due to data unavailability of nematodes associated with citrus, a detailed survey was conducted in the main citrus-growing regions of Morocco during 2020–2021 to assess the occurrence, distribution, and diversity of PPNs associated with rhizospheres of citrus trees. In addition, some soil properties have also been assessed for their impact on soil properties. Plant-parasitic nematode diversity was calculated using two ecological indexes, the Shannon diversity index (H′) and the Evenness index (E). The collected soil and root samples were analyzed, and eleven genera and ten species of plant-parasitic nematodes were identified. The results show that the most predominant PPN species were Tylenchulus semipenetrans (88%), Helicotylenchus spp. (75%), Pratylenchus spp. (47%), Tylenchus spp. (51%), and Xiphinema spp. (31%). The results showed that PPN distributions were correlated with soil physicochemical properties such as soil texture, pH levels, and mineral content. Based on the obtained result, it was concluded that besides the direct effects of the host plant, physicochemical factors of the soil could greatly affect PPN communities in citrus growing orchards.

Diversity of plant parasitic nematodes characterized from fields of the French national monitoring programme for the Columbia root-knot nematode.

Plant parasitic nematodes are highly abundant in all agrosystems and some species can have a major impact on crop yields. To avoid the use of chemical agents and to find alternative methods to manage these pests, research studies have mainly focused on plant resistance genes and biocontrol methods involving host plants or natural enemies. A specific alternative method may consist in supporting non-damaging indigenous species that could compete with damaging introduced species to decrease and keep their abundance at low level. For this purpose, knowledge about the biodiversity, structure and functioning of these indigenous communities is needed in order to carry out better risk assessments and to develop possible future management strategies. Here, we investigated 35 root crop fields in eight regions over two consecutive years. The aims were to describe plant parasitic nematode diversity and to assess the potential effects of cultivation practices and environmental variables on communities. Community biodiversity included 10 taxa of plant parasitic nematodes. Despite no significant abundance variations between the two sampling years, structures of communities varied among the different regions. Metadata collected for the past six years, characterizing the cultural practices and soils properties, made it possible to evaluate the impact of these variables both on the whole community and on each taxon separately. Our results suggest that, at a large scale, many variables drive the structuration of the communities. Soil variables, but also rainfall, explain the population density variations among the geographical areas. The effect of the variables differed among the taxa, but fields with few herbicide applications and being pH neutral with low heavy metal and nitrogen concentrations had the highest plant parasitic nematode densities. We discuss how these variables can affect nematode communities either directly or indirectly. These types of studies can help to better understand the variables driving the nematode communities structuration in order to support the abundance of indigenous non-damaging communities that could compete with the invasive species.

Occurrence, Diversity and Abundance of Nematode Pests of Pineapple (Ananas comosus) in Two Local Government Areas of Rivers State, Nigeria

Plant-parasitic nematodes (PPNs) contribute to yield losses in pineapple production. Limited studies have been conducted on plant-parasitic nematodes on pineapple despite reports of PPNs infecting it. A survey was conducted in Obio-Akpor and Ikwerre Local Government Areas (LGAs) of Rivers State to determine the occurrence, abundance and diversity of PPNs associated with pineapple. A total of 60 composite samples were collected from the two LGAs. Nematodes were extracted from soil and root samples using the modified Baermann technique and identified using standard procedures. Data were processed using relative frequency of occurrence (RFOC), relative importance values (RIVs), diversity indices, nematode population was calculated and analysis of variance. The most occurring plant-parasitic nematodes were Pratylenchus, Helicotylenchus, Meloidogyne, Scutellonema and Tylenchulus. In Obio Akpor LGA, Helicotylenchus with RFOC 33.3% was the most occurring nematode pests, while Pratylenchus was the most important plant-parasitic nematode (RIV 33.8%). In Ikwerre LGA, both Helicotylenchus and Pratylenchus have the same occurrence (RFOC 33.3%) with Pratylenchus being the most important nematode pest. Pratylenchus species with RIV of 52.4% were the most important PPNs associated with pineapple in both Obio-Akpor and Ikwerre LGAs. Dominance and Shannon- Weiner indices among the PPNs are 0.58 and 0.86, respectively. In Ikwerre and Obio-Akpor LGAs, Aluu (1530) and Rumuekini (630) pineapple farms have the highest population of PPNs, respectively. Ikwerre LGA (2,150) pineapple farms had more PPNs than Obio-Akpor LGA (660). Nematode pests are associated with pineapple in the two LGAs and could be contributing to yield losses.

The Effect of Abiotic Factors and Elevation on the Diversity of Plant Parasitic Nematodes in Garlic on Central Java, Indonesia

The Effect of Abiotic Factors and Elevation on the Diversity of Plant Parasitic Nematodes in Garlic on Central Java, Indonesia

Legacy of plant-parasitic nematode communities from past ecosystems and shift by recent afforestation

Ancient ecological legacies and past land use changes may inform on the present structure of biological communities. However, regions providing such successive ecosystems are scarce. In France, the ‘Landes de Gascogne’ area provides such ecological shifts since a few ancient moorland, peatland and oak areas prior the afforestation with maritime pine (Pinus pinaster) 160 years ago still remain. Focusing on soil-borne parasites such as plant-parasitic nematodes (PPN), because forests were recently increasingly impacted by the introduction of intensive agriculture, this study is therefore aimed at comparing the diversity and the community patterns of these organisms at different scales (intra- and intersites) and between different successive ecosystems. The understory vegetation as well as the pedo-climatic characterization of the sampled sites were also considered. Common diversity indices were not impacted by this transition from ancient to past ecosystems. Although the most colonizer nematodes prevailed in all the ecosystems, PPN community structures significantly diverged between both ecosystems. In the logged pine forests, the sediment legacy could have primarily impacted the diversity. Moreover, the PPN diversity would mainly respond to the soil hydromorphicity that determined the associated understory vegetation. Consequently, a significant shift in community structure from moorlands to logged pine to logged pine forests was observed, regarding especially high pathogenic species such as Pratylenchus spp. Thus, analyzing PPN community structure highlights the PPN potential risk to consider during the introduction of intensive cropping systems.

Differential Response ofMeloidogyne,Pratylenchus,Globodera, andXiphinemaSpecies to the Nematicide Fluazaindolizine

This research focused on the effects of fluazaindolizine on a diversity of plant-parasitic nematodes. In microwell assays, 24-h dose-response curves were generated for several species and populations of Meloidogyne, Pratylenchus neglectus, P. penetrans, Globodera ellingtonae, and Xiphinema americanum. In a greenhouse study, the impact of fluazaindolizine on fecundity of M. incognita, M. hapla, and M. chitwoodi was tested by exposing nematodes for 24 h in solution and inoculating on tomato. The average 24-h ED50s (dose that resulted in the immobility of 50% of exposed nematodes) for M. hapla, M. chitwoodi, and M. incognita were 325.7, 223.4, and 100.7 ppm, respectively. M. hapla had the most variation among populations, with 24-h ED50s ranging from 72 to 788 ppm. G. ellingtonae had the lowest 24-h ED50 at 30 ppm. Pratylenchus spp. were unaffected by fluazaindolizine. X. americanum was the only species where effects of fluazaindolizine were reversible, but had a 24-h ED50 that fell in the range of the Meloidogyne spp. In the greenhouse study, M. chitwoodi was the least sensitive with reproduction reaching 62% of the untreated control after a pre-exposure to 47 ppm, whereas M. incognita and M. hapla at the same exposure dose had reproduction rates of 27 and 36% of the untreated control, respectively. Despite varying in in vitro responses to fluazaindolizine, reproduction of all Meloidogyne spp. was suppressed after only 24 h of exposure. This study expanded our understanding of how G. ellingtonae, P. thornei, P. penetrans, and X. americanum respond to fluazaindolizine.

Diversity and Management Strategies of Plant Parasitic Nematodes in Moroccan Organic Farming and Their Relationship with Soil Physico-Chemical Properties

Organic farming has been increasing steadily over the last decade and is expected to grow drastically in the future. Plant parasitic nematodes (PPNs) are known as one of the most important pests attacking various plants in conventional and organic farming systems. A survey was conducted in January 2019 to determine the occurrence and diversity of PPNs, their associations with soil properties, and to assess their management methods in organically farmed fields in Southern Morocco. Twelve genera of PPNs were identified in soil and root samples collected from 53 organic fields, including Meloidogyne, Pratylenchus, Helicotylenchus, Tylenchus, Tylenchorynchus, Criconemoides, Trichodorus, and Xiphinema. The root-knot nematodes (Meloidogyne spp.) and the root-lesion nematode (Pratylenchus spp.) were the most prevalent PPNs. Vegetable crops (bean, onion, and tomato) had high nematode diversity indices compared to some aromatic and medicinal crops, including the Shannon, Evenness, and plant parasitic index (PPI). Our study underlined that several PPN genera were significantly correlated with soil physico-chemical properties, in particular, soil structure and organic matter. Therefore, it was concluded that soil properties have a considerable impact on PPN communities in organic farming systems located in Southern Morocco. There are numerous strategies for the control of PPNs in organic farming systems.

Spatial distribution of nematode genera in relation to host plants of Western Ghats, Tamil Nadu, India

A survey of plant parasitic nematodes (PPN) abundance and diversity was conducted in foothills of Western Ghats at Coimbatore and Nilgiris districts in Tamil Nadu, India. Our study pointed to evaluate the PPN association with weeds, shrubs, and herbs including some agricultural crop cover both agro and forest ecosystems. Soil samples were collected around the rhizosphere of the plants and nematodes were isolated, counted under a microscope and identified by morphological characters. We collected 415 soil samples around the rhizosphere of 84 major plant families. Among 84 plant families, we found 13 PPN genera those generally responsible for cash crop yield loss. The genus Helicotylenchus spp., and Meloidogyne spp., were found frequent (226,136 samples) and rarely Hemicycliophora spp.,. The PPN diversity was measured by Shannon diversity index which showed that the diversity of PPN found higher in plant species those from the families Rosaceae (2.20) and Rubiaceae (2.13). We also recorded the PPN richness was dominated in four plant families. This result reveals that the PPN diversity and richness are positively correlated with host plant species diversity and altitude. Further, our study concludes that a wild plant in the forest ecosystem behaves like a reservoir of PPN.

Popular Biofortified Cassava Cultivars Are Heavily Impacted by Plant Parasitic Nematodes, Especially Meloidogyne Spp.

The development of new biofortified cassava cultivars, with higher micronutrient contents, offers great potential to enhance food and nutrition security prospects. Among the various constraints affecting cassava production are plant parasitic nematodes (PPN), especially root-knot nematodes. In this study, six popular biofortified cultivars were field-evaluated for their response to PPN in Nigeria. A field naturally infested with a diversity of PPN but dominated by root-knot nematodes was used. Application of the nematicide carbofuran significantly reduced PPN densities, and at harvest, no root galling damage was observed, compared with untreated plots, which had heavy galling damage. Plant height, stem girth, plant weight, marketable storage root number and weight were significantly lower for most cultivars in untreated plots. Percentage yield losses in the range of 21.3–63.7% were recorded from two separate trials conducted for 12 months each. Lower total carotenoid and dry matter contents were associated with higher PPN densities in some biofortified cultivars, resulting in a loss of as much as 63% of total carotenoid and 52% of dry matter contents. The number and weight of rotted storage roots were significantly greater in untreated plots across cultivars, reducing in-field and post-harvest storability. This study demonstrates that natural field populations of PPN can substantially affect yield, quality and nutritional value of released biofortified cassava cultivars.

Diversity of plant parasitic nematodes associated with rhizosphere of maize from different areas of district Rajouri, Jammu and Kashmir, India

Diversity of plant parasitic nematodes in the rhizosphere of maize (Zea mays) from some areas of District Rajouri, Jammu and Kashmir was studied. A total of ten plant parasitic nematode species were found to be associated with the rhizosphere of maize plants in these areas. The nematode species were Pratylenchus zeae, P. brachyurus, Helicotylenchus dihystera, Longidorus brevicaudatus, L. elongatus, Xiphinema diversicadatum, X. elongatum, Tylenchorhynchus spp. Ditylenchus spp. and Criconemoides spp. The most dominant and frequently occurring species was found to be P. zeae, with absolute frequency of 86.66% followed by P. brachyurus (80%), H. dihystera, (76.66%) and L. brevicaudatus (73.33). Contrarily, the least frequent was Criconemoides spp. (36.66%) followed by Tylenchorhynchus spp. and Ditylenchus spp. with absolute frequencies of 53.33% and 60%. Similar trend was observed in case of relative frequencies. In case of P. zeae, mean density of 56 and relative density of 16.05% was observed followed by P. brachyurus and H. dihystera with mean densities and relative densities of 50.33, 14.43% and 49, 14.04% respectively. On the other hand, Criconemoides spp. and Tylenchorhynchus spp. showed mean densities of 6.33 and 23.33 and absolute densities of 1.81% and 6.68% respectively. P. zeae exhibited high prominence value of 57.85 followed by P. brachyurus (49.96). The least prominence value was found in Criconemoides spp. (4.05) followed by Tylenchorhynchus spp. with prominence value of 18.30.

May passive dispersal of fungal enemies with native substrates in olive nurseries help to control phytonematodes?

Description of the subject. In Morocco, expanding agricultural sector under “Morocco Green Plan” will also introduce plant diseases and plant parasitic nematodes (PPN). Soil substrate used in most of the olive nurseries is potentially inhabited by PPN and natural enemies. Objectives. This work assessed the co-occurrence of PPN and nematophagous fungi (NF) in substrates and potential of NF to suppress PPN. Method. The diversity of PPN and NF genera was characterized in 305 substrate samples, isolated from 25 olive nurseries and functional activity (nematicidal and enzymatic) of NF was evaluated. Results. High PPN diversity was detected in the isolated samples and substrates were differentiated by NF activity. Global partition between PPN and NF diversity patterns confirmed prey-predator antagonism. Moreover, PPN-NF patterns depend on the fungal survival (saprophytes vs obligate parasites) and antagonism (predation vs toxicity) processes. However, even the NF strains with maximum fitness (growth, sporulation, enzymatic activity) were not inevitably the most effective against PPN. Consequently, it was hypothesized that predation and competition could be an adaptation process of NF to overcome environmental stress and exploit alternative or supplementary nutrient sources. Conclusions. The use of diverse native NF from cultivated and wild soils offer future prospects for the development of PPN management strategies in olive nurseries.

Occurrence of vermiform plant-parasitic nematodes in North Dakota corn fields and impact of environmental and soil factors

Plant-parasitic nematodes (PPN) can negatively affect corn production. In this study, incidence and abundance of PPN were assessed in 300 corn fields across 20 counties in North Dakota during 2015 and 2016. Seventy-two percent of the fields were positive for PPN. The major genera identified were Helicotylenchus (incidence: 52%; mean density: 1513 nematodes kg−1 of soil; greatest density: 16 910 nematodes kg−1 of soil), Tylenchorhynchus (37%; 687; 9500), Paratylenchus (31%; 1484; 7800), Pratylenchus (20%; 399; 2125), Heterodera (9%; 555; 4500), Xiphinema (8%; 330; 900), Hoplolaimus (3%; 294; 500) and Paratrichodorus (1%; 124; 200). Neighbouring counties had greater similarity in PPN diversity than counties that are further apart, with western, north-eastern and south-eastern counties forming clusters of similar nematode occurrence and diversity. Canonical correspondence analysis was conducted to determine the association between incidence and abundance of these PPN populations and various soil edaphic and climatic factors. The analysis revealed that Hoplolaimus, Paratrichodorus, Paratylenchus and Pratylenchus were positively correlated with soil temperature, rainfall and per cent sand, while Helicotylenchus, Tylenchorhynchus and Xiphinema were positively correlated with pH, percent clay and percent organic matter. This is the first report of an extensive investigation of PPN communities in North Dakota corn fields. Research findings will be useful in future field experiments to determine the impact of PPN on corn in the Northern Great Plains.

Diversity of plant-parasitic nematodes on medicinal plants in melinh station for biodiversity, Vinh Phuc Province, Vietnam

Plant-parasitic nematodes are known as one of the most important pests attacking various plants in the world, and investigating the nematode component is very essential for management of this pest and prevent damage to plants in general. Our survey of plant-parasitic nematodes on medicinal plants in Melinh Station for Biodiversity, a place for conservation of precious plants and animals in Vietnam, identified ten species that belong to nine genera, five families, and two orders of plant-parasitic nematodes parasitizing six medicinal plants. Excoecaria cochinchinensis was parasitized by the highest number of nematode genera (5 genera, including Xiphinema, Discocriconemella, Meloidogyne, Helicotylenchus, and Hemicriconemoides), while Hymenocallis littoralis was associated with the highest number of plant-parasitic nematodes (2060 nematodes/250g soil). The results also showed that Discocriconemella limitanea was found to be a dominant species with the highest number of individuals on 6 medicinal plants, and the genus Helicotylenchus had the highest frequency of appearance (5/6 plants or 83.3%). These nematodes caused symptoms such as yellowing leaves, root galls, and root lesions, which directly affect the quality and yield of medicinal plants. Based on the results, this study showed that plant-parasitic nematodes are a potential threat to the cultivation of medicinal plants in Melinh Station for Biodiversity, and thus, control measures should be applied to ensure sustainable cultivation of medicinal plants in this place.