Nematode Densities Research Articles

Cavalcade Legume (Centrosema pascuorum) Used as Soil Amendment in RD41 Rice Fields: Short-term Effects on the Soil Nematode Community, Soil Properties, and Yield Components

Numerous phytoparasitic nematodes have been identified in Thailand’s paddy fields, which routinely cause substantial reductions in rice crop yields. However, effective strategies for their management have yet to be documented. In this study, cavalcade legume was used as a soil amendment in RD41 rice fields to examine its effects on the soil nematode community, soil properties, and yield components compared to untreated control plots. The results demonstrated that the population densities of plant-parasitic nematodes (PPNs) in the order Tylenchida, primarily Hirschmanniella sp., significantly decreased in cavalcade-treated plots across all soil sampling periods. Moreover, there was an increase in the populations of beneficial nematodes within the orders Dorylaimida and Araeolaimida. In contrast, greater PPN populations were observed in the control plots compared to the initial nematode population. In addition to reducing PPN populations, this legume showed other benefits, specifically increased soil properties (available P) and rice plant growth (plant height and number of tillers). While there was no statistically significant difference in soil organic matter (SOM) content, the application of this legume tended to increase SOM content, in contrast to a decrease in SOM content observed in the control plots. Overall, this study provides valuable insights into the substantial advantages of using cavalcade legumes in RD41 rice fields.

The Distribution of Reniform Nematode (Rotylenchulus reniformis) in Cotton Fields in Central Queensland and Population Dynamics in Response to Cropping Regime.

Reniform nematode (Rotylenchulus reniformis) causes significant yield loss in cotton worldwide. In 2012, its detection in the Dawson-Callide region of Central Queensland prompted extensive surveys of cotton fields. The nematode was confirmed in 68% of sampled fields, with populations ranging from 2 to 3870 R. reniformis/200 mL of soil. Soil monitoring revealed increasing populations associated with consecutive cotton crops. However, when corn or sorghum replaced cotton, soil nematode populations significantly decreased. A two-year replicated field trial demonstrated that growing a non-host crop (such as biofumigant sorghum 'Fumig8tor', grain sorghum, or corn) significantly reduced nematode populations in the top 15 cm of soil compared to cotton. Unfortunately, when cotton was replanted the following season, nematode populations rebounded regardless of the previous crop. Only the 'Fumig8tor'-cotton rotation resulted in significantly lower nematode populations than continuous cotton. Vertical soil sampling showed that rotating with a non-host crop significantly reduced nematode densities to a depth of 100 cm compared to cotton. However, when the field was replanted with cotton, nematode populations recovered, unaffected by cropping or soil depth. This study emphasises the importance of monitoring reniform nematodes in cotton soils for early detection and defining distribution patterns within a field, which may improve the effectiveness of management practices. These results suggest that one rotation out of cotton is not sufficient, as populations return to high levels when cotton is grown again. Therefore, two or more rotations out of cotton should be considered to manage this nematode.

Population density of plant-parasitic nematodes in rice fields associated with environmental variables in Malang, Indonesia

Population density of plant-parasitic nematodes in rice fields associated with environmental variables in Malang, Indonesia

How morphodynamic gradients shape the distribution of meiofauna and nematodes on sandy beaches of the Amazon region?

The present study analyzed how a small-scale morphodynamic gradient, based on the level of exposure to oceanic waves, shapes the spatial distribution patterns of the local meiofauna, with a special focus on the nematodes, of tropical macrotidal beaches on the Amazon coast (northern Brazil). The study focused on three sandy beaches, first compiling their physical characteristics (waves, currents and morphodynamic state), and then sampling biological and sediment samples at five different levels across the intertidal zone. Meiofauna was composed of 11 different groups, but was dominated by Nematoda. The nematode assemblage had a total of 89 genera, of which Daptonema and Theristus (both from family Xyalidae) were the most abundant on all studied beaches, at most intertidal levels. The diversity of nematode genera increased toward the low tide mark, while nematode density peaked in either the upper (on the protected and tide-dominated beaches) or intermediate levels (on the exposed, tide-modified beach). Distinct faunal zonation patterns were identified on the three beaches, which were influenced by their level of exposure to oceanic conditions, their granulometry, and the moisture of the sediment. While the variation in the characteristics of the meiofauna can be attributed to the level of exposure of beaches, horizontal distribution patterns were also closely related to habitat heterogeneity, including morphological features and freshwater inputs.

Seasonal Variation in Nematode Infestation Across Bahar Treatments in Pomegranate Cultivation

This study investigates the influence of three Bahar treatments—Ambe Bahar (spring flowering), Mrig Bahar (monsoon flowering), and Hasta Bahar (autumn flowering)—on the extent of nematode infestation in pomegranate orchards. The research was conducted in major pomegranate-growing regions of India, where soil samples were collected from fields practicing each of the Bahar treatments. The results revealed significant differences in nematode infestation levels across the three Bahar treatments. Mrig Bahar exhibited the lowest nematode density, with an average of 80 nematodes per 100g of soil, compared to 120 in Hasta Bahar and 150 in Ambe Bahar. Additionally, Mrig Bahar treatment was associated with the highest average yield (12.8 kg per plant) and superior fruit quality (Grade A). The findings suggest that Mrig Bahar offers a more conducive environment for nematode management, likely due to its timing relative to environmental conditions that may suppress nematode activity. The results revealed significant differences in nematode infestation levels across the three Bahar treatments. Mrig Bahar exhibited the lowest nematode density, with an average of 80 nematodes per 100g of soil, compared to 120 in Hasta Bahar and 150 in Ambe Bahar. Additionally, Mrig Bahar treatment was associated with the highest average yield (12.8 kg per plant) and superior fruit quality (Grade A). The findings suggest that Mrig Bahar offers a more conducive environment for nematode management, likely due to its timing relative to environmental conditions that may suppress nematode activity. This study underscores the importance of selecting the appropriate Bahar treatment to mitigate nematode infestation and optimize pomegranate production. The insights gained from this research can guide farmers in choosing the most effective cultivation practices, ultimately contributing to sustainable pomegranate farming and improved economic outcomes. Further research is recommended to explore the underlying mechanisms that confer resistance in Mrig Bahar and to develop integrated nematode management strategies tailored to specific Bahar treatments.

First report of Helicotylenchus dihystera parasitizing Lady Tankerville orchids (Phaius tankervilleae) in Vietnam.

Lady Tankerville, a rare orchid species (Phaius tankervilleae (Banks ex L'Hér.) Blume) in Vietnam, not only enhances the aesthetic value of the surroundings with its enchanting blooms but also holds high economic value (Aver'janov & Averyanova, 2003). Investigating the necrosis symptom on the root system and declined Lady Tankerville in the market in Hai Duong province in Vietnam from 11/2020 to 12/2021, we discovered a substantial infestation (24/24 plants were infected) of a spiral nematode, Helicotylenchus sp. The nematode population was extracted from the rhizosphere soil, roots, and stems of a single orchid using the modified Baermann tray technique (Whitehead & Hemming, 1965), for thorough characterization. The average nematode density was measured at 525±85 (350-670) nematodes/250 cm3 of soil, 202±56 (198-264) nematodes/15 g of roots, and 80±15 (72-95) nematodes/15 g of stem. Two hundred nematodes from the same population were inoculated into another healthy orchid for preservation and further infection tests. This species was morphologically identified as Helicotylenchus dihystera according to the key of Fotedar and Kaul (1985) and the description of Sher (1966). Morphometric measurements of the females (n = 12) are as follows: body length = 632-725 (681 ± 32) µm; a = 24-34 (28 ± 3); b = 5.1-7.2 (6.0 ± 0.6); b' = 4.3-6.4 (5.3 ± 0.6); c = 33-46 (39 ± 5); c' = 1.1-1.4 (1.2 ± 0.1); V = 62-78 (65 ± 4)%; O = 30 -49 (39 ± 6); stylet length = 21-26 (24 ± 2) µm; DGO = 9.2-12.4 (10.8 ± 1.1) µm. To validate morphological observations, molecular analyses of the ITS (Vrain et al., 1992) and the D2-D3 of 28S rRNA (Subbotin et al., 2006) were conducted. The ITS and D2-D3 sequences from this study (accession number: PP060444 and PP033748) exhibited the highest similarity of 99.8% and 100% to the sequence of H. dihystera in GenBank (KM506885 and MW023215), respectively. The infection test took place in a greenhouse at 28 ± 2℃. Three-month-old Phaius tankervilleae (n=8) were individually grown in 15 x 15 cm deep pots filled with sterilized sand and inoculated with 500 gravid females of H. dihystera (Rashid & Azad, 2013). Two noninoculated plants served as controls. After 60 days of inoculation, symptoms such as sunspots and root necrosis, observed in the market, appeared in the tested plants (Fig. S1). The presence and diagnosis of H. dihystera infestation in soil, roots, and stems across growth stages of orchids indicates the nematode to be an obligate parasite. The nematodes penetrate the roots, causing characteristic necrotic lesions initially yellow, then turn reddish-brown to black, along with brown root flecks in discolored tissues. Heavy infestations post-flowering led to extensive necrosis, distortion, and decay of the roots. The average reproduction factor (final population/initial population) of H. dihystera in this study was 22.2. Control plants remained symptom-free. Notably, 100% of tested plants were infected, highlighting the severe impact of H. dihystera. The nematodes were successfully reisolated and identified as H. dihystera through molecular analyses (accession number: PP060615 (ITS) and PP033748 (D2-D3)), reaffirming its identity. In addition to 32 host plants in Vietnam (Nguyen et al., 2023), our study reveals a strain of H. dihystera parasitizing Lady Tankerville orchids with a relatively high reproduction factor and infection rate. This marks the first reported instance of H. dihystera parasitizing Lady Tankerville orchids in Vietnam, emphasizing the need for proactive measures to protect this plant.

Plant-parasitic nematodes associated with maize, and their relationship with soil properties in southern and southwestern Ethiopia

Summary Maize is an important cereal crop in sub-Saharan Africa (SSA). Plant-parasitic nematodes significantly impact maize production. However, research on maize nematodes in SSA is limited. The current study aimed to assess the occurrences and densities of nematodes associated with maize and to assess the correlation of some soil physicochemical properties with nematodes in southern and southwestern Ethiopia. One hundred and eighty-six soil and root samples were collected from 62 maize fields (31 from Hawassa Zuria and 31 from Mana districts). Eleven plant-parasitic nematode genera were identified. The most important genera of plant-parasitic nematodes identified were Meloidogyne and Pratylenchus, followed by Helicotylenchus and Tylenchorhynchus. The nematodes Pratylenchus and Criconemoides were significantly and positively associated with pH, soil organic carbon (SOC) and soil organic matter (SOM). Additionally, Tylenchorhynchus, Pratylenchus and Rotylenchulus were significantly positively correlated with soil available phosphorus (SAP). However, Criconemoides and Meloidogyne had a strong negative correlation with soil bulk density (SBD). This study provides useful baseline information on maize-associated nematodes, and will be useful for agricultural policy makers, private farmers, non-governmental organisations and agricultural extension workers enabling them to establish sustainable maize nematode management strategies.

Biofumigation Treatment Using Tagetes patula, Sinapis alba and Raphanus sativus Changes the Biological Properties of Replanted Soil in a Fruit Tree Nursery

Apple replant disease (ARD) may cause significant losses both in commercial orchards and in fruit tree nurseries. The negative effects of ARD may be limited by using biofumigation. The aim of the study was to assess the influence of this treatment on the biological properties of replanted soil in a tree nursery. In two-year experiment, apple trees of the ‘Golden Delicious’ cultivar were used. The trees were planted into soil from two sites. The soil from one site had not been used in a nursery before (crop rotation soil). The other soil had been used for the production of apple trees (replanted soil). Three species of plants were used in the replanted soil as a forecrop: French marigold (Tagetes patula), white mustard (Sinapis alba), and oilseed radish (Raphanus sativus var. oleifera). The following parameters were assessed in the experiment: the enzyme and respiratory activity of the soil, the total count of bacteria, fungi, oomycetes and actinobacteria in the soil, as well as the count and species composition of soil nematodes. The vegetative growth parameters of the apple trees were also assessed. The biological properties of the replanted soil were worse than those of the crop rotation soil. In the replanted soil, the organic matter content, enzyme and respiratory activity as well as the count of soil microorganisms were lower. The biofumigants, used as a forecrop on the replanted soil, significantly increased its enzyme activity and respiratory activity. Dehydrogenase activity increased more than twofold. Growth parameters of the trees were significantly improved. The height of the trees increased by more than 50%, and the leaf area, weight and total length of side shoots were higher as well. The density of nematodes in the replanted soil after biofumigation was significantly reduced, with a larger reduction in the marigold fumigated soil. Eight of the eleven nematode species were completely reduced in the first year after biofumigation treatment.

Simulation and application assessment of the efficacy of fosthiazate-loaded microcapsules against root-knot nematode.

Although microencapsulation technology is an effective pesticide formulation method, the correlation between the release properties of microcapsules and pesticide concentrations in soil and their efficacy has not been thoroughly investigated. Here, the effects of the release properties of the nematicide Fosthiazate (FTZ) from microcapsules on their efficacy against the nematode Meloidogyne incognita were examined using experimental and mathematical approaches. Gradual release of FTZ from both polyurea microcapsules (PU-MC) and melamine-formaldehyde microcapsules (MF-MC) was observed over 30 days in the release test, and each release curve was completely distinct. In the biological test, the efficacy of both microcapsules against M. incognita 42 days after the application was 8-15% higher than that of the non-encapsulated FTZ at a concentration of 2.0 mg FTZ kg-1 soil. Soil degradation experiments suggested that the microcapsules worked effectively to protect the FTZ from degradation, which resulted in higher efficacy at a later stage. A simulation study to predict the concentration of FTZ outside the microcapsule found that the timing of supplying FTZ was important and suggested that the mixture of non-encapsulated FTZ (non-MC) and MF-MC showed enhanced efficiency for the entire cultivation period in the biological test; the efficacy against nematodes was also confirmed by the measurement of nematode density using the Bearman funnel method. The release properties of FTZ from microcapsules are critical for their effective application against M. incognita, and the established simulation study is a useful step in designing suitable release properties under complex soil conditions. © 2024 Society of Chemical Industry.

Media Kultur Alternatif In Vitro Pada Nematoda Entomopatogen

Entomopathogenic nematodes (ENPs) are prospective biological agents. The obstacles multiplication of NEP are limited access to purchasing and the high price of multiplication media. This research aims to determine effect of alternative media composition on the population density of Entomopathogenic Nematodes. This research was conducted in August-December 2022 using a completely randomized Design (CRD) with 7 treatments, its MA (4g rice bran), MB (4g coconut pulp), MC (4 g golden snail), MD (2 g rice bran + 2 g coconut pulp), ME (2 g rice bran + 2 g golden snail), MF (2 g coconut pulp + 2 g golden snail), MG (2 g rice bran + 1 g coconut pulp + 1 gram golden snail) was repeated 4 times. The observed variable is densitiy of Nematodes Population. The data obtained were analyzed using ANOVA and continued with the 5% Tukey test. The results showed a significant effect of alternative medium on the NEP population with the best treatment on MG medium, the average population in 1st week (1044.25J/0.25ml), 2st week (1120.75J/0.25ml), 3st week (177J/0.25ml) and 4st week (89.25J/0.25ml)

Caracterización de Meloidogyne spp. y densidad poblacional de nematodos fitoparásitos asociados a cultivos de aliáceas en la región Arequipa, Perú

Alliaceae crops includes several species of agricultural importance for the Arequipa region, among them the onion is the most produced in the country, however, these crops are affected by phytoparasitic nematodes, including Meloidogyne spp. which causes significant losses in the yield. The aim of the present study was to characterise the root-knot nematode (Meloidogyne spp) and determine the population density of phytoparasitic nematodes in alliaceae crops in the main producing localities of the Arequipa region. Samples of roots and soil were collected in onion, chinese onion, leek and chives crops in the provinces of Arequipa, Castilla, Caylloma and Islay. The identification of nematode genus was found by morphological characteristics and the characterization of Meloidogyne were performed by perineal patterns and electrophoretic pattern of esterase (Est). In the 38 soil samples, different genus of plant-parasitic nematodes was found: Aphelenchus, Dorylaimus, Helicotylenchus, Hemicycliophora, Meloidogyne, Mesocriconema, Mononchus, OGMA, Pratylenchus, Rotylenchus, Tylenchus, Xiphinema and free-living nematodes, in root samples, eight populations of Meloidogyne spp. were found. distributed among three species: (1) M. incognita phenotype Est I1, Rm: 1.0 with 33.33% of frequency and Est I2, Rm: 1.03, 1.07 (50%); (2) M. javanica Est J3, Rm: 1.03, 1.24, 1.37 (16.67%) and an atypical species named Meloidogyne sp. Rm: 0.85 (33.33%). The identification of genus and species phytoparasitic nematodes in alliaceae will allow the adoption of more efficient integrated management measures, because have a distinct parasitism behavior.

Phytoparasitic and free-living nematodes associated with the cultivation of Passiflora ligularis Juss. in the Sandia Valley, Puno Region, Peru

The identification of phytoparasitic nematodes, which is essential for the implementation of management strategies, is required for further study. The objective of this work was to identify, at the genus level, the phytoparasites and free-living nematodes associated with the cultivation of sweet granadilla (Passiflora ligularis Juss.) in the valley of Sandia, region Puno, Peru. For the study, 165 soil samples were evaluated, coming from eight communities from the district of Sandia, during the agricultural season 2018–2019. The samples were processed by the method of centrifugal fluctuation in sucrose solution, later identified on the basis of morphological characteristics. The results showed the presence of seven genera of phytoparasitic nematodes, Meloidogyne, Pratylenchus, Helicotylenchus, Mesocriconema, Xiphinema, Tylenchus, and Hemicycliophora, and two genera of free-living nematodes, Aphelenchus and Dorylaimus. The most harmful genera were Meloidogyne and Pratylenchus because they cause damage to other crops. In the nematode community, there was variability in the density and frequency of phytoparasitic and free-living nematodes in the evaluated localities.

Plant-parasite nematodes in soils cultivated with pecans in Rio Grande do Sul, Brazil

ABSTRACT Rio Grande do Sul State produces 70% of pecans in Brazil. There is a high density of phytopathogenic nematodes in orchards. This study characterises the populations of plant-parasitic nematodes and investigates their association with soil properties in pecan-cultivated areas. The genera Mesocriconema, Criconemoides, Discocriconemella, Xiphinema, Tylenchus, Pratylenchus, Helicotylenchus, and Aphelenchoides were all identified. Discocriconemella and Xiphinema were positively associated with soil organic matter, cation exchange capacity, clay content, copper, zinc, calcium, magnesium, and potassium. Conversely, Pratylenchus, Helicotylenchus, Tylenchus, Criconemoides, and Aphelenchoides were positively correlated with aluminium. Mesocriconema, the most commonly found nematode, negatively correlated with most soil chemical attributes. A significant correlation was observed between the genera Criconemoides, Mesocriconema, Aphelenchoides, and Tylenchus. Parasitic nematodes in pecan orchards have not previously been documented in this region of Brazil.

Resource diversity mitigates the effects of intraspecific competition in co-occurring cryptic nematode species

Intraspecific competition and resource diversity are considered major drivers of niche differentiation, which are expected to promote population niche expansion by driving individuals to feed on alternative resources and/or by enhancing individual diet specialization. Nevertheless, experimental studies on the interaction effects of both factors on animal behavior and population dynamics remain scant. Here, we investigate how resource diversity alters the impact of intraspecific competition on resource preference and fitness of three co-occurring cryptic species of the marine nematode complex Litoditis marina (Pm I, Pm III and Pm IV). For each cryptic species, two competition regimes (‘low nematode density’ and ‘high nematode density’) were established in microcosms with varying resource diversity (E. coli, low-, medium- and high-diversity food). Our results show differences in resource preference and population fitness depending on intraspecific competition and resource diversity, but the response also varied considerably between cryptic species. Pm III did not exhibit resource preference under low intraspecific competition, but preferred the two most diverse food sources under high intraspecific competition. Pm IV also showed preference for medium-diversity food under high competition, whereas no resource preference was observed in Pm I regardless of competition regimes and resource diversity. Nevertheless, all cryptic species exhibited enhanced adult population growth on a more diverse food source under stronger intraspecific competition. These results indicate that resource diversity can alleviate intraspecific competition and affect niche diversification, which may impact diversity maintenance in ecological communities.

Diversity of plant-parasitic nematodes associated with chickpea (Cicer arietinum L.) in the main growing areas of Ethiopia

Summary Chickpea is one of the most important legume crops in Ethiopia; however, its production is far below the mean international chickpea production due to biotic and abiotic stressors. Plant-parasitic nematode infestation is extensive in chickpea-growing areas worldwide. The distribution and population density of plant-parasitic nematodes in chickpea were determined during the September-December 2021 growing season. Ten plant-parasitic nematode taxa were identified from 27 localities across ten districts in the main chickpea-growing areas in Ethiopia. Pratylenchus had the highest prominence values, followed by Rotylenchulus and Meloidogyne spp. Helicotylenchus, Hoplolaimus, Scutellonema and Quinisulcius were more prevalent than Criconemoides and Ditylenchus. Sequences of different molecular markers, including D2-D3 of 28S rDNA, ITS of rDNA, and COI and Nad5 of mtDNA, revealed the presence of Meloidogyne javanica, Rotylenchulus parvus, Scutellonema clathricaudatum and Helicotylenchus caudatus. Helicotylenchus caudatus and R. parvus are the first reports from Ethiopia and chickpea, while S. clathricaudatum is the first report for chickpea. This study provides essential baseline information of nematode pest occurrence on chickpea in Ethiopia. This information will raise awareness among growers, agricultural officers, and extension advisors, enabling them to develop effective nematode management strategies for the chickpea production system in Ethiopia.

Eksplorasi Populasi dan Kepadatan Genus Nematoda Parasit pada Rizosfir Tanaman Kopi di Kota Solok, Sumatera Barat

Coffee is a plantation crop that has high economic value among other plantation crops and plays an important role as a source of foreign exchange for the country. The decline and low productivity of coffee plants in coffee production centers in Solok City, West Sumatra is one of the causes of plant parasitic nematode attacks. This nematode attack causes disrupted plant growth and reduces the value of crop production both in quantity and quality. This study aims to determine the diversity and population density of parasitic nematodes in the rhizosphere of coffee plants in Solok City, West Sumatra. This research was conducted from March to July 2023 at the Laboratory of Biological Control, Department of Plant Protection, Faculty of Agriculture, Andalas University. Soil samples were taken in two central areas of coffee plantations in Solok City, West Sumatra. In the rhizosphere of coffee plants in Solok City, four genera of parasitic nematodes were found, namely: the genera Pratylenchus, Helicotylenchus, Meloidogyne, Rotylenchulus, Paratylenchus, and Tylenchorhynchus. The highest frequency of presence of nematodes, namely the genus Rotylenchulus, was 50.99 belonging to the medium category in Jorong Kayu Aro, and 44.80 in the rare category in Jorong Kayu Jao.

Plant parasitic nematodes on soybean (Glycine max (L) Merr.) in the Metekel zone (Ethiopia) and varietal resistance evaluation to Meloidogyne javanica

AbstractPlant parasitic nematodes cause severe damage to soybean crops, leading to substantial losses in yield and quality. However, more information is needed regarding the occurrence, distribution and damage status of soybean PPNs in Ethiopia. A total of 180 samples of rhizosphere and roots were collected randomly from three major soybean‐producing districts of Metekel Zone. Nematodes were extracted and identified at the genus level based on their morphological characteristics, except Meloidogyne javanica, the deadly species, which was identified using morphological and molecular techniques. Seven nematode genera were recovered: Meloidogyne, Scutellonema, Pratylenchus, Helicotylenchus, Rotylenchulus, Hemicycliophora and Criconema. The genera Meloidogyne, Scutellonema and Pratylenchus were dominant and had FO% of 98.3%, 97.5% and 81.8%, respectively. The host status of 10 soybean varieties to M. javanica infection was determined. Data on the shoot height, root length, fresh shoot and root weight, gall number and nematode density were estimated 3 months after inoculation. The results revealed that Jalele variety suppresses M. javanica multiplication while the other nine supported it. Comparatively, Pawe‐3, Awassa‐95 and Koreme varieties supported the highest nematode multiplication 24.4, 16.2 and 15.3 reproductive factors, respectively. Nova experienced the highest shoot and root relative biomass losses (84%) and roots (63%). In contrast, Jalele did not experience any loss in all parameters. However, Jalele variety resisted M. javanica, making it a promising approach towards soybean breeding programs for nematode management.

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.

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.

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.