Plant-parasitic Nematode Communities Research Articles

Plant-Parasitic and Free-Living Nematode Community Associated with Oak Tree of Magoebaskloof Mountains, Limpopo Province, South Africa

A study was conducted in the mountains of Magoebaskloof, Limpopo Province, where oak trees grow along the banks of the Broederstroom River. This study revealed that 22 nematode genera were associated with oak trees (Quercus robur). The most frequently occurring nematodes were Aphelenchus sp. (100%) and Plectus sp. (100%), followed by Helicotylenchus sp. (90%). This study examined the relationship between nematodes and the physicochemical properties of the soil using Pearson correlation. It uncovered that the organic matter content (OMC) had a negative correlation with the number of Panagrolaimus sp. (r = −0.770) and Hemicycliophora sp. (r = −0.674). Conversely, the sand percentage positively correlated (r = 0.695) with the number of Hemicycliophora sp. The clay content of the soil showed a positive correlation (r = 0.617) with the number of Ditylenchus. Soil pH demonstrated a significant negative correlation with Acrobeloides sp. (r = −0.877). The canonical correspondence analysis (CCA) explained 63.3% of the relationship between nematodes and soil physicochemical properties. The CCA results indicated that Ditylenchus exhibited a positive correlation with OMC, while the Panagrolaimus and Hemicycliophora species showed a negative correlation with OMC. The results indicated that none of the soil sample sites were under stress. The soil food web analysis revealed that most soil samples were nutrient-enriched with a low C/N ratio. In conclusion, this study revealed that oak trees harbor a high diversity of plant-parasitic and free-living nematodes. The results suggest that soil nematodes, particularly free-living bacterivores, such as Panagrolaimus, can indicate organic matter content in the soil.

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.

Employing Plant Parasitic Nematodes as an Indicator for Assessing Advancements in Landfill Remediation

This research concentrated on the soil nematode communities inhabiting a reclaimed municipal waste landfill situated in Giedlarowa, southeastern Poland. The landfill, which was layered with natural soil in 2008 and cultivated with grass, served as the primary focus of the study. Samples for analysis were taken four times (October 2020 (Pf1), March 2021 (Pf2), October 2021 (Pf3), and March 2022 (Pf4)), with each time comprising three repetitions. The analysis was conducted employing microscopic examination, which enabled the identification of up to five trophic groups and species of plant-parasitic nematodes. During the assessment of nematode activity in the initial and subsequent growing seasons, it was found that Pratylenchus crenatus emerged as the predominant species among herbivorous nematodes in the plant-parasitic nematode (PPNs) community. Criconemoides informis, another nematode species, held a significant rank as well; their population during the third growing season formed the most substantial group among the PPN organisms dwelling in the soil. Nevertheless, interesting results were also obtained by populations of nematodes of the genus Hemicyclophora and Loofia, which were characterized by high densities. The analyzed soil environment showcased a C:N ratio spanning from 0.69 to 3.13. Furthermore, the soil samples exhibited variations in phosphorus content (P2O5), ranging from 4.02 mg/100 g to 10.09 mg/100 g. Criconemoides informis, Longidorus attenuates, Mesocriconema spp., and Bitylenchus maximus exhibited a positive correlation with soil mineral levels of calcium (Ca) and magnesium (Mg).

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.

Diversity and Structure of Plant-Parasitic Nematode Communities in Some Olive Nurseries Along the Coastal Region of Syria

Ali, N. 2024. Diversity and Structure of Plant-Parasitic Nematode Communities in Some Olive Nurseries Along the Coastal Region of Syria. Arab Journal of Plant Protection, 42(3): 281-290. https://doi.org/10.22268/AJPP-001258 Olive is one of the most important economic crops in Syria. Nurseries are often the main source for pathogens dissemination in olive orchards, especially soil-borne organisms such as Verticillium and plant-parasitic nematodes (PPN), and investigating their occurrence and distribution in olive nurseries seems of great importance. No scientific data on the distribution of PPN in olive nurseries along the Syrian coastal region is available. Therefore, the present study was conducted in order to: (i) explore for the first time the occurrence and diversity of PPN communities distributed in some olive nurseries along the Syrian coastal region, and (ii) compare the nematode diversity and their community structure between two olive varieties. One hundred eight soil samples were collected from different nurseries in Latakia and Tartous governorates, from two common olive varieties Khdiry and Qaissy. Taxonomical and functional indices were calculated and compared between olive varieties and soil mixture used. The community structure was defined by using principal component analysis (PCA). The results revealed the wide distribution of PPN in olive nurseries with a total of 17 genera identified. Aphelenchoides, Aphelenchus, Ditylenchus and Tylenchorhynchus were the most common. Impact of olive varieties or soil mixture on functional diversity was observed, but not on the taxonomical indices. PCA also revealed a distinct structure of communities in each of the two olive varieties as well as in the soil mixture. Economically important genera such as Meloidogyne and Pratylenchus were also recorded with high population densities in some nurseries, suggesting the inevitable introduction of such nematodes to olive orchards. Certification programs for plant propagation materials in nurseries seem extremely important to be adopted in Syrian nurseries to ensure the production and distribution of “healthy” seedlings to growers. Keywords: Diversity, nurseries, olive varieties; plant-parasitic nematodes, soil mixture, Syria

Plant-parasitic nematode community and enzyme activities in soils under no-till soybean crops in Brazil

Soybean is Brazil's largest agricultural crop, grown across a variety of climates and soil conditions, and it is subjected to a large number of pests, including plant-parasitic nematodes. In general, the occurrence of plant-parasitic nematodes in soybean is influenced by various soil physicochemical properties, such as the pH, texture, and nutrient content. These soil properties may determine the nematodes community composition and affect soil quality and functioning, which can be monitored by analysing of soil enzyme activity. In this sense, the analysis of β-glucosidase and acid phosphatase enzymes can provide valuable information to assist decisions in the sustainable management of soybean cultivated soils in Brazil. In this study, we used 216 samples collected from no-till soybean fields across Brazil. The samples were used to investigate the influence of soil physical and chemical properties on the plant-parasitic nematode community and enzymatic activity. We identified seven genera of plant-parasitic nematodes including Meloidogyne, Pratylenchus, Heterodera, Rotylenchulus, Helicotylenchus, Scutellonema, and Xiphinema. Our results indicate that clay content and soil pH were the main properties modulating the plant-parasitic nematode community. We observed a higher abundance of plant-parasitic nematodes in highly acidic soils when compared to slightly acidic. In addition, soil organic matter content, available P, and pH were the main properties modulating microbial activity in the soil. No significant correlations were observed between enzymatic activity and nematode population density. This is the first study to provide insights into plant-parasitic nematode community composition and soil enzymes activity in soybean cultivated soils on a national scale in Brazil.

Distribution, Diversity, and Soil Associations of Wine Grape Plant-Parasitic Nematodes in Georgia, U.S.A., Vineyards.

Wine grape (Vitis vinifera and V. vinifera hybrids) production in Georgia occurs in three distinct regions (North, West, and South) which can be characterized by sandy, sandy-loam, or sandy clay-loam soils. We studied plant-parasitic nematode (PPN) communities in 15 wine grape vineyards from the three primary growing regions to understand which nematodes are a concern and what soil characteristics are associated with their occurrence and relative abundance. Twelve genera of PPNs were detected throughout the state: Belonolaimus, Helicotylenchus, Hemicycliophora, Heterodera, Hoplolaimus, Meloidogyne, Mesocriconema, Paratrichodorus, Paratylenchus, Pratylenchus, Tylenchorhynchus, and Xiphinema. Nonmetric multidimensional scaling ordination and multirank permutation procedure identified PPN community differences and soil characteristics that were associated by region. Indicator species analysis identified Helicotylenchus, Mesocriconema, Tylenchorhynchus, and Xiphinema as statistically associated with the West while Meloidogyne and Paratrichodorus were associated with the South. Our analyses further suggested that soil texture (percent sand, percent clay, and percent silt) and the lime buffer capacity at equilibrium (LBCEQ) were associated with PPN community structure while pH was not. When focused on a single vineyard in the North, multiple logistic regression analysis suggested a statistically significant association between Meloidogyne spp. and soil characteristics, including percentages of sand, pH, and LBCEQ. Our study supports the association between soil characteristics and specific nematode genera, as well as the emergence of LBCEQ, the soil measurement with the strongest statistical association with nematode community structure and Meloidogyne presence.

The pervasive impact of global climate change on plant-nematode interaction continuum.

Pest profiles in today's global food production system are continually affected by climate change and extreme weather. Under varying climatic conditions, plant-parasitic nematodes (PPNs) cause substantial economic damage to a wide variety of agricultural and horticultural commodities. In parallel, their herbivory also accredit to diverse ecosystem services such as nutrient cycling, allocation and turnover of plant biomass, shaping of vegetation community, and alteration of rhizospheric microorganism consortium by modifying the root exudation pattern. Thus PPNs, together with the vast majority of free-living nematodes, act as ecological drivers. Because of direct exposure to the open environment, PPN biology and physiology are largely governed by environmental factors including temperature, precipitation, humidity, atmospheric and soil carbon dioxide level, and weather extremes. The negative effects of climate change such as global warming, elevated CO2, altered precipitation and the weather extremes including heat waves, droughts, floods, wildfires and storms greatly influence the biogeographic range, distribution, abundance, survival, fitness, reproduction, and parasitic potential of the PPNs. Changes in these biological and ecological parameters associated to the PPNs exert huge impact on agriculture. Yet, depending on how adaptable the species are according to their geo-spatial distribution, the consequences of climate change include both positive and negative effects on the PPN communities. While assorting the effects of climate change as a whole, it can be estimated that the changing environmental factors, on one hand, will aggravate the PPN damage by aiding to abundance, distribution, reproduction, generation, plant growth and reduced plant defense, but the phenomena like sex reversal, entering cryptobiosis, and reduced survival should act in counter direction. This seemingly creates a contraposition effect, where assessing any confluent trend is difficult. However, as the climate change effects will differ according to space and time it is apprehensible that the PPNs will react and adapt according to their location and species specificity. Nevertheless, the bio-ecological shifts in the PPNs will necessitate tweaking their management practices from the agri-horticultural perspective. In this regard, we must aim for a 'climate-smart' package that will take care of the food production, pest prevention and environment protection. Integrated nematode management involving precise monitoring and modeling-based studies of population dynamics in relation to climatic fluctuations with escalated reliance on biocontrol, host resistance, and other safer approaches like crop rotation, crop scheduling, cover cropping, biofumigation, use of farmyard manure (FYM) would surely prove to be viable options. Although the novel nematicidal molecules are target-specific and relatively less harmful to the environment, their application should not be promoted following the global aim to reduce pesticide usage in future agriculture. Thus, having a reliable risk assessment with scenario planning, the adaptive management strategies must be designed to cope with the impending situation and satisfy the farmers' need.

Prevalence and ecological factors affecting the distribution of plant-parasitic nematodes in Prunus groves in Spain

A wide survey was conducted to study plant-parasitic nematodes (PPNs) associated with Prunus groves in Spain. This research aimed to determine the prevalence and distribution of PPNs in Prunus groves, as well as the influence of explanatory variables describing soil, climate and agricultural management in structuring the variation of PPNs community composition. A total of 218 sampling sites were surveyed and 84 PPN species belonging to 32 genera were identified based of an integrative taxonomic approach. PPN species considered as potential limiting factors in Prunus production, such as Meloidogyne arenaria, M. incognita, M. javanica, Pratylenchus penetrans and P. vulnus, were identified in this survey. Seven soil physico-chemical (C, Mg, N, Na, OM, P, pH and clay, loamy sand and sandy loam texture classes), four climate (Bio04, Bio05, Bio13 and Bio14) and four agricultural management variables (grove-use history less than 10 years, irrigation, apricot seedling rootstock, and Montclar rootstock) were identified as the most influential variables driving spatial patterns of PPNs communities. In particular, younger plantations showed higher values for species richness and diversity indices than groves cultivated for more than 20 years with Prunus spp. Our study increases the knowledge of the distribution and prevalence of PPNs associated with Prunus rhizosphere, as well as on the influence of explanatory variables driving the spatial structure PPNs communities, which has important implications for the successful design of sustainable management strategies in the future in this agricultural system.

Diversity of plant-parasitic nematode communities infesting olive orchards in Tunisia in relation to agronomic factors

Diversity of plant-parasitic nematode communities infesting olive orchards in Tunisia in relation to agronomic factors

Plant parasitic nematode communities associated to apple orchards in the Southern Brazil

Plant parasitic nematode communities associated to apple orchards in the Southern Brazil

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.

Abundance, diversity, and distribution of plant-parasitic nematodes in horticultural soils under different management systems in a tomato-producing area in Argentina

Summary Monitoring the diversity and structure of plant-parasitic nematode (PPN) communities together with developing appropriate control strategies can reduce the occurrence of these pathogens and other plant pests in horticultural crops. In this context a study of the abundance, frequency, diversity and distribution of PPN in horticultural soils under glasshouse conditions from the Green Belt of La Plata, Buenos Aires, Argentina, under different management systems was undertaken. Soil samples were collected from three horticultural areas with different tomato crop managements: agroecological crop (AC); organic crop with Brassicaceae soil amendments (OC); intensive conventional crop treated with methyl bromide (MeBr) (IC). The parameters evaluated were: nematode genera richness (G); Shannon-Wiener diversity index () (Hutcheson’s t-test was applied for this index); equitability index (E); abundance; and frequency of genera. ANOSIM and SIMPER statistical analyses were performed to find significant differences between the nematode assemblages from the different sites. A total of 14 genera of PPN were identified among the three crop sites. Members of the feeding habits categories ectoparasites, semi-endoparasites, migratory endoparasites and sedentary endoparasites were observed. Statistical analysis enabled us to characterise each site based on the composition of the nematode assemblages. Helicotylenchus, Tylenchus and Nacobbus were the most frequent and abundant genera. AC and OC showed similar values of richness and diversity; the crop treated with MeBr (IC) showed the lowest diversity of PPN.

Influence of the Environment and Vegetable Cropping Systems on Plant-Parasitic Nematode Communities in Southern Georgia

Plant-parasitic nematodes (PPN) limit yields of vegetable production in the United States. During the spring and fall cropping seasons of 2018, 436 fields in bare ground and plastic bed cropping systems were randomly sampled from 29 counties in southern Georgia. The incidence (%), mean relative abundance, and maximum relative abundance (nematodes per 100 cm3 of soil) of the 10 different PPN genera detected in 32 vegetable crops in bare ground and plastic bed cropping systems include Meloidogyne spp. (67.3%; mean, 292; maximum, 14,144), Nanidorus spp. (49.4%; mean, 6; maximum, 136), Mesocriconema spp. (39.6%; mean, 17; maximum, 340), Helicotylenchus spp. (31.6%; mean, 20; maximum, 1152), Pratylenchus spp. (20.1%; mean, 2; maximum, 398), Rotylenchulus spp. (5.9%; mean, 1; maximum, 116), Hoplolaimus spp. (12.6%; mean, 1; maximum, 78), Heterodera spp. (2.3%; mean, <1; maximum, 60), Tylenchorhynchus spp. (0.9%; mean, <1; maximum, 12), and Xiphinema spp. (0.2%; mean, <1; maximum, 2). A nonmetric multidimensional scaling analysis indicated that most environmental and geological factors (i.e., longitude, precipitation, soil moisture, sand and silt content, and soil electrical conductivity) had no apparent relationship with nematode counts, except for latitude, soil pH, and temperature. The multirank permutation procedure followed by indicator species analysis and nonparametric Kruskal-Wallis analysis of variance indicated that Meloidogyne spp. are the predominant PPN associated with plastic beds in the south region sampled. The south region consisted mainly of commercial fields that rotated multiple vegetables crops through the same plastic beds. All other PPNs were associated with bare ground beds in the north region that are commonly rotated with row crops. This study validates that Meloidogyne spp. are the most important PPN in vegetable fields of southern Georgia and suggests that cropping systems have a greater effect on PPN population dynamics than the environment.

Plant-parasitic nematodes affecting vegetable crops in greenhouses.

This work focuses on investigating plant-parasitic nematodes that affect greenhouse vegetables. The study took place in the Rostov region (Russian Federation) between May 2019 and May 2020 and involved 180 samples of soil and roots of 30 different vegetables in the families Cucurbitaceae (6), Solanaceae (8), Umbelliferae (8), Lamiaceae (4) and Allioideae (4) from 20 intensive farming locations. In this study, 11 nematode genera were detected. The most common genus was Meloidogyne, followed by Helicotylenchus, Pratylenchus, and Scutellonema. The highest Meloidogyne densities were detected in cucumbers, green peppers, carrots, eggplants, basil, and celery. Onions were not infected with Meloidogyne at all. Plant diseases caused by Pratylenchus, Scutellonema and Helicotylenchus were present in 29.7%, 51.5% and 81.6% of all crops examined, respectively. Xiphinema were found exclusively in carrots and celery, while Ditylenchus were only present in tomatoes and carrots (for each, the prevalence was 2.1%). The relative abundance of Meloidogyne, Helicotylenchus, and Pratylenchus was 58.3%, 10.4%, and 2.1%, respectively. As regards other genera, the relative abundance was less than 1%. The results show that soil properties are as important for the abundance, distribution and structure of the plant-parasitic nematode communities as the host plant. Findings may be helpful in improving the vegetable pest controls.

Evaluation The Effect of Intercropping Garlic with Grapevines on Productivity, Phytoremediation, Competitive Indices and Plant Parasitic Nematode Community تقييم تأثير تحميل الثوم مع العنب على الإنتاجية والمعالجة النباتية والعلاقات التنافسية ومجتمع النيماتودا المتطفلة على النبات

The present investigation was carried out during winter of the consecutive seasons (2018/2019 and 2019/2020) on 9 year old Flame Seedless grapevines grown in a private vineyard at Sharkia Governorate, Egypt. Garlic (Balady cv) was intercropped with grapevines (Flame Seedless cv) on dripper irrigation lines, as a try to reduce numbers of phytonematodes in grapevine soil. For grapevines, the obtained results referred that intercropping insignificantly (P≤0.05) increased number of berries/bunch, weight of 100 berries and berry firmness, separation force, total soluble solids percentage, anthocyanin content and yield/ vine as well as bunch weight and width, berry length, berry diameter and berry shape index compared to sole grapevines. For garlic (Balady cv), the achieved results pointed out that plant height, number of leaves/plant, leaf fresh weight/ plant, nick diameter as well as bulb diameter, height and weight/ plant insignificantly decreased when garlic intercropped with grapevines compared to control. Competition indices; i.e., land equivalent ratio (LER), area time equivalent ratio (ATER) and land utilization efficiency (LUE) showed that, intercropping garlic with grapevines was more efficient than sole cropping system. Aggressively estimation demonstrated that grapevines were dominant advantages while garlic was dominated. Moreover, intercropping garlic (Balady cv) with grapevines was obviously decreased population density of phytonematodes infesting grapevine orchard. Generally, garlic together with other biocontrol agents in grapevine orchards has the potential to be an efficient and environmentally agricultural management method to reduce numbers of plant parasitic nematodes.

Unveiling the structure and distribution of plant-parasitic nematode communities in soybean fields in southern of the Brazil

Our study aimed to assess the structure and distribution of plant-parasitic nematodes in soybean [Glycine max (L.) Merr] in the south of Brazil. High taxonomical diversity was found, with records of 10 genera of plant-parasitic nematodes (PPNs), including important pests, such as Meloidogyne (mostly M. javanica with small esterase variability), Pratylenchus (mostly P. brachyurus) and Helicotylenchus spp. The Shannon-Weaver index (H′) ranged from 0 to 1.23 (mean = 0.37), whereas Pielou’s evenness (J) ranged from 0 to 1 (mean = 0.51). The amount of PPNs (0 to 22,050 per 250 cm3 soil, and 0 to 15,500 per 10 g roots), incidence and abundance for Meloidogyne (28.6%; 50 to 19,250 per 250 cm3), Pratylenchus (45.1%; 50 to 550 per 250 cm3), Helicotylenchus (91.2%; 50 to 9,150 per 250 cm3), Tylenchus (34.1%; 50 to 550 per 250 cm3), Xiphinema (33%; 50 to 250 per 250 cm3), Mesocriconema (15.4%; 50 to 2,000 per 250 cm3), Rotylenchus (8.8%; 50 to 1,900 per 250 cm3), Hemicycliophora (1.1%; 50 per 250 cm3), Discocriconemella (1.1%; 950 per 250 cm3) and Tylenchorhynchus (1.1%; 50 per 250 cm3) were related differently to the bioclimatic variables under analysis. Our findings provide an update for the status of PPNs in the south of Brazil and suggest important epidemiological issues linked to the management of these pests in the near future.

Differences in distribution and community structure of plant-parasitic nematodes in pecan orchards between two ecoregions of Georgia.

In Georgia, pecans are commercially grown in the Piedmont and Coastal Plain ecoregions which are characterized by sandy-loam, sandy, and/or clay soils. If well-drained, these soils are suitable for pecan production, but the soil characteristics differ enough between ecoregions in which the plant-parasitic nematode (PPN) communities could differ substantially. We studied PPN communities in pecan orchards to evaluate the potential for ecoregion differences. In total, 11 genera (Helicotylenchus, Hemicycliophora, Heterodera, Hoplolaimus, Meloidogyne, Mesocriconema, Pratylenchus, Paratylenchus, Paratrichodorus, Tylenchorhynchs, Xiphenema) were recovered from pecan orchards in the Piedmont and Coastal Plain ecoregions. However, Non-Metric Multi-Dimensional Scaling ordination, Multi-Rank Permutation Procedure, and Indicator Species Analyses indicated that the pecan PPN communities strongly differed between ecoregions and that different genera were strongly associated with different ecoregions. For 9 of the 11 PPN genera, the maximum counts occurred in Coastal Plain locations, suggesting that the well-drained sandy soils of the Coastal Plain and comparatively ill-drained red clay soils of the Piedmont may be conducive and unfavorable for movement/reproduction of PPNs, respectively.

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.

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.