Belowground Chemical Interactions: An Insight Into Host-Specific Behavior of Globodera spp. Hatched in Root Exudates From Potato and Its Wild Relative, Solanum sisymbriifolium

Understanding belowground chemical interactions between plant roots and plant-parasitic nematodes is immensely important for sustainable crop production and soilborne pest management. Due to metabolic diversity and ever-changing dynamics of root exudate composition, the impact of only certain molecules, such as nematode hatching factors, repellents, and attractants, has been examined in detail. Root exudates are a rich source of biologically active compounds, which plants use to shape their ecological interactions. However, the impact of these compounds on nematode parasitic behavior is poorly understood. In this study, we specifically address this knowledge gap in two cyst nematodes, Globodera pallida, a potato cyst nematode and the newly described species, Globodera ellingtonae. Globodera pallida is a devastating pest of potato (Solanum tuberosum) worldwide, whereas potato is a host for G. ellingtonae, but its pathogenicity remains to be determined. We compared the behavior of juveniles (J2s) hatched in response to root exudates from a susceptible potato cv. Desirée, a resistant potato cv. Innovator, and an immune trap crop Solanum sisymbriifolium (litchi tomato – a wild potato relative). Root secretions from S. sisymbriifolium greatly reduced the infection rate on a susceptible host for both Globodera spp. Juvenile motility was also significantly influenced in a host-dependent manner. However, reproduction on a susceptible host from juveniles hatched in S. sisymbriifolium root exudates was not affected, nor was the number of encysted eggs from progeny cysts. Transcriptome analysis by using RNA-sequencing (RNA-seq) revealed the molecular basis of root exudate-mediated modulation of nematode behavior. Differentially expressed genes are grouped into two major categories: genes showing characteristics of effectors and genes involved in stress responses and xenobiotic metabolism. To our knowledge, this is the first study that shows genome-wide root exudate-specific transcriptional changes in hatched preparasitic juveniles of plant-parasitic nematodes. This research provides a better understanding of the correlation between exudates from different plants and their impact on nematode behavior prior to the root invasion and supports the hypothesis that root exudates play an important role in plant-nematode interactions.

Co-Silencing of the Voltage-Gated Calcium Channel β Subunit and High-Voltage Activated α1 Subunit by dsRNA Soaking Resulted in Enhanced Defects in Locomotion, Stylet Thrusting, Chemotaxis, Protein Secretion, and Reproduction in Ditylenchus destructor

The voltage-gated calcium channel (VGCC) β subunit (Cavβ) protein is a kind of cytosolic auxiliary subunit that plays an important role in regulating the surface expression and gating characteristics of high-voltage-activated (HVA) calcium channels. Ditylenchus destructor is an important plant-parasitic nematode. In the present study, the putative Cavβ subunit gene of D. destructor, namely, DdCavβ, was subjected to molecular characterization. In situ hybridization assays showed that DdCavβ was expressed in all nematode tissues. Transcriptional analyses showed that DdCavβ was expressed during each developmental stage of D. destructor, and the highest expression level was recorded in the third-stage juveniles. The crucial role of DdCavβ was verified by dsRNA soaking-mediated RNA interference (RNAi). Silencing of DdCavβ or HVA Cavα1 alone and co-silencing of the DdCavβ and HVA Cavα1 genes resulted in defective locomotion, stylet thrusting, chemotaxis, protein secretion and reproduction in D. destructor. Co-silencing of the HVA Cavα1 and Cavβ subunits showed stronger interference effects than single-gene silencing. This study provides insights for further study of VGCCs in plant-parasitic nematodes.

Wheat Production Alters Soil Microbial Profiles and Enhances Beneficial Microbes in Double-Cropping Soybean

Plant-parasitic nematodes represent a substantial constraint on global food security by reducing the yield potential of all major crops. The soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) is widely distributed across important soybean production areas of the U.S., being the major soybean yield-limiting factor, especially in the Midwestern U.S. Double cropped (DC) soybean is commonly planted following winter wheat. We previously reported double-cropping soybean fields with reduced SCN counts compared to fallow at both R1 growth stage (beginning of flowering) (−31.8%) and after soybean harvest (−32.7%). To test if higher counts of beneficial and SCN antagonistic microorganisms could be correlated with the suppression of SCN in fields previously planted with wheat, three field locations with noted SCN suppression were selected for a metagenomics study. Ten subplots were selected (5 wheat and 5 fallow pre-soybean) from each location. A total of 90 soil samples were selected: 3 fields ×2 treatments × 3 timepoints × 5 replications. Three DNA markers targeted distinct microbial groups: bacteria (16S V4-V5), fungi (ITS2), and Fusarium (tef1). Amplicons were sequenced using an Illumina MiSeq platform (300 bp paired-end). Sequencing datasets were processed in R using the DADA2 pipeline. Fungal populations were affected by location in all sampling periods and differed significantly between DC and fallow plots at soybean planting and after harvest (P < 0.001). Several enriched fungal and bacterial taxa in wheat plots, including Mortierella, Exophiala, Conocybe, Rhizobacter spp., and others, were previously reported to parasitize SCN and other plant-parasitic nematodes, suggesting a potential role of beneficial microbes in suppression of SCN in soybean fields double-cropped with wheat.

Mapping of Plant-Parasitic Nematode Using GIS Technology in Tainal Watershed, Sulaimaniyah Province, Iraq

The present experiment was conducted to evaluate soil samples which had been taken from depths ranging from 0-30 cm in greenhouses planted with different vegetables such as cucumbers, tomatoes, peppers and eggplants in 24 agricultural sites in 19 villages. GIS application was used to make maps showing the results of a field survey that was conducted. The experiment was conducted for an area of 12 km2 in the Tainal Plain, west of Sulaimaniyah Province. Nearly 30% of the soil of the greenhouses were heavily infected. Plant analysis showed that the characteristics of ash, fat and moisture were significantly affected as a result of infection with nematodes. The spread of root-knot nematode juveniles in the villages of Al-Mahmoudia, Kani Pengsharma and Kani Shaya was 706, 695 and 622 per 250 g of soil. In tissues of the studied plants, the highest nitrogen content was 68.2 mg in Ziyeka, 60.4 mg in Gawani and 59.7 mg in Ali Bzaw. Phosphorus concentrations were highest in Kani Shaya, Shwankara and Ziyeka (25.5, 25.3 and 23.1 mg, respectively). Warmizyar had 91.8 mg of potassium, Kani Shaya had 78.6 mg and Kani Big had 71.6 mg. The calcium concentrations in Ziyeka, Gawani and Mewk were 54.5, 48.4 and 47.7 mg, respectively.

Studies on plant-parasitic nematodes associated with sweet potato (Ipomoea batatas L., Lam.) in Gombe State, Nigeria

Sweet potato (Ipomoea batatas L., Lam.) is one of the most frequently eaten food crops. Its production is affected by plant-parasitic nematodes as well as biotic factors. This study was conducted to document the different plant-parasitic nematodes (PPN) that limit the gainful production of sweet potato in Gombe State. Thirty soil core samples per hectare were collected at random from sweet potato farms in the three local government areas (Nafada, Kaltungo, and Yamaltu Deba) of Gombe state. The Whitehead and Hemming method and identification keys were used for the soil extraction and genera identification of the plant-parasitic nematodes respectively. A total of 15 plant-parasitic nematodes were recovered throughout the surveyed areas among which 7 are considered major nematode pests of global importance. Irrespective of the surveyed locations, Meloidogyne spp., was found to record the highest population density and prevalence value. The frequency of occurrence in Y/Deba and Nafada LGAs shows that Meloidogyne spp., wasthe most occurring (32 %) genera. In Kaltungo LGA however, Scutellonema spp., and Rotylenchusspp., were the most occurring (17 %) genera. There was a high similarity percentage (≥ 68 %) of PPN genera where 8 genera (Scutellonema spp., Nacobbus spp., Pratylenchus spp., Meloidogyne spp., Heterodera spp., Xiphinema spp., Trichodorus spp., and Rotylenchus spp.) were found to be common amongst the surveyed locations. This is the first report of plant-parasitic nematodes associated with sweet potato in Gombe state, Nigeria. Hence, it is critical to educate farmers in the regions about their effects on the crop and how to successfully manage them.

A Comparative Diversity Analysis of Soil Nematodes of Rajouri, Jammu and Kashmir, India

Diversity of Nematode communities in Pir Panjal range of Jammu and Kashmir along with nematodes’ driven indices were studied. Himalayan mountainous areas of district Rajouri were selected. Community composition and trophic structure (feeding types) were assessed and were analyzed at various altitudes and across varied habitats, which differ significantly on moving from low elevation to high elevation areas. A total of 47 genera were recorded across mountain clines. In terms of taxonomic groups, in higher elevations, the order Dorylaimids represent 55.18%, followed by Tylenchida 28.85%, Mononchida 2.38%, Rhabditida 2.18%, and Aphelenchida 2.05%, whereas in the lower reaches, the order Rhabditida represent 30.18%, followed by Dorylaimids 28.75%, Tylenchida 15.85%, Mononchida 10.05% and Aphelenchida 1.05%. In terms of trophic groups, in the upper reaches, omnivores (56.6%) predominate, representing highest number, followed by plant parasitic (33.4%), bacterivore (4.2%), predatory (3.2%) and fungivore (2.60%). In the lower reaches, Bacterivores (38.08%) predominates, followed by omnivores (29.85%), plant parasitic (18.5%), predatory (12.5%) and fungivores (1.07%). The total nematode abundance and diversity were found increasing with elevation This pattern applied to most genera and feeding types. Across the regions, nematode diversity and community composition increases positively with elevations and richer habitats as given by Simpson index and Shannon-Weaver index. We conclude that nematode assemblages are potentially good bioindicators of climate change. They reacted sensitively and predictably to the changing environment. Thus, nematodes have suitability for long-term monitoring of biodiversity and community changes. Sampling techniques are well standardized and inexpensive. Furthermore, feeding types of nematodes can be determined with minimal taxonomic skills.

Biodiversity and Community Analysis of Plant-Parasitic and Free-Living Nematodes Associated with Maize and Other Rotational Crops from Punjab, Pakistan

Maize (Zea mays L.) is one of Pakistan’s essential staple food crops. Plant-parasitic nematodes (PPNs) are a significant restraint in maize production. However, free-living nematodes (FLNs) provide crucial ecological functions such as suppressing pests and nutrient mineralization. This study aimed to assess the community analysis of plant-parasitic and free-living nematodes associated with maize and other rotational crops (those cultivated in sequence with the maize in the same field) from Punjab, Pakistan. The occurrence percentage was observed per 500 g soil for each nematode genus. The present study revealed that 24 species of plant-parasitic and free-living nematodes were identified from maize crops and other rotational crops from 16 localities through Punjab, Pakistan. Nematode communities were analyzed by absolute frequency, relative frequency, relative density, and prominence value, while cluster analysis was based on the presence or absence of nematode in different localities. The overall proportion of plant-parasitic nematodes was 35%, while free-living soil nematodes recovered 65%, out of 210 samples of maize and other rotational crops. Several major genera of plant-parasitic nematodes were reported during the present study viz., Ditylenchus, Filenchus, Helicotylenchus, Hemicriconemoides, Heterodera, Hoplolaimus, Malenchus, Pratylenchus, Psilenchus, Rotylenchulus, Seinura, Telotylenchus, Tylenchorhynchus, and Xiphinema Community relationship revealed the overall dominance of Heterodera zeae, with the highest incidence (55.71%) followed by Tylenchorhynchus elegans (33.33%) and Helicotylenchus certus (24.76%). The results provide valuable information on the community structure of nematodes in maize and other rotational crops of maize in Punjab, Pakistan. Moreover, this data can be used as a preventive measure before PPN incidence results in greater losses on maize.

Biochemical Analysis Based on Zinc Uptake of Chickpea (Cicer arietinum L.) Varieties Infected by Meloidogyne incognita

The significant constraints in Chickpea (Cicer arietinum L.) production hampers a bit more than 14% global yield loss due to plant-parasitic nematodes. Root-knot nematode (Meloidogyne sp.) is an endoparasite and a significant species affecting the chickpea plant. So, the chemical basis of management is more cost-effective, and pest resurgence building is enhanced in the pathogen. So, ecological-based nematode management is requisite, which also is got hampered due to breeding for resistance against such plant-parasitic nematodes. This was the primary reason to conduct this experiment to enhance resistance in the chickpea plants based on Zinc uptake by using bioagent, Pseudomonas fluorescens alone or in combination. where Different treatments including nematode, bacterium, and chemicals were used sustaining the enhancement of disease resistance in chickpea cultivars, RSG 974, GG 5, GNG 2144. Zinc content of chickpea variety GNG 2144 was found the highest in treatment, when only bacterium (P. fluorescens) was inoculated, i.e., 3.14 mg/100g of root followed by GG 5, i.e., 2.79 mg/100g of root and RSG 974 was, i.e., 2.35 mg/100g of root respectively in a descending order. Application of P. fluorescence combined or alone gradually increased the Zn concentration in roots of chickpea plants compared to healthy check followed by chemical treated plants.

Prevalence and Molecular Diversity of Plant-Parasitic Nematodes of Yam (Dioscorea spp.) in China, with Focus on Merlinius spp.

There is little information about nematode pests associated with yam in China. Between 2020 and 2021, surveys of yam fields were conducted to investigate the abundance and prevalence of plant-parasitic nematodes in major yam growing areas. A total of 110 bulk soil samples from the yam rhizosphere and 48 yam tubers were collected from seven counties in Jiangxi and Shandong provinces. Standard protocols were used to extract nematodes from soil and tubers and identified at the genus level. In this study, 16 species and 13 nematode genera were recorded. The five most prominent species on the yam rhizosphere according to mean population densities were Pratylenchus coffeae (291/individuals), Meloidogyne (262/individuals), Rotylenchulus reniformis (225/individuals), Merlinius (224/individuals), and Helicotylenchus dihystera (171/individuals). In the tubers, the three most prominent species were Pratylenchus coffeae (415/individuals), Meloidogyne (331/individuals), and Rotylenchulus reniformis (115/individuals). These species were verified with appropriate molecular analysis. The high prevalence of the ectoparasite (Merlinius spp.) on the rhizosphere of yam also revealed that Merlinius spp. May be more important to yam than previously thought. Morphological and molecular analyses further confirmed the identity of the species as Merlinius brevidens and were characterized for the first time on yam in China. Minor morphometrical differences (slightly longer body and stylet) were observed in Chinese populations of M. brevidens compared to the original description. Additionally, this study reveals that M. brevidens isolated from China showed a higher nucleotide sequence in the ITS region compared to M. brevidens populations from India. This finding provides baseline information on the nematode pest occurrence on yam in China and calls for effective management.

Chromatin Landscape Dynamics in the Early Development of the Plant Parasitic Nematode Meloidogyne incognita

In model organisms, epigenome dynamics underlies a plethora of biological processes. The role of epigenetic modifications in development and parasitism in nematode pests remains unknown. The root-knot nematode Meloidogyne incognita adapts rapidly to unfavorable conditions, despite its asexual reproduction. However, the mechanisms underlying this remarkable plasticity and their potential impact on gene expression remain unknown. This study provides the first insight into contribution of epigenetic mechanisms to this plasticity, by studying histone modifications in M. incognita. The distribution of five histone modifications revealed the existence of strong epigenetic signatures, similar to those found in the model nematode Caenorhabditis elegans. We investigated their impact on chromatin structure and their distribution relative to transposable elements (TE) loci. We assessed the influence of the chromatin landscape on gene expression at two developmental stages: eggs, and pre-parasitic juveniles. H3K4me3 histone modification was strongly correlated with high levels of expression for protein-coding genes implicated in stage-specific processes during M. incognita development. We provided new insights in the dynamic regulation of parasitism genes kept under histone modifications silencing. In this pioneering study, we establish a comprehensive framework for the importance of epigenetic mechanisms in the regulation of the genome expression and its stability in plant-parasitic nematodes.