Control of Globodera pallida Using Brassica juncea Seed Meal Extract and the Trap Crop Solanum sisymbriifolium.

Globodera pallida, the pale cyst nematode, is a regulated potato pest which is economically detrimental. Restrictions on use of the soil fumigant methyl bromide and lack of resistant russet type varieties for U.S. markets have led to investigations of alternative strategies to control this pest. The efficacy of Brassica juncea seed meal extract (SME; 0, 0.14, 0.28, 0.56, 1.12, and 2.24 t/ha) was studied, either alone or in combination with the trap crop Solanum sisymbriifolium under greenhouse and field conditions. The impact of the application of SME pre- or postplanting of S. sisymbriifolium was also determined. S. sisymbriifolium only induced hatch of G. pallida and significantly fewer (up to 57 and 55% in pre- and postplant experiments, respectively) encysted eggs remained at termination of the experiment compared with the untreated control. However, when SME was applied preplant, the encysted eggs remained unchanged, which may indicate that SME inhibited egg hatch in the presence of S. sisymbriifolium. When applied individually, S. sisymbriifolium in all experiments, or SME at all rates tested in the greenhouse or 0.56 t/ha or higher rates of SME in the field, significantly reduced the viability, hatch, and reproduction of G. pallida. Combined treatment with S. sisymbriifolium and SME at lower rates (0.14 t/ha for preplant or 0.56 t/ha or less for the greenhouse postplant experiment) reduced G. pallida egg hatch further than each strategy alone. In the field, a combination of S. sisymbriifolium and SME at 1.12 t/ha or less reduced G. pallida more effectively than SME alone. SME alone applied at higher rates (0.56 and 1.12 t/ha) in preplant greenhouse trials, whether or not combined with S. sisymbriifolium, eliminated G. pallida reproduction. Under field conditions, SME applied at a rate of 1.12 t/ha highly reduced G. pallida reproduction compared with the untreated control by 97 and 61% in 2019 and 2020, respectively. Furthermore, reproduction of G. pallida was eliminated when SME was combined with S. sisymbriifolium. Our results indicated that a combination of SME and S. sisymbriifolium reduces the amount of SME needed to control G. pallida and further decreases the potential reserve of the viable population remaining after individual treatment with each strategy.

Control of Globodera pallida Using Sinapis alba or 4-Hydroxybenzyl Alcohol with the Trap Crop Solanum sisymbriifolium or the Biofumigant Brassica juncea Seed Meal Extract.

The pale cyst nematode Globodera pallida is a highly specialized, economically important pest for potato production. The specialized hatching requirements, ability to adapt, and the loss of effective control strategies such as methyl bromide fumigation increase the challenge to eradicate G. pallida in Idaho. Without a suitable host, this nematode can remain dormant as encysted eggs in soil for up to 20 years. In this study, we first demonstrated that Sinapis alba seed meal extract (SME) or 4-hydroxybenzyl alcohol (HBA), under laboratory and greenhouse conditions, enhances G. pallida egg hatch rate when exposed to potato root diffusate (PRD). This hatch rate enhancement in the presence of PRD is speculated to be due to an increase in egg-shell permeability. We then tested the efficacy of (i) Solanum sisymbriifolium following prior treatment with S. alba SME (0 and 4.48 t/ha) or HBA (0 and 0.12 t/ha) and (ii) Brassica juncea SME (0, 0.14, 0.56, and 1.12 t/ha) following HBA treatment (0 and 4.48 t/ha) on egg viability, hatch rate, and reproduction of G. pallida encysted eggs. S. sisymbriifolium alone reduced the number of encysted eggs compared to the nontreated control by up to 67%, indicating that this trap crop triggered G. pallida eggs to hatch. When combined with S. alba SME or HBA, S. sisymbriifolium significantly reduced egg count, hatch rate, and viability more than S. sisymbriifolium alone. The combination of S. sisymbriifolium with HBA or S. alba SME eliminated G. pallida reproduction on the susceptible potato. All the tested rates of B. juncea SME alone or with HBA reduced egg hatch rate, viability, and reproduction compared to the nontreated control. Combining HBA and B. juncea SME further significantly reduced egg hatch rate, viability, and reproduction than those rates of B. juncea SME alone.

The Impact of Management Strategies on the Development and Status of Potato Cyst Nematode Populations in Switzerland: An Overview from 1958 to Present.

Globodera rostochiensis and G. pallida are some of the most successful and highly specialized plant parasitic nematodes and among the most regulated quarantine pests globally. In Switzerland, they have been monitored by annual surveys since their first detection in Swiss soil in 1958. The dataset created was reviewed to produce an overview of the development and actual status of potato cyst nematodes (PCNs) in Switzerland. Positive fields represent 0.2% of all the samples analyzed, and their distribution is limited to central-west and western Switzerland, suggesting that new introduction of PCNs and the spread of the initial introduced PCN populations did not occur. In this way, the integrated management used in Switzerland appears to be effective. However, the increasing availability of potato varieties with resistance to G. rostochiensis and the limited availability of varieties with resistance to G. pallida, together with other biotic and abiotic factors, have promoted changes in the dominance of either species. Consequently, an extended monitoring program is of interest to Swiss farmers, to avoid favoring virulent traits that could be present in Swiss Globodera populations.

Potato Cyst Nematode Egg Viability Assessment and Preparasitic Juvenile Screening Using a Large Particle Flow Cytometer and Sorter.

Potato cyst nematode (PCN) cysts consist of heterogenous populations of eggs, juveniles, and eggshells that make manual sorting of individual life stages cumbersome. The number of viable PCN eggs is a major determinant of crop damage. An accurate high-throughput PCN egg viability assay is useful for developing effective management and eradication plans. In this study, we present a method for rapid and precise enumeration and sorting of PCN eggs and juveniles, along with an egg viability assessment by staining eggs with the fluorescent stain, acridine orange, and sorting with the Complex Object Parametric Analyzer and Sorter (COPAS) system, a large particle flow cytometer. Both size sorting and fluorescent sorting capabilities of the COPAS were explored. By using the COPAS, sorting efficiency for eggs and preparasitic second-stage juveniles (J2s) was 97.6 and 97.2%, respectively, with 99% recovery at a flow rate of 15 events/s. Purity of sorted live and dead eggs was 95.5 and 94.1%, respectively. Sorting of J2s by size indicated that 15 to 16.4% of Globodera ellingtonae or G. pallida had an average body length of 436.1 ± 3.4 µm compared with an average size of 512.9 ± 4.4 µm for the majority of the J2 population for both species. A red autofluorescing J2 population was also identified through sorting. Sorting of eggs by flow cytometry did not significantly affect hatching (55.1 ± 1.2 and 53.9 ± 1.6%, respectively, for sorted or nonsorted eggs) or juvenile motility (91.3 ± 1.0 or 90.1 ± 1.1%, respectively), thus confirming that the method does not impair the biological activity of the nematode.

Improvement of diagnostic markers for resistance to Globodera pallida and application for selection of resistant germplasms in potato breeding.

Occurrence of pale potato cyst nematode, Globodera pallida (Stone) Behrens, was first recorded in Japan in 2015. Among several control measures, cultivation of resistant potato (Solanum tuberosum L.) varieties is the most effective in cost and environmental impact. As no G. pallida-resistant varieties have yet been developed in Japan, great emphasis is being placed on screening of germplasm possessing the resistance and development of the resistant varieties. In this study, we first improved previously reported DNA markers linked to the G. pallida resistance loci (GpaIVs adg and Gpa5) and then used these to screen more than 1,000 germplasms to select several candidate germplasms with resistance. We performed inoculation testing on the selected candidates and identified several resistant germplasms to the Japanese G. pallida population. Furthermore, we developed a simultaneous detection method combining three DNA markers linked to G. pallida and Globodera rostochiensis (Wollenweber) Behrens resistance loci. We validated the ability of C237-I marker to select resistant allele of GpaIVs adg and predict the presence of resistance in a Japanese breeding population. Resistant germplasms identified in this study could potentially be used to develop G. pallida-resistant varieties. The marker evaluation methods developed in this study will contribute to the efficient development of resistant varieties.

The relations of broad nematode resistance to quality characteristics as a consequence of marker-assisted selection in potato breeding programs.

Cultivating resistant varieties of potato is the most effective and environmentally sound method of protecting potato crops against pests and diseases. Potato cyst nematodes (PCN) are major nematode pests causing severe constraints in potato production worldwide. There are five pathotypes of Globodrea rostochiensis (Ro1-Ro5) and three of G. pallida Pa1-Pa3. Cultivation of potato varieties with broad nematode resistance may influence the growth of the wide spectrum of PCN pathotypes, but there is limited availability of such varieties on the market. The use of molecular markers allows for the effective selection of resistant genotypes at early stages of breeding. However, the impact of early selection for nematode resistance on the agronomic value of the final selected clones is a cause of concern for potato breeders. This study investigates the relationships between the presence of the combined resistance genes H1, Gro1-4 and GpaVvrn , which confer resistance to the nematodes, and certain agricultural traits. Clones with broad nematode resistance conferred by the genes H1, Gro1-4 and GpaVvrn presented yields and tuber morphology traits similar to those of the clones without identified resistance genes.

Effect of Steroidal Glycoalkaloids on Hatch and Reproduction of the Potato Cyst Nematode Globodera pallida.

Steroidal glycoalkaloids (SGAs) are phytoanticipins found in solanaceous crops that act as the first line of chemical defense against pathogen attacks. Solanum sisymbriifolium, a trap crop for potato cyst nematodes, has been shown to effectively reduce populations of Globodera pallida. S. sisymbriifolium contains α-solamargine and other solasodine-type glycoalkaloids that may contribute to plant defenses. This study evaluated the influence of solanaceous SGAs on G. pallida hatch, development, and reproduction. Exposure to α-solamargine and α-solamarine reduced G. pallida hatch by 65 and 87%, respectively. Exposure of G. pallida cysts with the glycoalkaloids α-solamargine and solasodine significantly reduced infection in susceptible potato 'Russet Burbank' by 98 and 94% compared with the control. Exposure of cysts to either solasodine or solamargine significantly reduced reproduction of G. pallida on 'Russet Burbank' by 99% compared with the control. The study demonstrated the deleterious effect of SGAs on G. pallida hatch, infection, and reproduction.

First report of morphological and molecular characterization of Moroccan populations of Globodera pallida.

Potato cyst nematodes (PCNs) are the most important potato pest causing major crop losses across the world with a quarantine status in many countries. In Morocco, several potato crops are infected with PCNs and the monitoring of potato production as well as the control of import and export of potato seeds are currently carried out by morphological methods. The present work was aimed to use molecular and morphometric methods for identifying and differentiating PCN species in Morocco for the first time. The morphological identification of PCN species from collected soil samples were carried out using the shape of the cysts, the length of the stylet, the number of cuticular ridges, and the Granek's ratio. The J2 had a slightly shorter body length, the number of cuticular ridges was 9 and the Granek's ratio averaged 2.2. The morphobiometric analysis revealed proximity of the Moroccan population to G. pallida species. PCNs sampled from contaminated fields were analyzed molecularly using PCR. DNA amplification was performed using the multiplex PCR method and PCR-RFLP from the ITS region of the total genomic DNA compared to multiplex PCR-specific DNA sequences. All confirmed the presence G. pallida in all samples of the Moroccan PCN populations.

A Spatiotemporal Analysis and Dispersal Patterns of the Potato Cyst Nematode Globodera pallida in Idaho.

The potato cyst nematode Globodera pallida is a globally regulated potato pest. It was detected for the first time in the United States in the state of Idaho in 2006, and as of February 2019, the infestation is limited to 1,326 hectares. G. pallida is a specialized obligate sedentary endoparasite that can survive in the soil for up to 30 years in the absence of its potato host. In highly infested fields, the nematode can reduce tuber yields up to 80% and is spread mainly through the movement of soil, tubers, or farm equipment. The objectives of this study were to describe the spatiotemporal pattern of G. pallida in infested fields and model its dispersal patterns in southeastern Idaho. We used geostatistical tools and simulation models for precise mapping and to describe the relationships between G. pallida incidence and the spatial configurations. We found that the nematode is spatially clustered and prevalent around edges of fields, and its dispersal pattern followed the direction of cultivation. We found that the absence of potato in an infested field significantly reduced the number of cysts sampled each year subsequent to the initial delimitation sampling in 2007. Phytosanitary measures prohibiting the growth of potato contributed to stopping nematode reproduction, and the use of chemical fumigants and biofumigant cover crops contributed to a significant reduction in egg viability. We observed a process of a nonlinear decline in the prevalence of cysts as the distance separation from the primary infestation focus increased. A power law model was used to fit G. pallida dispersal capabilities. This study contributed to describing G. pallida infestation for Idaho. The goal of this study is to provide information on the spatial pattern and landscape ecology of G. pallida in Idaho for policy makers, industry, and researchers as well as facilitate common understandings on the challenges and opportunities for controlling this pest in Idaho.

Exploring the causes of small effective population sizes in cyst nematodes using artificial Globodera pallida populations.

The effective size of a population is the size of an ideal population which would undergo genetic drift at the same rate as the real population. The balance between selection and genetic drift depends on the effective population size ( Ne), rather than the real numbers of individuals in the population ( N). The objectives of the present study were to estimate Ne in the potato cyst nematode Globodera pallida and to explore the causes of a low Ne/ N ratio in cyst nematodes using artificial populations. Using a temporal analysis of 24 independent populations, the median Ne was 58 individuals (min Ne = 25 and max Ne = 228). Ne is commonly lower than N but in the case of cyst nematodes, the Ne/ N ratio was extremely low. Using artificial populations showed that this low ratio did not result from migration, selection and overlapping generations, but could be explain by the fact that G. pallida populations deviate in structure from the assumptions of the ideal population by having unequal sex ratios, high levels of inbreeding and a high variance in family sizes. The consequences of a low Ne, resulting in a strong intensity of genetic drift, could be important for their control because G. pallida populations will have a low capacity to adapt to changing environments.

A Predictive Risk Model Analysis of the Potato Cyst Nematode Globodera pallida in Idaho.

Globodera pallida is a major nematode pest of potato (Solanum tuberosum) and is of great economic importance for the potato industry. Assessing potato yield loss caused by the Idaho G. pallida population under field conditions was not performed due to its quarantine status in Idaho, where it is prohibited by regulatory statutes to grow potato in any infested fields. The experimental data came from three trials that were conducted under greenhouse conditions. A predictive risk model analysis was performed to: (i) determine the effect of the Idaho population of G. pallida on potato yield; (ii) estimate reproduction rate from different initial nematode densities; and (iii) simulate potato yield losses in Idaho field conditions by integrating the coefficients of potato yield into the SUBSTOR-DSSAT crop simulation model. Experiments were conducted under greenhouse conditions using five initial G. pallida soil infestation levels (0, 10, 20, 40, and 80 eggs/g soil). The coefficients of potato yield achieved under each initial nematode density were integrated into the SUBSTOR-DSSAT potato growth simulation model. The model showed that tuber weight reached a maximum yield of 96 ton/ha in noninfested soil. Based on the greenhouse trials, the model predicted a minimum yield of 12 and 58 ton/ha in trial 1 and trial 2/3 respectively, when initial nematode density was 80 eggs/g soil. In trial 1, tuber weight was significantly reduced by 44% at 40 eggs/g soil and by 87% at 80 eggs/g soil, and 20% at 40 eggs/g soil and by 39% at 80 eggs/g soil in trial 2/3. The outputs of this study should facilitate common understanding between regulators, policymakers, and potato growers on the challenges and opportunities for controlling this economically important pest in Idaho.

Climate change is predicted to alter the current pest status of Globodera pallida and G. rostochiensis in the United Kingdom.

The potato cyst nematodes Globodera pallida and G. rostochiensis are economically important plant pathogens causing losses to UK potato harvests estimated at £50 m/ year. Implications of climate change on their future pest status have not been fully considered. Here, we report growth of female G. pallida and G. rostochiensis over the range 15 to 25°C. Females per plant and their fecundity declined progressively with temperatures above 17.5°C for G. pallida, whilst females per plant were optimal between 17.5 and 22.5°C for G. rostochiensis. Relative reproductive success with temperature was confirmed on two potato cultivars infected with either species at 15, 22.5 and 25°C. The reduced reproductive success of G. pallida at 22.5°C relative to 15°C was also recorded for a further seven host cultivars studied. The differences in optimal temperatures for reproductive success may relate to known differences in the altitude of their regions of origin in the Andes. Exposure of G. pallida to a diurnal temperature stress for one week during female growth significantly suppressed subsequent growth for one week at 17.5°C but had no effect on G. rostochiensis. However, after two weeks of recovery, female size was not significantly different from that for the control treatment. Future soil temperatures were simulated for medium- and high-emission scenarios and combined with nematode growth data to project future implications of climate change for the two species. Increased soil temperatures associated with climate change may reduce the pest status of G. pallida but benefit G. rostochiensis especially in the southern United Kingdom. We conclude that plant breeders may be able to exploit the thermal limits of G. pallida by developing potato cultivars able to grow under future warm summer conditions. Existing widely deployed resistance to G. rostochiensis is an important characteristic to retain for new potato cultivars.

Prospecting fungal parasites of the potato cyst nematode Globodera pallida using a rapid screening technique.

Seven filamentous fungal species were isolated from individual eggs of Globodera pallida cysts collected from infested fields in Shelley Idaho, USA and identified as Chaetomium globosum, Fusarium oxysporum, Fusarium solani, Fusarium tricinctum, Microdochium bolleyi, Purpureocillium lilacinum, and Plectosphaerella cucumerina. Their ability to reduce infection by G. pallida in planta were assessed in simple, reproducible micro-rhizosphere chambers (micro-ROCs). All fungi reduced G. pallida infection in potato, but greatest reduction was observed with C. globosum at an average reduction of 76%. Further non-destructive methods were developed to rapidly assess biological control potential of putative fungal strains by staining the infectious second stage juveniles of G. pallida with the live fluorescent stain PKH26. In comparisons between the standard, invasive acid fuchsin method and use of the live stain PKH26, no significant difference in infection level of G. pallida was observed whether roots were stained with PKH26 or acid fuchsin. For both methods, a similar reduction (77% for acid fuchsin, and 78% for PKH26 stain) in invasion of infectious stage of G. pallida was observed when potato plants were inoculated with C. globosum compared to non-inoculated potato.

Assessment of Globodera pallida RNA Extracted from Solanum Roots.

The introduction of high-throughput sequencing technologies has made transcriptome analyses of plant-pathogen interactions almost routine. Nevertheless, it is still challenging to obtain RNA from populations made up of two species. An RNA extraction method that worked well on free-living Caenorhabditis elegans failed when applied to isolated Globodera pallida J2 larva. Furthermore, alternative protocols that extracted RNA from free-living J2 larva produced less satisfactory results once the animals entered their hosts' roots. We have compared several extraction procedures to ascertain whether a single protocol was capable of recovering high-quality, high-molecular-weight RNA from newly hatched J2 larva as well as from larva embedded in roots of both potatoes (Solanum tuberosum L. cv. Desiree) and a very distantly related species, Solanum sisymbriifolium. Although it was possible to recover large amounts of RNA from J2 larvae using Proteinase K treatments, this protocol failed to yield high-quality nematode RNA from infected roots. By comparison, mechanical disruption procedures yielded lower amounts of RNA from infected roots, but what was recovered was of higher quality. We conclude that different extraction protocols need to be developed to sample mixed populations of organisms.

Chemosensory Responses of Plant Parasitic Nematodes to Selected Phytochemicals Reveal Long-Term Habituation Traits.

Plant parasitic nematodes (PPN) are important crop pests within the global agri-sector. Critical to their success is a complex and highly sensitive chemosensory system used to locate plants by detecting host cues. In addition to this, the nematode neuronal system has evolved mechanisms to allow adaptation to a changing environment. Clearly, there is a need to better understand the host-parasite relationship and the mechanisms by which PPN successfully locate and infect host plants. Here, we demonstrate the chemotactic response of two economically important PPN species, Meloidogyne incognita and Globodera pallida to selected phytochemicals. We further reveal an adapted chemotactic response in M. incognita second-stage juveniles preexposed to ethephon (Eth), potato root diffusate (PRD), and salicylic acid (SA), and present pharmacological evidence supporting the existence of long-term habituation traits acting via serotonergic-dependent neurotransmission.

Kaolinite nanoclay-shielded dsRNA drenching for management of Globodera pallida: An environmentally friendly pest management approach.

Globodera pallida, an obligate sedentary endoparasite, is a major economic pest that causes substantial potato yield losses. This research aimed to study the effects of gene silencing of three FMRFamide-like peptides (FLPs) genes to reduce G. pallida infestation on potato plants by using kaolinite nanoclay as a carrier to deliver dsRNAs via drenching. A dsRNA dosage of 2.0 mg/ml silenced flp-32c by 89.5%, flp-32p by 94.6%, and flp-2 by 94.3%. J2s incubated for 5 and 10 h showed no phenotypic changes. However, J2s of G. pallida efficiently uptake dsRNA of all targeted genes after 15 h of incubation. On the other hand, J2s that had been kept for 24 h had a rigid and straight appearance. Under fluorescence microscopy, all dsRNA-treated nematodes showed fluorescein isothiocyanate (FITC) signals in the mouth, nervous system, and digestive system. The untreated population of J2s did not show any FITC signals and was mobile as usual. The drenching of potato cultivar Kufri Jyoti with the dsRNA-kaolinite formulations induced deformation and premature death of J2s, compared with untreated J2s that entered J3 or J4 stages. This study validates that the nanocarrier-delivered RNAi system could be employed effectively to manage G. pallida infestations.

Development and evaluation of loop-mediated isothermal amplification assay for rapid and sensitive detection of potato cyst nematode, Globodera pallida from soil.

Potato cyst nematodes, Globodera pallida and G. rostochiensis, are economically important and difficult to manage pests of the potato crop. The cyst of both the species looks similar and it is difficult to differentiate once it turns brown upon maturity. Early detection of the PCN at the species level is crucial to avoid its further spread and for adopting the appropriate management strategies. Therefore, in the present study, highly specific and sensitive loop-mediated isothermal amplification (LAMP) assay was developed to amplify mitochondrial-Sequence Characterized Amplified Region (SCAR) sequence of potato cyst nematode, G. pallida. The LAMP assay was completed within a shorter incubation period of 60 min at 60 °C followed by the reaction termination at 80 °C for 5 min. The developed LAMP assay exhibited high specificity for G. pallida and did not detect any other species including its sibling species, G. rostochiensis. In sensitivity tests, the assay detected G. pallida at 1000 times less DNA concentration (10 fg/µl) as compared to conventional PCR (10 pg/µl). In addition to this, the developed LAMP assay was tested for the detection of G. pallida directly from the soil samples, and even a single cyst mixed with soil was successfully detected by the developed assay. Moreover, the utility of low-cost instruments like hot water bath was also demonstrated for the detection of G. pallida from the soil. The developed LAMP is a rapid, highly specific, sensitive, and cost-effective technique for the species-specific detection of G. pallida. The developed assay will facilitate the rapid detection of G. pallida at quarantine stations as well as from the fields which will help to stop its further spread in new areas and also to devise effective management strategies for sustainable potato production. Supplementary Information: The online version contains supplementary material available at 10.1007/s13205-023-03542-x.

A Comparison of Three Molecular Markers for the Identification of Populations of Globodera pallida.

Potato cyst nematodes cost the potato industry substantial financial losses annually. Through the use of molecular markers, the distribution and infestation routes of these nematodes can be better elucidated, permitting the development of more effective preventative methods. Here we assess the ability of three molecular markers to resolve multiple representatives of five Globodera pallida populations as monophyletic groups. Molecular markers included a region of the rbp-1 gene (an effector), a non-coding nuclear DNA region (the ITS region), and a novel marker for G. pallida, a ∼3.4 kb non-coding mitochondrial DNA (mtDNA) region. Multiple phylogenetic analysis methods were performed on the three DNA regions separately, and on a data set of these three regions combined. The analyses of the combined data set were similar to that of the sole mtDNA marker; resolving more populations as monophyletic groups, relative to that of the ITS region and rbp-1 gene region. This suggests that individual markers may be inadequate for distinguishing populations of G. pallida. The use of this new non-coding mtDNA marker may provide further insights into the historical distribution of G. pallida, as well as enable the development of more sensitive diagnostic methods.

Comparative Transcriptome Analysis Reveals the Specific Activation of Defense Pathways Against Globodera pallida in Gpa2 Resistant Potato Roots.

Cyst nematodes are considered a dominant threat to yield for a wide range of major food crops. Current control strategies are mainly dependent on crop rotation and the use of resistant cultivars. Various crops exhibit single dominant resistance (R) genes that are able to activate effective host-specific resistance to certain cyst nematode species and/or populations. An example is the potato R gene Gpa2, which confers resistance against the potato cyst nematode (PCN), Globodera pallida population D383. Activation of Gpa2 results in a delayed resistance response, which is characterized by a layer of necrotic cells formed around the developing nematode feeding structure. However, knowledge about the Gpa2-induced defense pathways is still lacking. Here, we uncover the transcriptional changes and gene expression network induced upon Gpa2 activation in potato roots infected with G. pallida. To this end, in vitro-grown Gpa2-resistant potato roots were infected with the avirulent population D383 and virulent population Rookmaker. Infected root segments were harvested at 3 and 6 dpi and sent for RNA sequencing. Comparative transcriptomics revealed a total of 1,743 differentially expressed genes (DEGs) upon nematode infection, of which 559 DEGs were specifically regulated in response to D383 infection. D383-specific DEGs associated with Gpa2-mediated defense mainly relates to calcium-binding activity, salicylic acid (SA) biosynthesis, and systemic acquired resistance (SAR). These data reveal that cyst nematode resistance in potato roots depends on conserved downstream signaling pathways involved in plant immunity, which are also known to contribute to R genes-mediated resistance against other pathogens with different lifestyles.

A Novel Rhabdovirus Associated with the Idaho Population of Potato Cyst Nematode Globodera pallida.

Globodera pallida, a potato cyst nematode (PCN), is a quarantine endoparasitic pest of potato (Solanum tuberosum) in the US due to its effects on yield and quality of potato tubers. A new rhabdovirus, named potato cyst nematode rhabdovirus (PcRV), was revealed and characterized in the G. pallida populations collected in Idaho through use of high-throughput sequencing (HTS) and RT-PCR and found to be most closely related to soybean cyst nematode rhabdovirus (ScRV). PcRV has a 13,604 bp long, single-stranded RNA genome encoding five open reading frames, including four rhabdovirus-specific genes, N, P, G, and L, and one unknown gene. PcRV was found present in eggs, invasive second-stage juveniles, and parasitic females of G. pallida, implying a vertical transmission mode. RT-PCR and partial sequencing of PcRV in laboratory-reared G. pallida populations maintained over five years suggested that the virus is highly persistent and genetically stable. Two other Globodera spp. reproducing on potato and reported in the US, G. rostochiensis and G. ellingtonae, tested negative for PcRV presence. To the best of our knowledge, PcRV is the first virus experimentally found infecting G. pallida. Based on their similar genome organizations, the phylogeny of their RNA-dependent RNA polymerase domains (L gene), and relatively high identity levels in their protein products, PcRV and ScRV are proposed to form a new genus, provisionally named "Gammanemrhavirus", within the family Rhabdoviridae.