Potato Cyst Nematode Globodera Pallida Research Articles

The hidden diversity of the potato cyst nematode Globodera pallida in the south of Peru.

Our knowledge of the diversity of potato cyst nematodes in their native areas still remains patchy and should be improved. A previous study based on 42 Peruvian Globodera pallida populations revealed a clear south to north phylogeographic pattern, with five well‐supported clades and maximum diversity observed in the south of Peru. In order to investigate this phylogeographic pattern more closely, we genotyped a larger collection of Peruvian populations using both cathepsin L gene sequence data and a new set of 13 microsatellite loci. Using different genetic analyses (STRUCTURE, DAPC), we consistently obtained the same results that led to similar conclusions: the presence of a larger genetic diversity than previously known suggesting the presence of cryptic species in the south of Peru. These investigations also allowed us to clarify the geographic borders of the previously described G. pallida genetic clades and to update our knowledge of the genetic structure of this species in its native area, with the presence of additional clades. A distance‐based redundancy analysis (dbRDA) was also carried to understand whether there was a correlation between the population genetic differentiation and environmental conditions. This analysis showed that genetic distances observed between G. pallida populations are explained firstly by geographic distances, but also by climatic and soil conditions. This work could lead to a revision of the taxonomy that may have strong implications for risk assessment and management, especially on a quarantine species.

The effector GpRbp-1 of Globodera pallida targets a nuclear HECT E3 ubiquitin ligase to modulate gene expression in the host.

SummaryPlant‐parasitic nematodes secrete effectors that manipulate plant cell morphology and physiology to achieve host invasion and establish permanent feeding sites. Effectors from the highly expanded SPRYSEC (SPRY domain with a signal peptide for secretion) family in potato cyst nematodes have been implicated in activation and suppression of plant immunity, but the mechanisms underlying these activities remain largely unexplored. To study the host mechanisms used by SPRYSEC effectors, we identified plant targets of GpRbp‐1 from the potato cyst nematode Globodera pallida. Here, we show that GpRbp‐1 interacts in yeast and in planta with a functional potato homologue of the Homology to E6‐AP C‐Terminus (HECT)‐type ubiquitin E3 ligase UPL3, which is located in the nucleus. Potato lines lacking StUPL3 are not available, but the Arabidopsis mutant upl3‐5 displaying a reduced UPL3 expression showed a consistently small but not significant decrease in susceptibility to cyst nematodes. We observed a major impact on the root transcriptome by the lower levels of AtUPL3 in the upl3‐5 mutant, but surprisingly only in association with infections by cyst nematodes. To our knowledge, this is the first example that a HECT‐type ubiquitin E3 ligase is targeted by a pathogen effector and that a member of this class of proteins specifically regulates gene expression under biotic stress conditions. Together, our data suggest that GpRbp‐1 targets a specific component of the plant ubiquitination machinery to manipulate the stress response in host cells.

The ribosomal intergenic spacer (IGS) in the potato and tobacco cyst nematodes, Globodera pallida, G. rostochiensis and G. tabacum

The potato cyst nematodes Globodera pallida and G. rostochiensis (PCN), and tobacco cyst nematode (TCN), G. tabacum, are the most important parasitic nematodes of potato and tobacco worldwide. Ribosomal DNA provides useful molecular data for diagnostics, the study of polymorphisms and for evolutionary research in eukaryotic organisms including nematodes. Here we present data on the structure and organization of a rarely studied part of the intergenic spacer (IGS) region of the PCN and TCN genome of cyst nematodes. This region has shown potential for diagnostic purposes and population studies in other organisms including nematodes. In nematodes, the ribosomal RNA gene cluster comprises three genes: 5.8S, 18S and 28S rRNA, which are separated by spacer regions: the intergenic spacer (IGS), non-transcribed spacer (NTS), externally transcribed spacer (EST) and the internally transcribed spacer (ITS). The intergenic spacer (IGS) region consists of an external transcribed spacer (ETS) and a non-transcribed spacer (NTS) which is located between the 28S of one repeat and the 18S gene of the next repeat within the rRNA genes cluster. In this study, the first flanking portion of the IGS was amplified, cloned and sequenced from PCN and TCN. Primers were then designed to amplify the whole IGS sequence. PCR amplification of IGS from G. tabacum, G. pallida, and G. rostochiensis yielded respectively: a single amplicon of 3 kb, three amplicons sized 2.5, 2.6 and 2.9 kb, and two amplicons sized 2.8 and 2.9 kb. Results showed that Globodera spp. has more than one variant copy of the IGS, with both long and short repetitive DNA elements. An approximately 400 bp long region without any internal repetitive elements, were identified in a position between the two repetitive regions suggesting that there is a 5S gene in the IGS of these species.

Current Status of Potato Cyst Nematodes in North America

The potato cyst nematodes (PCNs) Globodera rostochiensis and Globodera pallida are internationally recognized quarantine pests. Although not widely distributed in either the United States or Canada, both are present and are regulated by the national plant protection organizations (NPPOs) of each country. G. rostochiensis was first discovered in New York in the 1940s, and G. pallida was first detected in a limited area of Idaho in 2006. In Canada, G. rostochiensis and G. pallida were first detected in Newfoundland in 1962 and 1977, respectively, and further detections of G. rostochiensis occurred in British Columbia and Québec, most recently in 2006. Adherence to a stringent NPPO-agreed-upon phytosanitary program has prevented the spread of PCNs to other potato-growing areas in both countries. The successful research and regulatory PCN programs in both countries rely on a network of state, federal, university, and private industry cooperatorspursuing a common goal of containment, management/eradication, and regulation. The regulatory and research efforts of these collaborative groups spanning from the 1940s to the present are highlighted in this review.

The potato cyst nematode effector RHA1B is a ubiquitin ligase and uses two distinct mechanisms to suppress plant immune signaling.

Plant pathogens, such as bacteria, fungi, oomycetes and nematodes, rely on wide range of virulent effectors delivered into host cells to suppress plant immunity. Although phytobacterial effectors have been intensively investigated, little is known about the function of effectors of plant-parasitic nematodes, such as Globodera pallida, a cyst nematode responsible for vast losses in the potato and tomato industries. Here, we demonstrate using in vivo and in vitro ubiquitination assays the potato cyst nematode (Globodera pallida) effector RHA1B is an E3 ubiquitin ligase that employs multiple host plant E2 ubiquitin conjugation enzymes to catalyze ubiquitination. RHA1B was able to suppress effector-triggered immunity (ETI), as manifested by suppression of hypersensitive response (HR) mediated by a broad range of nucleotide-binding leucine-rich repeat (NB-LRR) immune receptors, presumably via E3-dependent degradation of the NB-LRR receptors. RHA1B also blocked the flg22-triggered expression of Acre31 and WRKY22, marker genes of pathogen‐associated molecular pattern (PAMP)‐triggered immunity (PTI), but this did not require the E3 activity of RHA1B. Moreover, transgenic potato overexpressing the RHA1B transgene exhibited enhanced susceptibility to G. pallida. Thus, our data suggest RHA1B facilitates nematode parasitism not only by triggering degradation of NB-LRR immune receptors to block ETI signaling but also by suppressing PTI signaling via an as yet unknown E3-independent mechanism.

Mapping the H2 resistance effective against Globodera pallida pathotype Pa1 in tetraploid potato

Key messageThe nematode resistance gene H2 was mapped to the distal end of chromosome 5 in tetraploid potato.The H2 resistance gene, introduced into cultivated potatoes from the wild diploid species Solanum multidissectum, confers a high level of resistance to the Pa1 pathotype of the potato cyst nematode Globodera pallida. A cross between tetraploid H2-containing breeding clone P55/7 and susceptible potato variety Picasso yielded an F1 population that segregated approximately 1:1 for the resistance phenotype, which is consistent with a single dominant gene in a simplex configuration. Using genome reduction methodologies RenSeq and GenSeq, the segregating F1 population enabled the genetic characterisation of the resistance through a bulked segregant analysis. A diagnostic RenSeq analysis of the parents confirmed that the resistance in P55/7 cannot be explained by previously characterised resistance genes. Only the variety Picasso contained functionally characterised disease resistance genes Rpi-R1, Rpi-R3a, Rpi-R3b variant, Gpa2 and Rx, which was independently confirmed through effector vacuum infiltration assays. RenSeq and GenSeq independently identified sequence polymorphisms linked to the H2 resistance on the top end of potato chromosome 5. Allele-specific KASP markers further defined the locus containing the H2 gene to a 4.7 Mb interval on the distal short arm of potato chromosome 5 and to positions that correspond to 1.4 MB and 6.1 MB in the potato reference genome.

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.

Effect of the trap crop, Solanum sisymbriifolium, on Globodera pallida, Globodera tabacum, and Globodera ellingtonae.

The effect of the nematode trap crop Solanum sisymbriifolium was assessed against three Globodera spp., the potato cyst nematode Globodera pallida (in Idaho), the recently described Globodera ellingtonae (in Oregon), and the tobacco cyst nematode Globodera tabacum (in Connecticut) in field trials. At all locations the ability of S. sisymbriifolium to reduce Globodera encysted second-stage juveniles (J2) in egg densities compared to fallow was considered. For G. ellingtonae, the impact of planting and termination dates of S. sisymbriifolium on final egg densities was also evaluated; and for G. pallida, the ability of the nematode to reproduce on potato (Solanum tuberosum) after exposure to S. sisymbriifolium was determined. Encysted J2 in egg densities of all three Globodera spp. declined from 25 to 68% after trap cropping with S. sisymbriifolium. For G. pallida, S. sisymbriifolium reduced final encysted J2 in egg density by 23 to 50% compared to the fallow treatment, and significantly decreased G. pallida reproduction on potato after exposure to S. sisymbriifolium by 99 to 100% compared to the fallow treatment (P < 0.0001). For G. ellingtonae, the planting date of S. sisymbriifolium in May or June did not impact final egg densities (P = 0.32). Rather, percentage reduction in G. ellingtonae encysted J2 in egg density was most influenced by the length of time to which nematodes were exposed to S. sisymbriifolium, with 30 and 81% reduction after 6 vs 12 wk of exposure, respectively (P < 0.0001). Similar levels of nematode reduction after S. sisymbriifolium were observed for G. tabacum after 12 to 14 wk of exposure to the trap crop; G. tabacum density changes consisted of a 114% increase after susceptible tobacco, a 65% decrease after resistant tobacco, and an 88% decrease after S. sisymbriifolium compared to bare soil. In conclusion, this research demonstrates the widespread applicability of S. sisymbriifolium in reducing a diversity of Globodera spp. present in the USA.

First Report of Potato Cyst Nematode Globodera pallida Infecting Potato (Solanum tuberosum) in Kenya

The potato cyst nematodes (PCN) Globodera pallida (Stone, 1973) and G. rostochiensis are key pests of potato, subject to strict quarantine regulations worldwide (EPPO 2013a). Indigenous to South America, they have spread to numerous potato-growing regions around the world. G. rostochiensis was reported from Kenya in 2015 (Mwangi et al. 2015). During a nationwide survey conducted in 2016, G. pallida was detected in Kenya at an altitude of 2,349 m above sea level in Nyandarua County (0.3150195° N, 36.48328° E). Cysts were extracted from a 200 cm³ soil sample following EPPO diagnostic protocol (EPPO 2013a), and then handpicked under a stereo microscope. The PCNs recovered showed morphometric characteristics of G. pallida and are reported here. For further studies, the Nyandarua field was resampled in February 2017 to collect additional soil samples and confirm the occurrence of G. pallida. From the collected cysts, 10 cysts were inoculated on potato (Solanum tuberosum L.) ʻShangiʼ in five pots with sterile soil and sand (1:1) and grown in a screenhouse for 3 months from May to July 2017; the multiplication rate at harvest was X― = 3.6 and PCNs were recovered from potato roots and soil. Morphometric characters showed: Granek’s ratio (n = 33) ranged from 1.53 to 4.52 µm (X― = 2.78 ± 0.78 µm), and the distance from anus to vulval basin was 34.03 to 91.45 µm (X― = 52.75 ± 13.73 µm). The stylet length of the second-stage juveniles (J2s) (n = 97) ranged from 15.87 to 25.18 µm (X― = 21.87 ± 1.43), stylet knobs displayed robust tulip/anchored shape. The lengths of the hyaline tail (HT) and the true tail (TT) ranged from 15.54 to 50.44 µm (X― = 23.94 ± 4.23) and 31.02 to 79.59 µm (X― = 50.64 ± 5.71 µm), respectively. Body length (n = 40) fluctuated from 338.41 to 468.34 µm (X― = 432.23 ± 24.95). DNA amplification was performed from 14 cysts and 25 J2s using the multiplex-PCR method adapted from Bulman and Marshall (1997) and the ITS1-5.8S-ITS2 regions (Tirchi et al. 2016). PCR cycling parameters were adjusted to a 5-min initial denaturation phase and 37 PCR cycles for multiplex-PCR (EPPO 2013b). The species-specific primers ITS5/PITSp4 for G. pallida (265 bp) and AB28/TW81 primers (1,188 bp) were used to amplify the small subunit of the 18s ribosomal RNA and the ITS region, respectively; PCR-amplicons were purified using the QIAquick PCR Purification Kit (Qiagen, U.S.A.) and the DNA sequences were manually edited using BioEdit Sequence Alignment Editor; in silico analyses were conducted with the NCBI-BLAST tool. The Kenyan ITS5/PITSp4 sequences (NCBI accession no. MG309873) presented 100% similarity to the G. pallida isolates KJ409623.1 and AF016869 (score = 481; E value = 5.02e⁻¹³²), while the Kenyan AB28/TW81 sequence (NCBI accession no. MG309920) showed 95 and 94% similarity to the G. pallida isolates HF583248.1 and HQ670272.1 (score = 1,218 and 1,221; E value = 0), respectively. This first report of G. pallida in sub-Saharan Africa has paramount phytosanitary and regulatory implications for potato growers and traders, national extension services, and policy makers in Kenya and the surrounding region.

A Spatial Analysis of the Potato Cyst Nematode Globodera pallida in Idaho.

The potato cyst nematode Globodera pallida is a globally regulated and quarantine potato pest. It was detected for the first time in the United States in the state of Idaho in 2006. A spatial analysis was performed to (i) understand the spatial arrangement of fields infested with G. pallida in southern Idaho using spatial point pattern analysis, and (ii) evaluate the potential threat of G. pallida for entry to new areas using spatial interpolation techniques. Data point locations, cyst numbers and egg viability values for each infested field were collected by USDA-APHIS during 2006 to 2014. Results showed the presence of spatially clustered fields infested with G. pallida (P = 0.003). We determined that the spread of G. pallida grew in diameter from the original center of infestation toward the southwest as an ellipsoidal-shaped cluster. Based on the aggregated spatial pattern of distribution, we determined that G. pallida spread followed a contagion effect scenario, where nearby infested fields contributed to the infestation of new fields, probably through soil contaminated agricultural equipment or tubers. We determined that the presence of G. pallida in southern Idaho is unlikely to be associated with new introductions from outside the state of Idaho. The aggregation pattern of fields infested with G. pallida, with an average of 4,263 cysts/ha and egg viability of 25%, facilitates quarantine activities and confines the propagation of this pest to a small area, which in 2017 was estimated to be 1,233 ha. The tools and methods provided in this study facilitate comprehensive approaches to improve G. pallida control and eradication programs as well as to raise public awareness of the problems surrounding this economically important potato pest.

Duplication of hsp-110 Is Implicated in Differential Success of Globodera Species under Climate Change.

Managing the emergence and spread of crop pests and pathogens is essential for global food security. Understanding how organisms have adapted to their native climate is key to predicting the impact of climate change. The potato cyst nematodes Globodera pallida and G. rostochiensis are economically important plant pathogens that cause yield losses of up to 50% in potato. The two species have different thermal optima that may relate to differences in the altitude of their regions of origin in the Andes. Here, we demonstrate that juveniles of G. pallida are less able to recover from heat stress than those of G. rostochiensis. Genome-wide analysis revealed that while both Globodera species respond to heat stress by induction of various protective heat-inducible genes, G. pallida experiences heat stress at lower temperatures. We use C. elegans as a model to demonstrate the dependence of the heat stress response on expression of Heat Shock Factor-1 (HSF-1). Moreover, we show that hsp-110 is induced by heat stress in G. rostochiensis, but not in the less thermotolerant G. pallida. Sequence analysis revealed that this gene and its promoter was duplicated in G. rostochiensis and acquired thermoregulatory properties. We show that hsp-110 is required for recovery from acute thermal stress in both C. elegans and in G. rostochiensis. Our findings point towards an underlying molecular mechanism that allows the differential expansion of one species relative to another closely related species under current climate change scenarios. Similar mechanisms may be true of other invertebrate species with pest status.

Phenotypic and Genomic Modifications Associated with Globodera pallida Adaptation to Potato Resistances

Studying phenotypic and genomic modifications associated with pathogen adaptation to resistance is a crucial step to better understand and anticipate resistance breakdown. This short review summarizes recent results obtained using experimentally evolved populations of the potato cyst nematode Globodera pallida. In a first step, the variability of resistance durability was explored in four different potato genotypes carrying the resistance quantitative trait loci (QTL) GpaVvrn originating from Solanum vernei but differing by their genetic background. The consequences of the adaptation to resistance in terms of local adaptation, cross-virulence and virulence cost were then investigated. Finally, a genome scan approach was performed in order to identify the genomic regions involved in this adaptation. Results showed that nematode populations were able to adapt to the QTL GpaVvrn, and that the plant genetic background has a strong impact on resistance durability. A trade-off between the adaptations to different resistant potato genotypes was detected, and we also showed that adaptation to the resistance QTL GpaVvrn from S. vernei did not allow adaptation to the colinear locus from S. sparsipilum (GpaVspl). Unexpectedly, the adaptation to resistance led to an increase of virulent individual’s fitness on a susceptible host. Moreover, the genome scan approach allowed the highlighting of candidate genomic regions involved in adaptation to host plant resistance. This review shows that experimental evolution is an interesting tool to anticipate the adaptation of pathogen populations and could be very useful for identifying durable strategies for resistance deployment.

Potato resistance to quarantine diseases

The causal agent of potato wart Synchytrium endobioticum (Schilb.) Perc. and golden potato cyst nematode (GPCN) Globodera rostochiensis (Wollenweber) Behrens are the quarantine species causing the most widespread and destructive diseases of potato in the Russian Federation and other countries. The pale potato cyst nematode Globodera pallida (Stone) Behrens is not found in Russia, although in the European Union it is found everywhere. This review provides information on the harmfulness of S. endobioticum and GPCN. To date, 43 pathotypes of S. endobioticum and 5 pathotypes of GPCN have been revealed in the world. In the Russian Federation, only the first (D1) pathotype of potato wart and pathotype Ro1 of GPCN have been found. Modern sets of differentials for S. endobioticum and GPCN and methods to determine the pathotype composition, including efforts to develop molecular markers (SSRs) to determine the race of S. endobioticum, are presented. The data on the resistance of commercial potato cultivars to these quarantine diseases and methods to determine resistance against them are reviewed. The modern data on the genetics of potato resistance to S. endobioticum, G. rostochiensis, and G. pallida, including mapping and cloning R-genes, are presented. The available published data on the molecular markers of R-genes for marker-assisted selection (MAS) and the evaluation of their effectiveness are presented. The use of multiplex systems allows the presence of several resistance genes to one or more pathogens to be analyzed at the same time. Mechanisms of potato’s quantitative resistance to S. endobioticum and GPCN and adaptation processes in pathogen populations resulting in overcoming the resistance of the host are discussed. The cultivation of varieties poorly susceptible to GPCN can stimulate the adaptive variability of the pathogen and induce virulent pathotypes for two or three pathogen generations.

Haloacetophenones as newly potent nematicides against Meloidogyne incognita

Acetophenones are a class of aromatic compounds frequently produced by plants as a response to a stress or as a protection reaction against parasites or herbivors. In the present research, we investigated the role of the carbonyl moiety in a series of commercially available aromatic ketones tested for their nematicidal activity against the root-knot nematode Meloidogyne incognita (Kofoid et White) Chitwood. Interestingly, we found that the presence of electron withdrawing groups onto the aromatic ring were highly efficient in inducing nematode paralysis and death (EC50/24h between 2.5 and 54.8mg/L and EC50/72h between 2.3 and 65.6mg/L, respectively). Moreover, a chlorine atom in α-position to the carbonyl functionality emerged as a key residue in improving acetophenones activity. In this paper, the nematicidal ability of a series of differently substituted acetophenones is reported and the preliminary structure-activity relationship studies are also discussed. We also performed an in vitro GC–MS metabolomics analysis on the potato cyst nematode Globodera pallida, after treatment with 2,4′-dichloroacetophenone (6) at 100mg/L for 24h. The 1-dodecanol and talose were evidenced as the main upregulated metabolites, suggesting a possible V-ATPase dysfunction.

Use of GFP-tagged Trichoderma harzianum as a tool to study the biological control of the potato cyst nematode Globodera pallida

The fungus Trichoderma harzianum strain ThzID1-M3 isolated in the Palouse region of the state of Idaho and transformed to express green fluorescent protein (GFP) was used as a biomarker to study the biological control processes of the potato cyst nematode Globodera pallida. Experiments were conducted to evaluate the effect of T. harzianum ThzID1-M3 on G. pallida infection and reproduction at 45 and 75days after inoculation respectively; and to observe, through microscopy rhizosphere chamber, the colonization of G. pallida second-stage juveniles and potato rhizoplane by T. harzianum ThzID1-M3 10days after inoculation. Significant reduction of G. pallida infection in potato roots was observed when soil was amended with T. harzianum ThzID1-M3. Globodera pallida cysts recovered from soil and G. pallida reproduction rate were significantly reduced by 49% and 60% respectively, when soil was amended with T. harzianum ThzID1-M3 compared to the non-amended soil. Microscopic observations showed that T. harzianum ThzID1-M3 colonized G. pallida second-stage juveniles and cysts, and proliferated in the rhizoplane and rhizosphere of potato. To our knowledge, this is the first report on the study of Trichoderma spp. marked with GFP against a potato cyst nematode. The use of GFP-tagged T. harzianum has the potential to monitor the biological control processes of G. pallida and the tools advanced in this study should facilitate the design of novel strategies to control this economically important nematode pest of potato.

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.

Nematode neuropeptides as transgenic nematicides.

Plant parasitic nematodes (PPNs) seriously threaten global food security. Conventionally an integrated approach to PPN management has relied heavily on carbamate, organophosphate and fumigant nematicides which are now being withdrawn over environmental health and safety concerns. This progressive withdrawal has left a significant shortcoming in our ability to manage these economically important parasites, and highlights the need for novel and robust control methods. Nematodes can assimilate exogenous peptides through retrograde transport along the chemosensory amphid neurons. Peptides can accumulate within cells of the central nerve ring and can elicit physiological effects when released to interact with receptors on adjoining cells. We have profiled bioactive neuropeptides from the neuropeptide-like protein (NLP) family of PPNs as novel nematicides, and have identified numerous discrete NLPs that negatively impact chemosensation, host invasion and stylet thrusting of the root knot nematode Meloidogyne incognita and the potato cyst nematode Globodera pallida. Transgenic secretion of these peptides from the rhizobacterium, Bacillus subtilis, and the terrestrial microalgae Chlamydomonas reinhardtii reduce tomato infection levels by up to 90% when compared with controls. These data pave the way for the exploitation of nematode neuropeptides as a novel class of plant protective nematicide, using novel non-food transgenic delivery systems which could be deployed on farmer-preferred cultivars.

Progressive metabolic impairment underlies the novel nematicidal action of fluensulfone on the potato cyst nematode Globodera pallida

BackgroundFluensulfone is a new nematicide with an excellent profile of selective toxicity against plant parasitic nematodes. Here, its effects on the physiology and biochemistry of the potato cyst nematode Globodera pallida have been investigated and comparisons made with its effect on the life-span of the free-living nematode Caenorhabditis elegans to provide insight into its mode of action and its selective toxicity. ResultsFluensulfone exerts acute effects (≤1h; ≥100μM) on stylet thrusting and motility of hatched second stage G. pallida juveniles (J2s). Chronic exposure to lower concentrations of fluensulfone (≥3days; ≤30μM), reveals a slowly developing metabolic insult in which G. pallida J2s sequentially exhibit a reduction in motility, loss of a metabolic marker for cell viability, high lipid content and tissue degeneration prior to death. These effects are absent in adults and dauers of the model genetic nematode Caenorhabditis elegans. ConclusionThe nematicidal action of fluensulfone follows a time-course which progresses from an early impact on motility through to an accumulating metabolic impairment, an inability to access lipid stores and death.

Validation of potato cyst nematode resistant genotypes through molecular markers

Forty-two potato genotypes exhibiting phenotypic resistance against Potato Cyst Nematode (PCN) species Globodera rostochiensis (golden) and Globodera pallida (white) were screened for molecular validation using tightly linked genetic DNA markers. H1 and GroV1 gene conferring resistance against golden nematodes were validated by TG 689 & 57R and X02 markers, respectively. Similarly, resistance against Globodera pallida governed by QTL GpaVvrn and QTLs Gpa5, Gpa6, was confirmed by corresponding markers HC and SPUD1636. On the basis of phenotypic and genotypic confirmation, this study identifies CP 1843, 1879 and JEX/A 267 as elite potato genotypes that can be utilized as parental lines for introgression of resistant genes against both PCN species.

Consistent action of two partially effective loci conferring resistance to Globodera pallida Pa2/3 across multiple nematode field populations

The potato cyst nematodes (PCN) Globodera rostochiensis and Globodera pallida are significant pests of potatoes worldwide. The most effective control methods are crop rotation and the deployment of resistant varieties. Complete resistance to G. rostochiensis based on a single resistance gene has successfully been integrated into many varieties. However, resistance to G. pallida has not been as successful to date, with current varieties only exhibiting partial resistance. Combining partially effective quantitative trait loci (QTLs) for resistance can increase the strength and breadth of the resistance. An additive effect on resistance has previously been demonstrated on combining two QTLs from Solanum tuberosum subsp. andigena (GpaIVsadg) and Solanum vernei (Gpa5). However, populations of G. pallida can be quite divergent and it was unclear whether the relative effects of the individual QTLs and the combined additive effect would be consistent across different G. pallida Pa2/3 populations. Using a mapping population segregating for both QTLs, the effect of the QTLs individually and combined was examined on four UK‐derived field populations of G. pallida pathotype Pa2/3, and the relative effects of the individual QTLs and the additive effect of the combination found to be consistent across all populations.