Potato Cyst Nematode Globodera Rostochiensis Research Articles

Alternative splicing: A novel mechanism of regulation identified in the chorismate mutase gene of the potato cyst nematode Globodera rostochiensis

Chorismate mutase (CM) secreted from the stylet of plant–parasitic nematodes plays an important role in plant parasitism. We isolated and characterized a new nematode CM gene ( Gr-cm-1) from the potato cyst nematode, Globodera rostochiensis. The Gr-cm-1 gene was found to exist in the nematode genome as a single-copy gene that has two different alleles, Gr-cm-1A and Gr-cm-1B, both of which could give rise to two different mRNA transcripts of Gr-cm-1 and Gr-cm-1-IRII. In situ mRNA hybridization showed that the Gr-cm-1 gene was exclusively expressed within the subventral oesophageal gland cells of the nematode. Gr-cm-1 was demonstrated to encode a functional CM (GR-CM-1) potentially having a dimeric structure as the secreted bacterial *AroQ CMs. Gr-cm-1-IRII, generated by retention of intron 2 of the Gr-cm-1 pre-mRNA through alternative splicing (AS), would encode a truncated protein (GR-CM-1t) lacking the CM domain with no CM activity. The quantitative real-time reverse transcription-PCR assay revealed that splicing of the Gr-cm-1 gene was developmentally regulated; Gr-cm-1 was up-regulated whereas Gr-cm-1-IRII was down-regulated in early nematode parasitic stages compared to the preparasitic juvenile stage. Low-temperature SDS-PAGE analysis revealed that GR-CM-1 could form homodimers when expressed in Escherichia coli and the dimerization domain was retained in the truncated GR-CM-1t protein. The specific interaction between the two proteins was demonstrated in yeast. Our data suggested that the novel splice variant might function as a dominant negative isoform through heterodimerization with the full-length GR-CM-1 protein and that AS may represent an important mechanism for regulating CM activity during nematode parasitism.

Expression of Two Functionally Distinct Plant Endo-β-1,4-Glucanases Is Essential for the Compatible Interaction Between Potato Cyst Nematode and Its Hosts

For the proliferation of their feeding sites (syncytia), the potato cyst nematode Globodera rostochiensis is thought to recruit plant endo-beta-1,4-glucanases (EGases, EC. 3.2.1.4). Reverse-transcription polymerase chain reaction experiments on tomato (Solanum lycopersicum) indicated that the expression of two out of the at least eight EGases, namely Sl-cel7 and Sl-cel9C1, is specifically upregulated during syncytium formation. In situ hybridization and immunodetection studies demonstrated that both EGases are specifically expressed inside and adjacent to proliferating syncytia. To assess the importance of Sl-cel7 and Sl-cel9C1 for nematode development, we decided to knock them out individually. Sl-cel9C1 probably is the only class C EGase in tomato, and we were unable to regenerate Sl-cel9C1-silenced plants. Potato (S. tuberosum), a close relative of tomato, harbors at least two class C EGases, and St-cel7-or St-cel9C1-silenced potato plants showed no obvious aberrant phenotype. Infection with potato cyst nematodes resulted in a severe reduction of the number of adult females (up to 60%) and a sharp increase in the fraction of females without eggs (up to 89%). Hence, the recruitment of CEL7, an enzyme that uses xyloglucan and noncrystalline cellulose as natural substrates, and CEL9C1, an enzyme that uses crystalline cellulose, is essential for growth and development of potato cyst nematodes.

THE INFLUENCE OF POTATO CYST NEMATODE G. ROSTOCHIENSIS INFESTATION ON DIFFERENT POTATO CULTIVARS

The potato cyst nematode Globodera rostochiensis is one of the most serious pests of potato in Slovenia. Precise nematode identification and knowledge about potato cultivars, which are most suitable for growing in the Slovenian climate conditions and most resistant to G. rostochiensis, are necessary to develop an effective integrated pest control. Here we report the results of the influence of G. rostochiensis pathotype Ro1/4 on the yield of different potato cultivars: the susceptible cultivar Desiree, the resistant cultivars White Lady, Miranda, Aladin, Sante and Adora, and the clone KIS 94-1/5-14. The yield of cv. White Lady was the highest and that of susceptible cv. Desiree the lowest. The influence of several resistant and one susceptible potato cultivars on population dynamics of G. rostochiensis was also determined. The total number of cysts/100 cm3 and the number of eggs and juveniles per cyst increased in the susceptible cv. Desiree and decreased in the resistant cultivars White Lady, Sante and Adora.

Genetic variability and differentiation of three Russian populations of potato cyst nematode Globodera rostochiensis as revealed by nuclear markers

Genetic variability of yellow potato cyst nematode G. rostochiensis from three Russian populations (Karelia, Vladimir oblast, and Moscow oblast) was investigated using two types of nuclear markers. Using RAPD markers identified with the help of six random primers (P-29, OPA-10, OPT-14, OPA-11, OPB-11, and OPH-20), it was possible to distinguish Karelian population from the group consisting of the populations from two adjacent regions (Moscow oblast and Vladimir oblast). Based on the combined matrix, containing 294 RAPD fragments, dendrogram of genetic differences was constructed, and the indices of genetic divergence and partition (P, H, and G(st)), as well as the gene flow indices N(m) between the nematode samples examined, were calculated. The dendrogram structure, genetic diversity indices, and variations of genetic distances between single individuals in each population from Karelia and Central Russia pointed to genetic isolation and higher genetic diversity of the nematodes from Karelia. Based on polymorphism of rDNA first intergenic spacer ITS1, attribution of all populations examined to the species G. rostochiensis was proved. Small variations of the ITS1 sequence in different geographic populations of nematodes from different regions of the species world range did not allow isolation of separate groups within the species. Possible factors (including interregional transportations of seed potato) affecting nematode population structure in Russia are discussed.

The Canon of Potato Science: 14. Cyst Nematodes

Cyst forming nematodes, or cyst nematodes, are one of the most specialized and successful plant-parasitic nematode pests of agriculture. The nematodes have a very narrow host range, which is opposite to root-knot nematodes which are polyphagous. In the case of potato, only the potato cyst nematodes (PCN) Globodera rostochiensis and G. pallida are able to infest the plants. The nematodes originate from South America, were introduced into Europe along with the potato tubers around 1600, and belong to the family Heteroderidae, genus Globodera. The life cycle of cyst nematodes is well adapted to the host and cyst nematodes can survive in various environments. The cyst, the dead body wall of the female, contains the eggs. The eggs hatch in the presence of the host, hatching being triggered by exudates from the host roots. Root exudates from Solanaceae, such as potato, tomato and woody nightshade (bitter sweet), activate these juveniles and can − under suitable environmental conditions − cause up to 80% of the nematodes to hatch. The juveniles enter the roots near the root tip and induce, by injecting saliva, a feeding cell or syncytial “transfer cell”. The juveniles become sedate and feed from the syncytia, until their development is complete after four moulds. After the 4th mould the female is round and swollen and protrudes from the root. The males are slender, leave the roots, mate and fertilize the females. After mating the female forms eggs and when the female dies, the cuticle tans to form a protective cyst with 200−500 eggs within. The life cycle is now complete and the whole cycle may take up to three months. The cyst falls of the root, waiting for the next suitable host plant. Cysts have the size of small pinheads and the juveniles are 0.5 mm long, so it is not the size but the number of nematodes that cause the damage. Infested plants show retarded growth and heavily infested fields normally show badly growing patches, especially under dry conditions. Potato yield can be decreased by up to 50%. Potato Research (2007) 50:259–262 DOI 10.1007/s11540-008-9076-3

Structural and functional characterization of a novel, host penetration‐related pectate lyase from the potato cyst nematode Globodera rostochiensis

SUMMARY The cell wall, a strong extraprotoplasmic layer surrounding plant cells that mainly consists of a variety of polysaccharides, constitutes a major barrier for potential parasites. Plant-parasitic nematodes are well equipped to overcome this barrier as they produce and secrete cell-wall-degrading enzymes. Expression profiling of various life stages of the potato cyst nematode Globodera rostochiensis revealed a novel pectate lyase gene (Gr-pel2, 759 bp). The Gr-PEL2 protein showed highest similarity to pectate lyases from the facultative plant-parasitic nematodes Bursaphelenchus mucronatus and B. xylophilus and the soil-inhabiting saprophytic Streptomyces and Frankia species (i.e. 40-42% identity and 58-60% similarity), whereas only a remote relatedness to the previously identified Gr-PEL1 was observed (i.e. 28% identity and 43% similarity). Transient expression of Gr-pel2 in leaves of Nicotiana benthamiana resulted in severe malformations of the infiltrated tissues, not relating to maceration and soft rot symptoms. Ca(2+) is known to be essential for pectate lyase activity, and the most likely calcium-binding site was identified in the Gr-PEL2 protein by combining homology modelling of the three-dimensional structure, site-directed mutagenesis and transient expression in leaves. A highly charged cleft in Gr-PEL2, which is likely to be involved in substrate binding and which is also significantly more hydrophobic in Gr-PEL1, was shown to be essential for protein activity. Our results underline the broad spectrum of pectate lyases and cell-wall-degrading enzymes necessary for successful parasitism by cyst nematodes.

Immunomodulating effect of elicitors and suppressors upon infection of potato with Globodera rostochiensis (Wollenweber, 1923) Beherens, 1975

Potato cyst nematode (PCN) Globodera rostochiensis is classified with the most dangerous and economically significant pathogens of the family Solanaceae. This nematode decreases the yield of potato (to 60%), worsens the quality and marketable condition of tubers, as well as enables potato infection with other diseases. Potato cyst nematode is a sedentary endoparasite of potato roots, fighting with which is hampered due to the good adaptation of the parasite to environmental conditions, long (10 to 15 years) lifespan of cysts in the absence of the host plant, and the threat of occurrence of aggressive pathotypes in the case of introduction of nematode-resistant potato cultivars in a monoculture. With regard for these facts, the method of resistance induction using elicitors is of special interest in terms of protecting potato from G. rostochiensis [1]. The first works indicating the possibility of application of elicitors for stimulation of plant resistance to phytohelminths were performed at the Institute of Parasitology, Russian Academy of Sciences, and the Bach Institute of Biochemistry, Russian Academy of Sciences. Those studies were performed with tomatoes infected with the cotton root-knot nematode Meloidogyne incognita [2, 3]. An increase in immune potential, induced by treatment with elicitors, resulted in a pronounced stimulation of growth and development of tomatoes, suppression of the severity of damage of roots by the nematodes, and caused changes in the morphophysiological and populational parameters of the parasite. The goal of this study was to investigate the effect of immunomodulators in the potato‐ G. rostochiensis system. A low-molecular-weight soluble chitosan with an average molecular weight of 5 kDa and acetylation degree of 15% [4] was used as an elicitor. Laminarin (Sigma, United States), a β -1,3-glucan with single side β -1,6 -bonds, was used as an immunosuppressant. Chitosan was used at a concentration of 100 µ g/ml; laminarin, 300 µ g/ml (this concentration was used in our previous studies). This study was performed with four potato cultivars: Krinitsa (PCN-resistant), Istrinskii (resistance to PCN is not determined), Superior (PCN-sensitive), as well as the transgenic potato carrying the ∆ -endotoxin gene from Bacillus thuringiensis var. tenebrionsis (Bt). The latter cultivar, resistant to the Colorado beetle, was obtained from cultivar Superior (Monsanto, United States). Before planting, potato tubers were treated with aqueous solutions of the immunomodulators at the specified concentrations. The control tubers were treated with water. Tubers were planted in 500-ml containers. On the fourth day after planting, soil was infested with a suspension of nematode larvae (10000 parasites per plant) as described earlier [5]. The experiment was performed in ten replicates. The degree of potato infection and the effect of immunosuppressants were assessed three months after planting. For this purpose, the number of cysts in soil, their size, and the number of eggs contained in them, as well as the weight of tubers of the new harvest were determined.

The occurrence and distribution of potato cyst nematodes in Croatia

Potato cyst nematodes (PCN) Globodera rostochiensis (Wollenweber, 1923) Behrens, 1975 and Globodera pallida (Stone, 1973) Behrens, 1975 are the most troublesome pests of potatoes worldwide. Since 1968 there have been no investigations of the presence of PCN in ware potato lands in Croatia although these pests were recognised as an A1 plant-health quarantine species. After the first discovery of G. rostochiensis in the locality of Belica (Medjimurska County) in 2001, intensive monitoring of the distribution of PCN in Croatia started. In 2001 G. rostochiensis was detected in 55% of soil samples taken in ware potato lands. In 2002 G. rostochiensis was detected in 4.1% of soil samples and in 0.08% of soil samples in mixed populations with G. pallida. The pathotype Ro1 was found in all tested populations and Ro1 and Pa 2/3 were detected in populations from localities Vidovec, Ivanovec and Sivice. In 2003 G. rostochiensis was detected in 1.03% of soil samples, and also in 12.8% of soil samples collected in 2004. In 2003 cysts of G. rostochiensis were detected in several seed potato fields. These results indicate the urgent need for the application of further control measures to determine the presence and distribution of PCN in ware and seed potato lands in Croatia, in order to prevent the spread of PCN to non-infested areas. Integrated management strategies, neglected until 2001, have now been implemented and will prevent the build-up of infestation and replace the previous practices of monoculture, the use of short rotations and growing susceptible cultivars.

Functionality of resistance gene Hero, which controls plant root‐infecting potato cyst nematodes, in leaves of tomato

The expression of host genomes is modified locally by root endoparasitic nematode secretions to induce the development of complex cellular structures referred as feeding sites. In compatible interactions, the feeding sites provide the environment and nutrients for the completion of the nematode's life cycle, whereas in an incompatible (resistant) interaction, the host immune system triggers a plant cell death programme, often in the form of a hypersensitive reaction, which restricts nematode reproduction. These processes have been studied in great detail in organ tissues normally infected by these nematodes: the roots. Here we show that host leaves can support a similar set of programmed developmental events in the potato cyst nematode Globodera rostochiensis life cycle that are typical of the root-invading nematodes. We also show that a gene-for-gene type specific disease resistance that is effective against potato cyst nematodes (PCN) in roots also operates in leaves: the expression of the resistance (R) gene Hero and members of its gene family in leaves correlates with the elicitation of a hypersensitive response only during the incompatible interaction. These findings, and the ability to isolate RNA from relevant parasitic stages of the nematode, may have significant implications for the identification of nematode factors involved in incompatible interactions.

Fate of the Potato Cyst Nematode Globodera rostochiensis During Composting

Effects of composting on survival and reproduction of the potato cyst nematode (PCN) Globodera rostochiensis were investigated in 150-liter pilot scale reactors. Small bags containing cysts of PCN were incubated in organic waste and composted for 8, 15 or 29 days. Temperatures in the areas close to the cyst bags were monitored. Survival, measured by hatching, was reduced by 99.9% already after 8 days of composting and at 29 days no hatching was recorded. A few eggs, however, still hatched after being composted for 15 days and exposed to temperatures higher than 60°C for several days. Maximal temperatures and thermal exposure time as such could not explain the hatching pattern of PCN, so other factors are likely to be involved in causing lethality. PCN failed to reproduce after 8 days of composting with temperatures reaching a minimum of 50°C during the period. Hence, eight days of composting where all material have reached a temperature of minimum 50°C during the period, could be regarded as a satisfactory method for sanitation of PCN.

Interactions Between the Potato Cyst Nematode Globodera rostochiensis and Diseases Caused by Rhizoctonia solani AG3 in Potatoes Under Field Conditions

Findings from 2 years of field experiments investigating the relationship between Globodera rostochiensis and Rhizoctonia solani on unique field sites are reported. In 2000, a field experiment was positioned on land that had previously been used for experimental work investigating integrated potato cyst nematode (PCN) management methods. This study had produced an ‘untypical’ mosaic of PCN population densities ranging from 5 to 221 eggs g−1 soil. In 2001, the field experiment was conducted on a different field site and overlaid on a focus of G. rostochiensis population densities ranging from 11 to 108 eggs g−1 soil. In each experiment, potatoes (cv. Desiree) were grown in plots with similar population densities of G. rostochiensis that were either uninoculated or inoculated with R. solani. A series of potato plant harvests were undertaken to investigate the effects of nematode infestation on the incidence and severity of R. solani diseases and the associated development of plants. In both experiments, a clear relationship was found between the density of G. rostochiensis juveniles present in potato roots and the incidence of stolons infected by R. solani, 6 weeks after planting. For the first time this interaction has been determined under field conditions. The results of the study suggest that the interaction between nematode and fungus is indirect and possible mechanisms are discussed.

Functional Analysis of Pathogenicity Proteins of the Potato Cyst Nematode Globodera rostochiensis Using RNAi

RNA interference (RNAi) has been used widely as a tool for examining gene function and a method that allows its use with plant-parasitic nematodes recently has been described. Here, we use a modified method to analyze the function of secreted beta-1,4, endoglucanases of the potato cyst nematode Globodera rostochiensis, the first in vivo functional analysis of a pathogenicity protein of a plant-parasitic nematode. Knockout of the beta-1,4, endoglucanases reduced the ability of the nematodes to invade roots. We also use RNAi to show that gr-ams-1, a secreted protein of the main sense organs (the amphids), is essential for host location.

Origin, distribution and 3D-modeling of Gr-EXPB1, an expansin from the potato cyst nematode Globodera rostochiensis

Southern analysis showed that Gr-EXPB1, a functional expansin from the potato cyst nematode Globodera rostochiensis, is member of a multigene family, and EST data suggest expansins to be present in other plant parasitic nematodes as well. Homology modeling predicted that Gr-EXPB1 domain 1 (D1) has a flat β-barrel structure with surface-exposed aromatic rings, whereas the 3D structure of Gr-EXPB1-D2 was remarkably similar to plant expansins. Gr-EXPB1 shows highest sequence similarity to two extracellular proteins from saprophytic soil-inhabiting Actinobacteria, and includes a bacterial type II carbohydrate-binding module. These results support the hypothesis that a number of pathogenicity factors of cyst nematodes is of procaryotic origin and were acquired by horizontal gene transfer.

Effect of production environments on radiation interception and radiation use efficiency of potato (Solanum tuberosum) grown in Canterbury, New Zealand

Four experiments were conducted over two growing seasons during 1995/96 and 1996/97 at Lincoln University and New Zealand Institute for Crop & Food Research, Lincoln, Canterbury, to assess whether radiation interception (RI) alone is a good predictor of potato (Solanum tuberosum) total dry matter (TDM) grown under different environments. In the two field experiments production environments were altered by different rates of nitrogen application and in bag experiments, the different production environments were created with the presence of different amounts of potato cyst nematode (Globodera rostochiensis) per ml of soil. The different production environments significantly affected leaf area index (LAI), RI, radiation use efficiency (RUE), and TDM. Increased soil fertility significantly increased RI, RUE, and TDM where as the presence of potato cyst nematode significantly decreased RI, RUE, and TDM. There was a strong (P < 0.001) positive linear relationship between RUE and applied nitrogen, whereas there was a linear, negative relationship between RUE and the numbers of potato cyst nematode per ml of soil. On the basis of this study it was concluded that under different production environments both RI and RUE must be known to accurately predict the TDM of potatoes.

Study of European and Czech populations of potato cyst nematodes (Globodera rostochiensis and G. pallida) by RAPD method

Potato cyst nematodes (PCN) are the big problem in worldwide planting of potatoes and another Solanaceous plants. Identification of individual pathotypes according to international scheme is very demanding but a very important part of the phytosanitary process to control these pests. Molecular genetic identification of different plant and animal species or individuals is a very interesting way at the present time and let&amp;rsquo;s hope that it will be important in future. This report presents results of the RAPD study of nine different real PCN populations. There were five Globodera rostochiensis populations and four G. pallida populations. Pathotypes Ro2, Ro2/3, Ro4, Ro5, Pa2 and Pa3 were from European populations; population Ro1 and X were of Czech provenance. Genetics variable of these populations was described by a set of six decameric primers (OPA 07, OPG 03, OPG 05, OPG 08, OPG 10 and OPG 13). Genetic dissimilarity was by Gel Manager for Windows evaluated. Detectable differences behind all populations were found and the dendrogram was compiled. The unknown population X was sorted into group of Globodera pallida species subgroup of Pa2 consequently.

Early responses of resistant and susceptible potato roots during invasion by the potato cyst nematode Globodera rostochiensis.

Signals from roots of resistant (cv. Maris Piper) and susceptible (cv. Désirée) potato cultivars during invasion by second stage juveniles (J2s) of the potato cyst nematode, Globodera rostochiensis, were investigated. Novel experimental chambers enabled the recording of electrophysiological responses from roots during nematode invasion. The root cell membrane potentials were maintained throughout the 3 d required to assess invasion and feeding site development. The steady-state resting membrane potentials of Désirée were more negative than those of Maris Piper on day 1, but the reverse on day 3. After 5 d there was no difference between the two cultivars. Intracellular microelectrodes detected marked spike activity in roots after the application of J2s and there were distinct and reproducible differences between the two cultivars, with the response from Désirée being much greater than that from Maris Piper. The responses to mechanical stimulation of roots by blunt micropipettes and sharp electrodes were consistent and similar in both cultivars to the responses in Maris Piper obtained after nematode invasion, but could not account for the marked response found in Désirée. Exogenous application of exoenzymes, used to mimic nematode chemical secretions, resulted in a distinct depolarization pattern that, although similar in both cultivars, was different from patterns obtained during nematode invasion or mechanical stimulation. The pH of homogenates prepared from roots of both cultivars was measured and a Ca2+ channel blocker was used to assess the role of Ca2+ in nematode invasion. The results indicated a role for Ca2+ in the signalling events that occur during nematode invasion.

Glutathione peroxidases of the potato cyst nematode Globodera Rostochiensis.

We report the cloning and characterisation of full-length DNAs complementary to RNA (cDNAs) encoding two glutathione peroxidases (GpXs) from a plant parasitic nematode, the potato cyst nematode (PCN) Globodera rostochiensis. One protein has a functional signal peptide that targets the protein for secretion from animal cells while the other is predicted to be intracellular. Both genes are expressed in all parasite stages tested. The mRNA encoding the intracellular GpX is present throughout the nematode second stage juvenile and is particularly abundant in metabolically active tissues including the genital primordia. The mRNA encoding the secreted GpX is restricted to the hypodermis, the outermost cellular layer of the nematode, a location from which it is likely to be secreted to the parasite surface. Biochemical studies confirmed the secreted protein as a functional GpX and showed that, like secreted GpXs of other parasitic nematodes, it does not metabolise hydrogen peroxide but has a preference for larger hydroperoxide substrates. The intracellular protein is likely to have a role in metabolism of active oxygen species derived from internal body metabolism while the secreted protein may protect the parasite from host defences. Other functional roles for this protein are discussed.

Low Temperature–Short Duration Steaming of Soil Kills Soil-Borne Pathogens, Nematode Pests and Weeds

Agricultural soil samples containing survival structures of the fungal crop pathogens Verticillium dahliae, Sclerotinia sclerotiorum, Sclerotium cepivorum, Pythium ultimum, potato cyst nematodes Globodera rostochiensis and G. pallida and weeds Chenopodium album and Agropyron repens [Elymus repens] were treated in the laboratory with aerated steam at temperatures ranging from 40 to 80°C in a specially constructed apparatus. Steaming at 50 or 60°C for 3min, followed by an 8-min resting period in the steamed soil and immediate removal from the soil thereafter, resulted in 100% kill of all weeds, diseases and nematodes. When steamed at 45°C, there was a small but significant reduction in the survival of V. dahliae microsclerotia but no reduction in survival of S. cepivorum.

Influence of temperature on the motility of Pseudomonas oryzihabitans and control of Globodera rostochiensis

The motility and efficacy of Pseudomonas oryzihabitans as a biocontrol agent against the potato cyst nematode Globodera rostochiensis were studied with respect to temperature. The influence of soil moisture on bacterial movement was also tested. In a closed container trial, P. oryzihabitans significantly reduced invasion of second stage juveniles (J2) of G. rostochiensis in potato roots, its effect being more marked at 25 and 21 °C than at 17 °C. P. oryzihabitans motility in vitro was optimal at 26 °C and inhibited at temperatures below 18 °C. In soil, both temperature and matric potential affected bacterial movement. At 16 °C its movement and survival were suppressed, but they were unaffected at 25 °C. At both temperatures the biocontrol agent moved faster in the wetter (−0.03 MPa) than in the drier soil (−0.1 MPa). These results suggest that temperature is a key factor in determining the potential of P. oryzihabitans as a biocontrol agent.

Investigations into the chemoattraction of the potato cyst nematodes Globodera rostochiensis and G. pallida towards fractionated potato root leachate

AbstractThe behaviour of stimulated second stage juveniles (J2) (i.e., hatched in root leachate from potato cv. Cara) and unstimulated J2 (spontaneously hatched in water) of Globodera rostochiensis and G. pallida in response to fractionated and unfractionated potato root leachate (PRL) was investigated in attraction assays. In PRL, fractionated by combined ion-exchange-gel permeation chromatography on Sephadex G-10, three classes of semiochemicals with activity towards J2 were distinguished: i) chemoattractants; ii) chemostats, and iii) chemorepellents. The motility of PRL-hatched G. rostochiensis J2 in one fraction (12) at 10 days after their removal from the root leachate was significantly greater than that of water-hatched J2 apparently due to sensitisation of PRL-hatched J2. PRL-hatched J2 of G. pallida were attracted to different fractions than those of G. rostochiensis, whereas the water-hatched J2 from the two species were attracted to common fractions, indicating that sensitisation by exposure to PRL was species selective. The attraction of PRL-hatched PCN J2 to unfractionated PRL appeared to be dependent on the ratio of chemoattractant to chemorepellent semiochemicals in the leachate. For both species there was no detectable correlation between hatching activity and either attractiveness of root leachates from 12 potato genotypes or chemoattraction in PRL fractions, indicating that hatching factors were not active chemoattractants.