A high-resolution map of the <Emphasis Type="Italic">Grp1</Emphasis> locus on chromosome V of potato harbouring broad-spectrum resistance to the cyst nematode species <Emphasis Type="Italic">Globodera pallida</Emphasis> and <Emphasis Type="Italic">Globodera rostochiensis</Emphasis>

The Grp1 locus confers broad-spectrum resistance to the potato cyst nematode species Globodera pallida and Globodera rostochiensis and is located in the GP21-GP179 interval on the short arm of chromosome V of potato. A high-resolution map has been developed using the diploid mapping population RHAM026, comprising 1,536 genotypes. The flanking markers GP21 and GP179 have been used to screen the 1,536 genotypes for recombination events. Interval mapping of the resistances to G. pallida Pa2 and G. rostochiensis Ro5 resulted in two nearly identical LOD graphs with the highest LOD score just north of marker TG432. Detailed analysis of the 44 recombinant genotypes showed that G. pallida and G. rostochiensis resistance could not be separated and map to the same location between marker SPUD838 and TG432. It is suggested that the quantitative resistance to both nematode species at the Grp1 locus is mediated by one or more tightly linked R genes that might belong to the NBS-LRR class. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. A. Finkers-Tomczak and S. Danan contributed equally to this research.     

Mapping of the cyst nematode resistance locus Gpa2 in potato using a strategy based on comigrating AFLP markers

 The nematode resistance locus Gpa2 was mapped on chromosome 12 of potato using information on the genomic positions of 733 known AFLP markers. The minimum number of AFLP primer combinations required to map Gpa2 was three. This demonstrates that a reference collection of potato AFLP markers may be a valuable tool for mapping studies in potato. By use of RFLP probes, Gpa2 was more precisely mapped at the distal end of chromosome 12. Gpa2 confers resistance to a distinct group of populations of the potato cyst nematode Globodera pallida and originates from the same potato accession as locus H1, conferring resistance to pathotype Ro₁ of G. rostochiensis. This study shows that these two nematode resistance loci are unlinked and that Gpa2 is linked to the Rx1 locus conferring resistance to potato virus X. The efficiency of AFLPs for genetic mapping of a highly heterozygous crop like potato is discussed and compared with the RFLP technique. Received: 24 February 1997/Accepted: 2 May 1997     

Two additive QTLs conferring broad-spectrum resistance in potato to Globodera pallida are localized on resistance gene clusters

Broad-spectrum resistance in potato to the potato cyst nematode (PCN) is commonly regarded as a complex inherited trait. Yet, in this paper we show that, by use of a selected set of PCN test populations, broad-spectrum resistance to the species Globodera pallida can be fully ascribed to the action of two loci: Gpa5 and Gpa6. These loci were readily mapped by means of a strategy based on two steps. Firstly, the chromosomal localization of both loci was assessed by use of an online catalogue of AFLP markers covering a substantial part of the potato genome (http://www.spg.wau.nl/pv/aflp/catalog.htm). Subsequently the chromosomal regions of both loci were identified by means of CAPS markers based on RFLP insert sequences. Locus Gpa5 explains at least 61% of the genetic variation. This locus maps to chromosome 5 on a region which has previously been shown to harbor resistance factors to viral (Nb, Rx2), fungal (R1) and nematodal (Gpa, Grp1) pathogens. The Gpa6 locus exhibits a minor effect on the resistance (24%) and acts additively to Gpa5. Interestingly, the Gpa6 locus maps to a region on chromosome 9 where, in the homoeologous tomato genome, the virus resistance gene Sw-5 resides as part of a resistance gene cluster. In potato, resistance to potato virus X has been reported in the vicinity of this region. The map location of Gpa6 indicates the presence of a resistance gene cluster at the end of the long arm of chromosome 9 of potato. Received: 10 January 2000 / Accepted: 31 January 2000     

Mapping of resistance to the potato cyst nematode Globodera rostochiensis from the wild potato species Solanum vernei

A population of diploid potato (Solanum tuberosum) was used for the genetic analysis and mapping of a locus for resistance to the potato cyst nematode Globodera rostochiensis, introgressed from the wild potato species Solanum vernei. Resistance tests of 108 genotypes of a F₁ population revealed the presence of a single locus with a dominant allele for resistance to G. rostochiensis pathotype Ro1. This locus, designated GroV1, was located on chromosome 5 with RFLP markers. Fine-mapping was performed with RAPD and SCAR markers. The GroV1 locus was found in the same region of the potato genome as the S. tuberosum ssp. andigena H1 nematode resistance locus. Both resistance loci could not excluded to be allelic. The identification of markers flanking the GroV1 locus offers a valuable strategy for marker-assisted selection for introgression of this nematode resistance.Abbreviations BSA bulked segregant analysis - RAPD random-amplified polymorphic DNA - RFLP restriction fragment length polymorphism - SCAR sequence-characterized amplified region     

Potato cyst nematodes in England and Wales - occurrence and distribution

Potato cyst nematodes (PCN) have been known to occur in the UK for nearly a hundred years. They are the most problematic pests of potatoes and can cause severe yield losses. Previous work has shown the two species, Globodera rostochiensis and G pallida, to be distributed throughout the UK. This paper reports the results of the first structured and statistically unbiased survey undertaken to assess their occurrence and distribution in the potato growing land of England and Wales. The survey showed that PCN were present in 64% of sites sampled. Of the populations found, 67% were G pallida, 8% were G rostochiensis and 25% contained both species. The results show an increase in the incidence of PCN since previous studies were completed and confirm the perceived shift towards G pallida as the predominant species. Of the infestations found, 62% had a population density of less than 10 eggs g^?1 soil.     

Effects of a mixed-isolate mycorrhizal inoculum on the potato – potato cyst nematode interaction

Inoculation of microplants of potato cv. Golden Wonder with Vaminoc, a mycorrhizal inoculum of three arbuscular mycorrhizal fungi (Glomus spp.), resulted in an increase in in‐sand hatch of Globodera pallida, but not G. rostochiensis, within 2 weeks. By this time, mycorrhized plants also supported a larger number of feeding nematodes of both PCN species (50% higher for G. rostochiensis) than did non‐mycorrhized plants, with a higher proportion of the G. pallida population being fertilised females than for G. rostochiensis. After 12 weeks, the multiplication rate of G. rostochiensis on mycorrhized plants was significantly greater than on non‐mycorrhized plants, whereas no such difference was observed for G. pallida. The principal component of PCN multiplication affected by mycorrhization was increased cyst number per plant from 6 to 12 weeks. Over this period, there was no increase in cyst number per plant for either PCN species on non‐mycorrhized plants, whereas the value increased on mycorrhized plants for both G. rostochiensis (by almost 200%) and G. pallida (57%). Mycorrhization resulted in significant increases in the root and shoot dry weights of plants grown in the absence of PCN. Although mycorrhized plants carried a larger PCN burden than non‐mycorrhized plants when grown on PCN‐infested medium, as a result of the increased PCN multiplication rate, they produced larger root systems than did nonmycorrhized plants, suggesting increased tolerance to PCN of the mycorrhized plants, particularly to G. rostochiensis. Of morphological characters investigated in the absence of PCN, only stem height (increased) was significantly affected by mycorrhization. Colonisation by mycorrhizal fungi resulted in increased tuber yield both in the absence (significant increase) and presence (non significant) of PCN, as a result of increased tuber number per plant. These results are discussed in the light of the possible use of AMF as part of an integrated PCN management plan.     

Control of potato cyst nematodes and economic benefits of application of 1,3-dichloropropene and granular nematicides

The two species of the potato cyst nematodes (PCN) Globodera pallida and G rostochiensis are the most problematic pests of the potato crop in the UK. There are no commercially available cultivars with full resistance to G. pallida and both crop rotation and granular nematicides are less effective at controlling this species than G. rostochiensis. In situations of very high PCN levels it may be possible to reduce populations and yield losses by using an autumn application of the soil fumigant 1,3-dichloropropene (1,3-D) followed by a spring application of a granular nematicide. Two field experiments were done to look at the integration of methods for the control of PCN. The Common Field experiment (G. rostochiensis infested) compared the use of 1,3-D with the granular nematicides aldicarb, oxamyl and fosthiazate when growing the susceptible cv. Estima. The Four Gates experiment (infested with both PCN species but mainly G rostochiensis) compared the performance of cv. Santé (partially resistant to G. pallida, fully resistant to G. rostochiensis) with that of the susceptible cv. Estima when treated with 1,3-D and oxamyl at full and half-rates. The results of the experiments show that an integrated approach to nematode control on heavily infested sites, including granular and fumigant nematicides and cultivar resistance, can lead to significant decreases in nematode population densities and reduce yield losses. An economic evaluation of the experiments modelled the gross margins from the different nematicide treatments. In Common Field, the highest gross margins were achieved with the combined use of fumigant and granular nematicides. In Four Gates, there was a clear economic benefit for both cultivars from the use of 1,3-D. In this experiment, oxamyl was of economic value to Estima but not to Sante and full-rate oxamyl was of more benefit than half-rate to Estima.     

Integrated control of potato cyst nematodes using small amounts of nematicide and potatoes with partial resistance

The control of potato cyst nematode (PCN) by less than approved amounts of nematicide combined with partially resistant potato clones was studied in a series of field experiments. On a site heavily infested with Globodera pallida only the most resistant clone (12380ac2) decreased the population density in untreated soil. With aldicarb at its full approved rate (3·36 kg ha^-1) numbers of PCN were decreased under all the genotypes, including the non-resistant Maris Piper. Aldicarb at 1·68 kg ha^-1significantly decreased populations on all clones except 12380ac2. Aldicarb at 0·84 kg ha^-1still significantly decreased population densities and multiplication rates of G. pallida on two clones with intermediate resistance (12243acl and 11233ab22). At two G. rostochiensis sites with light infestations nematode multiplication rates were greater and the control given by aldicarb and partially resistant genotypes of potato was not as great as that at the site with G. pallida. Tuber yields were not increased by the application of aldicarb at the G. rostochiensis infested sites. However, at the site heavily infested with G. pallida the yield of the most intolerant genotype (12380ac2) was increased seven-fold by the full rate of aldicarb (3·36 kg ha^-1) and four-fold by the quarter rate (0·84 kg ha^-1)-Yield of the most tolerant genotype (12243acl) was unaffected by the application of aldicarb.     

Observations on the distribution of potato cyst-nematodes, Globodera rostochiensis and G. pallida on two fenland potato farms

The distribution of potato cyst-nematodes, Globodera rostochiensis and G. pallida was surveyed in two widely separated fenland potato farms in Eastern England. Evidence was obtained of the suppression of G. rostochiensis and increase of G. pallida populations when Maris Piper and other potatoes with the same gene (H₁) for resistance to G. rostochiensis are grown. Numbers of G. rostochiensis and/or G. pallida in the soil could not be related directly to recent potato cropping histories of the fields. Identification of the two species of Globodera by the presence and colour of females on the roots of Désirée, Maris Piper, Cromwell (A27/20) and A25/11 potatoes were confirmed by agarose gel isoelectric focussing of general proteins. Cromwell exhibited little or no resistance to G. pallida at Woodwalton. A25/11 was more resistant to this species at Woodwalton but was susceptible to G. rostochiensis. The results of these surveys emphasise the need for carefully planned and integrated control programmes based on the use of resistant cultivars of potato, crop rotations and appropriate nematicide use to combat the growing problem of G. pallida, especially in organic soils.     

The management of potato cyst nematodes using resistant Solanaceae potato clones as trap crops

The concept of using a range of Solanaceae potato clones as trap crops for potato cyst nematode (PCN) management was investigated. A series of field trials were undertaken from 1999 to 2002 that evaluated 10 clones of either wild Solanum potato species, breeder’s hybrid lines or commercial cultivars. All had high resistance to all known PCN pathotypes (both Globodera rostochiensis and Globodera pallida) and the ability to stimulate high levels of PCN hatch. Investigations showed potential for the development of some clones as a means of reducing high PCN field population levels and for use by organic potato producers.     

Using SNP markers to dissect linkage disequilibrium at a major quantitative trait locus for resistance to the potato cyst nematode Globodera pallida on potato chromosome V

The damage caused by the parasitic root cyst nematode Globodera pallida is a major yield-limiting factor in potato cultivation . Breeding for resistance is facilitated by the PCR-based marker ‘HC’, which is diagnostic for an allele conferring high resistance against G. pallida pathotype Pa2/3 that has been introgressed from the wild potato species Solanum vernei into the Solanum tuberosum tetraploid breeding pool. The major quantitative trait locus (QTL) controlling this nematode resistance maps on potato chromosome V in a hot spot for resistance to various pathogens including nematodes and the oomycete Phytophthora infestans. An unstructured sample of 79 tetraploid, highly heterozygous varieties and breeding clones was selected based on presence (41 genotypes) or absence (38 genotypes) of the HC marker. Testing the clones for resistance to G. pallida confirmed the diagnostic power of the HC marker. The 79 individuals were genotyped for 100 single nucleotide polymorphisms (SNPs) at 10 loci distributed over 38 cM on chromosome V. Forty-five SNPs at six loci spanning 2 cM in the interval between markers GP21-GP179 were associated with resistance to G. pallida. Based on linkage disequilibrium (LD) between SNP markers, six LD groups comprising between 2 and 18 SNPs were identified. The LD groups indicated the existence of multiple alleles at a single resistance locus or at several, physically linked resistance loci. LD group C comprising 18 SNPs corresponded to the ‘HC’ marker. LD group E included 16 SNPs and showed an association peak, which positioned one nematode resistance locus physically close to the R1 gene family. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Comparative Responses of Globodera rostochiensis and G. pallida to Hatching Chemicals

Globodera rostochiensis and G. pallida responded similarly to hatch stimulation by potato root leachate, but proportionally more second-stage juveniles (J2s) of G. rostochiensis hatched than of G. pallida in response to picrolonic acid, sodium thiocyanate, alpha-solanine, and alpha-chaconine. Fractionation of the potato root leachate identified hatching factors with species-selective (active toward both species but stimulating greater hatch of one species than the other), -specific (active toward only one species), and -neutral (equally active toward both species) activities. In a comparison of two populations of each of the two potato cyst nematode (PCN) species, however, greater similarity in response to the individual hatching factors was observed among populations of different species produced under the same conditions than among different populations of the same PCN species. Smaller numbers of species-specific and species-selective hatching factor stimulants and hatching inhibitors than of hatching factors were resolved. In a study to determine whether the different hatching responses of the two species to the same root leachate were associated with different ratios of species-selective and species-specific hatching factors, G. rostochiensis pathotype Ro1 exhibited greater hatch than did G. pallida pathotype Pa2/3 in response to leachate from older plants (more than 38 days old), while G. pallida exhibited greater hatch in response to leachate from younger plants (less than 38 days old); the response of G. pallida pathotype Pal with respect to plant age was intermediate between the other two populations. Combined molecular exclusion-ion exchange chromatography of the root leachates from plants of different ages revealed an increase in the proportion of G. rostochiensis-specific and -selective hatching factors as the plants aged.     

Identification of RFLP markers closely linked to the H1 gene conferring resistance to Globodera rostochiensis in potato

Summary Resistance to the root cyst nematode Globodera rostochiensis is an agronomic trait that is at present incorporated into most new potato varieties. Major dominant genes are available that originate from wild and cultivated Solanum species closely related to the cultivated European potato (Solanum tuberosum ssp. tuberosum). One of those genes, H1, from S. Tuberosum ssp. andigena, was mapped to a distal position on potato chromosome V using restriction fragment length polymorphism (RFLP) markers. The H1 locus segregates independently from Gro1, a second dominant gene presumably from S. Spegazzinii that confers resistance to G. Rostochiensis and which has been mapped to chromosome VII. One marker, CP113, was linked without recombination to the H1 locus.     

A potato hypersensitive resistance gene against potato virus X maps to a resistance gene cluster on chromosome 5

 The dominant Nb gene of potato confers strain-specific hypersensitive resistance against potato virus X (PVX). A population segregating for Nb was screened for resistance by inoculating with PVX strain CP2, which is sensitive to Nb. Through a combination of bulked segregant analysis and selective restriction fragment amplification, several amplified fragment length polymorphism (AFLP) markers linked to Nb were identified. These were cloned and converted into dominant cleaved amplified polymorphic sequence (CAPS) markers. The segregation of these markers in a Lycopersicon esculentum×L. pennellii mapping population suggested that Nb is located on chromosome 5. This was confirmed by examining resistant and susceptible potato individuals with several tomato and potato chromosome-5-specific markers. Nb maps to a region of chromosome 5 where several other resistance genes– including R1, a resistance gene against Phytophthora infestans, Gpa, a locus that confers resistance against Globodera pallida, and Rx2, a gene that confers extreme resistance against PVX–have previously been identified. Received: 2 January 1997/Accepted: 7 February 1997     

Morphological variability of potato cyst nematodes (Globodera spp.) in the Canary Islands

Thirty populations of potato cyst nematode (Globodera spp.) from the Island of Tenerife and two populations from the UK were assessed for several morphometric and non-morphometric characters thought to discriminate between the species G. rostochiensis and G. pallida. Also 200 cysts from each population were analysed by isoelectric focusing of soluble proteins. Correlation analysis, analysis of variance and principal component analysis were used to investigate relationships between the morphometric characters, how the relationships varied between species and between populations, and which characters were most useful for discriminating between species. The two species differed significantly for each of the four morphometric characters: stylet length, fenestra length, anus-fenestra distance and the number of ridges. The stylet length and fenestra length also showed differences between populations of G. rostochiensis while stylet length and number of ridges showed differences between populations of C. pallida. In general, populations of G. pallida showed greater variation than populations of C. rostochiensis. Principal component analysis of the population means indicated that over 73% of the variation in the characters could be explained by the contrast of stylet and fenestra lengths against the anus-fenestra distance and number of ridges. A plot of the first two principal components separated the two species. Stepwise discriminant analysis provided a linear combination of these four variables which discriminated between the species. Stylet length was found to be the most useful characteristic for distinguishing the species whilst anus-fenestra distance was the least useful.     

Effect of the nematicide oxamyl on the multiplication of Globodera rostochiensis and G. pallida and on the haulm growth and yield of six potato cultivars with different levels of resistance and tolerance

The effect of a pre-planting application of oxamyl on the yields of six potato cultivars was studied in co-operative field trials in 1981. Two sites were ‘uninfested’ with potato cyst nematodes (PCN), two were lightly infested (<25 eggs/g soil) and six were moderately to heavily infested (three with Globodera rostochiensis and three with G. pallida). At the uninfested and lightly infested sites oxamyl had little effect on mid-season haulm weights or on final tuber yields. At sites moderately to heavily infested with G. rostochiensis the haulm growth of all cultivars tended to be increased by a similar amount on plots treated with oxamyl, Pentland Dell being least responsive. Yield was increased by different amounts, the increases being least for cvs Cara and Maris Piper and most for Corsair and Pentland Dell. At the sites moderately to heavily infested with G. pallida Cara was again tolerant, its yield being increased little by oxamyl compared with the other cultivars. Maris Piper gave the largest yield increase. Final populations of PCN on non-resistant cultivars were reduced by oxamyl at some sites but not at others. Resistant cultivars also decreased the final numbers of PCN at most sites. Two cultivars derived from Solanum vernei with different degrees of resistance, appeared to be almost equally effective in controlling G. rostochiensis and G. pallida.     

Molecular Variability and Evolution of the Pectate Lyase (<Emphasis Type="Italic">pel</Emphasis>-2) Parasitism Gene in Cyst Nematodes Parasitizing Different <Emphasis Type="Italic">Solanaceous</Emphasis> Plants

While pectate lyases are major parasitism factors in plant-parasitic nematodes, there is little information on the variability of these genes within species and their utility as pathotype or host range molecular markers. We have analysed polymorphisms of pectate lyase 2 (pel-2) gene, which degrades the unesterified polygalacturonate (pectate) of the host cell-wall, in the genus Globodera. Molecular variability of the pel-2 gene and the predicted protein was evaluated in populations of G. rostochiensis, G. pallida, G. “mexicana” and G. tabacum. Seventy eight pel-2 sequences were obtained and aligned. Point mutations were observed at 373 positions, 57% of these affect the coding part of the gene and produce 129 aa replacements. The observed polymorphism does not correlate either to the pathotypes proposed in potato cyst nematodes (PCN) or the subspecies described in tobacco cyst nematodes. The trees reveal a topology different from the admitted species topology as G. rostochiensis and G. pallida sequences are more similar to each other than to G. tabacum. Species-specific sites, potentially applicable for identification, and sites distinguishing PCN from tobacco cyst nematodes, were identified. As both G. rostochiensis and G. pallida display the same host range, but distinct from G. tabacum, which cannot parasitize potato plants, it is tempting to speculate that pel-2 genes polymorphism may be implicated in this adaptation, a view supported by the fact that no active pectate lyase 2 was found in G. “mexicana”, a close relative of G. pallida that is unable to develop on cultivated potato varieties.     

The resistance of six potato cultivars to English populations of potato cyst-nematodes, Globodera pallida and G. rostochiensis

Six cultivars of potato (Santé, Morag, Paladin, Glenna and Fingal bred for resistance to both potato cyst-nematodes (Globodera rostochiensis and G. pallida) and Valiant bred for resistance to G. pallida alone) were exposed to 28 English populations of G. pallida and eight English populations of G. rostochiensis in pots. Susceptible cv. Désirée potatoes served as controls for all 36 populations. Inoculum (Pi) was 12000 eggs in cysts per 400ml pot of soil. Average increase of G. rostochiensis (Pf/Pi) on cv. Désirée was 23.5 but on cvs Sante, Glenna and Fingal it was < 1.0 and on cv. Morag it was 2.2. In contrast, cvs Paladin and Valiant were susceptible (average Pf/Pi = 17.4 and 26.5, respectively). Against G. pallida populations, average Pf/Pi for cv. Désirée was 21.7; on cvs Paladin, Santé and Glenna it was 2.9, 2.6 and 2.4, respectively; cvs Morag and Fingal were less resistant (7.4 and 5.6, respectively) and cv. Valiant was quite susceptible (11.0). Resistance to the different populations of G. pallida and G. rostochiensis varied but for the most resistant cultivars (Santé, Glenna and Paladin) the variation was usually small. The value of the six resistant cultivars studied to the integrated control of potato cyst-nematodes in England and the genetic diversity of the nematode populations to which they were exposed are discussed.     

Hatching Behavior of Potato Cyst Nematodes from the Canary Islands

The present work investigated early hatching differences in naturally occuring field populations and newly reared populations of potato cyst nematodes from the Canary Islands. Hatching behavior of the two species appears to be distinct, with more juveniles hatched from G. pallida that hatch earlier and over a shorter time than G. rostochiensis. The hatching rate of 3-year-old PCN populations was more than double (mean 44.5% ñ 1) that shown by newly reared populations (mean 19.1% ñ 12.5), and those that could be classified as pathotype Pa 1 (Pa 1 and P 13) were found to hatch particularly poorly. Significant differences were also observed in the juveniles released in tap water between newly reared populations of both species, with mean hatch significantly higher for G. rostochiensis. The results are discussed in relation to the implication that these findings may have for competition between the two species of PCN in the field.     

Single nucleotide polymorphism (SNP) genotyping as basis for developing a PCR-based marker highly diagnostic for potato varieties with high resistance to Globodera pallida pathotype Pa2/3

Globodera pallida is a parasitic root cyst nematode of potato, which causes reduction of crop yield and quality in infested fields. Field populations of G. pallida containing mixtures of pathotypes Pa2 and Pa3 (Pa2/3) are currently most relevant for potato cultivation in middle Europe. Genes for resistance to G. pallida have been introgressed into the cultivated potato gene pool from the wild, tuber bearing Solanum species S. spegazzinii and S. vernei. Selection of resistant genotypes in breeding programs is hampered by the fact that the phenotypic evaluation of resistance to G. pallida is time consuming, costly and often ambiguous. DNA-based markers diagnostic for resistance to G. pallida would facilitate the development of resistant varieties. A tetraploid F₁ hybrid family SR-Gpa segregating for quantitative resistance to G.␣pallida was developed and evaluated for resistance to G. pallida population ‘Chavornay’. Two subpopulations of 30 highly resistant and 30 susceptible individuals were selected and genotyped for 96 single nucleotide polymorphism (SNP) markers tagging 12 genomic regions on 10 potato chromosomes. Seven SNPs were found significantly linked to the nematode resistance, which were all located within a resistance ‘hotspot’ on potato chromosome V. A haplotype model for these seven SNPs was deduced from the SNP patterns observed in the SR-Gpa family. A PCR assay ‘HC’ was developed, which specifically detected the SNP haplotype c that was linked with high levels of nematode resistance. The HC marker was only found in accessions of S.␣vernei. Screening with the HC marker 34 potato varieties resistant to G. pallida pathotypes Pa2 and/or Pa3 and 22 susceptible varieties demonstrated that the HC marker was highly diagnostic for presence of high levels of resistance to G. pallida pathotype Pa2/Pa3.Amirali Sattarzadeh and Ute Achenbach contributed equally to the work