Comparison of resistance to potyviruses within Solanaceae: infection of potatoes with tobacco etch potyvirus and peppers with potato A and Y potyviruses

The reaction of several cultivated potato varieties (Solarium tuberosum L.) to three strains of tobacco etch potyvirus (TEV-F, TEV-Mex21 and TEV-ATCC) and the reaction of several pepper lines (Capsicum annuum L. and C. chinense L.) to two strains of potato Y potyvirus (PVY^O and PVY^N) and one strain of potato A potyvirus (PVA-M) was tested. The potato varieties included in this study carried resistance genes against PVY, PVA and potato V potyvirus, but all were susceptible to TEV and developed mottle and mosaic symptoms. TEV was readily transmitted by mechanical inoculation from tobacco and potato to potato, whereas transmission from pepper to potato occurred infrequently. TEV was transmitted through potato tubers, and from pepper to potato plants by aphids. Lack of detectable systemic infection following graft-inoculation indicated extreme resistance to PVY^O and PVA in several pepper lines. No pepper line was systemically infected with PVY^N following mechanical inoculation (graft-inoculation was not carried out with PVY^N). The development of necrotic lesions following mechanical and graft-inoculation indicated hypersensitive response to PVY^O in several pepper lines which resembled the resistance responses to these potyvirus strains in potato. Results of this study together with previous work indicate that C. annuum cv. Avelar is resistant to four potyviruses [PVY, PVA, pepper mottle potyvirus (PepMoV) and some isolates of TEV]; C. annuum cv. Criollo de Morelos and C. chinense PI 152225 and PI 159236 are resistant to three potyviruses (PVY, PepMoV and PVA; and PVY, PepMoV and TEV, respectively); C. annuum 9093–1 and 92016–1 are resistant to PVY and PepMoV; and C. annuum cv. Jupiter and C. annuum cv. RNaky are resistant to PVY^N and PVA.     

The novel gene Ny-1 on potato chromosome IX confers hypersensitive resistance to Potato virus Y and is an alternative to Ry genes in potato breeding for PVY resistance

Hypersensitive resistance (HR) is an efficient defense strategy in plants that restricts pathogen growth and can be activated during host as well as non-host interactions. HR involves programmed cell death and manifests itself in tissue collapse at the site of pathogen attack. A novel hypersensitivity gene, Ny-1, for resistance to Potato virus Y (PVY) was revealed in potato cultivar Rywal. This is the first gene that confers HR in potato plants both to common and necrotic strains of PVY. The locus Ny-1 mapped on the short arm of potato chromosome IX, where various resistance genes are clustered in Solanaceous genomes. Expression of HR was temperature-dependent in cv. Rywal. Strains PVY^O and PVY^N, including subgroups PVY^NW and PVY^NTN, were effectively localized when plants were grown at 20°C. At 28°C, plants were systemically infected but no symptoms were observed. In field trials, PVY was restricted to the inoculated leaves and PVY-free tubers were produced. Therefore, the gene Ny-1 can be useful for potato breeding as an alternative donor of PVY resistance, because it is efficacious in practice-like resistance conferred by Ry genes.     

Potato protein tyrosine phosphatase StPTP1a is activated by StMKK1 to negatively regulate plant immunity

Phytophthora infestans causes severe losses in potato production. The MAPK kinase StMKK1 was previously found to negatively regulate potato immunity to P. infestans. Our results showed that StMKK1 interacts with a protein tyrosine phosphatase, referred to as StPTP1a, and StMKK1 directly phosphorylates StPTP1a at residues Ser-99, Tyr-223 and Thr-290. StPTP1a is a functional phosphatase and the phosphorylation of StPTP1a at these three residues enhances its stability and catalytic activity. StPTP1a negatively regulates potato immunity and represses SA-related gene expression. Furthermore, StPTP1a interacts with, and dephosphorylates, the StMKK1 downstream signalling targets StMPK4 and −7 at their Tyr-203 residue resulting in the repression of salicylic acid (SA)-related immunity. Silencing of NbPTP1a + NbMPK4 or NbPTP1a + NbMPK7 abolished the plant immunity to P. infestans caused by NbPTP1a silencing, indicating that PTP1a functions upstream of NbMPK4 and NbMPK7. StMKK1 requires StPTP1a to negatively regulate SA-related immunity and StPTP1a is phosphorylated and stabilized during immune activation to promote the de-phosphorylation of StMPK4 and −7. Our results reveal that potato StMKK1 activates and stabilizes the tyrosine phosphatase StPTP1a that in its turn de-phosphorylates StMPK4 and −7, thereby repressing plant SA-related immunity.     

Potato StMPK7 is a downstream component of StMKK1 and promotes resistance to the oomycete pathogen Phytophthora infestans

A cascade formed by phosphorylation events of mitogen-activated protein kinases (MAPKs) takes part in plant stress responses. However, the roles of these MAPKs in resistance of potato (Solanum tuberosum) against Phytophthora pathogens is not well studied. Our previous work showed that a Phytophthora infestans RXLR effector targets and stabilizes the negative regulator of MAPK kinase 1 of potato (StMKK1). Because in Arabidopsis thaliana the AtMPK4 is the downstream phosphorylation target of AtMKK1, we performed a phylogenetic analysis and found that potato StMPK4/6/7 are closely related and are orthologs of AtMPK4/5/11/12. Overexpression of StMPK4/7 enhances plant resistance to P. infestans and P. parasitica. Yeast two-hybrid analysis revealed that StMPK7 interacts with StMKK1, and StMPK7 is phosphorylated on flg22 treatment and by expressing constitutively active StMKK1 (CA-StMKK1), indicating that StMPK7 is a direct downstream signalling partner of StMKK1. Overexpression of StMPK7 in potato enhances potato resistance to P. infestans. Constitutively active StMPK7 (CA-StMPK7; StMPK7^{D198G, E202A}) was found to promote immunity to Phytophthora pathogens and to trigger host cell death when overexpressed in Nicotiana benthamiana leaves. Cell death triggered by CA-StMPK7 is SGT1/RAR1-dependent. Furthermore, cell death triggered by CA-StMPK7 is suppressed on coexpression with the salicylate hydroxylase NahG, and StMPK7 activation promotes salicylic acid (SA)-responsive gene expression. We conclude that potato StMPK7 is a downstream signalling component of the phosphorelay cascade involving StMKK1 and StMPK7 plays a role in immunity to Phytophthora pathogens via an SA-dependent signalling pathway.     

Aphid Transmission of Potato aucuba mosaic virus Strains Mediated by Different Strains of Potato virus Y

Three British strains of potato aucuba mosaic virus (PAMV) were tested for transmissibility by the aphid Myzus persicae. None was aphid transmissible on its own but all three were transmitted in the nonpersistent manner by aphids that had previously been fed on a source of the potyvirus potato virus Y (PVY). Different PVY strains mediated PAMV transmission from Nicotiana clevelandii to Capsicum annuum to different degrees, and different PAMV strains were transmitted at different frequencies when assisted by the same PVY strain. These results are compatible with the idea that subtle differences in the PAMV coat protein and in the PVY helper component are responsible for diffrences in frequencies of transmission of PAMV, without however, excluding the possibility of effects of other undefined factors. Transmission of PAMV was no less frequent when mediated by a PVY strain that was unable to infect C. annuum than when a C. annuum‐infecting PVY strain was used.     

Crop borders reduce potato virus Y incidence in seed potato

Crop borders of soybean (Glycine max), sorghum (Sorghum bicolor), winter wheat (Triticum aestivum) and potato (Solanum tuberosum) were tested as a means of reducing potato virus Y (PVY) incidence in seed potato. Borders of fallow cultivated ground served as controls. Aphid landing rates were monitored weekly in plots using green tile traps, and PVY incidence was assessed by serologically testing tuber progeny from selected rows in each plot. Average weekly aphid landing rates in fallow-bordered and crop-bordered plots were not significantly different in 1992 (29.4 and 25.2 aphids, respectively) or 1993 (7.3 and 6.6 aphids, respectively). However, crop borders significantly reduced PVY incidence. In 1992, fallow-bordered and soybean-bordered plots averaged 47.8% and 35.0% PVY infection, respectively. In 1993, PVY infection averaged across all crop (soybean, sorghum, and wheat) bordered plots was 2.7% compared to 6.8% in fallow-bordered plots. PVY incidence in the centre rows of fallow-bordered and crop-bordered plots was statistically equivalent, while outer rows of crop-bordered plots had significantly less PVY than outer rows of fallow-bordered plots. Crop borders apparently reduced the number of viruliferous aphids landing on the edge of the plot. The choice of crop species used as a border, or treating the border with a systemic insecticide, did not affect aphid landing rates or PVY incidence. In 1995, PVY incidence in the centre 10 row block of potatoes averaged 2.1% across all crop borders (potato and soybean). PVY infection in the four row potato border averaged 5.7%. Crop borders are readily adaptable to current production practices, although the greatest benefits in reducing PVY incidence would occur in average sized, generation 0 (< 0.2 ha), elite seed potato fields.     

Comparison of transmission efficiency of various isolates of Potato virus Y among three aphid vectors

Potato virus Y (PVY) strains are transmitted by different aphid species in a non‐persistent, non‐circulative manner. Green peach aphid (GPA), Myzus persicae Sulzer, is the most efficient vector in laboratory studies, but potato aphid (PA), Macrosiphum euphorbiae Thomas (both Hemiptera: Aphididae, Macrosiphini), and bird cherry‐oat aphid (BCOA), Rhopalosiphum padi L. (Hemiptera: Aphididae, Aphidini), also contribute to PVY transmission. Studies were conducted with GPA, PA, and BCOA to assess PVY transmission efficiency for various isolates of the same strain. Treatments included three PVY strains (PVY^O, PVY^N:O, PVY^NTN) and two isolates of each strain (Oz and NY090031 for PVY^O; Alt and NY090004 for PVY^N:O; N4 and NY090029 for PVY^NTN), using each of three aphid species as well as a sham inoculation. Virus‐free tissue‐cultured plantlets of potato cv. Russet Burbank were used as virus source and recipient plants. Five weeks post inoculation, recipient plants were tested with quantitative DAS‐ELISA to assess infection percentage and virus titer. ELISA‐positive recipient plants were assayed with RT‐PCR to confirm presence of the expected strains. Transmission efficiency (percentage infection of plants) was highest for GPA, intermediate for BCOA, and lowest for PA. For all aphid species, transmission efficiency did not differ significantly between isolates within each strain. No correlations were found among source plant titer, infection percentage, and recipient plant titer. For both GPA and BCOA, isolates of PVY^NTN were transmitted with greatest efficiency followed by isolates of PVY^O and PVY^N:O, which might help explain the increasing prevalence of necrotic strains in potato‐growing regions. Bird cherry‐oat aphid transmitted PVY with higher efficiency than previously reported, suggesting that this species is more important to PVY epidemiology than has been considered.     

Evidence for utility of the same PCR-based markers for selection of extreme resistance to Potato virus Y controlled by Rysto of Solanum stoloniferum derived from different sources

The tuber‐bearing wild potato species, Solanum stoloniferum, carries a dominant gene, Ry_sto, which confers extreme resistance (ER) to Potato virus Y (PVY). This gene was introgressed to cultivated potato germplasm (Solanum tuberosum) using accessions of S. stoloniferum maintained in European gene banks. It is mainly used in potato breeding programmes in Europe. Ry_sto was recently mapped to potato chromosome XII. However, in this study, a different accession of S. stoloniferum (PI275244; Haw1293) was used as a female parent in a cross to obtain a diploid (2n = 2x = 24) potato population of 112 F1 genotypes. From this accession, ER to PVY has been introgressed to the potato breeding programmes at the International Potato Center (Peru). As expected, ER to PVY was inherited in a dominant, monogenic fashion in the F1 population. Marker‐specific choices of DNA polymerase and adjustments of PCR conditions were made to optimise marker detection. The corresponding gene (Ry_sto) was mapped to the chromosome XII using the previously described and new cleaved amplified polymorphic sequence (CAPS) markers, which are based on the restriction fragment length polymorphism loci GP122 (six markers) and GP269 (one marker), and the simple sequence repeat marker STM0003. Four GP122‐based CAPS markers and STM0003 detected the same genotypes expressing ER to PVY. Because of a few recombinants, that is ER genotypes lacking the markers and the genotypes that react with necrosis but contain the markers, the marker distance from Ry_sto was estimated as 15.2 cM in this F1 population. However, the distance may be less if necrosis was considered an altered response also controlled by Ry_sto. The markers also specifically detected independent European potato cultivars that express ER to PVY derived from S. stoloniferum. Phylogenetic analysis of the sequences amplified from the GP122 locus of S. stoloniferum and potato cultivars further confirmed that the Ry_sto gene from independent accessions of S. stoloniferum can be selected using the same markers and the protocols described in this study.     

Effect of mineral oil on Potato virus Y acquisition by Rhopalosiphum padi

Seed potato crops are currently sprayed weekly with mineral oil to prevent transmission of the Potato virus Y (PVY; Potyviridae: Potyvirus), one of the most prevalent and important non‐persistent viruses affecting potato production. In spite of its wide usage as inhibitor of virus transmission, the mode of action for mineral oil is poorly known. The objective of this study was to quantify the effect of dosage and time from application of mineral oil on the inhibition of PVY acquisition. The bird cherry‐oat aphid, Rhopalosiphum padi (L.) (Hemiptera: Aphididae), known as vector of PVY, was used in all the experiments. The results indicated that mineral oil efficiently decreased PVY acquisition by 75 and 70% 1 day after application of 5 and 10 l ha^?1, respectively. The inhibition effect decreased with time from application; mineral oil inhibits acquisition for less than 4 days at 5 l ha^?1 and between 8 and 12 days at 10 l ha^?1. As mineral oil was detected in the body of fewer aphids when they fed on plants 1 day after oil application, a change in the aphid probing behaviour on mineral oil‐treated plants was deduced. These results support the hypothesis that mineral oil physically inhibits the binding of the virus at the tip of the stylets.     

黑龙江马铃薯Y病毒P1基因的特点北大核心CSCD

【目的】本研究通过对不同PVY分离物基因的测序及分析,从而了解PVY株系的多样性,进而对PVY病毒的分子检测及防治提供重要的资料和参考。【方法】本研究针对黑龙江15个马铃薯Y病毒样品的P1基因进行克隆测序和进化树分析。【结果】经比对分析,样品被分成两组,有10个样品的基因类型高度同源,且相对保守,是本地区的优势群组,无论是与国内其它地区样品比较还是与国外样品比较,其亲缘关系都有一定距离;而另一组中的5个样品的P1基因与本地优势组群有较大差异,且这5个样品间也有一定的差异,并与国内其它地区和国外一些样品的P1基因序列比较接近。通过比对Gen Bank中已上传的序列提供的PVY株系的信息,得知本次试验的P1基因与PVY^(NTN-NW)株系是相似的,且这15个样品与国内其他样品一样都是由PVY^N株系演变而来。【结论】由P1基因分析表明,PVY受环境影响较大,黑龙江10个样品的PVY在长期的进化中产生了具有地方特点的变化,而后来的5个样品说明中国大部分PVY有可能是跟随国外品种资源的引进进入,同时PVY也随国内不同区域间资源交流和种薯调运而传播。     

Extreme resistance to Potato virus Y in potato carrying the Rysto gene is mediated by a TIR‐NLR immune receptor

Potato virus Y (PVY) is a major potato (Solanum tuberosum L.) pathogen that causes severe annual crop losses worth billions of dollars worldwide. PVY is transmitted by aphids, and successful control of virus transmission requires the extensive use of environmentally damaging insecticides to reduce vector populations. Ry_sto, from the wild relative S. stoloniferum, confers extreme resistance (ER) to PVY and related viruses and is a valuable trait that is widely employed in potato resistance breeding programmes. Ry_sto was previously mapped to a region of potato chromosome XII, but the specific gene has not been identified to date. In this study, we isolated Ry_sto using resistance gene enrichment sequencing (RenSeq) and PacBio SMRT (Pacific Biosciences single‐molecule real‐time sequencing). Ry_sto was found to encode a nucleotide‐binding leucine‐rich repeat (NLR) protein with an N‐terminal TIR domain and was sufficient for PVY perception and ER in transgenic potato plants. Ry_sto‐dependent extreme resistance was temperature‐independent and requires EDS1 and NRG1 proteins. Ry_sto may prove valuable for creating PVY‐resistant cultivars of potato and other Solanaceae crops.     

Transfer of resistance to potato leafroll virus, potato virus Y and potato virus X from Solarium brevidens to S. tuberosum through symmetric and designed asymmetric somatic hybridisation

Resistance to potato leafroll virus (PLRV), potato virus Y (PVY^o) and potato virus X (PVX) was studied in symmetric and asymmetric somatic hybrids produced by electrofusion between Solanum brevidens (2n=2×=24) and dihaploid S. tuberosum (2n=2×=24), and also in regenerants (B-hybrids) derived through protoplast culture from a single somatic hybrid (chromosome number 48). All of the somatic hybrids between 5. brevidens and the two dihaploid lines of potato cv. Pito were extremely resistant to PLRV and PVY^oand moderately resistant to PVX, irrespective of their chromosome number and ploidy level (tetraploid or hexaploid). Most (56%) of the asymmetric hybrids of irradiated S. brevidens and the dihaploid line of potato cv. Pentland Crown (PDH40) had high titres of PVY^osimilar to those of PDH40, whereas the rest of the hybrids had PVY^otitres less than a tenth of those in PDH40. Three B-hybrids had a highly reduced chromosome number (27, 30 and 34), but were however as resistant to PLRV, PVY^oand PVX as 5. brevidens. Two asymmetric hybrids and one B-hybrid were extremely resistant to PLRV but susceptible to both PVY and PVX. The results suggested that resistance to PLRV in 5. brevidens is controlled by a gene or genes different from those controlling resistance to PVY and PVX, and the gene(s) for resistance to PVY and PVX are linked in S. brevidens.     

Information‐theory‐based model selection for determining the main vector and period of transmission of Potato virus Y

Potato virus Y (PVY, genus Potyvirus, family Potyviridae) is transmitted non‐persistently by aphids. It causes major losses in potato production (Solanum tuberosum), especially following seed tuber‐borne infection of plants. To limit the risk of PVY infection, seed potato production is located preferably in regions where vector pressure is low. The northern‐most high‐grade seed potato production area (HG zone) of Europe is in Finland. The aim of this study was to determine the incidence of aphid species with documented ability to transmit PVY and to use a modelling approach to determine their relative importance as vectors of PVY in the HG zone of Finland. Winged aphids were caught from six to seven potato fields in each of three growing seasons (2007–09) using yellow pan traps that were examined twice a week. Identification of more than 30 000 individuals indicated that 37% of the aphids belonged to nine species reported to transmit PVY. Incidence of PVY in seed lots was low (0–5.6%) and the seasonal increase of PVY incidence was also low in the potato crops. No potato‐colonising aphids were found on the plants in any of the years. The seasonal increase in PVY incidence was modelled using aphid counts in traps, the relative vector efficiencies of the aphids, virus resistance of cultivars, and the initial infection rate of the seed tubers as explanatory variables in generalised linear mixed modelling. Akaike's information criterion was employed to find the best set of explanatory variables for PVY in harvested tubers. Results of this modelling approach showed that the incidence of seed‐borne PVY infection and the early‐season vector flights are the most important factors contributing to the incidence of PVY in the yield. Compared to models with data from all potential vector species, models containing data from Aphis fabae only showed a better model fit with regard to the incidence of PVY in the harvested tubers. The explanatory power of the models was lost when A. fabae was omitted from the vector data, suggesting that other species play a negligible role as vectors of PVY in the HG zone of Finland. Results can be used to devise appropriate strategies for enhanced control of PVY.     

Forecasting virus disease in seed potatoes using flight activity data of aphid vectors

We compiled data from the Swiss seed certification programme for the country‐wide incidence of viruses in seed potato crops for the years 1989–2012. Model selection techniques were used to regress year‐to‐year variation in the incidence of potato viruses – largely dominated by Potato virus Y (PVY) – in three susceptible varieties against the abundance of virus vectors (winged aphids), obtained in a suction trap, to identify the most important vector species. The ultimate aim of this study was to develop a decision‐support system capable of forecasting virus spread during the current season using trap data of aphid flights. The average virus incidence in the varieties Bintje, Sirtema and Charlotte varied considerably among years, ranging from 1.0% in 2009 to 13.6% in 1989 (N = 150–611 seed lots per year). A linear regression model including the cumulative sums (until mid‐June) of two aphid species (Brachycaudus helichrysi and Phorodon humuli) as predictor variables for virus disease was remarkably well supported by the data (R² = 0.86). Similarly, using counts of B. helichrysi alone resulted in a good model fit (R² = 0.81). Cross‐validation revealed high predictive accuracy of the model. Although prediction root mean squared errors (RMSE) calculated for different timings of forecasts were high for extremely early forecasts, they rapidly declined for forecasts conducted by the end of May (i.e. 2–4 weeks after potato emergence). Winter temperature (January–February) was positively correlated with the abundance of B. helichrysi in early summer as well as with post‐harvest virus incidence. Remarkably, the abundance of Myzus persicae, often considered the main vector of PVY, was not correlated with virus incidence. Taken together, our analysis suggests that the early migrating aphid B. helichrysi, rather than M. persicae, is the main vector of PVY in Switzerland, and that suction trap data are useful for the design of decision‐support systems aimed to optimise virus control in seed potato production.     

Efficacy of Three Strategies Based on Insecticide,Oil and Elicitor Treatments in Controlling Aphid Populations and Potato virus Y Epidemics in Potato Fields

Potato virus Y (PVY), the potato virus with the highest economic impact in Europe, is transmitted by aphids in a non‐persistent manner. A two‐year field experiment was conducted in Switzerland to evaluate the efficacy of three strategies for controlling aphid populations and the spread of PVY, consisting of treatment with one insecticide (Karate Zeon^®), one elicitor (Bion^®) and one oil (Telmion^®), respectively. The elicitor strategy proved to be ineffective for controlling aphid populations and inadequate for controlling PVY spread. The insecticide strategy gave incomplete protection from aphid infestations, owing to the selection of aphid‐resistant clones. The insecticide gave too little protection against PVY spread for it to be considered a suitable candidate for the purpose. The oil strategy had no effect on aphid populations, but was the best option to reduce PVY spread.     

Ergebnisse von Untersuchungen über die Effektivtemperatursummen einzelner Entwicklungsstadien der Getreidehähnchen (Lema spp.)

Various methodical approaches for the discovery and selection of virus-resistant potato forms are analysed. The optimum methods and conditions of PVM, PVY and PVX plant inoculation by evaluation to immunity are revealed, a possibility of realisation of complex inoculations on Lycopersicon esculentum Mill. (cv Nevsky) infected by PVM + PVX mixture, what accelerates an evaluation and increases its efficiency. The necessity of the controlled infectious backgrounds creation by evaluation of potato selection material for field (relative resistance to PVM + PVY + PVX complex) is shown.     

Strain group specific and virus specific hypersensitive reactions to infection with potyviruses in potato cultivars

When 12 potato cultivars were inoculated with isolates (one each) of potato virus Y (PVY) ordinary (Y^o), C (Y^c) and tobacco veinal necrosis (Yⁿ) strain groups, potato virus A (PVA) and potato virus V (PVV), none of them responded hypersensitively to Yⁿ. However, with Y^o, Y^c, PVA and PW specific hypersensitive reactions developed depending on isolate-cultivar combination which were all independent of each other. When field isolates of PVY thought to be Y^oor Y^cwere inoculated to the same 12 cultivars, two did not fit into either strain group giving hypersensitive reactions in only two cultivars instead of seven with Y^oor eight with Y^c. These two isolates may represent a previously unreported PVY strain group (Y^z). When Y^owas graft-inoculated to seedlings of the cross Desiree × Maris Piper (hypersensitive × non-hypersensitive for Y^o), the segregation ratio obtained for non-hypersensitive:hypersensitive reactions was close to 1:1 suggesting that a single dominant gene (Ny_tbr) determining Y^ospecific hypersensitivity may be present in cv. Desiree (simplex condition). In tests using PVV and Desiree × Maris Piper (non-hypersensitive × hypersensitive for PVV) seedlings, the segregation ratio obtained was close to 1:5 indicating that a single dominant gene (Nv) determining PVV specific hypersensitivity may be present in cv. Maris Piper (duplex condition). Cultivars Corine, Pirola and clone G5457(4) which each carry one of the extreme resistance genes (Ry) from Solanum stoloniferum were graft-inoculated with Yⁿ, Y^o, Y^c, PVV and PVA. G5457(4) gave a strong localised hypersensitive reaction in all instances, while cv. Pirola did so with all except PVA to which it was immune. In cv. Corine a severe localised hypersensitive reaction developed with PVA, generalised hypersensitivity with PVV but an immune response with the three PVY strain groups. Large-scale grafting of Yⁿto plants of cvs Corine and Pirola gave no evidence of selection of a strain which overcomes Ry genes.     

Novel resistances to four potyviruses in tuber-bearing potato species, and temperature-sensitive expression of hypersensitive resistance to potato virus Y

Novel potyvirus resistance specificities were found in eight tested wild potato species (clones): hypersensitive resistance (HR) to potato Y potyvirus (PVY) strain groups PVY^O in Solanum megistacrolobum and S. polyadenium and PVY^N in S. stoloniferum; HR to potato V potyvirus (PW) in S. maglia, S. polyadenium, S. stoloniferum, S. sparsipilum and S. sucrense, HR to potato A potyvirus (PVA) strain group 1 in S. sucrense, and extreme resistance (ER) to PVA in S. polyadenium. S. commersonii and S. stoloniferum expressed HR to tobacco etch potyvirus (TEV) which has not been reported previously in potato species. The studied clone of S. stoloniferum expressed HR to all potyviruses and potyvirus strains tested. The clone of S. stoloniferum (2n = 48; nuclear DNA content (2C) = 3.6 pg) and S. chacoense (2n = 24; 2C=1.9 pg) were crossed and one hybrid (2n = 36; 2C = 2.9 pg) was obtained. The hybrid expressed HR to all tested potyviruses except PVA, which indicated that HR to PVA was controlled by a gene which is different from the genes (or gene) controlling HR to PVY^O, PVY^N, PVV and TEV in S. stoloniferum. On the other hand, S. chacoense and the hybrid expressed ER to cucumber mosaic cucumovirus (CMV), whereas S. stoloniferum was susceptible to CMV. All tested wild species and the six tested potato cultivars (S. tuberosum subsp. tuberosum) expressed HR to PVV. Expression of HR following infection with PVY^N induced systemic acquired resistance (SAR) in S. chacoense. HR to PVY^N in S. sparsipilum and S. sucrense and to PVY^O in potato cv. Pito was efficiently expressed at lower temperatures (16/18°C) indicated by the development of distinct necrotic lesions and/or vein necrosis in inoculated leaves, whereas the HR was rendered less effective at higher temperatures (19/24°C) which was indicated by the development of systemic infection with leaf-drop and mosaic symptoms.