Strong resistance to potato tuber necrotic ringspot disease in potato induced by transformation with coat protein gene sequences from an NTN isolate of Potato virus Y

The potato cv. Igor is susceptible to infection with Potato virus Y (PVY) and in Slovenia it has been so severely affected with NTN isolates of PVY causing potato tuber necrotic ringspot disease (PTNRD) that its cultivation has ceased. Plants of cv. Igor were transformed with two transgenes that contained coat protein gene sequence of PVY^NTN. Both transgenes used PVY sequence in a sense (+) orientation, one in native translational context (N‐CP), and one with a frame‐shift mutation (FS‐CP). Although most transgenic lines were susceptible to infection with PVY^NTN and PVY^O, several lines showed resistance that could be classified into two types. Following manual or graft inoculation, plants of partially resistant lines developed some symptoms in foliage and tubers, and virus titre in the foliage, estimated by ELISA, was low or undetectable. In highly resistant (R) lines, symptoms did not develop in foliage and on tubers, and virus could not be detected in foliage by ELISA or infectivity assay. Four lines from 34 tested (two N‐CP and two FS‐CP) were R to PVY^NTN and PVY^O and one additional line was R to PVY^O. When cv. Spey was transformed with the same constructs, they did not confer strong resistance to PVY^O.     

Determination of aphid transmission efficiencies for N, NTN and Wilga strains of Potato virus Y

Potato virus Y (PVY, genus Potyvirus, family Potyviridae) causes high economic losses worldwide, especially in the production of seed potatoes (Solanum tuberosum). PVY control systems rely on measuring virus pressure and vector pressure in the field. Calculation of the vector pressure is based on the relative efficiency factors (REFs) of aphid species. These REFs express the transmission efficiency of aphid species in relation to the transmission efficiency of Myzus persicae, the most efficient vector of PVY. In this paper, we report on the determination of aphids' relative transmission efficiency factors (REFs) for isolates of the PVY strains PVY^N, PVY^NTN and PVY^N-Wi. Biotype Mp2 of M. persicae was tested for its transmission efficiency for six PVY isolates (one PVY^N, three PVY^NTN and two PVY^N-Wi isolates) and showed comparable average transmission efficiencies for all isolates. The transmission rate of this biotype for the six PVY isolates was set to 1 and Mp2 was used as an internal control in transmission experiments to determine the REFs of three other biotypes of M. persicae and 16 other aphid species (three biotypes per species when available) for the six PVY isolates. Comparing the calculated REFs for PVY^N with the REFs reported in the previous century for PVY^N, we observe overall comparable REFs, except for Aphis fabae, Aphis spp., Hyperomyzus lactucae, Macrosiphum euphorbiae and Rhopalosiphum padi, which have a lower REF in our experiments, and Aphis frangulae and Phorodon humuli, which have now a higher REF. Comparing the new REFs found for the PVY^NTN strains with the new REFs for PVY^N, we observe that they are overall comparable, except for A. frangulae (0.17 compared with 0.53) and Schizaphis graminum (0.05 compared with 0.00). Comparing the REFs calculated for PVY^N-Wi with those calculated for PVY^N, we can observe six aphid species with higher REFs (Acyrthosiphon pisum, A. fabae, Aphis nasturtii, Aphis spp., P. humuli and R. padi). Only the species A. frangulae shows a lower REF for PVY^N-Wi compared with the transmission efficiency of PVY^N. Three aphid species (Aulacorthum solani, Myzus ascalonicus and S. graminum) for which no REF was determined earlier were found to be capable to transmit PVY and their REFs were determined.     

The Genetic Structure of Populations of Potato virus Y in Japan; Based on the Analysis of 20 Full Genomic Sequences

The genetic structure of Potato virus Y (PVY) populations in Japan was analysed using 20 isolates; five were retrieved from the public DNA sequence databases, and an additional 15 complete genomic sequences were determined using field samples collected in Japan. Recombination and phylogenetic analyses of a total of 149 isolates from Japan and other countries showed that PVY has three major lineages (C, N and O); at least one, two and six sublineages in C, N and O lineages, respectively. One recombination pattern was newly found among Japanese PVY^NTN strain isolates, which was most closely related to the PVY^NTN strain isolates previously found in Europe and North America. On the other hand, PVY^O was a complex of several divergent lineages, and there were at least three non‐recombinant subpopulations in Japan. Studies on nucleotide diversities of populations and phylogenetic relationships of the isolates in the PVY sequences showed that Japanese PVY populations were in part distinct from the European and North American populations.     

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.     

Somatic Hybrids Between Potato and S. berthaultii Show Partial Resistance to Soil‐Borne Fungi and Potato Virus Y

Three tetraploid somatic hybrid lines produced by protoplast fusion between a dihaploid potato, Solanum tuberosum, cultivar BF15 and the wild potato species Solanum berthaultii were evaluated here for their response to different soil‐borne pathogens, that is Fusarium solani, Pythium aphanidermatum and Rhizoctonia solani as well as to infection by potato virus Y (PVY). Both hybrid and BF15 plants grown in vitro were inoculated with the tested pathogen strains, that is R. solani, P. aphanidermatum, or F. solani. The growth level and disease severity index of these plants were compared to the susceptible commercial cultivar Spunta. A better growth of inoculated hybrid plants and restricted disease symptoms were observed in comparison with the commercial plants. Under glasshouse conditions and after inoculation with R. solani and P. aphanidermatum, improved resistance of the hybrid plants to these pathogens was confirmed. Indeed, these plants showed no significant damage following inoculation and a better development in R. solani‐infected plants. The susceptibility of the hybrid tubers to R. solani, P. aphanidermatum, and to F. solani infection was also determined. A significant reduction of tissue colonisation was observed in all the hybrid lines compared to the cultivated cultivars. The STBc and STBd hybrids also showed improved resistance to the PVY ordinary strain (PVY^o) under glasshouse conditions.     

Linking belowground and aboveground phenology in two boreal forests in Northeast China

Plants are frequently attacked by both pathogens and insects, and an attack from one can induce plant responses that affect resistance to the other. However, we currently lack a predictive framework for understanding how pathogens, their vectors, and other herbivores interact. To address this gap, we have investigated the effects of a viral infection in the host plant on both its aphid vector and non-vector herbivores. We tested whether the infection by three different strains of Potato virus Y (PVY^NTN, PVY^NO and PVY^O) on tomato plants affected: (1) the induced plant defense pathways; (2) the abundance and fecundity of the aphid vector (Macrosiphum euphorbiae); and (3) the performance of two non-vector species: a caterpillar (Trichoplusia ni) and a beetle (Leptinotarsa decemlineata). While infection by all three strains of PVY induced the salicylate pathway, PVY^NTN induced a stronger and longer response. Fecundity and density of aphids increased on all PVY-infected plants, suggesting that the aphid response is not negatively associated with salicylate induction. In contrast, the performance of non-vector herbivores positively correlated with the strength of salicylate induction. PVY^NTN infection decreased plant resistance to both non-vector herbivores, increasing their growth rates. We also demonstrated that the impact of host plant viral infection on the caterpillar results from host plant responses and not the effects of aphid vector feeding. We propose that pathogens chemically mediate insect–plant interactions by activating the salicylate pathway and decreasing plant resistance to chewing insects, which has implications for both disease transmission and insect community structure.     

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.     

Generation of transgenic potato plants highly resistant to potato virus Y (PVY) through RNA silencing

In this study we applied RNA silencing to engineer potato plants that are resistant to potato virus Y (PVY). We expressed double-stranded (ds) RNA derived from the 3 terminal part of the coat protein gene of PVY, which is highly conserved in sequence amongst different PVY isolates, in transgenic potatoes of the commercial variety Spunta. Transgenic plants were analyzed for generation of transgene-derived short interfering RNAs (siRNAs) prior to virus inoculation. Twelve of fifteen transgenic lines produced siRNAs and were highly resistant to three strains of PVY, each belonging to three different subtypes of the virus (PVY^N, PVY^O and PVY^NTN). Infection of transgenic plants with Potato virus X (PVX) simultaneously or prior to the challenge with PVY did not interfere with PVY-resistance.Anastasia Missiou: M.A. and K.K. have contributed equally to this workKriton Kalantidis: M.A. and K.K. have contributed equally to this work     

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.     

Effects of Potato Virus YNTN Infection on Gas Exchange and Photosystem 2 Function in Leaves of Solanum tuberosum L.

Photosynthetic responses of potato (Solanum tuberosum L. cv. Chunzao) were examined during potato virus Y (PVY^NTN) infection. PVY^NTN infection significantly reduced net photosynthetic rate and stomatal conductance, but had little influence on intercellular CO₂ concentration. As the disease developed, the maximum carboxylation velocity of ribulose-1,5-bisphosphate carboxylase/oxygenase and the maximum electron transport rate contributing to ribulose-1,5-bisphosphate regeneration gradually decreased, followed by substantial reductions in the relative quantum efficiency of photosystem 2 (PS2) electron transport, the efficiency of excitation energy capture by open PS2 reaction centres, and photochemical quenching, but not in sustained photoinhibition. Thus PVY^NTN depressed photosynthesis mainly by interfering with the enzymatic processes in the Calvin cycle which resulted in a down-regulation of electron transport.     

NtTPN1: a RPP8‐like R gene required for Potato virus Y‐induced veinal necrosis in tobacco

Potato virus Y (PVY) is one of the most damaging viruses of tobacco. In particular, aggressive necrotic strains (PVY^N) lead to considerable losses in yield. The main source of resistance against PVY is linked to the va locus. However, va‐overcoming PVY isolates inducing necrotic symptoms were observed in several countries. In this context, it is important to find va‐independent protection strategies. In a previous study, the phenotyping of 162 tobacco varieties revealed 10 accessions that do not carry the va allele and do not exhibit typical PVY^N‐induced veinal necrosis. Despite the absence of necrotic symptoms, normal viral accumulation in these plants suggests a va‐independent mechanism of tolerance to PVY^N‐induced systemic veinal necrosis. Fine mapping of the genetic determinant(s) was performed in a segregating F2 population. The tolerance trait is inherited as a single recessive gene, and allelism tests demonstrated that eight of the 10 tolerant varieties carry the same determinant. Anchoring the linkage map to the tobacco genome physical map allowed the identification of a RPP8‐like R gene, called NtTPN1 (for t abacum P VY‐induced 相似文献   

Effect of mineral oils on host plant selection and probing behavior of Rhopalosiphum padi

Aphids that colonize and reproduce on potato are some of the most efficient vectors of Potato virus Y (PVY) (Potyviridae: Potyvirus), and hence these aphids have been the focus of the majority of studies to date. However, other non‐colonizing aphids can also function as vectors. Mineral oil is the only product available to growers that effectively prevents the spread of PVY in potato seed production. Most previous studies focused on the effect of mineral oil on the behavior of aphids on their preferential host plant, and consequently there is a lack of information for non‐colonizing aphids on potato plants. The objective of this study was to determine the effect of spraying potatoes with one of two mineral oils, Superior 70 or Vazyl‐Y, on host selection and probing behavior of the non‐colonizing aphid Rhopalosiphum padi (L.) (Hemiptera: Aphididae). The electrical penetration graph (EPG) technique, combined with ethological observations, determined that there was no difference in R. padi behavior on potato plants treated with Superior 70. However, there were few significant changes in R. padi behavior on plants sprayed with Vazyl‐Y, including a delay in the initiation of stylet penetration and an increase in the duration of xylem sap ingestion. These new data support previous results and confirm that the mode of action of mineral oil in the reduction of the spread of PVY is not solely due to the modification of the behavior of aphids.     

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.     

Primary Metabolism,Phenylpropanoids and Antioxidant Pathways Are Regulated in Potato as a Response to Potato virus Y Infection

Potato production is one of the most important agricultural sectors, and it is challenged by various detrimental factors, including virus infections. To control losses in potato production, knowledge about the virus—plant interactions is crucial. Here, we investigated the molecular processes in potato plants as a result of Potato virus Y (PVY) infection, the most economically important potato viral pathogen. We performed an integrative study that links changes in the metabolome and gene expression in potato leaves inoculated with the mild PVY^N and aggressive PVY^NTN isolates, for different times through disease development. At the beginning of infection (1 day post-inoculation), virus-infected plants showed an initial decrease in the concentrations of metabolites connected to sugar and amino-acid metabolism, the TCA cycle, the GABA shunt, ROS scavangers, and phenylpropanoids, relative to the control plants. A pronounced increase in those metabolites was detected at the start of the strong viral multiplication in infected leaves. The alterations in these metabolic pathways were also seen at the gene expression level, as analysed by quantitative PCR. In addition, the systemic response in the metabolome to PVY infection was analysed. Systemic leaves showed a less-pronounced response with fewer metabolites altered, while phenylpropanoid-associated metabolites were strongly accumulated. There was a more rapid onset of accumulation of ROS scavengers in leaves inoculated with PVY^N than those inoculated with PVY^NTN. This appears to be related to the lower damage observed for leaves of potato infected with the milder PVY^N strain, and at least partially explains the differences between the phenotypes observed.     

Recombination of strain O segments to HCpro‐encoding sequence of strain N of Potato virus Y modulates necrosis induced in tobacco and in potatoes carrying resistance genes Ny or Nc

Hypersensitive resistance (HR) to strains O and C of Potato virus Y (PVY, genus Potyvirus) is conferred by potato genes Ny_tbr and Nc_tbr, respectively; however, PVY N strains overcome these resistance genes. The viral helper component proteinases (HCpro, 456 amino acids) from PVY^N and PVY^O are distinguished by an eight‐amino‐acid signature sequence, causing HCpro to fold into alternative conformations. Substitution of only two residues (K269R and R270K) of the eight‐amino‐acid signature in PVY^N HCpro was needed to convert the three‐dimensional (3D) model of PVY^N HCpro to a PVY^O‐like conformation and render PVY^N avirulent in the presence of Ny_tbr, whereas four amino acid substitutions were necessary to change PVY^O HCpro to a PVY^N‐like conformation. Hence, the HCpro conformation rather than other features ascribed to the sequence were essential for recognition by Ny_tbr. The 3D model of PVY^C HCpro closely resembled PVY^O, but differed from PVY^N HCpro. HCpro of all strains was structurally similar to β‐catenin. Sixteen PVY^N605‐based chimeras were inoculated to potato cv. Pentland Crown (Ny_tbr), King Edward (Nc_tbr) and Pentland Ivory (Ny_tbr/Nc_tbr). Eleven chimeras induced necrotic local lesions and caused no systemic infection, and thus differed from both parental viruses that infected King Edward systemically, and from PVY^N605 that infected Pentland Crown and Pentland Ivory systemically. These 11 chimeras triggered both Ny_tbr and Nc_tbr and, in addition, six induced veinal necrosis in tobacco. Further, specific amino acid residues were found to have an additive impact on necrosis. These results shed new light on the causes of PVY‐related necrotic symptoms in potato.     

Capacity assessment of <Emphasis Type="Italic">Myzus persicae,Aphis gossypii</Emphasis> and <Emphasis Type="Italic">Aphis spiraecola</Emphasis> (Hemiptera: Aphididae) to acquire and retain PVY<Superscript>NTN</Superscript> in Tunisia

The study was carried out to investigate the ability of three aphids, Myzus persicae, Aphis gossypii and Aphis spiraecola, to acquire and retain the Potato Virus Y (PVY) isolate, PVY^NTN. Tobacco plants, Nicotiana tabacum var. Xanthi, were used as test plant for the virus inoculation and aphid acquisition. The serological test double-antibody sandwich enzyme-linked immunosorbent assay was applied for virus detection on the test plants and aphids. Furthermore, virus retention by aphids was also assessed using a monoclonal anti-PVY^N. Although a duration of 2 min was enough for the virus acquisition, the three tested aphids showed different capacities to retain PVY^NTN. The retention of PVY^NTN was 3 h for M. persicae and A. spiraecola, and 2 h for A. gossypii. This study provides basic information of the virus retention by potato-colonizing aphid species, which may increase our understanding of PVY epidemiology in Tunisia.     

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.