Population Growth of Myzus persicae on Potato Plants Infected with Different Strains and Variants of Potato virus Y

Potato virus Y (PVY) is one of the most economically important viruses affecting the potato crop. Several strains of the virus, including PVY^O, PVY^N, recombinant isolates; PVY^N:O (PVY ^N-Wi) and PVY^NTN and several variants of PVY^O have been reported from North American potato-production areas. The green peach aphid, Myzus persicae Sulzer, is a colonizer of potatoes and is considered the most important vector of PVY. The objective of this study was to measure the population growth of M. persicae on potato plants infected with different strains and genetic variants of PVY. The initial population of ten winged adults of M. persicae was allowed to develop on a potted plant for 12 days. Results clearly indicated that infections by different strains and genetic variants of PVY did not influence the population growth of M. persicae on potato plants during this period.     

Potato plants transformed with a potato virus Y P1 gene sequence are resistant to PVYO

The cloned P1 sequence of PVY^O was transferred in sense orientation into the potato cultivar Pito usingAgrobacteriummediated transformation. Sixteen of the putatively transformed plants (NPTII positive) were assayed for PVY^O resistance. No PVY^O was detected in four plants, representing two lines, 21 days after two sap-inoculations and 35 days after graft-inoculation, and the plants remained symptomless, whereas other tested plants showed mosaic symptoms and had high PVY titers similar to those of the control plants. No line was resistant to PVY^N and potato viruses A and X. Southern analysis confirmed the presence of the transgene(s) in the two PVY^O-resistant and one susceptible line examined, but no signal was detected in nontransformed Pito. These results suggest a high level of protection against PVY^O in potato transformed with P1 sequence of PVY^O.     

Potato Cultivar and Seed Type Affect the Development of Systemic <Emphasis Type="Italic">Potato virus Y</Emphasis> (PVY<Superscript>N-Wi</Superscript>) Infection

Potato virus Y (PVY) infection is one of the greatest challenges to seed potato production in the United States. To determine how cultivar and seed type affect the development of systemic PVY infection, Russet Burbank and Russet Norkotah Colorado 3 cultivars were grown from two types of pre-nuclear seed (i.e., plantlets and minitubers) and Generation 3 (G3) tubers and challenged with PVY strain Wilga (PVY^N-Wi). Systemic PVY infection was measured by assaying spread of virus from the inoculation site to upper non-inoculated leaves. The Burbank cultivar had a lower incidence of systemic PVY infection compared to the incidence of systemic PVY that developed in the Colorado 3 cultivar. Furthermore, Burbank plants grown from G3 tubers had a lower incidence of systemic PVY infection, as compared to Burbank plants grown from plantlets. Together our results indicate that both cultivar and seed type affect the development of systemic PVY^N-Wi infections post-inoculation.     

Differential Spread of <Emphasis Type="Italic">Potato virus Y</Emphasis> (PVY) Strains O,N:O and NTN in the Field: Implications for the Rise of Recombinant PVY Strains in New Brunswick,Canada

Potato virus Y (PVY) is a major cause of yield and quality loss in potato crops worldwide. Recently, populations of PVY strains have shifted dramatically toward recombinant strains such as PVY^NTN and PVY^N:O. A 2010 to 2016 survey of PVY strains in commercial fields of New Brunswick (NB), Canada, and five field trials tracking PVY spread in NB and Manitoba, were conducted to study the current status of PVY strains and their relative rates of spread. In NB, PVY^O dropped from 82% of infections in 2010 to 14% in 2016, replaced mostly by PVY^NTN (64%) and PVY^N:O (22%).In field trials with Russet Burbank and Gold rush varieties, PVY^NTN spread most effectively compared to PVY^N:O and PVY^O. Strain-specific PVY spread varied with the potato variety, possibly due to selective PVY^O resistance in Goldrush, mostly expressed at the plant-to-plant transmission level with little difference in transduction to tubers in infected plants. Relevance of in-field differences in spread of strains to changes in regional PVY populations, and potential mechanisms responsible, are discussed.     

Evidence of <Emphasis Type="Italic">Potato virus Y</Emphasis> Spread through Post-Emergence Management Practices in Commercial Potato Fields

Potato virus Y (PVY) transmission was studied in six commercial potato fields in 2015 and 2016 in New Brunswick, Canada. Plants emerged from PVY-positive tubers, or PVY-free plants that were artificially inoculated with PVY shortly after emergence, were used as PVY inoculum plants in the study. In all trials, equal numbers of PVY inoculum plants from each of three strains common in the region, PVY^O, PVY^N:O and PVY^NTN, were used. PVY inoculated into tractor-traffic rows showed 2 to 7 times as much PVY spread to previously virus-free plants by the end of the season (up to 48.5% in one tractor row, compared to a maximum of 16.3% in a distant control row unaffected by tractor traffic). Evidence supporting a hypothesis that tractor traffic enhances PVY transmission through aphid disturbance was observed by PVY spread in both directions along the rows, not biased in the direction of tractor travel, and that the ratio of spread of the three strains was nearly indentical in control and tractor rows. However, the lack of spread to immediately adjacent rows, and statistically significant spatial pattern matching the circumference of tractor wheels specific to each field support the hypothesis that direct mechanical transmission of wounded plant sap could also be a factor in the enhanced PVY transmission.     

The development of mature plant resistance in four potato cultivars against aphid-inoculated potato virus YO and YN in four potato cultivars

Summary Field-grown potato plants of cvs King Edward, Record, Maris Piper and Désirée were inoculated on seven different dates during the growing season of 1987 and 1988 with either potato virus Y^O (PVY^O) or PVY^N, using three viruliferous peach-potato aphids (Myzus persicae) per plant. In each cultivar, the proportion of progeny tubers infected with PVY^O or PVY^N was high in plants inoculated during the four weeks following emergence, the proportion declining to zero or close to zero in the subsequent 4–6 wks.     

Census Report of the <Emphasis Type="BoldItalic">Potato Virus Y</Emphasis> (PVY) Population in Swiss Seed Potato Production in 2003 and 2008

The status of the Potato virus Y (PVY) in Swiss seed potato production was investigated in the years 2003 and 2008 by analysing 385 leaf samples of field-grown, suspicious potato plants collected in four representative seed control fields. Serological investigations by ELISA showed that in c. 84% of the PVY-positive samples in both years, viruses belonging to the PVY^N group were found. All 124 serologically positive PVY samples collected in 2003 and a selection of 81 isolates of 2008 were further typified by molecular tests and by biological assays on tobacco and potato plants. These tests largely confirmed the predominance of the PVY^N group and, within this group, the prevalence of recombinant PVY^NTN, with 81.4% and 70.4% in 2003 and 2008, respectively. The percentage of PVY^N-Wilga (PVY^N-Wi) increased from c. 6% to 17% between the two years. PVY^O was detected only in 10.5% and 4.9% of all molecularly analysed samples in 2003 and 2008, respectively. The persistent predominance of recombinant PVY^NTN in Swiss seed potatoes indicates that this strain group is now widespread, representing a considerable threat to Swiss seed potato production.     

Translocation of the potato viruses YN and YO in some potato varieties

Summary In experiments on the rate of translocation of the potato viruses Y^N and Y^O in the varieties Bintje, Eigenheimer, Doré and Sirtema it was found that both viruses infect tubers of Bintje much more readily than those of Eigenheimer. The tubers of the four varieties proved to be infected by PVY^N to a higher degree than by PVY^O. Tubers of the variety Doré became infected by PVY^N to a very high degree, whereas the PVY^N infection of those of the variety Sirtema reached the same level as Bintje tubers. Mature plant resistance could be demonstrated with respect to both viruses, but it was much more pronounced in the experiments with PVY^O than in those with PVY^N.     

Potato Virus Y NTN : A Coat and P1 Protein Sequences Analysis of a Brazilian Isolate

Potato tubers (Solanum tuberosum L. cv. Monalisa) showing superficial necrotic rings typical of Potato virus Y ^NTN (PVY^NTN) infection were collected from commercial potato fields in the State of São Paulo (Brazil). An isolate named IAC-PVY^NTN was characterized by sequencing 822 and 836 nucleotides from the coat protein and P1 protein coding genes, respectively. The IAC-PVY^NTN was observed as a European/North American recombinant isolate closely related to three Eu-PVY^NTN isolates that share an alternative recombination site in the coat protein cistron near position 144. Therefore, the IAC-PVY^NTN isolate may represent a novel recombinant variant between PVY^N N-605 Swiss (European) and PVY O-139 Canadian (North American). Cluster analysis of the P1 sequences found IAC-PVY^NTN in the sub-cluster of Eu-PVY^N/NTN/N:O. This study supports previous evidence of a common origin for PVY^N/NTN in Europe and Brazil.     

Response of potato cultivars to North American isolates of PVYNTN

Potato cultivars were assessed for their sensitivity to potato tuber necrotic ringspot disease (PTNRD) induced by two North American isolates (Tu619 and Tu660) of the tobacco veinal necrosis strain of potato virus Y (PVY^N) and belonging to the tuber necrosis (PVY^NTN) sub-group. Several widely grown cultivars (e.g. Norchip and Ranger Russet) were found to be highly sensitive to PTNRD, while others (e.g. Russet Burbank, Russet Norkotah and Shepody) were not. The foliage symptoms induced by these isolates were distinct from those reported to be produced by European isolates of PVY^NTN, in that systemic necrotic rings and chlorophyll figures on the leaves were not produced. Instead, the symptoms were similar to those of normal strains of PVY^N. The apparent correlation between resistance to the PVY^O (common) strain group and cultivar sensitivity to PTNRD is discussed.     

Host range,symptomology, and serology of isolates of potato virus Y (PVY) that share properties with both the PVYN and PVYO strain groups

In surveys for the tobacco veinal necrosis strain of potato virus Y (PVY^N) in potato, two isolates (I-136 and I-L56) were obtained that shared properties with both the PVY^N and the common (PVY^O) strain groups. The isolates produced veinal necrosis on tobacco (Nicotiana tabacum L.) and mild symptoms on potato (Solanum tuberosum L.) cv. Jemseg, typical of PVY^N but their symptoms on some other indicator species such asCapsicum frutescens L.,Chenopodium amaranticolor Coste & Reyn.),Physalis angulata L.,P. floridana Rybd. were more typical of PVY^O. Their serological properties were also more typical of PVY^O in that they reacted with a PVY^O-specific monoclonal antibody (MAb) in ELISA and they failed to react with four PVY^N-specific MAbs. The possible taxonomic position of these isolates is discussed.     

Importance and control of potato virus YN (PVYN) in seed potato production

Summary The tobacco veinal necrosis strain of potato virus Y (PVY^N) first became epidemic in several European countries in the 1950s. To prevent PVY^N-infections, account must be taken of virus sources both within and without potato fields; for forecasting, the aphid vector species, their vector efficiency, and their flight activity must all be known. Well-timed haulm destruction needs knowledges of PVY^N-translocation in potato plants and of the development of mature plant resistance. For successful virus control, also reliable methods for virus detection are needed, and for this ELISA has been well established for many years in seed potato certification schemes. A combined treatment of mineral oil and pyrethroids reduces aphid populations and the spread of stylet-borne viruses in the fields. In breeding for resistance, the major gene Ry induces complete protection against infections of all known PVY-strains.     

Control of the Potato Virus X Through Application of Root Extracts of Chlorophytum nepalense to Potato Plants and Tubers

The perennial herb Chlorophytum nepalense (Lindley) Baker, widely distributed throughout the northern parts of Tripura State of India, is used traditionally by Tripuri farmers as a root extract to control dark viral necrotic lesions of sprouted potato tubers and plants. The root extracts strongly reduced infection of potato plants and sprouted tubers by Potato virus X under glasshouse conditions. The root extract was found to contain the three plant-viricidal compounds chlorogenic acid, kaempferol-3-O-(3′,6′di-O-E-p-coumaroyl)-β-d-glucopyranoside, and luteolin and suggests that the isolated compounds may have the potential to be used as natural plant-viricidal compounds.     

Evaluation of tuber-bearingSolanum species for symptomology,as diagnostic hosts,and sources of immunityto potato virus Y necrotic strain (PVYN)

A total of 258 Plant Introductions (PI) belonging to 69Solarium species were evaluated in the greenhouse for their reaction to the tobacco veinal necrosis strain of potato virus Y (PVY N). One hundred and thirty-one (50.7%) of the PI accessions produced mosaic symptoms ranging from mild to severe. Local lesion and veinal necrosis symptoms were observed in 19 PI accessions (7.3%) and a variety of other symptoms were observed in another 11 PI accessions (4.2%). Only 97 PI accessions (37.5%) were symptomless carriers of PVY^N. PI accession 473505 ofS. sparsipilum and PI accession 498021 ofS. brachycarpum developed local lesions and veinal necrosis with PVY^N, but necrotic spots and mosaic with PVY^o. Common mechanically-transmitted potato viruses A, S, M, and X did not interfere with PVY symptom development inS. sparsipilum andS. brachycarpum. Thus, PI 473505 and PI 498021 can be used as indicator plants for specific identification of PVY^N. PI accession 472819 ofS. chacoense developed local lesions with systemic spread in PVY^o, but without systemic spread in PVY^N. Thus, this can be used as a differential host plant for PVY strains. Two PI accessions ofS. stoloniferum, PI 160372 and 161171 were immune to PVY^N.     

Elimination of viruses and hypersensitivity to potato virus Y (PVYo) in an important sudanese potato stock (Zalinge)

Viruses that infect naturally an important Sudanese potato stock Zalinge were detected using enzyme-linked immunosorbent assay, immunosorbent electron microscopy and sap-inoculation to test plants. All of the 19 plants of Zalinge tested were infected with potato leaf roll virus (PLRV) and potato virus S (P VS), and five plants also with potato virus X (PVX). No potato virus Y (PVY), A (PVA) nor M (PVM) were found. The viruses were eradicated with thermo and chemotherapy using standard procedures. The combination of both therapies did not result in any virus-free plants, but resulted in poor plant survival. Thermotherapy reduced the incidence of PLRV and PVS by 45% and 50%, respectively, and one virus-free plant was obtained. It grew vigorously in the greenhouse, was symptomless and had a significantly increased tuber yield compared to the virus-infected plants. Following sap-inoculation with PVY^O, Zalinge showed mosaic symptoms, developed necrosis in the leaves and stem and died 14 days post-inoculation. However, the plants of Zalinge infected with PVY^N remained symptomless, which suggested that hypersensitivity was specific to PVY^O. The fast development of lethal necrosis following infection with PVY^O may contribute to the low incidence of PVY in Zalinge in the field in Sudan.     

General resistance against potato virus Y introduced into a commercial potato cultivar by genetic transformation with PVYN coat protein gene

Summary Transgenic cv. Folva potato plants expressing the coat protein gene of potato virus Y strain N (PVY^N) were produced usingAgrobacterium tumefaciens mediated transformation. Forty independent transformants were selected for resistance screening. Four clones showed complete resistance to mechanical inoculation with all the five PVY isolates tested: the PVY^N isolate from which the coat protein gene was derived, two PVY^O isolates, and two PVY^NTN isolates. Two of the fully resistant clones contained only one copy of the transgene, demonstrating that it is possible by genetic engineering to obtain highly virus resistant potato clones that can also be useful in future breeding programmes.     

Protection against potato virus Y (PVY) in the field in potatoes transformed with the PVY P1 Gene

Lines of potato cv. Pito transformed with the P1 gene ofPotato virus Y (PVY^o) in sense or antisense orientation were evaluated for resistance to PVY in the field in 1997 and 1998. The transgenic resistance fully protected the crop from infection with PVY^o transmitted by aphids in both years. These plants were not resistant to the field isolates of the PVY^N strain group, which is in agreement with our greenhouse experiments. Consequently, several transgenic lines produced higher yields than the nontransgenic cv. Pito plants. These results showed that the P1 gene-mediated resistance provides significant benefits under conditions were the incidence of infections and damage by PVY^o are considerable.     

Evidence of Recombinant Isolates of Potato Virus Y (PVY) in Argentina

In order to make a first approach in the identification of the genetic diversity of Potato virus Y (PVY) in Argentina, 46 PVY isolates from different potato growing regions of Argentina were characterized both, biological and serologically. Five of them (ST11, RCA5a, RCA6, RCA14b and SSF6) were selected for further genomic analyses. Four genomic fragments containing hot spot regions of recombination (HSR) reported previously were sequenced in each isolate and compared to PVY^N (CS434575.1) and PVY^O (U09509.1) reference genomes looking for genomic recombinations. Isolates with one, two or three recombination points were identified among these, including the two strains considered typical PVY^N (RCA5b) and PVY^O (SSF18) used as controls. This is the first report of the presence of recombined PVY in Argentina using a combination of biological, serological and molecular tools that shed light on the genetic diversity of PVY viruses in this country.